Verfahren zur Reinigung niedrigmolekularer Alkylester der ª‡-Chloracrylsaeure

摘要

Lower alkyl esters of a -chloroacrylic acid which on polymerization yield polymers of good colour initially and a reduced tendency to develop colour over long periods of time are made by mixing and subsequently separating by distillation or steam distillation, a lower alkyl ester of a -chloroacrylic acid as normally made and a hydrazine derivative having one or both of the hydrogen atoms of one of the -NH2 groups in the hydrazine molecule replaced by an R CO-group where R is an organic radicle, an -NH2 group or an -NH2 group having one or both of the H atoms replaced by an organic radicle. The esters are those of aliphatic monohydric alcohols of not more than 4 carbon atoms. Specified hydrazine derivatives are:-semicarbazide, benzoyl hydrazine, unsym dibenzoyl hydrazine, malonyl dihydrazine, isobutyryl hydrazine, unsym diisobutyryl hydrazine, acetyl hydrazine, unsym diacetyl hydrazine, phenyl semicarbazide and diphenyl semicarbazide. Semicarbazide may be used as the hydrochloride, the free base being isolated by caustic potash in methanol solution. Polymerization of the product is advisably effected as soon as possible after treatment with the hydrazine derivative and in the absence of air. The hydrazine derivative is separated before polymerization which may be effected by heat treatment with or without actinic light or by polymerization catalysts. In examples methyl a -chloroacrylate, which may be made as in Specification 550,854, [Group IV (b)], is photopolymerized anaerobically and heat treated to yield colourless resins after treatment with benzoyl or isobutyryl hydrazine or a 10 per cent. methanolic solution of semicarbazide, benzoyl hydrazine, malonyl dihydrazine or acetyl hydrazine. The products may be used in windows, roof-lights, windshields and aircraft cockpit covers.ALSO:Lower alkyl esters of a -chloroacrylic acid which on polymerization yield polymers having good colour initially and a reduced tendency to develop colour over long periods of time are made by mixing and subsequently separating by distillation or steam distillation; a lower alkyl ester of a -chloroacrylic acid is normally prepared and a hydrazine derivative having one or both of the hydrogen atoms of one of the -NH2 groups in the hydrazine molecule replaced by an acyl group of formula R.CO-, where R is an organic radicle, an -NH2 group or an -NH2 group having one or both of the hydrogen atoms replaced by an organic radicle. The esters are those of the acid with aliphatic monohydric alcohols containing not more than four carbon atoms. Specified hydrazine derivatives are:-semi-carbazide, benzoyl hydrazine, unsym. dibenzoyl hydrazine, malonyl dihydrazine, isobutyryl hydrazine, unsym. diisobutyryl hydrazine, acetyl hydrazine, unsym. diacetyl hydrazine, phenyl semicarbazide and diphenyl semicarbazide. Semicarbazide may be used as the hydrochloride, the free base being isolated with caustic potash in methanol solution. Usually not more than 2.0 per cent of hydrazine derivative based on weight of ester is required, quantities of about 0.1-1.0 per cent generally being satisfactory. The hydrazine derivative may be added to the ester at room temperature, optionally in a solvent, preferably an organic solvent, e.g. ether or methanol, in concentrations of about 10 per cent by weight. When the hydrazine derivative is used in small quantities, e.g. less than about 1.0 per cent, the mixture should be allowed to stand before distillation. In examples methyl-a -chloroacrylate in the presence of tertiary butyl catechol is treated with (1) and (3) 10 per cent methanolic semicarbazide; (2) 10 per cent methanolic benzoyl hydrazine; (4) benzoyl hydrazine; (5) 10 per cent methanolic malonyl dihydrazine; (6) isobutyryl hydrazine; and (7) 10 per cent methanolic acetyl hydrazine and after standing for about 15 hours is distilled under nitrogen to yield the ester. The methyl-a -chloroacrylate may be made as in Specification 550,854.