spong - 25-10-2010 at 18:06
I'm after some formaldehyde, preferably paraformaldehyde that could be stored and weighed easily and dissolved when a solution is needed.
First I tried an acid catalyzed depolymerization to formaldehyde gas which would then be bubbled through water to make the solution which I would use
to make paraformaldehyde. I bought some trioxane tablets and powdered them and added some of the powder to a 3 neck RBF along with some H2SO4, nothing
happened at room temp, I also tried HCl but still no reaction.
I then heated the H2SO4/trioxane and it did begin to depolymerize, at quite a high temperature though. Unfortunately most of it repolymerized on the
walls of the flask or in the hose leading to the water, I did get some paraformaldehyde though both from the water (a very fine, cloudy suspension)
and from the hose/hose adapter (bigger, crispy flakes) but I got barely anything for the amount of trioxane that went in, plus it's not the safest
way, the hose adapter was very close to being clogged on all 3 attempts at this method.
Then I tried dissolving the trioxane in toluene in which it is quite soluble and heating that with both conc and then relatively dilute H2SO4,
according to the paper I've attached this is supposed to work as paraformaldehyde is insoluble in toluene, precipitating and collecting on the walls
of the reaction vessel. The one with conc H2SO4 just formed a black/yellow gunk in the bottom of the test tube. The dilute H2SO4 slowly ended up
dissolving the dye from the tablets when heated, no precipitate formed however, some did form when I added cold water to the now dark blue acid/water
layer, a white coating all over the test tube, I'm pretty sure I smelled formaldehyde over the stench of toluene left in the tube so it wasn't just
trioxane that precipitated out.
To summarize, I'm looking for a cleaner and more efficient way of doing it, paraformaldehyde is awful to clean from flasks and that 3 neck is covered
in it along with crud left over from the fuel tablets. Has anyone had success with this before?
Attachment: Trioxane-Formaldehyde.pdf (487kB)
This file has been downloaded 821 times
[Edited on 26-10-2010 by spong]
Eclectic - 26-10-2010 at 04:42
Easy way to purify trioxane is sublimation....I've done 50lbs in 3, 5 gallon plastic buckets with lids and a heating pad under them. It takes about a
week. Smaller quantities will work just fine in a widemouth quart mason jar set on top of the water heater or a shelf with a source of gentle heating
such as a lightbulb under it.
unionised - 26-10-2010 at 12:47
Please don't mix HCl with formaldehyde (or its precursors)
You get this
http://en.wikipedia.org/wiki/Bis(chloromethyl)_ether
The yield isn't great but it doesn't need to be.
spong - 28-10-2010 at 17:58
I'm looking to convert it to paraformaldehyde, not sublime it. It does form the nicest crystals on sublimation though, I had just powdered all the
tablets and put the dust in a jar and came back in about 10 minutes to use it and a few very, very thin needle-like crystals had made their way all
the way to the top of the jar. I thought a spider had started making a web in there when I first opened it 
Yeah the HCl probably wasn't a good idea but I wanted to see if it worked any better than H2SO4, it was dumped out pretty quickly.
Eclectic - 28-10-2010 at 21:12
Just saying, for first step isolation and purification from fuel tablets, no need to powder, just use sublimation to get pure trioxane, 10-15 lbs at a
time in 5 gallon plastic bucket with snap lid. Why convert to Paraformaldehyde? Just use the Trioxane in it's place.
[Edited on 10-29-2010 by Eclectic]
spong - 29-10-2010 at 03:44
I'd just powdered them for the reaction, I may try subliming them if I don't end up making paraformaldehyde though, I'm sure trioxane would come in
handy at some point. I wanted formaldehyde because it's a bit more reactive than trioxane. Before I give up I might try making formaldehyde from
H2SO4, hexamine and water.
EDIT: it's dried now, all up I ended up with 12g paraformldehyde from 2 packs of those pellets. Not on. I did keep the solution though which will be
boiled away, hopefully giving me a few more grams but still pretty crumby.
[Edited on 30-10-2010 by spong]
ChemNub - 5-12-2010 at 22:39
So I've been trying to use Trioxane as a source of formaldehyde in solution.. but having some problems with the depolymerization.
On two separate occasions I left a gram or so of trioxane(previously sublimated) in 4M sulfuric acid for several hours at 75C.. both times the result
was a scary looking bright yellow-orangish solution.. so something else is definitely happening here.. Is this an intermediate? or possibly a
polyoxymethylene variant?
I'll go ahead and upload the pdf I have-- It's pretty old and all the rates are recorded with regards to sulfuric acid 'normality.' Now I don't know
if they have a different conception of normality than I do- perhaps it's listed as normality with respect to the trioxane? This confused me but may be
what screwed things up..
Attachment: TrioxaneFormaldehyde.pdf (487kB)
This file has been downloaded 849 times
spong - 6-12-2010 at 05:42
Yeah mine changed colour too, I ended up with an awful brown colour although it could have been due to the dyes and whatnot in the tablets. I
eventually gave in and bought a 500g tub of it. The trioxane can be saved for a rainy day.