Acid Chloride Reactions: Ester formation using Alcohols and Pyridine

Acid chlorides react with alcohols (ROH) to form esters:

If there is an alcohol group on the same molecule, a ring structure may form:

The reaction mechanism is depicted below:

In the first step, the lone pair electrons on the oxygen atom attack the carbonyl-carbon, breaking the double bond and sending those electrons to the oxygen atom.

In the second step, a nearby alcohol removes the proton from the alcohol group that was just added to the molecule. The negatively charged oxygen atom removes a proton from an positively charged alcohol group.

In the third step, lone pair electrons on the oxygen atom re-form the double bond with the carbon atom, leading to the chloride atom being kicked off.

In the fourth step, the recently removed chloride ion removes the proton from the positively charged oxygen molecule, forming HCl as a byproduct (not shown) and the ester product.

Pyridine (pyr) is used in this reaction as a base to counteract the HCl that is generated as a byproduct of this reaction.

Practice this reaction using our Reaction Solver!