Hydrochloric Acid → 2,5-Dichlorobenzoylpiperidine

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A wide variety of 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 (e.g. 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 an excess of benzene or substituted benzenes (e.g. toluene, anisole, or 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-dichloro-benzoylpiperidine are prepared from the reaction of 2,5-dichloro-benzoylchloride and either morpholine or piperidine, respectively, in toluene with pyridine added to trap the hydrogen chloride 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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