Abstract: An improved process for the preparation of terephthaloyl and isophthaloyl dichlorides by chlorination of dimethyl terephthalate and isophthalate with chlorine gas at temperatures from 100.degree.-250.degree. C., optionally in the presence of light and/or catalysts promoting side-chain chlorination of aromatic compounds, according to which 20 to 200% by weight, relative to the weight of dimethyl terephthalate and/or isophthalate, of terephthaloyl and/or isophthaloyl dichloride are added to the dimethyl terephthalate and/or isophthalate for the chlorination.

Abstract: Benzoyl chloride is prepared by a process in which the high-boiling residue obtained in the catalytic oxidation of toluene with oxygen or oxygen-containing gases in the liquid phase is largely freed of heavy metal salts which are present, and is then chlorinated at elevated temperatures, optionally under the action of light, and the benzoyl chloride is then separated off.

Abstract: A process for color stabilizing aromatic carboxylic acid chloride against discoloration which comprises introducing into a composition containing an aromatic carboxylic acid chloride 0.001 to 2% by weight of a color stabilizer, based upon the amount of said aromatic carboxylic acid chloride. The use of aldehydes, ketones, olefins, phosphorus and arsenic containing compounds are contemplated as stabilizer.

Abstract: A process for the preparation of optionally substituted benzoyl chloride from optionally substituted benzotrichloride at elevated temperature in the presence of a catalyst is described wherein optionally substituted benzotrichloride or a mixture thereof with optionally substituted benzoyl chloride is reacted with an excess of 1 to 20 mol percent of optionally substituted benzoic acid and/or water and the hydrogen chloride-containing off-gases formed during the reaction are washed with optionally substituted benzotrichloride or the mixture of optionally substituted benzotrichloride and optionally substituted benzoyl chloride.

Abstract: An improved process for the preparation of benzaldehyde by hydrolysis of benzal chloride wherein hydrolysis is carried out at an elevated temperature in the presence of an excess of aqueous hydrochloric acid and in the absence of another catalyst.