Photochemical reaction process using a halosilane-coated vessel

Photochemical reactions, for example the reaction of benzene and maleic anhydride with benzophenone as sensitizer giving the adduct or the reactions of o-xylene with maleic anhydride, benzene with chloromaleic anhydride or maleic anhydride with itself are carried out by a process in which the reaction mixture is exposed to light from a source which is separated from the reaction mixture by means made at least in part of glass, and the surface of the glass which is in contact with the reaction mixture has been previously coated with a compound RmSiXn, where each R is alkyl or aryl, each X is halogen other than fluorine, m is 1, 2 or 3, and (m + n) is 4, the glass being then heated to above 20 DEG C.