Sciencemadness Discussion Board

over heating of benzoyl chloride

andre178 - 15-3-2011 at 13:12

I've been trying various methods of preparing pure benzoyl chloride from thionyl chloride and bz acid. I've been heating for 30 minutes.

Benzoyl chloride = colorless liquid

Product of reaction, pale yellow, clear liquid starting at about 30 minutes, reaction running at 80 deg C. I thought this may be due to water vapor or other contaminants, but have not found anything like that to be the cause.

As a test, I placed the slightly yellow product in 180 degree silicon bath and the product quickly started to turn to dark orange before completely evaporating.

I was hoping someone can help me to understand what this could be?

I'm using thionyl chloride in slight excess 1.5 mmol to 1 mmol of benzoic acid.

Thanks for any input

[Edited on 3-15-2011 by andre178]

matei - 16-3-2011 at 06:13

Your benzoyl chloride should be pure enough for making benzoate esters or whatever you want to do with it.

~Anthrax~ - 16-3-2011 at 09:18

I can't help you with the product formed, but an easier way to make Benzoyl Chloride from Benzoic Acid would be to react it with PCl5 (Phosphorus Pentachloride)

I only say this because, as far as I know, the reaction proceeds without heating. Provided there is minimal contact with water, this reaction should be pretty feasible.


andre178 - 16-3-2011 at 09:29

the reason behind making it with thionyl chloride is that I need to make hot C14-benozyl chloride and, this method seems to be the most direct and easiest on the wallet *C14 benzoic acid isn't super expensive.