GB825476A - Abnormal addition of hydrogen bromide to vinylaromatic compounds - Google Patents

Abstract

The reaction of gaseous hydrogen bromide with a mono- or a divinylaryl compound, such as styrene or divinylbenzene, to form 2-bromoethyl substitution products, is carried out in the presence of ultra-violet radiation from which wavelengths of less than 2900 have been filtered out, whereby the polymerization of the vinyl compound and the formation of an opaque film on the radiation-transmitting window are obviated. The transmitted radiation should have wavelengths of 2900 to 7000 , preferably 2900 to 3700 . In addition to styrene and divinylbenzene, the following compounds may be hydrobrominated by the method:-vinyltoluene, dimethylstyrenes, vinylmesitylene, chlorostyrene, dichlorostyrenes, chloromethylstyrene, methoxystyrene, hydroxystyrene, chlorodivinylbenzene, and divinylnaphthalene. The vinyl compound is preferably dissolved in an inert solvent such as pentane, hexane, heptane, benzene, toluene, chlorobenzene, tetrachloroethylene, carbon tetrachloride or 1,1,1-trichloroethane. Certain types of glass or an aqueous solution of copper sulphate may be used as radiation-filters. A circulating stream of copper sulphate solution may be used both as a filter and as a heat-transfer medium to maintain the reaction-temperature within the desired range, viz. 0-50 DEG C. When the reaction is complete, the reaction-mixture is neutralized with anhydrous sodium carbonate, water-washed, dried and distilled, preferably in the presence of iron, or from an iron pot, to decompose any small amounts of the 1-bromoethyl substitution product which may have been formed. Examples 1, 2, 3 and 5 describe the production of 2-bromoethylbenzene by hydrobromination of styrene. Example 4 describes the production of methyl-(2-bromoethyl)-benzene by hydrobromination of vinyltoluene. This example also refers to the hydro-bromination of chloromethylstyrene, and of an isomeric mixture of dichlorostyrenes. Bis - (2 - bromoethyl)benzene is produced by hydrobromination of divinylbenzene. Specification 554,499, [Group IV], is referred to.