Acylation or substitution?

Take the three following reactions:

1) Acyl Chloride + Alcohol -> Ester
2) Acyl Chloride + c.NH3 -> Primary amide
3) Acyl Chloride + c.R-NH2 -> Secondary amide

Every textbook I've seen classes all three reactions as acylation.

I can't for the life of me figure out why. Because surely acylation implies an R-COCl group is being transferred to another molecule, as many other sources I find seem to state?

I'd personally classify 1) as esterification because an ester is formed, and both 2) and 3) as a substitution because the -Cl group is being swapped for either an R-NH or an NH2 group. Yet all three seem to be classed in the textbook as acylation. Which is it?

Also why is a Friedel-Crafts acylation called an acylation when a -CO-R group is being transferred to the benzene ring and not an -COCl group?

Reply 1

charco

Study Forum Helper

Original post by spleenharvester

Acylation is the substitution of the R-CO- group, this is known as an acyl group as opposed to an alkyl group which is just R-.

With benzene the R-CO- substitutes a hydrogen atom.

Reply 2

spleenharvester

Original post by charco

Acylation is the substitution of the R-CO- group, this is known as an acyl group as opposed to an alkyl group which is just R-.

With benzene the R-CO- substitutes a hydrogen atom.

Oh man I didn't realise that haha, I've been racking my brain over this one for ages. Thankyou man, appreciated!

Reply 3

charco

Study Forum Helper

Original post by spleenharvester

Oh man I didn't realise that haha, I've been racking my brain over this one for ages. Thankyou man, appreciated!

No problem ... :smile:

Reply 4

spleenharvester

Oh yeah one last thing, is the most accurate term for 1) esterification or acylation? Because technically it's both isn't it?

Reply 5

oversizedcarrot

Original post by spleenharvester

Oh yeah one last thing, is the most accurate term for 1) esterification or acylation? Because technically it's both isn't it?

It's definitely both since both an acylation reaction is occurring and you are also forming an ester product which would make it an esterification reaction also.

I think the most important thing to know here is that the mechanism of the reaction involves a nucleophilic-addition-elimination mechanism and then the preceding mechanism drawn out to show how the ester is made in this acylation esterification reaction.

I've never seen any AQA questions ever on any exam paper asking to name the type of reaction occuring when involving an acyl chloride reaction. I have seen one involving an alcohol and acid to form an ester which is of course esterification. But say we do get a question on an acyl chloride reacting with alcohol to form an ester and having to give the type of reaction occuring, I'd assume you'd get a mark for writing either the acylation or esterification as an answer.

Just make sure if you'r asked you know what they're looking for in terms of if they want the type of reaction occuring or if they want the mechanism.I hope that answers that.