GB792860A - Process for making (chloromethyl) styrene - Google Patents

Abstract

A (chloromethyl)styrene is prepared by dehydrochlorination of a (chloroethyl)benzyl chloride by heating vapours thereof at 420 DEG to 700 DEG C. at a pressure for the vapours not greater than 0.2 atmospheres and for a time such that not more than 10 per cent by weight of the (chloroethyl)benzyl chloride which is dehydrochlorinated undergoes pyrolysis to form by-products of lower boiling-points than that of the (chloromethyl)styrene. The (chloroethyl)benzyl chloride may be the ortho-, meta- or paraisomer or mixtures of these and the chlorine atom may occupy either the a - or b -position in the ethyl side-chain. An inert diluent such as carbon dioxide, nitrogen, helium, a saturated lower aliphatic hydrocarbon, vapours of a benzene hydrocarbon or steam can be used, advantageously at 500 DEG to 620 DEG C. for 0.01 to 10 seconds at total pressures between 0.01 and 1.5 atmospheres absolute pressure, the diluent being employed in such amount that the pressure of the (chloroethyl)benzyl chloride does not exceed 0.2 atmospheres. Advantageously, a mixture comprising one part by weight of a (chloroethyl)benzyl chloride and from one to 10 parts by weight of steam is used, the process being conducted in a conventional manner, preferably with the steam being superheated and supplying at least a portion of the heat, with final cooling of the vapours to condense liquid product which is then distilled. Polymerization inhibitors such as sulphur, dinitro-o-cresol, tert.-butyl catechol or hydroquinone may be added at any stage of the reaction or distillation or to the final products. In examples: (1) a mixture of about 70 per cent by weight p-(chloroethyl) benzyl chloride and 30 per cent of the o-isomer, containing 95 per cent of (alpha-chloroethyl) benzyl chlorides and 5 per cent of the beta-isomers is mixed with steam and dehydrohalogenated at 550 DEG to 600 DEG C. for 0.25 seconds, the vapours being condensed to a liquid product which is fractionally distilled to give 95 per cent pure (chloromethyl)styrene; (2) the process of (1) is repeated at 580 DEG to 610 DEG C. and 60 to 80 mm. absolute pressure for 0.4 seconds; (3) para(chloroethyl)benzyl chloride containing 95 per cent by weight of the alpha-isomer and 5 per cent of the beta-isomer is dehydrohalogenated in three separate experiments, the conditions being similar to those employed in (1) with minor variations in time and temperature; (4) a mixture similar to that used in (1) is dehydrohalogenated in the absence of steam, the reaction time being 0.7 second at 385 DEG to 500 DEG C. and 20 to 30 mm. pressure, to give a product containing 68 per cent by weight of (chloromethyl)styrene which is purified by distillation. Specification 792,859 is referred to.