Patent GB-792859-A (GB)
Title: Catalytic dehydrochlorination of (chloroethyl) benzyl chloride
IPC: C07C22/04
Filed: 1956-04-26
Abstract: The invention comprises (chloromethyl) styrenes of the formula <FORM:0792859/IV (b)/1> and their preparation by dehydrochlorinating a (chloroethyl)benzyl chloride by contacting its vapours with a dehydrohalogenation catalyst at 200 DEG  to 420 DEG  C. and at a pressure for said vapours not greater than 0.2 atmosphere and for such a time that not more than 10 per cent by weight of the (chloroethyl)benzyl chloride which is dehydrohalogenated undergoes pyrolysis to form by-products of lower boiling points than that of the (chloromethyl)styrene.  The starting material can be the ortho-, meta- or para-isomer or mixtures of these and the chlorine atom can occupy either the a - or the b -position in the ethyl side-chain.  An inert diluent such as carbon dioxide, nitrogen, helium, saturated lower aliphatic hydrocarbons, vapours of aromatic benzene hydrocarbons or steam may be used, advantageously at from 240 DEG  to 360 DEG  C. for a reaction time of 0.01 to 10 seconds at pressures between 0.01 and 1.5 atmospheres, the diluent being employed in such amount that the vapour pressure of the (chloroethyl) benzyl chloride does not exceed 0.2 atmosphere.  Advantageously, steam is employed in amounts of from 1 to 10 parts by weight per part by weight of the (chloroethyl)benzyl chloride used.  Suitable catalysts are activated aluminium oxide, calcium sulphate, aluminium silicate, calcium phosphate, magnesium phosphate, barium phosphate, mixtures of alkaline earth metal phosphates and oxides of nickel, cobalt, chromium or manganese, or mixtures of aluminium oxide and an oxide of one or more of the metals cobalt, chromium, manganese, tungsten, molybdenum or nickel.  Superheated steam may be used to supply at least a portion of the heat for the reaction which is conducted in a conventional manner, the vapours on completion of the reaction being cooled to condense liquid product which is then distilled. Polymerization inhibitors such as sulphur, dinitro-o-cresol, tert.-butylcatechol or hydroquinone may be added at any stage of the cooling or fractionating operations or to the final product.  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 chloride and 5 per cent of the beta isomer is mixed with steam and dehydrohalogenated over activated aluminium oxide at 235 DEG  to 360 DEG  C. for 0.3 seconds at 20 to 60 mm. absolute pressure, the vapours being condensed to liquid product containing 43 per cent by weight of (chloromethyl)styrene and 57 per cent of (chloroethyl)benzyl chloride; (2) a similar mixture is dehydrochlorinated over an aluminium oxide-tungsten oxide catalyst for 0.7 seconds at 210 DEG  to 250 DEG  C. and 10 to 30 mm. giving a product containing 72.5 per cent (chloromethyl)styrene; (3) to (8) similar experiments, with minor variations in time, temperature and pressure, are conducted, other catalysts used being calcium sulphate, kaolin, nickel oxide, mixed calcium phosphatenickel phosphate and mixed aluminium oxidemolybdenium oxide, steam being omitted in one example and replaced by xylene in another, and details of the fractionation of the liquid product and analysis of the fractions obtained being given in some cases; and (9) a liquid mixture of a (chloromethyl)styrene and (chloroethyl) benzyl chloride is fractionally distilled and the physical constants and chlorine content of the (chloromethyl) styrene product determined.ALSO:A (chloromethyl) styrene is polymerized to a hard thermoplastic product soluble in toluene by allowing to stand in a stoppered bottle at room temperature for 60 days.