Sciencemadness Discussion Board - Acetaldehyde synthesis

Acetaldehyde synthesis

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12AX7 - 6-6-2006 at 18:15

Quote:

Originally posted by Elawr
What does ethyl acetate smell like?

Not far from ether I'd say. Maybe more, er, "body" or something, but I don't associate it with any particular fruit or anything.

Tim

stoichiometric_steve - 6-6-2006 at 23:25

Quote:

Originally posted by 12AX7

Quote:

Originally posted by Elawr
What does ethyl acetate smell like?

Not far from ether I'd say. Maybe more, er, "body" or something, but I don't associate it with any particular fruit or anything.

Tim

sometimes cantaloupe melons smell like ethyl acetate.

Acetaldehyde

CycloKnight - 7-6-2006 at 12:28

There is another route to acetaldehyde that I didn't see mentioned in the posts above.
This is the method used here:
http://www.sciencemadness.org/talk/viewthread.php?tid=2223&a...

...to convert cinnamaldehyde to benzaldehyde.

Acetaldehyde is the main byproduct produced in that process.
Read psychokitty's post in the link, it contains a quote from the patent and also mentions the acetaldehyde formation.

The attachment

markgollum - 7-6-2006 at 13:34

I re-scanned the pages on the lowest quality setting and am now at 560Kb so it should work this time.

Attachment: The Hydration of Acetylene.pdf (556kB)
This file has been downloaded 1810 times

Zinc - 30-6-2006 at 13:03

Be careful when working with acetaldehyde. It is a probable carcinogen.
http://en.wikipedia.org/wiki/Acetaldehyde

JohnWW - 30-6-2006 at 17:25

If it really is a "probable carcinogen", then everyone who drinks alcohol is at risk, because it is an intermediate degradation product of ethanol. I do not think so.

guy - 30-6-2006 at 17:46

That's probably why drinking IS bad for you.

http://www.reboundhangover.com/acetaldehyde.htm

Rosco Bodine - 1-11-2006 at 18:26

Update :

Found an interesting old German acetaldehyde patent that
needs translation to English ....if anyone would be
so kind .

[Edited on 2-11-2006 by Rosco Bodine]

Attachment: DE422729 Acetaldehyde in 90+% Yield via Air Oxidation of Ethanol using Silver Wire Catalyst.pdf (69kB)
This file has been downloaded 1481 times

Rosco Bodine - 1-11-2006 at 22:32

And for electrolytic oxidation of ethanol to acetaldehyde ,
the yield is quantitative when the electrolysis is carried
out with the voltage limited to the range of 1.3 to 1.66 volts using a platinum anode . See the attached page .

Perhaps another anode material might work adequately well .

Both of these references are from publications in the
ScienceMadness Library .

Attachment: Page 60 from electrochemistry_of_organic_compounds.pdf (435kB)
This file has been downloaded 1549 times

fractional - 2-11-2006 at 04:27

@ Rosco Bodine
Et voilá, the English translation...

I don't think that this process is more interesting than the standard one using copper-wire/ copper-mesh as catalyst.

This method seems not to get many favourable reviews, but I think it is perfectly reasonable once an important modification is applied: External heating of the copper-catalyst with e.g. a bunsen-burner in order to kick-start the reaction is clearly not practicable on any but the smallest scales, but one can also use the copper wire as direct heating element by passing an electric current through it. This ensures an equal and controlled heating of all the copper surface.

The setup to use is a pipe with a spiral of copper-wire inside that's connected to a low-voltage power supply with sufficient current to bring the wire to red heat. The Volts/Amps rating of course depends on the length and the thickness of the wire used.

Attachment: Method for the Production of Acetaldehyde from Ethanol.pdf (11kB)
This file has been downloaded 2997 times

Rosco Bodine - 2-11-2006 at 07:54

@fractional

Thank you for that translation .

Silver has such a pronounced catalytic effect on the
oxidation of ethanol selectively to acetaldehyde , it
makes me wonder if a silver or silver oxide anode may
have similar value in an electrolytic cell .

Also concerning the value of silver and copper both as
contact catalysts for the air oxidation of ethanol at elevated temperature .....

the old German patent encourages an idea which I have been considering for an experimental method and catalyst which could be useful for the oxidation of ethanol to acetaldehyde .

There is a familiar example in many chemistry books
about how metallic silver will precipitate from a solution
of silver nitrate upon a piece of copper wire immersed
in the silver nitrate solution .

And there are also methods for the precipitation of metallic copper from solutions of copper salts using organic reducing agents .

While researching refractory materials I came across a
high fired granular porous clay material which is used
as an artificial soil for aquatic plants in decorative ponds
and aquariums , as a substitute for ordinary gravel ,
and it occured to me that this might make a useful carrier
for a catalyst . A similar material is a porous alumina
which is used in water filtration as a substrate on which
grow beneficial bacteria and algae , and this ceramic
could be broken up into granules using a hammer , and
the granules could also be useful as a porous substrate
for carrying a finely divided catalyst .

http://www.drsfostersmith.com/product/prod_display.cfm?pcati...

This sort of ceramic filter media is available in different
molded forms from aquarium suppliers and probably
pet shops .

The idea for the catalyst carrier is to agitate the granulated material violently in a copper salt solution
as reduced metallic copper is being precipitated into the pores and onto the surfaces of the granules . And then
subsequently to agitate the copper bearing granules
violently in a solution of silver nitrate so that metallic silver is also deposited . The granular material is then
dried and poured and tamped inside a long copper tube ,
whose inside walls may also have been silvered by
filling the tube previously with silver nitrate . Alternately the copper bearing granules might be placed in the copper tube first , and then the assembly silvered by circulating silver nitrate solution through , depositing
the metallic silver on the granules and the inside walls
of the copper tube simultaneously . Afterwards the
catalyst filled tube is spiral wrapped into a coil but having
a conical form , as if it were coiled around the outside of
a funnel being used as a form for the winding . This
funnel shaped coil can be inverted above a single burner
on something like a gas hotplate or camp stove burner ,
so that the entire coil catches the heat from the one burner , distributed across a considerable length of
catalyst filled tube which forms the coil , having its free ends brought horizontally away by some distance to provide cooled sections as intake for the alcohol and air vapor and exhaust of the acetaldehyde to a separate
condenser .

An aquarium pump could supply the airflow to an airstone
at the bottom of a column of ethanol , and the richness
of the entrained vapor in ethanol could be varied simply
by warming or cooling the ethanol through which the air is bubbled . A three way needle valve manifold as is
used on aquariums for balancing the airflow between separate airstones could be used for achieving a proper mixture , if it was found necessary to blend the vapors
from the ethanol evaporator with additional plain air .

The acetaldehyde vapors exiting the catalytic section
could be initially cooled in a coil air condenser , and then
in a water cooled coil section , then ice water cooled
section , and finally captured by bubbling through an
airstone into icewater in a column cooled by an ice salt bath .

Regarding your suggestion to use electrical heating of
a copper coil , it presents difficulty due to the enormous
current which would be required for causing copper to
get hot from IR heating . What would be required is
some sort of inductive heating of a shorted loop , as
if it was a stalled motor armature and the field coil would be a substantial endeavor . If a copper coil was
to be used , it would be easier to wrap it around some
sort of sheathed cylindrical heating element , and let
the isolated nichrome element in the core do the job of
heating the copper .

An idea that just occurred to me is related to that copper braided sleeve material woven of fine wire that is used as the outer conducter in coaxial cable . That braided copper
sleeving could be silvered by immersion in silver nitrate ,
and it would probably work beautifully inside a copper tube
loosely filled with parallel pieces of the braid . Alternately
the braid could be cut in short lengths and pushed inside
the open end of the tube by the end of a dowel , like
pushing wads into a muzzle loaded rifle using a ramrod .
Silvered copper may work fine as a catalyst , providing
the greater economy of the copper as a substrate for the
silver which has greater activity and efficiency .

Tinned copper braid is commercially available , and it may just be that silvered copper braid is also available , and if so it could be used directly . I know that silvered copper wire
is manufactured , so it seems logical that somebody is probably weaving copper braid using silvered copper wire ,
for use in some high end coaxial cable or other application .

[Edited on 2-11-2006 by Rosco Bodine]

fractional - 2-11-2006 at 09:44

I fear I have not been clear enough before: the copper wire is the actual heater, it is not heated by some external source with which it must exchange heat energy by radiation. The currents needed to heat it up to red heat are not all that outrageous for a typical application. I have done some back of the envelope calculations:

Used PC power supplies are great and dirt-cheap power sources for low voltages and high Amps. Let's assume one rated at 5 Volts, 20 Amperes. The external resistance needed to draw the rated current at the rated voltage is 5V / 20A = 0.25 Ohms.

A copper wire with a diameter of 0.5mm has a resistance of about 0.0876 Ohms per meter. The length of this wire needed to give 0.25 Ohms is 0.25 / 0.0876 = 2.85 meters. This length of wire can be easily fitted as a kind of spool or bobbin inside a reasonably-sized (glas)-pipe.

Let's calculate the expected temperature of this spool operated at 20 Amperes: This depends on the surface area of the wire-assembly (l=2.85m, dia=0.5mm), which is 0.0045 square-meters. It also depends on the emissivity epsilon, which is 0.13 for polished copper (from published tables of materials properties).

The temperature assuming radiative heat transfer only (which is of course a major simplification) is given by Stefan-Bolzmann's law:

Texp4 = q / (Sigma*epsilon*SurfaceArea) + Tenv exp4

T is the temperature of the wire in Kelvin, Tenv is the environmental temperature in Kelvin. q is the power, sigma is Bolzmann's constant (5.67051exp-8).

When you put in the numbers q=100W, Tenv=20 degC = 293 Kelvin, SurfaceArea = 0.0045 m2 the expected temperature of the wire is 1318 Kelvin or 1045 degC, which is actually way beyond red-hot.

Of course there will be losses in the system by conduction and convection, so the temperature will be lower, but I think this is a good starting point, and I think it shows that such a system is feasible.

I have read with interest your ideas about producing a copper catalyst-bed with a high surface area. I am not sure, however, if this will really help for the specific purpose of producing acetaldehyde. The main point of the German patent is that too finely divided silver makes the reaction too violent and reduces the yield, so that "more compact" forms of the catalyst should be used, so I think that the compact form of copper wire should do the trick nicely.

I have not tried this out yet, because I am currently trying to oxidise ethanol using TCCA, with limited success so far (yield 1ml of acetaldehyde using 60ml of ethanol...). If this turns out to be a no-go I will come back to this copper-wire method.

Rosco Bodine - 2-11-2006 at 10:03

I have been doing too many ammeter shunt calculations lately and handling too large conductors ....losing perspective

Of course you are right , and coiling
the element like a long spiral spring would allow for
even larger wire to be used . If this was wound upon
a solid rod and placed inside a glass tube , the vapor would be forced the travel the spiral groove and
would get very good contact and intermixing in
the reaction zone .

I still think that using silver plated copper may have advantage , as the reported yields for the silver are
much higher than for copper alone , in the references
which I have seen , the yield reported for silver is
increased by 50% over that gotten for copper in
a single pass oxidation .

Also I found that the silvered copper braid material is indeed available in various sizes . Alpha wire products
is one of the suppliers .

http://www.electrospec.com/alpha/product_list.asp?c1=05&...

The silver plated tubular braid material is available down to
1/16" ( 1.6 mm ) size , and depending on the cross sectional
area of the conductors , this may also be within reach for
electrical heating if it was used as a coiled element .

BTW , I didn't do the calculations , but just off hand it would
have been my guess that about 400% or even much more current would have to be put through that nearly 3 meters of copper wire to get it red hot in free air initially , but of course after the reaction starts , the exotherm of the reaction will keep the catalyst plenty hot , and the power supply would only need to labor hard for a brief time to initiate the reaction .

[Edited on 2-11-2006 by Rosco Bodine]

gsd - 2-11-2006 at 10:13

Let me make it clear that I have not gone through this thread completely as it is fairly a long one; so kindly excuse me if I am repeating the posted matter.

While doing my engineering, I had done summer vacational training in an "ethanol to acetaldehyde - air oxidation" plant.

Ethanol vapours and air are premixed and immediately fed into a reactor which is a squat cylindrical vessel having vertical tubes on which several layers of gauze made from very pure silver metal are tightly wound. The vapour air mixture passes across this layer of catalyst. The reaction is exothermic and the bed temperature is maintained at 550 Deg C., by coolant circulation in the tubes. The contact time is very short ( < 0.1 sec), per pass conversion is about 48 % and yield about 85-90 %

The Interesting this about this reactor was the startup procedure. To this big reactor ( Diameter about 1.2 m, I don't recollect exactly) are attached 3 small pilot reactors of 200 mm dia and 300 mm length, at 120 Deg angle. These small reactors are packed completely with copper wire gauze and are heated with electrical resistance heaters packed within the copper wire gauze layers.

The same feed of ethanol + air mixture is passed thru' each of there reactors and the outcoming hot vapours from small reactors are directed onto the silver wire gauze of main reactor. These vapours slowly heat up the silver catalyst and after it is above 300 Deg C., Feed is stared to the main reactor and the pilot reactors are discontined.

gsd

Jdurg - 2-11-2006 at 10:25

I haven't had a chance to read through the entire thread and while it's been many years since I had biochemistry, would it not be possible to take some ground up beef liver (which should be fairly cheap) and use the alcohol dehydrogenase contained within to convert the ethanol to acetaldehyde? Or, as I'm guessing, is the yield so poor and the extraction so complex that it's really not worth it?

Rosco Bodine - 2-11-2006 at 10:29

I wonder what the catalytic heater element used on
those propane fueled portable camping and icefishing heaters would do if it was fed an ethanol vapor fuel
instead of propane ?

There may already even be such infrared heaters designed
to operate on denatured alcohol , and it could very well
be that acetaldehyde is an intermediate oxidation product ,
which could be made the principal product if the air supply
was restricted to prevent its further oxidation .

Mooooo......Mooooooo , Mooooooooo

Sorry , I couldn't resist

@ fractional
Have you taken a look at that Dony-Henault article
reporting a quantitative yield of acetaldehyde via
electrolysis at a specifically limited voltage of 1.3 to 1.66 ?
That was on a platinum anode , and I wonder what silver
would do .

Anybody got access to that reference ?

Dony-Henault

Ztschr. f. Elektrochemie 6 , 533 , ( 1900 )

[Edited on 2-11-2006 by Rosco Bodine]

S.C. Wack - 2-11-2006 at 16:02

Tried that when the sportcats came out a few years ago. Oddly enough I found those better at making formaldehyde (with MeOH obviously) than acetaldehyde, though my experiments were crude and so far just for hahas. Not being engineering-minded, I felt that experiments with it were best directed elsewhere.

Vapor indeed. Unless the feed of either air or vapor is dilute much of the alcohol will burn off due to the exothermic self-sustaining nature of the reaction and the small amount of heat necessary to get it going.

Rosco Bodine - 2-11-2006 at 16:51

What I was thinking is maybe put the catalytic burner head inside a sealed chamber with an observation port
and a thermometer , and control the air supply and the
alcohol vapor flow to the burner . Fire it up in a normal
heat producing mode where it is getting plenty of air
to burn the fuel all the way to CO2 , and then start
reducing the air until it is outputting CO , and then gradually reduce the air further until hopefully the
aldehyde is what is being produced . There may be
a niche condition of temperature and mixture where
the reaction would proceed pretty well at a stable rate
and produce lots of the desired aldehyde .

fractional - 3-11-2006 at 01:19

Rosco,
I also think that silver-plated wire is the way to go. It gives you the catalytic performance of silver at the price of copper wire (or just a bit more). The conductivity of the wire will not change much, but the emissivity will. I found a figure for the emissivity of silver plating of 0.06. For the previous example of a length of 2.85m of 0.5mm dia. wire siver-plating would yield a temperature of 1326 degC which is probably too high, even considering losses. A 0.6mm dia. wire, length 4.1m, brings you back to 1123 degC, which is probably more realistic.

All these calculations show that the emissivity is a crucial factor in the calculations and the published figures are often miles apart, so if one wants to put such a system in place one should perform a few dry-runs first, using a power source that can be regulated somewhat.

> @ fractional
> Have you taken a look at that Dony-Henault article
> reporting a quantitative yield of acetaldehyde via
> electrolysis at a specifically limited voltage of 1.3 to 1.66 ?
> That was on a platinum anode , and I wonder what silver
> would do .

> Anybody got access to that reference ?

> Dony-Henault

> Ztschr. f. Elektrochemie 6 , 533 , ( 1900 )

Yes, I did read it and I find it extremely interesting. A platinum electrode is one of those things one would like to have, isn't it? Electrochemistry is not my strong side (to put it mildly) so I don't know what the use of a different anode material would do, e.g. the effects of overvoltage, etc. I tried to find an article from 1899 also in the "Zeitschrift f. Elektrochemie" on the production of Chloral by electrolysis, but with no success so far.

What I can say is that if some good soul scans the article I will be more than happy to translate it and put it on the board.

not_important - 3-11-2006 at 01:22

SCW is right, once you get above a few hundred C and there is oxygen present then the reaction tends to go to full oxidation and thermal runaway. The industrial processes use a rather high speed flow of reactants to help avoid too much loss from that route, like NOx production from air - quickly heat and chill.

Another thing to remember is that the Cu/Ag route will produce aldehyde without any oxygen present, the added O2/air is used to remove hydrogen to force the reaction further to completion. Those catalytic burners are targeted at full oxidation of hydrocarbons, they may not function well for this more limited reaction.

Rosco Bodine - 3-11-2006 at 07:10

Some of the campstoves and lanterns which burn white gasoline use a pressurized tank for the liquid fuel which
is squirted under pressure through a very small orifice
into a larger bore tube which is heated by the burner ,
and the liquid spray is flash boiled to a vapor in that
" vapor generator tube " which preheats and vaporizes the liquid fuel on its path to the burner , scavenging heat from the final output for the preheating of the fuel .

The same principle and indeed the same fuel tank and
fuel generator tube , perhaps with a couple of added
sections in length .....might be directly applicable for
an ethanol vapor generator if the copper tube containing
the catalytic material was coiled around the generator
tube and then insulated around the outside with a sleeve
of kaowool or fiberglass . A thermocouple could be attached to monitor the temperature . The first few inches of the generator tube and the first three or four
coil loops of catalyst containing tubing could be left partly uncovered with insulation so it could be exposed to
external heating by a bunsen burner for initial heating
when firing up the apparatus . A Tee fitting and needle valve could be interposed between the fuel tank and the vapor generator tube , or perhaps at a third of the length of the catalyst containing tube , for admitting air as needed to speed the warmup of the apparatus by complete oxidation of the fuel initially , which should get the converter temperature high enough , that the oxidation could then be transitioned to the more anaerobic production of acetaldehyde by gradually reducing the airflow .

Supplemental electrical heating could be provided if needed by a cylindrical heating element , a " watt rod " along the
outside of the coil under the insulation , or a few of the coils could be wound around the heating element directly .

The idea of loading the catalyst inside a coil of copper tubing
is perhaps not the optimum arrangement , if a short contact
time with the catalyst is what is desired , a straight
section of larger tubing , or a concentric arangement of
inner vapor tube and an outer tube containing the catalyst
may serve better . A compact assembly the size of a soup can may have superior characteristics to something larger the size of a map case or blueprint tube .

Another arrangement of catalytic burner which may be applicable is similar to the vertical " fluidized bed " concept . A funnel shaped copper bell , like a large reducer adapter sleeve solder fitting at the large opening and threaded at the smaller bottom opening ,
could be filled with layered pieces of silver coated copper wire braid and chopped wire whiskers , and fed with ethanol vapor from the bottom through a copper tubing having two or three loops of the tubing wound around the outside
of the reducing adapter to provide preheating of the entering vapor . A grid of wires laced across the large opening could be used to keep the spongy wad of catalyst pieces secured inside the catalytic " burner " head . Something like this would provide a rapid transit and brief
contact time for the ethanol vapor . A length of straight
copper pipe could be added to the copper bell to increase
the depth of the catalyst bed if needed , until the optimum
reaction zone dimension for the particular apparatus was discovered by testing .

To simplify greatly this whole endeavor I think it would be best to first use a modification on the patents method .
The catalytic reactor section need not be made of quartz
nor should the wire material be made of pure silver if
my earlier guess is correct that silvered copper braid material
should work about as well . All that should really be required
is a straight four inch section of 3/4" copper tube stuffed with layers of the catalyst wire mesh and having its ends
fitted with 3/4" to 1/4" brass or stainless compression reducer couplings for the vapor inlet and exit . The catalyst section is compact enough to be preheated easily by a meker burner with a wing adapter flame spreader . The brass compression couplings on the ends of the catalyst chamber could be wrapped with fiberglass ribbon for insulation , and the bare 3" middle section heated by the burner . The smaller copper inlet line could be hairpin bent
( U-bend ) back across the coupling and spiraled around
the catalyst containing section for vapor preheating , a
smaller copper capillary tubing such as is used in refrigeration would be needed for this tight spiral preheater .
I believe I have seen this small copper capillary tubing used
as supply tubing to pilot lights on gas appliances , and I will
do some shopping and scrounging to see what can be found in the way of fittings for making a modest lab scale device .

The silvered copper braid is something which will have to ordered , but simply treating ordinary copper braid scavenged from coaxial cable with silver nitrate may be the better approach in keeping the experiment to over the counter materials .

For the vapor - air mixture control , the setup will be based
on a bubbler in ethanol and an aquarium pump as described earlier .

[Edited on 3-11-2006 by Rosco Bodine]

Eclectic - 3-11-2006 at 14:56

There is a knitted copper mesh material available from www.partyman.se and other alcohol oriented places that they sell for column packing. It's used industrially for scouring the crud from plastic injection molding machinery parts. Chore-Boy (used to be Chore-Girl brand) copper scrubbers are similar.

[Edited on 3-11-2006 by Eclectic]

Rosco Bodine - 3-11-2006 at 15:30

Yeah I think this sort of setup is entirely workable
and could be made into a suitcase sized apparatus .
If ~90% yield is gotten in a single pass through
a catalytic converter of compact size , that is
entirely efficient enough for a practical method
and source for acetaldehyde as an intermediate .

Thinking further on the design , any unreacted
ethanol vapor could be stripped from the output simply by bubbling through an airstone in warm water , the alcohol would enter the water , but the more volatile acetaldehyde would blow through , while it could
be cooled further in an empty glass jug in an ice bath ,
and then bubbled into cracked ice and water in a
cylinder cooled in an ice salt bath . I believe that this
" Two jug - one tall bottle " sort of arrangement and
using gas dispersion stones in the first and last ,
with a swirling flow in the second , would work better
for purifying and capturing the extremely volatile
product in frigid water solution , than would trying
to condense it in conventional condensers .

Acetaldehyde from PET ?!?!?!

Aqua_Fortis_100% - 20-1-2007 at 19:58

firstly sorry by ressussiting this old thread but when i searched some things about acetadehyde in portuguese , the google show me a special result :

Quote:

from this page :
O acetaldeído é subproduto da degradação do PET. Ele é formado quando a resina PET é submetida a altas temperaturas, normalmente utilizadas na fabricação e transformação da resina, onde o polímero é aquecido acima de sua temperatura de fusão.

A preocupação com a presença de acetaldeído nas embalagens de PET se deve à alteração de gosto que este pode causar no produto embalado.

something as :
" the acetaldehyde is a subproduct of the decomposition of PET. It is formed when the PET resin is submited high temperatures , usually used in resin manufacture and modification, where the polymer is heated above of their melting point.
The worry with the Acetaldehyde presence in PET containers is due the taste which this can cause in the wrapped products (foods) ."

^sorry, this is a poor english but is some compreensible (eh?) ^

anyone tried getting acetaldehyde from this "method"? what about???

Quote:

originally posted by vulture:
The main problem with the production of acetaldehyde from ethanol is that when you use water as a solvent, you're always wasting aldehyde by conversion to acetic acid.

I'm actually only interested in acetaldehyde due the pentaerythritol manufacture... if i try distill this directely in cooled CHOH (with some Ca(OH)2

this will improve the yield of the CH3CHO coleted? Because the acetaldehyde react with formaldehyde (before?) the conversion for acetic acid in contact whit water..(?????)
or maybe, try DRY destill in the receiving cooled flask, then adding this in calcium hydroxide/formaldehyde solution..
thanks and sorry for anything...

[Editado em 21-1-2007 por Aqua_Fortis_100%]

guy - 20-1-2007 at 21:40

Ethanol + copper acetate (or palladium) + Sodium acetate(base) ---heat---> Acetaldehyde??

Make sure there is no water or else it will convert to acetic acid.
============

Copper catalyzed alcohol oxidation to ketones and aldehydes

Abstract:
An efficient, copper-based catalyst has been discovered that oxidizes a wide range of
alcohols into aldehydes and ketones under mild conditions. This catalytic system utilizes
oxygen or air as the ultimate, stoichiometric oxidant, producing water as the only
by-product.

[Edited on 1/21/2007 by guy]

Aqua_Fortis_100% - 21-1-2007 at 05:50

guy ,this is a very nice pdf!!!

but i have a doubt : they discribes a catalyst made from CuCl ,phenanthroline(phen) , K2CO3 and some others substances @ 70 to 90°C...
about the CuCl: the oxigen in process oxodizes the copper in Cu II ? has this similar or same eficience as catalyst?
thanks

guy - 21-1-2007 at 13:51

This method is less complicated, provided you have pyridine and palladium acetate. Works with normal pressure. The reason it works with palladium is because it can make the alcohol do a beta-hydride elimination.

Attachment: palladium_catalyzed_alcohol_oxidation.pdf (62kB)
This file has been downloaded 1457 times

Nerro - 21-1-2007 at 14:46

pyridinium chlorochromate is an oxidizer which should oxidize only to the CHO (rather than proceed to the COOH).

I've used it in a practical and it worked quite well.

Magpie - 24-1-2007 at 16:04

Oops. I thought this thread was "aldehyde synthesis." My apologies.

I have been oxidizing n-butanol to n-butyraldehyde using the classic and well known dichromate method:

3CH3(CH2)2CH2OH + Na2Cr2O7 +4H2SO4 --->
3CH3(CH2)2CHO +Na2SO4 +Cr2(SO4)3 + 7H2O

This reaction is a bit hard to control as it is exothermic. And one has to keep the pot hot enough so that the aldehyde will be immediately driven to the condenser before it has a chance to oxidize further to butyric acid. But you don't want the pot too hot or you will drive off too much water and butanol into the distillate. The apparatus I used is shown in the attached photo. As you can see the clear alcohol is being added via dropping funnel. Although I have not done final workup this procedure appears to have given me some nominal amount of aldehyde.

My procedure (Brewster, 1962) specifies something I don't understand. It calls for dichromate at a mole ratio to alcohol of 1:1 instead of the stoichiometric 1:3. The same text, however, in a 1977 edition, changes from n-butanol to n-propanol, and uses a stoichiometric ratio. It also reverses the dropping funnel reactant to dichromate/H2SO4/water, with the n-propanol in the pot. I tried this with the n-butannol and it was a complete failure (disaster), never getting hot enough to flash off the aldehyde and then giving me a runaway when 90% of the dichromate had been added.

So if you have any ideas about the mole ratios specified for this type of reaction I'd like to hear them.

[Edited on 25-1-2007 by Magpie]

n-butyraldehyde.jpg - 59kB

Rosco Bodine - 24-1-2007 at 17:23

Here's something that is relevant and perhaps directly
applicable to what you are doing , with the bonus of having
an easily regenerable reagent which reportedly has a good efficiency in both the oxidative reaction as well as the regeneration .

[Edited on 25-1-2007 by Rosco Bodine]

Attachment: US4297520 Aldehydes via Dichromate Oxidation with electrolysis regenerable reagent.pdf (326kB)
This file has been downloaded 1414 times

bio2 - 24-1-2007 at 18:16

Magpie, that's an interesting looking heating mantle
you've got there.

Did you make it yourself with that metal ring looking
heater?

Magpie - 24-1-2007 at 19:34

bio2, that is just a regular Glas-Col 500 mL mantle sitting in an iron ring with fiberglass fabric support straps sewn onto it in an "X" pattern. These rings are specially made for that purpose in different sizes and are available through the scientific supply houses. I have a 500mL and a 100 mL size as these are my mantle sizes. With these mantles I can heat all of my RBF's from 25mL to 500mL.

chemrox - 27-1-2007 at 16:41

So given a way to make acetaldehyde.. it doesn't last very long unless you polymerize it to paraldehyde a substance with certain virtues of its own not the least of which include its use in certain biological test reagents .. so extending the discussion, does anyone have a facile method for taking acetaldehyde to paraldehyde? I tried one published on Erowid and it was bogue...

fractional - 28-1-2007 at 04:51

From Cohen, Practical Organic Chemistry, 1910:

" Add a drop or two of concentrated sulphuric acid to 1 c.c. of [acet]aldehyde. The mixture becomes hot in consequence of the aldehyde undergoing polymerisation to paraldehyde (C2H4O)3, b.p. 124deg, which separates as an oil on adding water."

The sulphuric acid serves as a catalyst here. This reaction can be used advantageously to transform acetaldehyde to paraldehyde immediately, rather than storing (or trying to store...) acetaldhyde. Acetaldehyde produced in whatever way is led into a suitably sized RBF with a few drops of sulphuric acid (typically "one drop per cc. of acetaldehyde"), yiedling paraldehyde.
The reverse reaction takes place when paraldehyde is heated again with a few drops of sulphuric acid. "Paraldehyde does not show the characteristic aldehyde reactions; on destillation with dilute sulphuric acid it is converted back to the ordinary variety" (Gattermann, Practical Methods of Organic Chemistry). The liberated acetaldehyde can be collected in a cold-trap (e.g. cooled with an ice/salt mixture, etc.).

[Edited on 28-1-2007 by fractional]

Rosco Bodine - 28-1-2007 at 08:22

Paraldehyde is physiologically active IIRC , it is a hypnotic similar in action to chloral hydrate . So you might wish to be careful with this material , so as not to nod out unexpectedly .....and I don't recall what was the route of exposure ....contact , inhalation , or ingestion ....but
it is not a benign material .

fractional - 29-1-2007 at 04:20

Rosco is absolutely right about paraldehyde: it is physiologically active and a controlled substance (at least here in Europe). One can avoid handling this substance by applying a minor modification to the procedure:

"If aldehyde is cooled and treated with sulphuric acid, or if at the ordinary temperature gaseous hydrochloric acid, sulphur dioxide, or other compounds are passed into it, a solid polymerisation product, metaldehyde, is formed; this can also be coverted back into the ordinary variety." (Gattermann).

As a solid, metaldehyde is easy to handle, but it is also toxic, especially by inhalation. Wikipedia claims that it used as camping fuel for small stoves. I don't know about this, though.

Magpie - 1-2-2007 at 17:09

This is a followup to my post on making n-butyraldehyde from n-butanol using dichromate. I made 3 batches. The 2nd two were an effort to improve the control or efficiency of the 1st. The 1st was "by the book," only 1/3 scale because of the smaller size of my 19/22 glassware.

I didn't bother to calculate yields from each batch but just combined them for a final distillation to isolate the aldehyde. Upon review I think the book procedure is the best. The 2nd batch where I added the oxidant instead of the alcohol was pretty much a failure/disaster/runaway. For the 3rd batch I tried to conserve oxidant by using 2/3's of the specified alcohol and 1/2 of the specified oxidant. Near the end of the alcohol addition I ran out of oxidant as was evident from a lack of reaction as the alcohol was dripping into the pot.

I ended up with about ten mLs of aldehyde as a distillate from a fractional distillation using a 4 inch (10 cm) column packed with broken glass. Instead of coming over at the specified boiling point range of 72-76C (bp = 76C) it came over at 66C. I believe that this likely is an azeotrope with water which is 90.3% aldehyde and has a bp = 68C. I don't know what else to think.

I ran some qualitative tests on this distillate. It gave a positive test for Tollen's reagent (silver mirror) but a negative test for Fehling's reagent (Cu2O ppt). It gave a positive test with 0.3% KMnO4. It produced a small amount of white crystals after mixing with a saturated solution of potassium metabisulfite and cooling.

In conclusion I feel that this is an interesting but touchy way to make an aldehyde, and that one shouldn't expect a high yield. I would be interested in hearing about anyone else's experiences with this method.

Edit: I also wanted to mention that my aldehyde had a smell reminiscent of squeezed orange peels. It was pungent and overwhelming if I smelled too much of it.

[Edited on 2-2-2007 by Magpie]

fractional - 3-2-2007 at 04:13

Butyraldehyde forms an azeotrope with water:

b.p. 68,0 degC, with 90.3% butyraldehyde and 9.7% H2O in the azeotrope. (My source, a table of azeotropes from an old edition of the HB of Chem and Physics, only says "butyraldehyde", so I can only assume that they mean n-butyraldehyde)

So this seems to explain the lower boiling point. However, the table also indicates that two phases should be formed (with 96.8% butyraldehyde and 3.2% H2O in the upper and 7.1% butyraldehyde and 92.9% H2O in the lower layer). Is this in line with your observations?

Magpie - 3-2-2007 at 10:19

@fractional: Interesting. No, I cannot see two phases. I am giving some thought to dewatering with 3A molecular sieves and then rechecking the boiling point.

Nicodem - 4-2-2007 at 13:15

Magpie, you might want to try out the method from the attached paper. It is ridiculously easy, but therefore also kind of suspicious (especially since it is from Tet. Letters and there is no experimental data). It would be nice if someone verify it and report back the results, since I might have a use for it on an aliphatic alcohol as well. n-Butanol is not one of the substrates tested, but the yield from n-pentanol to n-pentanal was 65% which sounds really good for an aliphatic alcohol.

PS: Molecular sieves on aliphatic aldehydes does not sound as a very good idea…

Attached is: Tetrahedron Letters, 43 (2002) 8843-8844. doi:10.1016/S0040-4039(02)02234-7

Attachment: Selective solvent-free oxidation of alcohols with K2Cr2O7.djv (170kB)
This file has been downloaded 1263 times

Magpie - 4-2-2007 at 15:56

@Nicodem: Thanks for that reference. It seems like a simple method for making aldehydes and I might give it a try.

Why do you say not to use molecular sieves to dry an aliphatic aldehyde?

not_important - 5-2-2007 at 00:57

Quote:

Originally posted by Magpie
Why do you say not to use molecular sieves to dry an aliphatic aldehyde?

The sieves can function as bases or acids, depending, and give condensation and/or cross-redox products.

Sodium sulfate for a first drying, polish with MgSO4.

leu - 19-3-2007 at 13:37

Butyraldehyde is synthesized from butanol using manganese dioxide using a column in Proceedings of the Chemical Society 110 (1964)

[Edited on 20-3-2007 by leu]

Attachment: harrison.zip (20kB)
This file has been downloaded 1043 times

more interesting info about V2O5:H2O2

Rosco Bodine - 21-12-2007 at 04:00

This should have many possible uses .

Attachment: Synthesis of Vanadium Oxide Gels from Peroxovanadic Acid Solutions A 51V NMR Study.pdf (119kB)
This file has been downloaded 3510 times

Siddy - 23-12-2007 at 21:17

^ I cant work that link?

What about thought Ethyl Chloride (Chloroethane)?

EtOH + HCl > EtCl
(ZnCl2 catalyst)

EtCl + H2O2 > EtO
(catalyst?)

carbonic - 22-2-2008 at 15:03

I have a paraldehyde synth that's up for discussion or debunking. I was not trying to make paraldehyde, just to test some oxidizers so I wasn't taking notes or anything but it's easy to repeat if someone would like to check it against a Tollin's test or something.

I used two routes, percarbonate alone and percarbonate with ferric chloride. It seemed to me that percarbonate was a nice way to get a gently basic H2O2 oxider so I used ethanol as a test platform. H2O2 solution plus iron is called Fenton's reagent and is commonly used to oxidize contaminants all the way to carbon dioxide. It seems the ferrous (not ferric) ion busts the H2O2 into hydroxyl radicals, which are vicious oxidizers. From my tests, the ferric chloride just precipitates iron which makes all the H2O2 fizz out of solution. So although I got similar results using each method, I doubt the ferric was helping.

At any rate, the synth was simple: Add oxiclean (basically pure percarbonate with some borate stabilizers) to vodka and heat. About a scoop of percarbonate to 100ml 50% EtoH was what I used but I did not try to optimize. After heating for about 10 minutes, what I found was upon cooling, the solution split into two layers. One test was to pipette some of the lower layer into a test tube run under cold water - it solidified. Run under hot water it melted again, and would be kind of sludgy if left at room temp.

The second test was to filter the whole shebang (to get out the insoluble carbonates) and drop in an ice cube and stick it in the fridge. Almost the whole hundred ml turned to sludge which was then filtered and subjected to the same melting/freezing tests.

At first I was a bit puzzled, as I had expected acetaldehyde as a water-soluble product, but then it occurred to me that peroxide was a very efficient polymerization initiator so the acetaldehyde was probably polymerizing as soon as it was formed, creating a less-soluble product that eventually dropped out of solution. The data on peraldehyde seemed to match the liquid that I had, so I called it a day and dumped it out.

Well that's it: oxiclean as an oxidizer, who knew? I may try again soon to see if the mystery liquid haloforms, but I think Tollen's would be a better test. I might get some useful data from haloforming it, because ethanol gives a really weak haloform, whereas real ketones/aldehydes haloform almost violently.

My results are easy to duplicate, so if anyone out there has the capability to better analyze this product, please let us all know!

Edited to add another question: Why the hell would anyone want paraldehyde or acetaldehyde anyway? What's it good for?

[Edited on 22-2-2008 by carbonic]

Filemon - 24-2-2008 at 13:54

I read in Organic Sintheses, it may reduce to aldehyde from carboxilyc acid with formic acid. Making the pyrolysis of the calcic double salt. I have looked for the reference but I don't find it.

Nicodem - 24-2-2008 at 23:06

You forgot to look for those references on this forum as well:
https://sciencemadness.org/talk/viewthread.php?tid=2223&...

carbonic - 25-2-2008 at 09:48

but really, what is acetaldehyde good for?

Sobrero - 26-2-2008 at 05:08

Pentaerythritol synthesis

JohnWW - 26-2-2008 at 13:19

Yes, pentaerythritol, C(CH2OH)4, is made by the reaction of CH3CHO and CH2O in the presence of a strong alkali like KOH. The stuff is used for the manufacture of powerful nitro-explosives, especially the tetranitrate ester.

[Edited on 27-2-08 by JohnWW]

PHILOU Zrealone - 27-2-2008 at 03:34

Quote:

Originally posted by carbonic
but really, what is acetaldehyde good for?

Reactive molecule to introduce CH3-CHOH- or CH3-CH= moiety into a bunch of molecules displaying affinity for the carbonyl part.

[Edited on 27-2-2008 by PHILOU Zrealone]

Filemon - 11-3-2008 at 17:04

Quote:

Originally posted by solo
Note : here is a recent posting on the subject at the Hive,.......".Novel Discussions"

slothrop
(Newbee)
12-17-02 10:58
No 390260
Benzyl alcohols to Benzaldehydes

From Synlett 2002, 12, pp2041-42,
A Novel and Efficient Oxidation of Benzyl Alcohols to Benzaldehydes with DMSO Catalyzed by Acids
Typical procedure: A mixture of 557 mg of benzyl alcohol, 0.15 mL of HBr (48 %) and 5 mL of DMSO was stirred in an oil bath at 100°C. TLC (petroleum ether/diethyl ether, 1:1) was used to indicate the completion of the reaction (3 h). To the reaction mixture were added 5 mL brine followed by extraction with 30 mL of diethyl ether. The ether layer was washed with brine (5 mL x 4). Evaporation of the ether and subsequent buld to buld distillation produced 530 mg of benzaldehyde in 95 % yield.
//Tyrone Slothrop

How does it work?

MagicJigPipe - 11-3-2008 at 17:20

This sounds almost too good to be true. Has anyone even heard of this before? Or tried it?

I suppose I'll try it tomorrow since I have all of those reagents.

PHILOU Zrealone - 12-3-2008 at 02:26

Quote:

Originally posted by MagicJigPipe
This sounds almost too good to be true. Has anyone even heard of this before? Or tried it?

I suppose I'll try it tomorrow since I have all of those reagents.

CH3-SO2-CH3 is maybe a mild enough oxydiser...I suspect it must turn into CH3-SO-CH3 and maybe into CH3-S-CH3...but then you will notice by the very distinctive smell of it

Nicodem - 12-3-2008 at 03:39

It is some kind of a variation on the Swern oxidation, but it can only work on benzyl alcohols. Alcohols having alpha-hydrogens succumb to side reaction under such harsh conditions. Instead they require acid scavengers and acid chlorides or anhydrides for the DMSO activation under <0°C temperatures.

PS: DMSO is not Me-SO2-Me, it is Me-SO-Me and after reduction with benzyl alcohol (or whatever else) it converts to dimethyl sulfide (Me2S).

detritus - 28-4-2008 at 18:30

In the dictonary of applied chemistry on google books, p103 second column the dichromate + sulfuric oxidation is mentioned, but also another another I thought was good.

Manganese dioxide - aka the black packed substance in an alkaline battery. If you cut open the bottom of a big battery like a D cell, you can scoop out the zinc powder anode and save it. Watch out, it is caustic (er, alkaline).

Then, bend the case a bit to crack apart the 50+g of MnO2. I put a few g of this MnO2 plus a g or so of bisulfate beads into a jar and added everclear. Not much happening instantaneously, but when left overnight I saw a "dew" of droplets had appeared at the top of the walls. Opening and smelling, it was undoubtedly the light, clear fruity scent of acetaldehyde.

I suppose that conc. H2SO4 is better suited for this than the weaker bisulfate salt, but at least it proves that the cheap and readily available MnO2 can oxidize a primary alcohol to an aldehyde.

Formatik - 29-4-2008 at 16:44

Quote:

Originally posted by detritus
In the dictonary of applied chemistry on google books, p103 second column the dichromate + sulfuric oxidation is mentioned, but also another another I thought was good.

Manganese dioxide - aka the black packed substance in an alkaline battery. If you cut open the bottom of a big battery like a D cell, you can scoop out the zinc powder anode and save it. Watch out, it is caustic (er, alkaline).

Then, bend the case a bit to crack apart the 50+g of MnO2. I put a few g of this MnO2 plus a g or so of bisulfate beads into a jar and added everclear. Not much happening instantaneously, but when left overnight I saw a "dew" of droplets had appeared at the top of the walls. Opening and smelling, it was undoubtedly the light, clear fruity scent of acetaldehyde.

I suppose that conc. H2SO4 is better suited for this than the weaker bisulfate salt, but at least it proves that the cheap and readily available MnO2 can oxidize a primary alcohol to an aldehyde.

That MnO2 is also mixed in with carbon, so be careful using that in any experiments, e.g. as a catalyst in the thermal decompsition of KClO3 to generate oxygen gas.

detritus - 30-4-2008 at 15:28

good point. do you happen to know the approxamate ratios used in alkaline cells? Carbon to MnO2, that is...

Formatik - 2-5-2008 at 01:07

Quote:

Originally posted by detritus
good point. do you happen to know the approxamate ratios used in alkaline cells? Carbon to MnO2, that is...

I'm not sure exactly. I think there might be a patented formulation for the certain battery types. Will have to look into it more later.

Extraction of the pure compound would be some hard work. Some ideas of extraction: Any water solubles like the chloride could be removed by heating the solid with water and strong stirring. The carbon is insoluble in water but so is MnO2, though MnO2 will dissolve in HCl (Caution: chlorine gas): MnO2 + 4 HCl -> Cl2 + MnCl2 (pink) + 2 H2O. The carbon should be insoluble. Should be able to get MnCO3 (insoluble) from MnCl2 and Na2CO3 solutions. Then heat MnCO3 to 260°C (in air), and react the residue with very dilute cold HCl acid to get MnO2. It is also said to form by precipitating from MnCl2 with an alkaline hypochlorite solution, etc.

[Edited on 2-5-2008 by Schockwave]

Jimmymajesty - 9-7-2009 at 10:48

Sorry for bringing up an old tread.

I once made peroxi-acetone in my old kewl days. I didn't read forums like this at that time, so I thought that the warmer the solution the more peroxi-acetone will form

, so I mixed acetone with hydrogen peroxide, I can't remember the ratios (I also didn't care too much with it

) but I seem to remember that the acetone were in large excess.

I dumped the HCl into the mix by mililiters until it got warmed then put it into my cellar, after a couple of days filtered off the product...

The interesting point is... when i took the remained most-wit-buddha-knows-what-in-there solution, heated up a copper wire and put in it and it started to foam and heat immeadiately, I never had acetaldehyde only did tube experiments with hot penny, but the smell was the same IIRC, the whole solution (about 300ml) were boiled out of the jar, a lot of gas were generated!

Does somebody has a guess what could that be?

Any answer or guesswork would be appreaciated. Thanks!

DJF90 - 2-9-2009 at 14:59

Seeing as the thread is "alive" again I'll add something.

@Nicodem: This is the Kornblum oxidation. The HBr is there to form the alkyl bromide, which is attacked Sn2 style to form the same activated complex as all the other related DMSO oxidations (pfitzner moffatt, swern, onodera-albright, albright-goldman etc etc.) The reaction is NOT limited to benzyl alcohols. The original work was done with alpha-haloketones to yeild glyoxals, but some modifications were introduced to make it work better for other substrates. In fact the benzyl halides reacted to give poor yields of benzaldehyde. Generally the conditions consist of an alkyl halide, NaHCO3 as a base, and DMSO as solvent, temperature ca. 140C. If X= Cl or Br, then 1.5eq. NaI can be added to facilitate reaction. The reaction generally works better with the corresponding tosylates (X= OTs) and this will work with primary substrates to give the corresponding aldehyde. The tosylate can be prepared as "normal" using TsCl on the appropriate alcohol, or by using silver tosylate (TsOAg) on the corresponding halide. The tosylate is then reacted with DMSO, and the conditions are somewhat milder if I remember correctly; Stirring the tosylate in DMSO at room temperature is sometimes satisfactory.

Jimmymajesty - 3-9-2009 at 11:39

I made acetaldehyde by refluxing 93% ethanol on hot copper, after 4 hour of refluxing the acetaldehyde started to distill over the column... I think it was heavily contaminated but sniffing it behaved the same way as formaline.
Theres nothing in the first couple of seconds then you cry like hell...

I also pured a small amount of destillate (I do not know what was the contaminant but the boiling point of the distillate was much higher than 20°C) into saturated NH3 solution and it warmed a lot and gave a white emulsion (I think it would have been impossible to filter) anyway my three necked flask broken at the 5th hour. So I shut down the setup... When I went back to check the setup the whole thing burned... scared the shit out of me to put it soft...

I ordered another flask for my home-made acetaldehyde plant and I will give this another try when I have the time and post the results.

By the way I can post picture of the whole setup taken before it fell apart if anyone is interested.

Picric-A - 3-9-2009 at 12:01

Can NaHSO4 be substituted for KHSO4 in the dehydration of tartaric acid to pyvuric acid?

Klute - 3-9-2009 at 14:04

Please, do post theses pictures!

Pictures from the setup

Jimmymajesty - 5-9-2009 at 08:15

The first picture is talking to itself... the tube were filled with copper foil peeled off from gauging rods

The second is destined to illustrate the small tube in the three necked RB flask. It is necessary for the continuous reflux of ethanol.

The setup is on the third picture...

The condensation front in the condenser was kept at the level of the second bubble IIRC.

I inserted two scrubbers opposed to each other to the end of the plastic tube so as to the starting point of the oxidation would be indicated, when the reaction started I sampled the generated gas once in a while in a test tube, smelled and lit it... it seemed to mainly consist of hydrogen because it was odourless and burned with a blue flame in dark.

I am gona buy a controller for the next run too to keep the reactor temperature below 300°C.

I saved the milk like product, which I think mainly consists of aldehydeammonia... I do not know what to do with it in this form... any idea?

Klute - 5-9-2009 at 17:32

Beautifull setup! Unfortunate that the experiment wasn't very conclusive.. Please let us know of futur tries!

Jimmymajesty - 11-10-2009 at 04:38

Ok... everithing gone to waste what I wrote abot half an hour, this is definitely not my day.

So, I gradually increased the setpoint of the glass reactor from 280°C to 420°C.

From two liter ethanol after a couple of hours of run, I fractionated about 50ml foul smelling liquid T=20-60°C wich gave cristallyne solid on addition of NaHSO3.

I am gona try again with copper foil.

Because... I used stripped copper cord stuffed in the glass tube at this experiment.

[Edited on 11-10-2009 by Jimmymajesty]

Da_Boss - 13-10-2009 at 01:36

Could you make acetaldehyde from chloral hydrate?

DJF90 - 13-10-2009 at 05:48

Not likely, unless you want to spend a long time/expensive reagents removing them chlorine atoms...

Aqua-regia1 - 23-11-2009 at 11:32

Reply Post: 2312 ethylene glycol - again

Has anybody acces to this paper:
Tetrahedron Volume 58, Issue 11, 11 March 2002, Pages 2091-2094 Ethylene glycol to acetaldehyde-dehydration or a concerted mechanism

Sedit - 23-11-2009 at 11:44

Since this is not the place for it you may have better luck in the Reference request thread then you will here.

bbartlog - 7-12-2009 at 18:51

Looking back through this thread, I see that ethylene glycol has been discussed in the context of sulfuric acid oxidation, but not otherwise (and it looks like dioxane is actually what you'll get...).
However, after seeing this: www.sciencemadness.org/talk/files.php?pid=75149&aid=1734 elsewhere here, I wonder about hypochlorite as a way of oxidizing ethylene glycol to acetaldehyde.

In this case, it looks like the primary products are formaldehyde, acetaldehyde and ethylene. But they're discussing an uncontrolled oxidation with concentrated oxidizer. It seems like slow addition of hypochlorite solution to hot ethylene glycol, with condensation of any evolved gas, might result in a greater proportion of acetaldehyde.

I'll try this and report on the results.

So far as dioxane (or the possibility of other products) is concerned, it seems like the production of such a compound might be heavily influenced by the amount of water present in the system. It looks like condensation to dioxane would be driven by the water-withdrawing nature of H2SO4, so that some difference in conditions (like more water in the system) might instead allow the H2SO4 to act as oxidizer, and result in different products.

not_important - 7-12-2009 at 22:23

First, they are referring to polyethyleneglycol, H(-OCH2CH2O-)nH, not ethylene glycol.

Second, this is not a simple oxidation, the paper explicitly mentions radical mechanisms, look on page #5 of the PDF. I suggest that you might show how oxidation of HOCH2CH2OH (C2H6O2) leads to CH3CHO (C2H4O)

Third, attempting to keep it controlled looks as if doing so may be difficult; there are plenty of easier and higher yielding ways.

Nicodem - 8-12-2009 at 02:07

Bbartlog, ethylene glycol and acetaldehyde are in the same oxidation state. Therefore, you can not obtain acetaldehyde from ethylene glycol oxidation. I suggest you to learn how to count oxidation states as this is pretty much basic chemistry without which you can not do.

You can not just rearrange ethylene glycol or 1,4-dioxane to acetaldehyde using protic acids because primary alcohols do not undergo eliminations that easily, while the conditions required would be too harsh for the acetaldehyde to "survive". It might be possible by passing ethylene glycol or 1,4-dioxane vapors over some some solid acid (alumina, acidic zeolites, silica, etc.) at high temperature (300°C or more). Such heterogenous conditions should prevent the acetaldehyde to decompose, but still yielding a mixture of products. But this is not easily done in an amateur setting and besides I was not able to find any references confirming such an idea would work.

Aqua-regia1 - 8-12-2009 at 12:59

The pinacol rearragement of ethylen glycol doesn't work. I tested it, with several H2SO4 conc. The only one way: dehydratation route. (to difficult in home lab, therefore expensiv too) But dehydratation is not to very same oxidation.

bbartlog - 8-12-2009 at 13:34

I see what you mean about the oxidation states, C2H6O2 versus C2H4O. This is in line with what not_important says about the polyethylene glycol, not ethylene glycol, being the substance oxidized.

Quote:

I suggest that you might show how oxidation of HOCH2CH2OH (C2H6O2) leads to CH3CHO (C2H4O)

Looks like it can't. Oxidative glycolic cleavage might still be possible, leading to formaldehyde? Anyway, there is a reaction, but I have yet to distill the solution to try to separate the product(s). An interesting parallel between the Ca(OCl)2 / polyethyene glycol reaction and the one I observed (6% NaOCl + ethylene glycol) is that both seem to be delayed. They describe a 30 second delay before a fairly sudden hissing and fireball, while in the case of my mixture nearly five minutes (with shaking of the test tube) passed before the solution rapidly heated up. Could be purely thermal runaway, I might try a test tube in a beaker of ice water and see what happens. If it still heats suddenly after a similar delay then something else is going on.

Jimmymajesty - 24-3-2010 at 14:24

At the production of dioxane small amount of acetal forms which on hydrolysis releases acetladehyde but the acetladehyde reacts with alcohols (glycol in this case) to form acetals (I think).

It may wort to try to warm ethanol and drip NaOCl solution into it, here the product would be croton aldehyde which can also be used to make stuff

The home performed dehydrogenation is actually feasible, read the attached paper (oxidative dehydrogenation), it is not that difficult to make similar apparatus at home.

I collected some info on the web regarding acetaldehyde synth by dehydrogenation which I want to share with you not only for informational purposes!

I hope some of you will try out and improve the method, and finally post the results.

+Catalytic dehydrogentation is a better method to make acetaldehyde due to less side reactions. The copper catalysts perform better than type of silver and lasts longer.

+Cu-Co-Cr2O3 @ 280-350°C is used industrially (5w%Cobalt+2w%Chrome+93w%Copper), the method of cat. prep. consists of coprecipitation from acetate salts, and calcining at 550°C max. Then one have to reduce the cat. by hydrogen... I think it is not necessary as the cat. will be reduced under ethyl alcohol wapors anyway.

+The Cu to Cr mole ratio is optimal at 10:1.

+The yield is affected by the water content of the original water+alcohol mixture the more the alcohol the more ethyl acetate will form.

+Copper from electroplating seemingly do not catalyse dehydrogenation, high surface are is required! (When I read this I stopped electroplating copper to steel sponge

)

I also have the suspicion that the converter (catalyst used to oxidize stull like NxOy and CH into water etc. may be used to make acetladehyde in a controlled manner.

Attachment: Acetaldehyde production experimental.pdf (179kB)
This file has been downloaded 1666 times

Melgar - 29-3-2010 at 06:10

I actually made some of this stuff recently. I took a piece of copper pipe and dissolved it in aqua regia. Then I neutralized with a base. You can use any base, but you can burn away the ammonia salts if you use ammonia, to get a purer CuO. The catalyst works even if sodium salts are present though. Anyway, once you neutralize, then boil away all the water, and the mixture will turn black. That's CuO, with other salts mixed in. If you neutralized with ammonia, the mixture will smoke and burn at points as the ammonium nitrate decomposes or oxidizes other components of the mixture.

The next step was putting the CuO into a big test tube. Then I got a two-hole stopper and ran a stainless steel tube to the bottom of the tube, then ran another one from the top of the tube to a beaker of cold water. I'm sure glass or copper tubes would work fine too, I just happened to have SS on hand. I boiled alcohol in a bottle connected to the inlet tube, then put an alcohol lamp underneath the test tube of CuO. As vapors entered the test tube, I could see patches of black CuO turning into pink patches of copper metal. The acetaldehyde vapors smelled like a fruitier, not-as-nasty version of formaldehyde. As in, it smelled a little like formaldehyde, but didn't burn my eyes and throat.

I realize I didn't control the temperature of the catalyst and thus probably generated some formaldehyde in addition to acetaldehyde, in which case the fruity smell was probably the acetaldehyde. It did work, although I have to add that this stuff has too low of a boiling point to be able to condense it efficiently or have it around in a pure state. You pretty much have to dissolve it in a liquid.

Melgar - 31-3-2010 at 14:49

Just discovered two more ways of making acetaldehyde. First is reduction of acetonitrile with tin(II) chloride in hydrochloric acid. This turns tin(II) chloride to tin(IV) chloride and acetonitrile to an iminium salt which is hydrolyzed to acetaldehyde. Look up the "Stephen aldehyde synthesis" for this one.

The other method is the ozonolysis of propylene. Those yellow torch tanks you find at the hardware store are mostly propylene, and you can CAREFULLY!!! bubble them into a polar solvent (preferably a nonflammable one) to dissolve it, then bubble ozone in to split it into acetaldehyde and formaldehyde. You need to do it in a reducing environment to get these products though. Also, the gas from these tanks typically has an odorant added to it, which will give it that sulfury gas smell, but that is at a really low concentration and shouldn't affect the chemical properties, although it would make it harder to tell by smell what your products are.

Fleaker - 31-3-2010 at 16:20

The sulfury gas smell would be rendered odourless by ozone! Not that my idea of fun is making ozone and using it as an oxidiser!

Interesting on the stannous chloride side. Please post more information/mechanism and references. I love my tube furnace reactions, but this method sounds VERY intriguing.

Melgar - 31-3-2010 at 23:47

Quote: Originally posted by Fleaker

The sulfury gas smell would be rendered odourless by ozone! Not that my idea of fun is making ozone and using it as an oxidiser!

You're right, although the gas is detectable even at really low concentrations so you'd probably still smell it if you didn't get it all. I have an ozone generator that I use to deodorize/sanitize stuff on occasion so I've already got that covered. On the bright side, the odorants tend to be methyl/ethyl sulfides, which are used as reducing agents in ozonolysis anyway.

Quote:

Interesting on the stannous chloride side. Please post more information/mechanism and references. I love my tube furnace reactions, but this method sounds VERY intriguing.

Apparently it requires tin(II) chloride dissolved in ether, then saturated with hydrogen chloride. Check out the attachment.

Yet another synthesis appears to be the destructive distillation of calcium formate and calcium acetate, which would also produce low yields and a lot of acetone, CO2, and hydrogen, but at least it's really straightforward.

Attachment: stephen aldehyde synthesis.pdf (254kB)
This file has been downloaded 1937 times

[Edited on 4/1/10 by Melgar]

Melgar - 31-3-2010 at 23:56

Also, tin is pretty easily obtained from lead-free solder, since I have yet to see a lead-free solder that is less than 95% tin. However, the hardware store muriatic acid I have has quite a bit of iron dissolved in it, (visible by the yellow color) and this immediately plated onto the tin solder and seemed to prevent it from dissolving very much. Still, this seems to be a good way to get the iron out of my muriatic acid, if nothing else.

Jimmymajesty - 1-4-2010 at 00:04

Nice try! But I am afraid you only made small amount of the required stuff

I am going to co-precipitate cobalt and copper hydroxydes, pour the slurry to MgO, activated carbon, or alumina, and heat it to 500°C for some hours. Another way would be the one suggested by Melgar, that is to dissolve the hydrohydes in aq. ammonia, pour the solution to something porous and inert, vacuum treat the stuff then heat it then crush it in a mortar to granules. I can see one problem with MgO carrier, namely it absorbs water so when alcohol wapor is passed ower it it would become a gel and loose catalytic properties, so my preferred mat. would be activated carbon particles, they have a lot of surface and can not be dissolved in alcohol ofc. Or rather! the insulation from kanthal heating filaments, they are made of 96w% Al2O3, being totally heat and corrosion resistant.

Acetonitrile method? I also know some exotic procedure during which acetaldehyde is liberated, some diazotization e.g. but i dunno if you could make decent quantity of acetaldehyde by that..

Propylene ozonolysis in home lab?

I can only see countless problems. e.g. generation of ozone in useful quantities is a PITA. BTW the smell is probably from ethyl mercaptan which is oxidized by ozone to SO2 then SO3 if you use excess of ozone, I also have a suspicion that sulfur containing material are more prone to oxidation that propylene, also IIRC propylene+ozone=explosion unless low temps are used.

I am goint to try out the above posted catalysts asap and post the results.. that means months unfortunately.

Oh! When I made acetaldehyde with my previous setup by catalytic dehydrogenation, the smell was rather unpleasant and spicy when you took a nosefull of it, it means that a lot of side reaction occurred?!.. The themp of the condenser was not controlled, and the temp. control in the reaction zone was crude too.. I have to overcome these problems!

Melgar - 1-4-2010 at 01:12

My ozone generator can do 600 mg an hour in air, meaning it can make a little less acetaldehyde than that. The formaldehyde is a bonus if you can use it. Since it uses a 1/3 duty cycle on its highest setting, that's like a gram and a half overnight. Also, in an insulated container with lots of ice and calcium chloride, chances of explosions are minimal if your solvent isn't flammable. CH2Cl2 is used a lot for this reason, although I personally have yet to try it. Still looking for a decent reducing agent. Also, I'm pretty sure ozone attacks double bonds preferentially, then sulfur compounds after that. Oh, and mercaptans are oxidized to different things depending on the oxidizer, but rarely to SO2 or SO3.

Actually, the acetonitrile method seems like it would be the most likely to give good, consistent yields, since the iminium salt precipitates out and can be filtered from the ether. I'll probably try the destructive distillation route too since I have the formic acid, acetic acid, calcium chloride, and sodium hydroxide that are required.

Activated carbon will burn if there's oxygen present and it's hot enough, so there's a good chance it could reduce your copper oxide to copper metal and leave as CO2. Aluminum oxide is available as sandblasting grit, and that seems to be a good catalyst substrate. It's used a lot in industry anyway. Plus it's white, so you'd be able to distinguish your catalyst from the substrate if nothing else. Even silica (sand) seems like it could do the job well enough.

hissingnoise - 1-4-2010 at 04:36

Quote:

Actually, the acetonitrile method seems like it would be the most likely to give good, consistent yields, since the iminium salt precipitates out and can be filtered from the ether. I'll probably try the destructive distillation route too since I have the formic acid, acetic acid, calcium chloride, and sodium hydroxide that are required.

Hydration of acetylene seems simpler, requiring only C2H2, H2SO4 and Hg.

Jimmymajesty - 1-4-2010 at 05:34

A gram and a half overnight is not that much unfortunately.. but try it and post the results please! I am working in an olefin plant so pure propylene is not that hard to get

My ozone generator are made of a test tube with Al foil wrapped around it and a tiny wire in it, I drive the generator with a flyback transformer from an old television... without the current rectifier part. But a germicide lamp would also do the job.

I dont have such things like DCM or acetonitrile, and based on a quick search, acetonitrile is not that easy to make at home..

I would prefer dehydrogenation rather than catalytic oxidation, but if I were to apply catalytic oxidation as a last resort. I would make silver mirror to a glass tube then stuff the tube with silver sponge made of fusing AgCl and Na2CO3. To cut it short I try the activated carbon first (large surface area) then Al2O3 insulation rings.

The idea which was discussed upthread is more feasible than the formiate etc methods. Namely you melt tartaric acid with KHSO4 to get pyruvic acid, and that readily decomposes to acetaldehyde however I am not sure about the conditions and temps that the last part requires. The first part of the synth: tartaric+KHSO4 is on org synth webpage. BTW the tartaric acid is more OTC here than sodium hydroxide that is a big plus!

Lambda-Eyde - 1-4-2010 at 07:59

Quote: Originally posted by Melgar

However, the hardware store muriatic acid I have has quite a bit of iron dissolved in it, (visible by the yellow color) and this immediately plated onto the tin solder and seemed to prevent it from dissolving very much. Still, this seems to be a good way to get the iron out of my muriatic acid, if nothing else.

Let me see if I got this right - you just leave a piece of soldering tin in the hydrochloric acid, and the yellow color dissappears? I'm not pleased with the coloring of my acid, and I don't have reagent grade at the moment.

Some tin will dissolve anyways, so I think distillation of 20% HCl would be the best way to go if I want it somewhat metal-free.

Melgar - 1-4-2010 at 14:03

Well, I tried putting some solder in my HCl again today, and the iron didn't come out as quickly as I thought it would, although it did come out eventually. I think the yellow iron chloride just gets replaced by colorless tin chloride. I'm not sure how much success would come from distilling HCl, since it's a gas dissolved in water. My plan was to combine CaCl2 and H2SO4 to form HCl gas, then bubble that into distilled water. Unfortunately, that reaction got a little out of hand and sulfuric acid got spilled all over the place. I'll try that again with more precautions once my workbench is de-acidified.

To make acetaldehyde via destructive distillation you need hydrated lime, formic acid, and acetic acid. Hydrated lime is dirt cheap at the hardware store but you can make it from NaOH and CaCl2 if you just need a little and don't feel like making a special trip. The reaction seems as though it would produce CO2, formaldehyde, acetone, and acetaldehyde. Probably more acetaldehyde than anything else, although I hear destructive distillation yields suck anyway.

Melgar - 1-4-2010 at 14:23

Quote: Originally posted by Jimmymajesty

I dont have such things like DCM or acetonitrile, and based on a quick search, acetonitrile is not that easy to make at home..

DCM is actually really easy to get. Just go to the solvent section of your local hardware store (our favorite section!) and find the paint strippers. They all have warning labels on them saying "CAUTION, FLAMMABLE!", "CAUTION, POISON!" or both. Look for the ones that don't say "flammable". Since DCM is practically the only nonflammable solvent in this aisle, any paint stripper that doesn't seem to be flammable is probably mostly DCM. Also, look for the sprayable stuff, as in, the stuff that doesn't come as a gooey paste. It's a lot easier to distill.

Acetonitrile isn't that cheap at $50 a liter or so, but every so often a reaction calls for it as a solvent, so I have a bottle on hand. Supposedly, a recent shortage drove prices up and they aren't normally that high.

DJF90 - 1-4-2010 at 14:32

Paint stripper is generally (at least in the UK) a blend of dichloromethane and methanol, so should still bear the "flammable" warning... you'll just have to read the label (this applies to wherever you are; theres nothing worse than buying something, attempting extraction and finding the desired material is not a component).

Lambda-Eyde - 1-4-2010 at 14:37

Quote: Originally posted by Melgar

Well, I tried putting some solder in my HCl again today, and the iron didn't come out as quickly as I thought it would, although it did come out eventually. I think the yellow iron chloride just gets replaced by colorless tin chloride. I'm not sure how much success would come from distilling HCl, since it's a gas dissolved in water.

I have distilled HCl with success, but it's only the 20,2 % azeotrope that comes over. That is, theoretically, as I haven't quantitatively measured it.
The 30 % acid first fumes like crazy until it reaches the azeotropic point, when it starts to distill over. Interestingly, the azeotropic concentration has a much higher vapor pressure than the 30 % concentation - Just like the distillate I obtained. I don't like the idea of using precious (at least precious to me) H2SO4 to make HCl. There is an alternative way which involves using CaCl2 as a drying agent to extract the water from aqueous HCl, making gaseous HCl.

Bubbling HCl gas made with this method through the distilled 20 % acid is a much more attractive method for me than using sulfuric acid. Alternatively I can wait a while and buy a liter from Chiron or Fisher Scientific...

But hey, this is going very off-topic. Sorry!

JohnWW - 1-4-2010 at 14:47

Paint stripper containing CH2Cl2 poses a hazard well beyond the fact that it is inflammable. When it burns, the major product would be phosgene, COCl2, which is deadly poisonous, and which was used, along with "mustard gas", by the Germans in WW1. Besides, volatile chlorocarbons are also known as liver toxins, if ingested or inhaled in any large quantity.

manimal - 1-4-2010 at 16:06

Quote: Originally posted by Melgar

Just discovered two more ways of making acetaldehyde. First is reduction of acetonitrile with tin(II) chloride in hydrochloric acid. This turns tin(II) chloride to tin(IV) chloride and acetonitrile to an iminium salt which is hydrolyzed to acetaldehyde. Look up the "Stephen aldehyde synthesis" for this one.

I'm pretty sure the Stephen aldehyde synthesis is done anhydrously with dry HCl gas being piped in.

The H2SO4 dehydration/rearrangement works, but only under pressure. At atmospheric pressures, the glycol gets etherified and escapes the reaction. There is a US patent somewhere on H2SO4 dehydration of simple glycols in a pressurized still.

Melgar - 1-4-2010 at 17:52

Quote: Originally posted by Lambda-Eyde

Eh, if I use cheap-ass buffered H2SO4 drain cleaner and CaCl2 driveway ice melter, it's not that expensive. I kind of like that reaction because it converts all the Cl and H ions to HCl and it goes slow enough that you don't get a room full of HCl vapors instead of getting them in solution. The CaCl2 + muriatic one is good too, although I don't think it's as efficient and it seems like you have to use a lot of CaCl2. But that stuff is cheap so who cares.

Quote:

Paint stripper is generally (at least in the UK) a blend of dichloromethane and methanol, so should still bear the "flammable" warning... you'll just have to read the label (this applies to wherever you are; theres nothing worse than buying something, attempting extraction and finding the desired material is not a component).

Yeah, that's true for the paint stripper here too, but I figured the methanol level must be comparatively low because the containers weren't marked as flammable. And yeah, reading the labels is always key.

Quote:

I'm pretty sure the Stephen aldehyde synthesis is done anhydrously with dry HCl gas being piped in.

Yeah, I post a more detailed explanation a few posts down.

Jimmymajesty - 6-4-2010 at 00:44

Hi folks!

If I were to make gaseous HCl I would pour 20w% HCl sol. into conc H2SO4 and distill off the gas, then lead it through a H2SO4 wash bottle to absorb traces of H2O, the H2SO4 then could be regenerated by heating.

I would not even attempt the CaCl2+H2SO4 method based on the Ca(NO3)2+H2SO4 experience, you will make an awfull mess for sure!

My problem is acetonitrile, I was a trainee once in an isocianate plant, acetonitrile was used as a solvent for HPLC uses, but I forgot to steal some..

I could buy DCM but it is expensive so I won't! BTW DCM based solvents is being drawn out from hypermarkets, at least in my country. I could buy it a year before or so, the methanol content was 10w%, but also there was a slurry layer on the bottom which was IIRC some kind of pine resin which during distillation solidifies maybe polyemrizes into the flask!

Melgar! you have all the necessary chems to give the procedure a try! so it is your turn!

Nicodem - 6-4-2010 at 00:59

If you only want a small amount of acetaldehyde you can just try with the Kornblum oxidation of ethyl bromide. Ethyl bromide can be made from ethanol, KBr/NaBr/NH4Br and H2SO4 (there are examples on the forum). Ethyl bromide reacts with DMSO fairly rapidly, so all you need to do is stir a solution of ethyl bromide and NaHCO3 in DMSO for a day at room temperature and then distil out acetaldehyde (mind the condenser cooling!). The Kornblum oxidation generally requires heating at 80-100°C for most alkyl halides, which is not an option for the volatile EtBr, but I think its reaction with DMSO to give the intermediate S-ethoxysulfonium ion, occurs at lower temperatures already.

Melgar - 6-4-2010 at 01:24

Quote: Originally posted by Jimmymajesty

Hi folks!

If I were to make gaseous HCl I would pour 20w% HCl sol. into conc H2SO4 and distill off the gas, then lead it through a H2SO4 wash bottle to absorb traces of H2O, the H2SO4 then could be regenerated by heating.

I would not even attempt the CaCl2+H2SO4 method based on the Ca(NO3)2+H2SO4 experience, you will make an awfull mess for sure!

Weird, I've done both reactions and they never gave me much trouble. The end result is CaSO4, aka gypsum. But it's gypsum as a powder which is easily washed out with water. Granted, the H2SO4 is a loss, but I found a pretty cheap local source ($10 a liter) so it's not a major problem.

I think heating the H2SO4/water/HCl mixture would give off a lot of fumes. But I guess you could send the vapors through any basic solution to minimize smells.

Quote:

My problem is acetonitrile, I was a trainee once in an isocianate plant, acetonitrile was used as a solvent for HPLC uses, but I forgot to steal some..

My problem is lack of ether. I have some, but it's definitely not very clean or dry, and probably is contaminated with water and ethanol. I'm trying to dry it using an aluminum amalgam, since that should theoretically work almost as well as sodium or potassium. It'd be nice if I didn't have to make it myself from Everclear.

As for the other two reactions, they both produce formaldehyde, and I want to try and make formaldehyde-free acetaldehyde so I can make sure I recognize the smell.

Lately I've been trying to make my own ethanol from distiller's yeast and sugar water. It's been a little tricky initially, especially hooking my distillation apparatus up to a practical boiler device. However, I did notice something VERY interesting. When it's hooked up, the first bit to come over smells identical to what I smelled when I ran ethanol vapors over copper oxide. No formaldehyde smell either. This makes sense, because these buckets have been sitting around for at least a month beyond when they were ready, as I've been trying to make time to distill them. They weren't airtight, so it seems plausible that oxidizing bacteria have gotten in and started to oxidize the ethanol to acetaldehyde. The next step would be acetic acid, but that has a higher boiling point and they probably haven't gotten there yet. If this really is acetaldehyde, this would be a really easy way to make it, although there would have to be a way to get it out of the ethanol/water/acetic acid that it's dissolved in.

By the way, the smell that I think is acetaldehyde is a sweet, fruity smell that smells vaguely like overripe plums. I'm still not sure how to get it out. Making an imine perhaps? But then, how to isolate the imine? And would it be especially temperature-sensitive?

[Edited on 4/6/10 by Melgar]

Melgar - 6-4-2010 at 13:37

Just did the acetonitrile reaction in ether, but even though it was successful, it was kind of a letdown to do all that work for a test tube half full of something that smelled like overripe plums. But anyway, I think that's the last time I'm going to do that reaction. I can make liters of the stuff by fermenting sugar in buckets and letting it oxidize beyond the initial fermentation. Plus, I learned that sodium bisulfite will react with acetaldehyde to form a precipitate. The precipitate can be made to release acetaldehyde by treating it with a base. You can probably get sodium bisulfite from brewing stores, but you can also make it yourself. I did. Basically, you have to bubble SO2 through an aqueous solution of Na2CO3. I got the SO2 by burning sulfur in a jar and having an aquarium pump pumping in fresh air, while the fumes were going out an exhaust pipe and into the Na2CO3 flask. It was a fairly cool and very easy reaction, while not being all that dangerous either.

Jimmymajesty - 8-4-2010 at 12:26

The case is the same with DMSO.. unfortunately i do not have any.

I think the best method would be ethanol dehydrogenation or catalytic oxidation, as there wold be no side products, (maybe some ethyl acetate and acetic acid which can be fractionated and used for something else). If croton aldehyde formed due to harsh reaction conditions it could still be used for making penataeritrithol.

I am not familiar with fermentation processes, but Melgar promised to try it out and post the results as his next experiment so I leave it for him

Be careful with yeast because it can easily overoxidize your desired product to acetic acid, and it will certinly do so in that conditions.

Yes saturated NaHSO3 (best if freshly made because it has the tendency to absorb oxygen) solution and acetaldehyde forms a crystalline compound which can be decomposed by adding a strong acid, the case is the same with cc NH3 solution, you can make aldehyde ammonia then release the aldehyde by adding H2SO4.
BTW in wine shops potassium metabisulphite can be bought which formula is K2S2O5, maybe you can convert it to KHSO3 by adding KOH I am not sure of that, I am also uncertain if K2S2O5 forms precipitate with aldehydes.

When pure sulphur is burnt SO3 forms too which makes a white smoke with atmospheric moisture, so your sulphite will not be purer than 92% of the theoretical at saturation (IIRC).

Oh! Have you identified the aldehyde by silver mirror test?

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