CwisGons - 6-7-2021 at 15:46
I wish to create phenol from salicylic acid by decarboxylation and subsequent distillation. While I heard that a catalyst is not necessary, I wish to
use one because I want higher yields. I looked online and heard of the Dumas reaction, in which soda lime is used to decarboxylate many carboxylic
acids, including making benzene from sodium benzoate.
https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Supplemental_Modules_(Organic_Chemistry)/Carboxylic_Acids/Reactivity_of_Carboxylic_Acids/The
_Decarboxylation_of_Carboxylic_Acids_and_Their_Salts
While I am unable to get soda lime, I thought of mixing sodium hydroxide and hydrated lime, which I can easily find.
I read that "Soda lime contained 95% calcium hydroxide, either sodium or potassium hydroxide, and the balance as water."
How much soda lime should I use per gram of salicylic acid? I don't want to use too much soda lime, because I'm using borosilicate glass. Also, I'm
afraid of the formation of sodium phenolate, which I don't think that I can distill. Any advice?
Amos - 7-7-2021 at 07:16
I think a small amount, nothing close to equimolar, wouldn't hurt. Because you're performing a decarboxylation, though, the soda lime will quickly
convert to calcium and sodium carbonates (if their salicylate salts do decarboxylate as intended). These are basic enough to deprotonate more
salicylic acid, but once the hydroxide moieties are expended, the mixture shouldn't be alkaline enough to react appreciably with phenol. The
carbonates will probably also compete with the formation of phenyl salicylate, an intermediate which traditionally leads to some of the salicylic acid
irreversibly converting to xanthone.
In short, I don't know this method to afford any benefits over the usual way, but as long as sodium and calcium salicylates cleanly decarboxylate as
benzoates do, I think it's worth a shot. Maybe try a test tube scale reaction where you merely heat the two together and see if you smell any phenol.