A mixture of 40 parts of α,α-bis(4-fluorophenyl)-1-(phenylmethyl)-4-piperidinemethanol, 120 parts of a hydrochloric acid solution and 50 parts of acetic acid was stirred and refluxed for 2 hours. The reaction mixture was cooled and water and methylbenzene were added: three layers were obtained. The two supernatant phases were separated and treated with ammonium hydroxide. The organic phase was separated, dried, filtered and evaporated. The residue was crystallized from 2,2'-oxybispropane, yielding 26 parts of 4-[bis(4-fluorophenyl)methylene]-1-(phenylmethyl)piperidine (intermediate 13).
