GB841522A - Improvements in or relating to the purification of acrylic and methacrylic esters - Google Patents

Abstract

Monomeric esters of acrylic or methacrylic acid and aliphatic alcohols containing 1-6 carbon atoms, prepared by direct esterification or alcoholysis in the presence of an esterification catalyst, usually an acid, and more particularly an acid containing hexavalent sulphur, e.g. H2SO4 or p-toluenesulphonic acid, and a polymerization inhibitor, usually of the quinone or reduced quinone type, e.g. p-benzoquinone, hydroquinone or phenanthrenequinone, are purified by subjecting the products of esterification or alcoholysis, containing the ester, to fractionation and steam distillation in the presence of liquid water and thereafter removing the ester from the distillate. When using alcoholysis, the alcohol formed is removed as it is formed either by azeotropic distillation or, preferably, using a liquid/liquid extractor as described in Specification 841,521. The fractionation step is to remove the excess low-boiling starting material and preferably precedes the steam distillation. Suitable esters mentioned are methyl, ethyl, propyl, n-butyl, iso-butyl, n-pentyl and n-hexyl acrylates and methacrylates. In examples, n-butyl methacrylate and n-hexyl methacrylate are prepared by ester exchange between methyl methacrylate and the appropriate alcohol in the presence of p-benzoquinone as polymerization inhibitor and H2SO4 as ester exchange catalyst; the crude reaction product is fractionated at atmospheric pressure to remove excess methyl methacrylate, water added and the residue steam distilled, the desired ester being separated from the distillate. The Provisional Specification refers also to the application of the above purification process to other unsaturated esters which tend to polymerise such as maleates and fumarates.