Aromatic compounds can be alkylated with olefinically unsaturated compounds employing a catalyst consisting essentially of aluminum halide and molecular iodine. Additionally, molecular iodine or iodine-containing compounds are useful in other catalytic conversions such as for example, Grignard reactions, carbonylation reactions, and the like. A problem encountered with such reactions is the removal of the iodine components from the reaction mixture so that color formation in the product is avoided. Methods disclosed in the prior art, such as for example, extraction with thiosulfate or bisulfite; treatment with other oxidants; distillation in the presence of acid or base, however, are not always successful in completely removing color forming impurities from the reaction mixture which contains the desired product.