blacklung
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Formaldehyde from Paraformaldehyde
Anyone tried making formaldehyde from paraformaldehyde found in the "CampaChem" product at Wal-Mart?
It is heavily dyed blue, and near impossible to wash the dye out with alcohol(s). One method I've read says to put the paraformaldehyde in a solution
of water and NaOH, and heat it to make 40% formaldehyde. This seems less than acceptable considering a lot of junk will be in the solution, too.
The interesting method, though, says to heat the paraformaldehyde up to like 200C (I think, don't quote me), and that it will depolymerize to form
formaldehyde gas, which is then bubbled into 600gms of water, weighing until you reach 1000gms, which should make 40% formaldehyde solution.
How reasonable does this sound? Anyone tried it?
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kclo4
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There is a lot of information on this on the board and the rest of the internet. Google more.
Since I am posting a comment anyways:
Methanol can extract the blue dye, and heating it with sulfuric acid can cause it to depolymerize producing formaldehyde - the effectiveness of
sulfuric acid depends on concentration, also concentration and temperature will determine if the formaldehyde comes of as a gas (likely) or if it
remains in solution.
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smuv
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My Experience with the stuff (the 'blue dyed' paraformaldehyde used was champa chem). I think for any serious chemistry you should save yourself
the headache and exposure to formaldehyde and get formalin as I ended up doing. It is OTC for pond care and many products are 37% formalin solution.
Formalin seems to have a lower vapor pressure than a formaldehyde solution and for this reason I believe it is a fair bit safer to work with.
I would not recommend acid catalyzed de-polymerization of paraformaldehyde as I believe the obtained solutions are more unstable w/ respect to
repolymerization.
There is a great book all about formaldehyde and its polymers + oglimers in the forum library.
PS You can wash the stuff w/ alcohol but noticeable amounts of the dye remain. In the presence of acid the dye turns pale yellow, but upon
neutralization the color returns to blue.
PPS I just remembered I successfully removed the dye by heating the campa-chem to ~200c and holding it there using a heating element (do this
OUTSIDE w/ a lid over whatever you do this in to minimize loss of formaldehyde). At this temperature the dye chars and a formaldehyde solution can be
prepared from the crude product and filtered to produce a nearly water white solution. The paraformaldehyde dissolves w/ more difficulty though after
this treatment.
[Edited on 4-16-2009 by smuv]
[Edited on 4-16-2009 by smuv]
"Titanium tetrachloride…You sly temptress." --Walter Bishop
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chemrox
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@Smuv: I understood "formalin" to be the 37% aqueous solution of formaldehyde in water. When I buy it, I ask for formaldehyde and get the 37% stuff.
I belive it is aqueous Meam that is 40% in water.. other percentages in alcohol available too.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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smuv
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| Quote: | | I belive it is aqueous Meam that is 40% in water.. |
I'm sorry I don't understand this scentance, however...
Formalin is a solution of 37% (by mass) formaldehyde contianing ~10% methanol. My understanding is that the methanol to some extent end caps the
short polymer chains of polyoxymethylene that exist in solution. These end capped chains are less likely to further polymerize and settle out of
solution. If you take a solution of formalin and add a fair quanitity of hydrochloric acid (1ml per 10ml formalin) and let it sit, you will however
get slow precipitation of polyoxymethylenes (noticeable over a day).
It has been a while, but I believe I tried to make formalin once from paraformaldehyde or maybe by adding methanol to a formaldehyde solution I
prepared. All of the formaldehyde solutions I have ever prepared (in any form) were uncomfortable to work with because of the vapor pressure of
formaldehyde; the commercial formalin I bought on the other hand is so un-offensive, I bet you could take a sniff a few inches above the solution
without coughing (not that I would recommend it). It is also possible that since I prepared my formaldehyde solutions as needed, over time the
polymers in solution would get longer, making the solution less offensive to work with; who knows...
"Titanium tetrachloride…You sly temptress." --Walter Bishop
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panziandi
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Formalin is a concentrated formaldehyde solution: 37% by weight or 40% by volume of formaldehyde and contains 10% methanol, indeed as a stablizer. The
concentrations are the average concentrations and they are sometimes quoted as +/- 1% or so. Most pharmaceutical grades are supplied with the
concentration quoted in 40% and lab grades seem to be supplied as 37%.
smuv: my concentrated formaldehyde is VERY strong. It makes me cough and isn't nice to handle in quantity.
I used to use it quite niavely as a kid making phenolic resins on my windowsil! Probably why I am "blind"
Wear gloves and work in a ventilated room. Concentrated formaldehyde is toxic, corrosive and quite flammable too! And if I spill some or touch a drop
on my hand, I can still smell it even once rinsed.
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kclo4
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How does it make you go blind from the vapors? Crosslinking or something on the surface of the eye?
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DJF90
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I would assume it to be the same reason that drinking methanol makes you go blind, seeing as formaldehyde is the metabolite.
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chemrox
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I get mine without the methanol.... I guess that makes it aqueous formaldehyde? I have some trioxane as well and that should convert to formaldehyde.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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chemrox
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How much base?
The wiki on paraformaldehyde and some other forum posts (anybody mind if I call it para?) suggest that the stock 37% solutions can be obtained by
making a 37% weight solution in water with a little NaOH. How much NaOH? Another post suggested acid.. a drop or two of H2SO4. Commercial solutions
usually have a little MeOH as well as a stabilizer. I'd like to leave that out and only make the amount I need. Have any of you done this and can
remember whether acid or base was used and how much was used or really needed?
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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Crowfjord
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I've made ~37% formaldehyde solution using base to depolymerize. I think to make around 30 milliliters I used 3-5 drops of 25% (w/w) sodium hydroxide,
in a 100 mL RBF and heating (not quite boiling) for maybe 15 minutes to get full dissolution.
[Edited on 27-8-2014 by Crowfjord]
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Leben
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You don't need an acid or a base to go from paraformaldehyde to formaldehyde. Paraformaldehyde upon heating naturally 'unzips' to formaldehyde. I
usually heat it for 30 minutes at 50 degrees in the same reaction I am planning to use it. Bases or acids may allow for room temperature unzipping but
I do not know much about that.
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Crowfjord
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Interesting. I've never gotten it to work without base, but then I only was going for a strong solution. What concentration did you use? I believe you
can also also make formaldehyde gas by heating paraformaldehyde dry, but I don't know at what temperature.
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S.C. Wack
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The success of adding this, that, or nothing to get it to dissolve depends on the exact nature of the "paraformaldehyde". It may dissolve readily or
not in whatever.
There are other threads concerning the OTC product in question. Depolymerize, distill over with water, then remove the water with vacuum distillation.
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Leben
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Come to think of it I suppose I did use it in the presence of a base. I have only ever used it on amines (Methoxybenzylamine), and I usually just add
it directly to the solution of amine/solvent in the absence of water. I was never concerned with concentration. I never saw much of a point to making
formaldehyde solutions from it when I can just use it directly from the powder form in the solution where I need it. Paraformaldehyde can be unzipped
in use in a number of organic solvents, not just water.
Here is one prep.
http://www.rndsystems.com/ihc_detail_objectname_formaldehyde...
The authors drip 1M NaOH in with heating until it starts to dissolve. It appears to only require a catalytic amount for all of it to start
unzipping, which can be followed up by neutralization of the base.
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unionised
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Quote: Originally posted by smuv  |
If you take a solution of formalin and add a fair quanitity of hydrochloric acid (1ml per 10ml formalin) and ...
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Don't.
You risk forming one of the more potent carcinogens.
http://en.wikipedia.org/wiki/Bis(chloromethyl)_ether
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