Sciencemadness Discussion Board

OCHEM reaction mechanism question for a beginner

yoyoils - 10-8-2011 at 23:32

Would anybody know just off the top of your head if Propane with a carboxylic acid could produce Propionic acid? The only few things I can find so far is propionaldehyde aerobic oxidation to propionic acid with the presence of cobalt ions,
or would it even be possible somehow to halogenate gaseous propane and + R-C=O-OH(carboxylic acid) for a propionic acid prep?

or is there anyway to make it from acetic acid? im trying to figure out a way to get an extra methyl group to pure acetic acid if possible somehow..

[Edited on 11-8-2011 by yoyoils]

TerryFlamingo - 11-8-2011 at 02:39

Propane as is has nothing to oxidize to form the carboxylic acid. What you would probably want is 1-propanol or propene as a reagent to start with.

bbartlog - 11-8-2011 at 06:19


1) Can I combine propane with a carboxylic acid to make propionic acid? Why, no.
2) Can I halogenate propane and then turn that into propionic acid? Eh, not really. There probably is some impractical path involving multiple steps, low yields, and conditions out of reach for the amateur, but the answer really is no.
3) Can I make propionic acid from acetic acid? Again, not by any practical means.
4) How can I get my hands on some propionic acid, man? It's not a watched chemical; you can just order it. It gets used as a hay preservative, see e.g. http://www.harvesttec.com/agco/hay_preservatives.html (the AGCO stuff is buffered somehow, though, so separation would be required; but someone certainly sells the pure acid in large quantities as well; use the Google...).
5) Actually I really just wanted to *make* some propionic acid, how do I do it? Well, it's not actually a particularly trivial synthesis for a beginner, as far as I can tell. Best bet might be performing the haloform reaction on some methyl ethyl ketone (bleach and MEK both OTC), recovering the sodium propionate and then acidifying it back to propionic acid; but having done this variation of the haloform myself I can say that it seems a bit messy (lower yield than I expected, I assume side reactions) and you might find the workup to extract the acid tiresome.

yoyoils - 11-8-2011 at 07:23

Quote: Originally posted by bbartlog  

1) Can I combine propane with a carboxylic acid to make propionic acid? Why, no.
2) Can I halogenate propane and then turn that into propionic acid? Eh, not really. There probably is some impractical path involving multiple steps, low yields, and conditions out of reach for the amateur, but the answer really is no.
3) Can I make propionic acid from acetic acid? Again, not by any practical means.
4) How can I get my hands on some propionic acid, man? It's not a watched chemical; you can just order it. It gets used as a hay preservative, see e.g. http://www.harvesttec.com/agco/hay_preservatives.html (the AGCO stuff is buffered somehow, though, so separation would be required; but someone certainly sells the pure acid in large quantities as well; use the Google...).
5) Actually I really just wanted to *make* some propionic acid, how do I do it? Well, it's not actually a particularly trivial synthesis for a beginner, as far as I can tell. Best bet might be performing the haloform reaction on some methyl ethyl ketone (bleach and MEK both OTC), recovering the sodium propionate and then acidifying it back to propionic acid; but having done this variation of the haloform myself I can say that it seems a bit messy (lower yield than I expected, I assume side reactions) and you might find the workup to extract the acid tiresome.



my goal is to at least have a 90% concentrated propionic acid. i'm looking at the haloform reaction right now just figuring out how MEK+NaOCl produces the sodium propionate . How did your workup run? if you dont mind me asking.

bbartlog - 11-8-2011 at 20:17

I was mainly trying to see whether the yield of chloroform was comparable to that when you use acetone in the reaction, rather than methyl ethyl ketone. It isn't; I think the yield was something like 25%, versus 50-70% when using acetone. I don't know exactly why but tend to think that there are a lot of ways for the chlorination to go wrong when using MEK - for example, it may be that initially chlorinating the 'wrong' carbon would make the reaction run off the rails (for that molecule), whereas either terminal carbon on acetone would be fine.
That aside, I did make an attempt to salt out the propionic acid after acidifying the solution with HCl (after separating it from the chloroform). This failed, probably because I didn't use enough CaCl2; in subsequent experience with salting out stuff that is only marginally separable by this means (which would include propionic acid) I've come to realize that you really need to fully saturate the aqueous phase, which in this case would have involved a couple additional kilos of CaCl2.
Anyway, I am actually not sure of the best workup for the messy solution that results from doing the haloform this way. You have sodium hydroxide, sodium formate (from hydrolysis of chloroform), sodium chloride, sodium propionate, and likely a little bit of sodium chlorate (bleach decomposition) and sodium hypochlorite (unreacted), along with likely other stuff from aldol condensation side reactions and the like. Because propionic acid forms an azeotrope with water, acidifying and distilling doesn't look like a good solution, at least by itself. So salting out first seemed like a reasonable approach. If I were to do it again, I would boil down the resulting solution until things began to precipitate out, cool and filter, *then* acidify, before trying to salt out the propionic acid. Would need a lot less salt, and some impurities would likely be precipitated.
Note that the resulting propionic acid would still have a lot of impurities. But it could be fractionally distilled once it had been dried to remove water (maybe distillation over H2SO4 would work).


Fleaker - 12-8-2011 at 08:08

Why don't you just buy some n-propanol and oxidize it with permanganate, or just buy the stuff.

yoyoils - 22-8-2011 at 15:06

i cant find anywhere that sells it

[Edited on 22-8-2011 by yoyoils]

barley81 - 22-8-2011 at 15:56

Elementalscientific.net sells n-propanol at $9 per 16 oz.
http://www.elementalscientific.net/store/scripts/prodView.as...
Sigma Aldrich and Alfa Aesar would likely have it.

redox - 22-8-2011 at 16:02

Go on ebay and buy a pound or so of calcium propionate. I bought a pound a few months ago for about 15$. Simply acidify with sulfuric acid and distill.

H2SO4 + Ca(CH3CH2COOH)2 ---> CaSO4 + 2CH3CH2COOH

I did it under a fume hood, which made the smell bearable. My yield was about 65%, which is low for such a simple reaction, but my stirrer got jammed so that certainly had an effect.

[Edited on 23-8-2011 by redox]

yoyoils - 22-8-2011 at 17:59

wow.... i couldnt find it before, i guess because i was searching sodium propionate but i thank you guys enormously!!!!!!

[Edited on 23-8-2011 by yoyoils]