[SinkingTako]

Hello, I'm confused regarding the reaction of PCl₅ with aldehydes. I know that benzaldehyde will react with PCl₅ to form benzoyl chloride. Is this reaction specific to benzaldehyde or can this reaction be applied to all C=O groups in general (to form CCl2)?

Also it's stated somewhere that CCl2 groups hydrolyse in H2O to form C=O group. (from some fishy source). Can I clarify if this is correct, and what are the exact conditions involved?

Thank you!

[opsomath]

I know that benzaldehyde will react with PCl5 to form benzoyl chloride

I'm afraid you've gotten benzaldehyde (PhCHO) mixed up with benzoic acid (PhCOOH). PCl5 generally converts ketones and aldehydes from R-CO-R' or R-CO-H to R-CCl2-R' / R-CCl2-H respectively.

In other words, this reagent sucks the oxygen out of carbonyls and replaces with two chlorine atoms instead.

[insertwittyname]

So, if I needed to add only one chlorine atom to a carbonyl group, will I have to reduce the carbonyl to an alcohol before reacting it with PCl₅?