Sciencemadness Discussion Board

Formaldehyde from Acetaldehyde and Formic Acid

TheNerdyFarmer - 30-9-2016 at 18:12

I am fairly new to organic chemistry so if this is a stupid idea feel free to let me know. As a home chemist starting a lab I have been looking for OTC chemicals to stock it. But, I can't find formaldehyde seeing as it is kind of restricted. So I tried to come up with an idea on how to make some. I was wandering if you used acetaldehyde and formic acid if it would yield formaldehyde and Acetic acid as a byproduct.

Here is my chemical equation:

CH3CHO+HCOOH-> H2CO+CH3COOH

It seems like it would work but I've heard that organic chemistry is a bit tricky. If this would not work it would be much appreciated if you all could give constructive criticism and maybe a better way to do it. Thanks a bunch!

Metacelsus - 30-9-2016 at 19:19

I don't think it would work (I can't think of any plausible mechanism). You might get some lactic acid produced. Alternatively, you could end up making carbon dioxide and ethanol. In either case, you'd have to use high temperatures and pressures (see: https://pubs.acs.org/doi/abs/10.1021/jp710688u)

In any case, acetaldehyde is usually harder to get than formaldehyde (which you can buy as paraformaldehyde).

Edit: Added reference

[Edited on 10-1-2016 by Metacelsus]

Crowfjord - 30-9-2016 at 19:21

I see your reasoning there, but I think if a reaction proceeded between acetaldehyde and formic acid, the opposite would happen. That is, the formic acid would act as reductant rather than oxidant. Formic acid, usually along with a catalyst of some sort tends to react along the lines of HCOOH --> CO2 + H+ + e-. Mainly because carbon dioxide is very thermodynamically stable, and carboxylic acids are pretty difficult to reduce.

Although formaldehyde solution has become difficult to find these days, paraformaldehyde remains fairly well available. Paraformaldehyde easily dissolves in refluxing methanol or refluxing water with a few drops of 25% sodium hydroxide. I've made formaldehyde this way, it only takes about 2-4 hours.

Edit: it seems Metacelsus made a similar response as I was typing

[Edited on 1-10-2016 by Crowfjord]

Cryolite. - 30-9-2016 at 20:53

Quote: Originally posted by Crowfjord  

Although formaldehyde solution has become difficult to find these days, paraformaldehyde remains fairly well available. Paraformaldehyde easily dissolves in refluxing methanol or refluxing water with a few drops of 25% sodium hydroxide. I've made formaldehyde this way, it only takes about 2-4 hours.

[Edited on 1-10-2016 by Crowfjord]


Sorry for the off-topic, but where do you get paraformaldehyde locally? I have looked for it in the past, but the only source I could find was incredibly overpriced mildew odor removers.

Crowfjord - 1-10-2016 at 06:53

I haven't seen anything of decent quality OTC in stores, though it might exist. I get mine from Photographers Formulary. Pure paraformaldehyde might be available via ebay, as well. Another formaldehyde source to keep an eye out for also would be trioxane (solid camp fuel).

Magpie - 1-10-2016 at 08:01

The OP says he wants formaldehyde. Assuming he means an aqueous solution, ie, formalin, this is readily available over the internet, including Amazon.

Gaseous formaldehyde is another matter and is a bit tricky to get in pure form.