GB986634A - Styrene derivatives - Google Patents

Abstract

Vinyl halobenzenes are prepared by dehydrobromination of a bromoethylhalobenzene preferably by passing the bromoethylhalobenzene with superheated steam over a calcium sulphate catalyst at a temperature of at least 180 DEG C. and preferably within the range of 275-325 DEG C. The halogen nucleous substituent may be fluorine, chlorine or bromine. The bromoethylhalobenzene may be prepared by bromination of ethylhalobenzene by mixing the ethylhalobenzene with the theoretical amount of bromine and exposing the mixture to light in a visible and infra-red spectrum at room temperature. The compounds are used for incorporating in a polymeric material to produce a self-extinguishing polymeric material. In an example of the preparation of vinyl dibromobenzene, ethyldibromobenzene is prepared by brominating ethylbenzene which is then mixed with bromine and passed through a cylindrical glass annulus where it is irradiated with light from a tungsten or "daylight" fluorescent lamp located within the annulus to produce bromoethyldibromobenzene. The latter is passed through a dehydrobromination apparatus consisting of a vertical tube with a thermocouple tube fused axially therein, the annular space between the inner and outer tubes being packed with granular calcium sulphate. The tube is wound with two independently controlled heating elements of 250 watts and is heavily lagged. An efficient condenser and receiving system is connected to the bottom of the tube. At the top of the tube is mounted a vaporizer consisting of a vertical tube 10 inches long by 1 1/4 inches internal diameter packed with glass helices and wound with a 250 watt variable heating element, and to which superheated steam is supplied. The bromoethyldibromobenzene and water in the ratio of about 1 to 3 parts by volume are metered to the vaporizer and water evaporator respectively. The superheater and vaporizer outlet temperatures are governed at 220 DEG C. and 200 DEG C. respectively. The dehydrobromination reaction is endothermic and heating of the reaction tube is set to give a temperature of about 275 DEG C. in the centre of the top portion and 300 DEG C. in the bottom portion. The vinyl dibromobenzene condenses along with dilute aqueous hydrobromic acid and separates as a very pale yellow lower layer, which is separated, washed till neutral and dried with calcium chloride. In another example, vinyldichlorobenzene is prepared by methods analogous to the above. Specifications 837,696, 927,281, U.S.A. Specifications 2,432,737 and 2,485,524 are referred to.ALSO:Vinylhalobenzenes, in particular vinyldibromo and dichlorobenzenes are incorporated during the manufacture of polymers of ethylenically-unsaturated compounds, in particular polymers and copolymers derived by the polymerization or copolymerization of styrene e. g. polystyrene, unsaturated polyester-styrene copolymers, butadienestyrene copolymers and styrene-acrylonitrile copolymers.