oneup - 17-1-2006 at 11:46
Can anyone tell me if this hexmine synthesis will work:
Mix 15g Potassium Permanganate and 50mL 50% Sulfuric Acid,
And some water if the potassium permanganate does not dissolve.
React this with 10mL methanol. this results in the formation of formaldehyde (dissolves in the solution), Manganese Sulfate (also dissolves) and
Potassium Sulfate (dissolves as well).
Now add 70mL 5% Ammonia solution. this reacts with the formaldehyde to form hexamine. (the sulfuric acid is already gone in this stage, becouse we
took an excess of methanol, so the sulfuric acid won't react with the ammonia). The solution is boiled down. the residue should be a mixture of
manganese sulfate, potassium sulfate and hexamine. hexamine is soluble in alcohol, potassium sulfate and manganese sulfate are not. this will be used
to purify the hexamine.
12AX7 - 17-1-2006 at 12:24
What prevents the permanganate from oxidizing the methanol all the way to formic acid, or CO2 for that matter?
The rest seems like it'll work... just remember when you add the alcohol, everything insoluble precipitates and you need to filter and wash.
Tim
woelen - 17-1-2006 at 12:26
No, this will not work. It will result in a terrible mess with a lot of crap, which cannot be easily separated. Not all permanganate will react
cleanly to Mn(2+) ions if you don't have a large excess amount of sulphuric acid. Besides that, a lot of the methanol will be oxidized further to
formic acid, or even to carbon dioxide.
Making hexamin can indeed be done by reacting ammonia with formaldehyde (I have done that recently), but you need the real formalin. It can be
purchased at some drug stores at 37% concentration, buit you have to search carefully. Also keep in mind, that formaldehyde is terribly toxic,
irritating and a carcinogen.
If you want hexamine, go out to a camping shop (as a dutch citizen, you probably know "De Vrijbuiter" in Roden or a similar shop) and buy Esbit
tablets. These are used for camping stoves, which use solid fuel. Just ask for that. I purchased a few boxes of that stuff, for just a few euros per
box.
oneup - 17-1-2006 at 13:06
hmmm. that sucks. that shop you mentioned is very far away from where I live, and I've been to nearly every store in town to ask for esbit tablets,
but noone knew where I was talking about 
I also can't get formaldehyde anymore, they used to have it some years ago but becouse it's toxicity it has been replaced by hydrochloric acid.
might there be another way to make hexamine with potassium permanganate/dichromate, sulfuric acid, methanol and ammonia?
Esplosivo - 17-1-2006 at 13:25
If you're into some experimenting frogfot built a good oxidation apparatus for conversion of methanol to methanal (formaldehyde) which is quite cheap
(requires only a Cu pipe, a heat source and obviously methanol). Here is the link. The apparatus need not be exactly the same, but the Cu tube and the inner coil (where one can easily use stripped fine Cu wire) is essential
for effective air oxidation by heat. Frogfot does a good job in explaining the rest of the details so you can easily follow the procedure. If you
have any questions you can easily ask here.
I would discourage the use of permanganate because of its strong oxidative properties. I doubt if formaldehyde can ever be formed when using
permanganate, unless using a very large excess of alcohol. The dichromate route might be feasible, but quite expensive. I suggest the Cu tube.
[Edited on 17-1-2006 by Esplosivo]
h0lx - 17-1-2006 at 13:52
If you want hexamine, you could try looking for "Urotropine" in pharmacies, it is used for disinfecting uric tracts or something.
chochu3 - 17-1-2006 at 20:35
As 12AX7 mentioned what will keep it from forming formic acid, you could distill as the aldehyde is formed, but this might create the paraformaldehyde
due to no methanol (for some: methanol keeps formaldehyde from polymerizing). This has happened to me in trying to distill a store bought formalin
solution from a local store (it polymerized in distillate flask).
Woe, barbituates and Crown Royal. Hope it spells right.
runlabrun - 18-1-2006 at 02:12
another idea could be to obtain formaldehyde using the proceedure that used to be listed in the library (i think basf started it?). So long as one is
extreemly carefull.
From formic acid -->
CaCO3 + 2HCOOH --> CO2 + Ca(HCOO)2 + H2O
Dry heating of calcium formate gives formladehyde gas which needs to be condensed (toxic hazard) -->
Ca(HCOO)2 --> HCHO + CaCO3
-rlr
oneup - 18-1-2006 at 09:52
can I just make formic acid with methanol and permanganate? i'll just use an excess of oxidizer so i'm sure all the methanol gets oxidized.
Esplosivo - 18-1-2006 at 10:14
Woelen correctly remarked that permanganate, especially if in excess, will oxidized the formic acid produced to carbon dioxide. Infact this occurs
pretty readily especially in the presence of a low pH. In a few words, no, AFAIK it isn't possible to stop the oxidation of methanol to formic acid
(methanoic acid) using permanganate in one step.
One possible way could be by using an excess of methanol, but this would result in a mixture of products. The acid is reacted with a base to form the
respective formate, say sodium formate. This salt is then crystallized by evaporation of the liquid mixture. The salt is reacted with an acid (conc.
H2SO4 will dehydrate the formic acid, so don't use it in the conc. form) and the mixture distilled. You would get a dilute formic acid soln in water.
I don't know if the first step of methanol oxidation step can lead to formic acid though, and somebody else must confirm this.
oneup - 18-1-2006 at 10:33
I don't know if this will work that well becouse the sulfuric acid from the oxidizer mixture would also react with a base.
mantis - 18-1-2006 at 12:01
can I use TCCA to oxidize Methanol (or other alcohol) to formaldehyde (or other aldehydes) and whats about Ca(ClO)2.?
woelen - 18-1-2006 at 12:07
It will be really hard to stop at the formic acid stage. Formic acid, however, is not a product, worthwhile to make yourself. Solutions of this can be
purchased at shops for bee holding for just a few euros.
An example in the Netherlands is given here:
http://www.bijenhuis.nl/bijenhuis_internetwinkel2/Results1.a...
This is just an example. There are many places for bee-holders (imkers), where formic acid can be purchased. I expect this will be the same in other
countries.
mantis - 18-1-2006 at 12:45
But I can use the TCCA to oxidize a primary alcohol to the acid?
12AX7 - 18-1-2006 at 20:02
Won't it give some whacky chloride?
I think you need something with oxygen (manganese in +4 or +7, chromate, persulfate, etc., or just plain oxygen itself, presumably with a catalyst),
so as to add oxygen to the molecule instead. Chlorine is less reactive than oxygen (that is to say, oxygen gas can sometimes oxidize chloride to
chlorine gas, for example), so it tends to chlorinate things rather than "oxi"dize.
But such melding of organic and inorganic chemistry doesn't really work if you ask me, since once the -CH2OH unit oxidizes to -CHO (presumably, any
two of the hydrogens are oxidized, in any case leaving an oxygen atom that wraps around to form a double bond), nothing keeps it from oxidizing with
more nearby reagent up to -COOH, or COO (i.e., CO2 gas) for that matter. You can't selectively oxidize very well since there's no specific graduation
of oxidation potential, and I don't think that works anyway (anyone even got ballparks for redox potential of -CH3 > -CH2OH > -CHO > -COOH
> CO2?). Besides, I have a sneaking suspicion that aldehyde is easier to oxidize than alcohol anyway -- reducing sugars have a loose -CHO, while
non-reducing sugars have the -CHO joined in an ether bond or such.
Tim
runlabrun - 19-1-2006 at 00:40
PCC is usually used to oxidise methanol to formic acid without risking the carbon dioxide evolution, there is no reliable way to stop methanol -- >
CO2 using permangenate or dichromate, you may be able to fluke it but yields would be low.
Try making formic acid via glycerol + oxalic acid. Heat glycerol to ~150c and hold for 10min to remove water (glycerol bp = 290c) leave to cool down
to ~100c and add oxalic acid (dried in the oven for a 10min), the production will be immediate (watch out for formic acid vapour) and these can be
condensed to a reciever, yields are good.
-rlr
The_Davster - 19-1-2006 at 05:53
Another route to formic acid, which avoids the heating of glycerin(as that makes acrolein) is chloroform reacting with NaOH to get sodium formate, and
then distilling the sodium formate with dilute sulfuric acid.
oneup - 20-1-2006 at 08:27
yesterday I managed to obtain some formaldehyde solution, the bottle says it has a concentration of 26%. I tried to make some hexamine with this, so I
did the math and calculated the ratios. So when I mixed in the ammonia it got very hot, that's good as it is a sign of reaction. almost immediately
after adding the ammonia it smelled neutral, while ammonia and formaldehyde stink as hell. (duh) so I thought it was a success, but when I boiled it
down, I got some kind of brown shit, so apperantly there are some impurities in my formaldehyde (not in my ammonia solution, i made it myself by
bubbling ammonia through water) the stuff i get stinks, but not like formaldehyde or ammonia, some kind of rotten smell. it is flammable though, like
hexamine should be, So i'm sure it at least contains SOME hexamine. does anyone know how to get rid of the impurities?
Nicodem - 20-1-2006 at 10:19
Are you sure you did not over heat it while boiling it down?
You would better vacuum strip off the water in a warm water bath. But if you don't have an aspirator you can boil it off just do it really carefully.
You can recrystalize hexamine from water/ethanol.
woelen - 20-1-2006 at 12:29
A few important things when making hexamine.
1) Always use excess ammonia if you care about your health. Breathing some ammonia fumes is not pleasant, but not nearly as bad as breathing even a
little formaldehyde.
2) Heat, until the liquid becomes turbid and a crystalline mess appears. Occasionally add a little more ammonia in order to keep excess of this.
3) Let cool down and then put the white and wet crystalline mess on a paper tissue. This sucks out most water and ammonia. Just let all material dry
on warm air (e.g. above a radiator). The nice thing of this synth is that all impurities are volatile and simply drying makes the material pure.
In this way I made a few grams of nice white hexamine. Right now I do not need the synthesis anymore, because I have Esbit tablets, but apparently
these are hard to get at many places.