Patent GB-604983-A (GB)
Title: Improvements in and relating to the manufacture of halogen-containing organic compounds
IPC: C07C17/04
Filed: 1945-04-28
Abstract: Compounds useful as insecticides or as intermediates therefor, of the general formula <FORM:0604983/IV(b)/1> (where X1, X2 and X3 represent halogen atoms, and R1 and R2 benzene rings, at least one of which carries at least one halogen, cyano, nitro or alkyl substituent), are manufactured by adding on halogen, under the action of light, to a monohalogenostilbene <FORM:0604983/IV(b)/2> which in turn may be made by heating with alcoholic caustic alkali or a strong organic nitrogen base an a  : b -dihalogeno-a  : b -diarylethane <FORM:0604983/IV(b)/3> (wherein X4 represents a halogen atom), or (when X1 represents chlorine) heating a desoxybenzoin R1COCH2R2 with phosphorus pentachloride.  In examples: (1) a  : b -bis-(4-chlorophenyl)-a  : b -dichloroethane is refluxed with methanolic caustic potash, and the resulting a  : 4 : 41-trichlorostilbene is treated with a solution of chlorine in carbon tetrachloride in diffused daylight to produce a  : b -bis-(4-chlorophenyl)-a  : a  : b -trichloroethane; (2) 4 : 41-dichlorodesoxybenzoin is heated with phosphorus pentachloride to form a  : 4 : 41-trichlorostilbene, which is treated as in (1); (3) 4 : 41-difluorodesoxybenzoin is similarly treated to give a -chloro-4 : 41-difluorostilbene and a  : b -bis-(4-fluorophenyl)a  : a  : b -trichloroethane; (4) a -chloro-4 : 41-difluorostilbene is treated with a solution of bromine in carbon tetrachloride, producing a  : b -bis-(4-fluorophenyl)-a  : b -dibromo-a -chloroethane; (5) a  : 4 : 41-trichlorostilbene similarly yields a  : b -bis-(4-chlorophenyl)-a : b -dibromo-a -chloroethane; (6) a  : p  4 : 41-tribromostilbene is treated with chlorine in carbon tetrachloride to give a  : b -bis - (4 - bromophenyl - a  : b  - dichloro - a  - bromoethane; (7) a  : b -bis-(4-bromophenyl)-a  : b -dichloroethane is treated as in (1) to yield a  : b  - bis - (4 - bromophenyl) - a  - chloroethylene and a : b -bis-(4-bromophenyl)-a  : a  : b -trichloroethane; (8) 4-methyldesoxybenzoin is treated as in (2) to form a -chloro-4-methylstilbene and a  - p - tolyl - b  - phenyl - a  : a  : b -trichloroethane; (9) chlorine is passed into a solution of a -chloro-4 : 41-dinitrostilbene heated on an oil bath and strongly illuminated with ultra-violet light, producing a  : b -bis-(4-nitrophenyl)-a  : a  : b -trichloroethane; (10) 4 : 41-dicyanostilbene dichloride is heated with pyridine in a sealed tube and the resulting a -chloro-4 : 41-dicyanostilbene is chlorinated as in (9) to give a  : b -bis-(4-cyanophenyl)-a  : a  : b -trichloroethane.  a  : b -Dihalogeno-a  : b -diarylethanes of the general formula above are obtainable by direct halogenation of the corresponding stilbene derivatives.  Thus the starting materials of examples (1) and (7) above are made by the action of chlorine in carbon tetrachloride on 4 : 41-dichloro- and -dibromo-stilbene respectively, and that of (10) similarly from 4 : 41-dicyanostilbene dissolved in nitrobenzene.  4 : 41-Dichlorodesoxybenzoin is prepared by condensing chlorobenzene in the presence of aluminium chloride with p-chlorophenylacetyl chloride (obtained by heating the acid with phosphorus trichloride).  4 : 41-Difluorodesoxybenzoin is made similarly, but working in carbon disulphide solution, from fluorobenzene and p-fluorophenylacetyl chloride (obtained by heating the acid with thionyl chloride).  4-Methyldesoxybenzoin is obtained similarly from phenylacetic acid, phosphorus trichloride, toluene and aluminium chloride.