Sciencemadness Discussion Board

Decarboxylations

thelonious - 14-7-2012 at 14:24

I've decided I would like to do a decarboxylation. I first thought of niacin to pyridine, but reading the msds for pyridine it seems too poisonous to be working with in a home lab. Are there any carboxylic acid derivatives that provide interesting decarboxylation which is not too complicated, and whose products or reactants aren't extremely poisonous or illegal?

[Edited on 14-7-2012 by thelonious]

Lithium - 14-7-2012 at 14:56

try salycilic acid to phenol

you could also post your results on decarboxylation of terephthalic acid, which is easily made from pet plastic

[Edited on 15-7-2012 by Lithium]

cAMP - 14-7-2012 at 16:54

Yes please. If you can figure out how to do the decarboxylation of salicylic acid to phenol, please post a procedure. I've looked, and all I can seem to find is the pyrolysis, and I'm not exactly sure it works. When I attempt it, I smell phenol, but I can't get any kind of yield.

Anyone know if there is a quick test for distinguishing phenol from salicylic acid? Reacting with FeCl3 turns both purple, because it's simply reacting with any phenolic compound.

Lambda-Eyde - 14-7-2012 at 19:55

Quote: Originally posted by thelonious  
I've decided I would like to do a decarboxylation. I first thought of niacin to pyridine, but reading the msds for pyridine it seems too poisonous to be working with in a home lab. Are there any carboxylic acid derivatives that provide interesting decarboxylation which is not too complicated, and whose products or reactants aren't extremely poisonous or illegal?

Pyridine isn't extremely poisonous. It's rated as "Harmful", not "Very Toxic". Don't trust MSDS sheets, they're made for people who have absolutely no training in handling chemicals, and are mostly used by companies to cover their asses in case an accident happens (but the MSDS said so and so...). Hazard ratings are much more useful in judging the dangers of a chemical. Decarboxylation of niacin to pyridine would be a nice experiment, preparing the catalyst is an experiment in itself (I'd worry more about the barium and dichromate in the catalyst than the end product, pyridine), and pyridine is a very useful reagent to have in the laboratory. It can be used as a mild base for soaking up HCl etc. as well as preparing PDC and PCC, two dichromate-based oxidants, used for preparing aldehydes and ketones from alcohols.

Another nice decarboxylation to do is benzoic acid to benzene. Benzene is extremely useful to the amateur, used as a scaffold for a multitude of organics. I'd worry more about benzene than pyridine, though. It's rated as toxic and it is a carcinogen. Use good ventilation, proper safety equipment and care.

Hexavalent - 15-7-2012 at 00:30

Quote: Originally posted by Lambda-Eyde  
I'd worry more about the barium and dichromate in the catalyst than the end product, pyridine


I have a thread in the Organics section of the forum where someone has successfully prepared pyridine using basic copper carbonate.

barley81 - 15-7-2012 at 06:14

The procedure for production of phenol from salicylic acid is on the Hyperlab forum. When you translate it to English (with google of course), it sort of makes sense. There was a US patent on the subject that they were using. I have attached it to this post.

Here is the link to that page on the forum:
https://www.hyperlab.info/inv/index.php?s=&act=ST&f=...


Attachment: US2488472__Phenol.pdf (780kB)
This file has been downloaded 912 times

vmelkon - 15-7-2012 at 17:32

I guess the reaction would be similar to the case of sodium benzoate + NaOH + heat => benzene + Na2CO3. Just search on youtube. It will give you an idea of the procedure.

barley81 - 15-7-2012 at 17:41

In the case of salicylic acid decarboxylation, the calcium hydroxide is used as a catalyst. It probably reacts to form calcium carbonate/phenoxide, but more CO2 is formed than calcium carbonate. Benzene decarboxylation is different in that a stoichiometric amount of base is required. The procedure is different. Here's a quote from the patent:
"Salicylic acid is decarboxylated by heating the acid with 1% of slaked lime at a temperature ranging from 170C to 185C until the reaction is complete, as evidenced by the cessation of evolution of carbon dioxide gas. The residue when cooled to room temperature assumes the typical crystalline structure of phenol."

A person at Hyperlab distilled the phenol off from the reaction mixture after the reaction was complete, in order to separate it from calcium stuff and phenyl salicylate.