Sciencemadness Discussion Board

acetaldehyde?

Lithium - 31-3-2012 at 23:55

hello

down in my lab, i have been making various hypochlorites.
anyway, i mixed 55ml of super saturated Ca(OCl)2 solution with 30ml of metho ( 95%+ EtOH). the solution did nothing for a while, but after about 5 mins the solution got too hot too touch and a small amount of bubbling occured. my lab now smells very fruity, and the sol. smells fruity too(kind of like the smell of ripened fruit that grows off of a plant in our yard, it is called a Monstera deliciosa.) the smell is very intense. there was also a precipitate that formed. i have saved the solution in a small dish. have i made acetaldehyde solution? if so, how would i go about seperating it from other impurities in there( i have no distillation setup:()

any help is very much appreciated:)

Li

frenchemist - 1-4-2012 at 00:30

Hello,

This is probably acetaldehyde, you could test the solution with 2,4-dinitrophenylhydrazine, if a precipitate occur, it's an aldehyde.

Alex

weiming1998 - 1-4-2012 at 00:31

It's not exactly acetaldehyde, at least not the main part of it. It is mainly chloroform. Google "chlorination of ethanol by hypochlorites". http://www.erowid.org/archive/rhodium/chemistry/chloroform.h...
This link has an explanation of what happens when ethanol is chlorinated by hypochlorites. The Ca(OCl)2 simultaneously oxidizes and chlorinates the ethanol, producing trichloroacetaldehyde, or chloral, and Ca(OH)2, which reacts with the chloral to form chloroform and calcium formate(which, along with excess Ca(OH)2 and other contaminants in your Ca(OCl)2) by the following reaction: C2HCl3O+Ca(OH)2===>CHCl3+Ca(COOH)2.

As for making acetaldehyde, combine ethanol, KMnO4 and some catalytic H2SO4(diluted) or NaHSO4+water together. You get a mix of MnO2, CH3CHO, and Na/K sulfate salts. As the sulfates are not very soluble in cold water, chill the solution as much as possible, then filter out the resulting precipitate. The acetaldehyde, being a gas, is more soluble in cold water than hot, and will not fall out of solution.

Lithium - 1-4-2012 at 01:02

oh, dissapointment.:D

i don't have a use for MeCHO, but i just wanted to isolate some for fun.

do you think i should just chuck the sol. out, or should i make some sort of ghetto distillation setup.

does MeCHO polymerise like H2CO?

Li

weiming1998 - 1-4-2012 at 01:18

http://www.mindfully.org/Plastic/Monomers/Acetaldehyde-Polym...
Different acetaldehyde polymers.

Also, don't chuck your solution out. Filter it, then separate the bottom layer of chloroform with a syringe or a pipette. Then add this to sodium hydroxide. Sodium formate is formed. React that with a strong acid to make formic acid.

Lithium - 1-4-2012 at 01:23

there is no CHCl3 layer, and it doesn't smell at all like it.

i have already filtered it.

i don't think there is any CHCl3 in my solution.

Li

weiming1998 - 1-4-2012 at 02:00

There is no layer because the chloroform is miscible with ethanol, which is miscible with water, which gives you a homogenous solution. To test and see if any chloroform is in your solution, react the solution with sufficient NaOH, then boil it down. After, extract with large amount of methanol/ethanol, evaporate and react with sulfuric/oxalic acid. Then react the resulting solution with CaCO3, filter and boil down. Stop when something precipitates. When cooled down, if the amount of precipitate did not get significantly larger, then you have chloroform in your solution.

That, or boil with pyridine and NaOH, as described: http://www.jbc.org/content/58/2/641.full.pdf
Use the one that's the most available to you.

AndersHoveland - 1-4-2012 at 02:10

Acetaldehyde is also found in some insecticides sold in stores, where it is referred to as "metaldehyde".

Lithium - 1-4-2012 at 02:34
Quote:
by weiming1998
Also, don't chuck your solution out. Filter it, then separate the bottom layer of chloroform with a syringe or a pipette. Then add this to sodium hydroxide. Sodium formate is formed. React that with a strong acid to make formic acid.
Quote:

There is no layer because the chloroform is miscible with ethanol, which is miscible with water, which gives you a homogenous solution.


confusing much?

i am going to throw out this solution and reperform the synth using potassium hypochlorite instead.

just wondering, is a 10% KClO sol as stable as it's sodium analogue?

i think i have been exposed to too many chlorine containing compounds, i will do some stuff throughout the school holidays.

every time i am exposed to chlorine and hypochlorites, the front of my forehead feels warm and my brain feels a certain way(not good or bad, just weird)
then of course i smell like chorine for the rest of the day, which makes me feel sick.

my original idea was to use 1methoxy 2 propyl glycol ether, but i could not open the lid( my fingers started bleeding, so i gave up:o)

does anyone know what the outcome of that would be?

(i have just noticed that i usually end my post with a question)

edit: damn, your a national hazard now weiming1998!yay!:o:cool:
Li

[Edited on 1-4-2012 by Lithium]

[Edited on 1-4-2012 by Lithium]

weiming1998 - 1-4-2012 at 03:19

Quote: Originally posted by Lithium  

Quote:
by weiming1998
Also, don't chuck your solution out. Filter it, then separate the bottom layer of chloroform with a syringe or a pipette. Then add this to sodium hydroxide. Sodium formate is formed. React that with a strong acid to make formic acid.
Quote:

There is no layer because the chloroform is miscible with ethanol, which is miscible with water, which gives you a homogenous solution.


confusing much?

i am going to throw out this solution and reperform the synth using potassium hypochlorite instead.

just wondering, is a 10% KClO sol as stable as it's sodium analogue?

i think i have been exposed to too many chlorine containing compounds, i will do some stuff throughout the school holidays.

every time i am exposed to chlorine and hypochlorites, the front of my forehead feels warm and my brain feels a certain way(not good or bad, just weird)
then of course i smell like chorine for the rest of the day, which makes me feel sick.

my original idea was to use 1methoxy 2 propyl glycol ether, but i could not open the lid( my fingers started bleeding, so i gave up:o)

does anyone know what the outcome of that would be?

(i have just noticed that i usually end my post with a question)

edit: damn, your a national hazard now weiming1998!yay!:o:cool:
Li

[Edited on 1-4-2012 by Lithium]

[Edited on 1-4-2012 by Lithium]


Sorry, for the contradicting talk about layers of chloroform, that happened because I thought you have all your ethanol reacted away. When you said that there were no layers, I realized that you still have some ethanol left in your solution, and that caused the "no layers" problem.

Potassium hypochlorite is as stable as sodium hypochlorite, and will not decompose unless it was heated, and even then the green colouration of the solution won't go away until over half is boiled away! But if you use too much of KClO, the chloroform might be decomposed to potassium formate by:
First KClO+H2O<===>KOH+HClO. Removal of KOH by CHCl3 causes a shift of the equilibrium to the right, causing you to end up with a solution of slowly decomposing HClO, K formate and KCl. Same thing happens to Ca(ClO)2, but since Ca(OH)2 is only slightly soluble, and reacts with CHCl3 very slowly, or not at all because the formed Ca formate is very soluble, this is much less of an issue. So, if you want to use KClO, make sure you do a calculation, use a scale, and if unsure, use excess ethanol!

barley81 - 1-4-2012 at 05:56

@Lithium,
The huge, ancient thread about making acetaldehyde:
http://www.sciencemadness.org/talk/viewthread.php?tid=55

It seems like your best bet is dehydrogenation/oxidation of ethanol vapors with a copper catalyst. Read for more details.

[Edited on 1-4-2012 by barley81]

Lithium - 1-4-2012 at 22:31

hello

i have left the solution to sit and it now has formed a white precipitate. it no longer smells like fruits, rather a mixture of CHCl3 and EtOH(funny that;))

i have chucked it out though, i did not realise that it could have polymerised MeCHO!:o

just a warning: when i was mixing the K2SO4 and Ca(OCl)2, the hypochlorite solution spilt on to an old towel. the little bits of undissolved 'pool hypo' clung to the fibres, and resulted in the towel first smoking violently, then it bursted into flames!:o

Li

weiming1998 - 2-4-2012 at 00:42

Quote: Originally posted by Lithium  
hello

i have left the solution to sit and it now has formed a white precipitate. it no longer smells like fruits, rather a mixture of CHCl3 and EtOH(funny that;))

i have chucked it out though, i did not realise that it could have polymerised MeCHO!:o

just a warning: when i was mixing the K2SO4 and Ca(OCl)2, the hypochlorite solution spilt on to an old towel. the little bits of undissolved 'pool hypo' clung to the fibres, and resulted in the towel first smoking violently, then it bursted into flames!:o

Li


Really? I filter my KClO with just old cloth, and the only thing that happens is that later, when the towel is dried, the cloth becomes extremely weak. If I filter with paper towel though, it can eat a hole through the paper in no time! No smokes though, just a hole. Wet Ca(ClO)2 doesn't cause paper towels to spontaneously combust either, as far as I know.

The precipitation, though, might not be polymerized acetaldehyde. It might be that your solution evaporated a bit(the ethanol evaporates more than the water in the mix), and the various salts dissolved the ethanol precipitated out. Next time, if you get the precipitate again, then try and light it on fire. Polymers of short-chained aldehydes are, when exposed to high temperatures, extremely flammable, while if it is a salt, then it isn't flammable.

Lithium - 2-4-2012 at 02:22

it could not be precipitated salts because the solution was kept in a capped bottle for a day.

the filter paper just fell to bits, no combustion or smoking, just heavily broken down.

in fact i could not distinguish it from the CaSO4 ppt i was filtering

the towel on the other hand, well let's not go there;)

i had to use 5 filter papers for filtration, and i couldn't even find them afterwards!

in the school holidays, i will be experimenting a lot with hypochlorites and perchlorates( can't wait for my cell to finish,in 2 weeks!)

Li