Hydrochloric Acid → 2,5-Dichlorobenzoylpiperidine

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2,5-dichlorobenzoyl-containing compounds (e.g. 2,5-dichlorobenzophenones and 2,5-dichlorobenzamides) can be readily prepared from 2,5-dichlorobenzoylchloride. Pure 2,5-dichlorobenzoylchloride is obtained by vacuum distillation of the mixture obtained from the reaction of commercially available 2,5-dichlorobenzoic acid with a slight excess of thionyl chloride in refluxing toluene. 2,5-dichlorobenzophenones (2,5-dichlorobenzophenone, 2,5-dichloro-4'-methylbenzophenone, 2,5-dichloro-4'-methoxybenzophenone, and 2,5-dichloro-4'-phenoxybenzophenone) are prepared by the Friedel-Crafts benzoylations of benzene and substituted benzenes (e.g. toluene, anisole, diphenyl ether, respectively), with 2,5-dichlorobenzoylchloride at 0°-5° C. using 2-3 mole equivalents of aluminum chloride as a catalyst. The solid products obtained upon quenching with water are purified by recrystallization from toluene/hexanes. 2,5-dichlorobenzoylmorpholine and 2,5-dichlorobenzoylpiperidine are prepared from the reaction of 2,5-dichlorobenzoylchloride and either morpholine or piperidine, respectively, in toluene with pyridine added to trap the HCl that is evolved. After washing away the pyridinium salt and any excess amine, the product is crystallized from the toluene solution.

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