Abstract: A process for arylating an olefinic compound by addition of an aryl group to a double bond of said olefinic compound consisting in diazotizing an arylamine in an aqueous acidic solution comprising a lower alkanoic acid to form a solution of an aryldiazonium salt and reacting said aryldiazonium salt solution with an olefinic compound in an organic solvent in the presence of a catalytically effective amount of a copper halide.The amount of alkanoic acid is about 15 to 37% by volume of the total solvents used. The alkanoic acid is preferably acetic acid and the copper halide cuprous chloride.