| 摘要 |
A methacrylic ester of an aliphatic primary alcohol having 8-18 carbon atoms is separated from a mixture including the higher alcohol and said ester thereof by treating the mixture at an elevated temperature with a calculated quantity of sulphuric acid so as to transform the free alcohol into its hydrogen sulphate and separating the methacrylate by washing with an aqueous solution of a water-miscible organic solvent which dissolves the hydrogen sulphate of the higher alcohol and decanting. The method is particularly useful in a preparation of the above methacrylates which comprises treating methacrylamide with water, sulphuric acid and the higher alcohol at an elevated temperature, separating the resulting liquid into an organic phase containing the methacrylate of the higher alcohol, free higher alcohol and methacrylic acid and an aqueous phase containing sulphuric acid, and ammonium sulphate, esterifying in the organic phase the free methacrylic acid with higher alcohol and transforming the excess higher alcohol into its hydrogen sulphate, by treating the organic phase at an elevated temperature with a calculated amount of sulphuric acid, and washing and decanting the methacrylate as above. The methacrylamide may be obtained by hydrolysing acetone cyanhydrin with sulphuric acid. The crude esters containing free higher alcohol may also be those obtained by esterification of methacrylic acid or by interesterification of methyl methacrylate. The separation processes may be effected in continuous manner. The sulphuric acid using in the sulphation may be in the form of oleum. In examples, acetone cyanohydrin is heated with excess 100% sulphuric acid, the reacted mixture is heated with water and technical lauryl alcohol, the product is settled, the organic phase comprising lauryl methacrylate, lauryl alcohol and methacrylic acid is heated with 100% sulphuric acid, the resulting organic phase is separated from an aqueous sulphuric acid phase, washed twice with aqueous methanol and then stripped of solvent to leave purified lauryl methacrylate. Technical stearyl methacrylate may be obtained in like manner. The methanol may be replaced by ethanol or acetone. |
