Process for preparing a purified methacrylic acid ester

A process for preparing a purified methacrylic acid ester from a crude methacrylic acid ester containing an isobutyric acid ester as an impurity which comprises the steps of:

• 1. firstly distilling said crude methacrylic acid ester in the presence of water to separate as the distillate the isobutyric acid ester and water together with part of the methacrylic acid ester and recover as the bottoms a first purified methacrylic acid ester,
• 2. separating said distillate into an aqueous phase and an organic phase consisting substantially of the isobutyric acid ester and the methacrylic acid ester, and
• 3. secondly distilling the thus separated organic phase in the presence of water to separate as the distillate the isobutyric acid ester and water together with a very small amount of the methacrylic acid ester and recover as the bottoms a second purified methacrylic acid ester, thereby obtaining the purified methacrylic acid ester, wherein the water is present in each of the steps (1) and (3) in such amounts that substantially the whole of the isobutyric acid ester contained in the crude methacrylic acid ester is distilled off while minimizing the amount of the methacrylic acid ester distilled off.