3,4-Dichlorobutene-1 is produced by a process comprising the step of contacting 1,4-dichlorobutene-2 with either 1) a ferric carboxylate catalyst of the formula where R is an alkyl or alkenyl group of 4-18 carbon atoms, a cycloalkyl or cycloalkenyl group of 6-18 carbon atoms or an aryl group selected from phenyl, benzyl, xylyl, tolyl, and naphthyl groups, whereby a portion of the 1,4-dichlorobutene-2 is isomerized to form 3,4-dichlorobutene-1, or 2) a ferric carboxylate catalyst of the formula where R, R′ and R″ are independently alkyl or alkenyl groups of 4-18 carbon atoms, cycloalkyl or cycloalkenyl groups of 6-18 carbon atoms or aryl groups selected from phenyl, benzyl, xylyl, tolyl, and naphthyl groups, the sum of m, n and o is 3 and m, n and o are independently 0, 1 or 2, whereby a portion of the 1,4-dichlorobutene-2 is isomerized to form 3,4-dichlorobutene-1.