| 摘要 |
Dimethyl terephthalate containing an aldehyde impurity, e.g the methyl ester of p-formylbenzoic acid, is purified by admixing the impure ester with a compound having a reactive methylene group, heating the resuling mixture for a time and a temperature sufficient to bring about a reaction between the said compound and aldehyde impurity with the formation of a condensation product and thereafter separating, e.g. by distillation, the condensation product from the dimethyl terephthalate. Reactive methylene compounds which may be used include ethyl acetoacetate, diethyl malonate, ethyl cyanoacetate, a nitro-benzyl ketone and phenyl benzyl ketone. A catalyst is preferably used to promote the condensation reaction. Catalysts specified are caustic alkalis, alkali metal carbonates, ammonia and amines, alkali metal alcoholates, metal alkoxides and Friedel Crafts catalysts. Generally 0.05 to 5.0% by weight of the reactive methylene compound, and catalyst if employed, based on the weight of the crude ester are added and the reaction mixture heated for about 1 to 6 hours at a temperature in the range of from 145 to 300 DEG C., preferably 200 DEG C. In examples reactive methylene compounds used are ethyl acetoacetate and diethyl malonate and catalysts employed are aluminium chloride, potassium carbonate, sodium methylate, aluminium isopropoxide, zinc chloride, ferric chloride and stannic chloride. |
