Procedure for obtaining acid chlorides or-chloromethyl.

Procedure for obtaining acid chlorides o-chloromethylbenzoyl of formula ** ** wherein R1 to R4 may be the same or different and are hydrogen, alkyl having 1 to 4 carbon atoms, halogen or trifluoromethyl, by reacting benzo-fused lactones, in which R1 to R4 have the abovementioned meaning, with thionyl chloride, wherein the reaction is carried out in the presence of catalytic amounts of a Lewis acid and catalytic amounts of a phosphine derivative, in the rd to R?- that may be the same or different and are alkyl having 1 to 10 carbon atoms or phenyl unsubstituted or substituted by alkyl having 1 to 4 carbon atoms, the index n is 0 or 1 and X is oxygen or two chlorine atoms linked by a single bond.