Vinylidene fluoride is a useful monomer in the preparation of fluorocarbon polymers which have excellent weathering and chemical resistant properties. Vinylidene fluoride is currently manufactured on an industrial scale by the dehydrochlorination of 1,1-difluoro-1-chloroethylene (142b) which must first be prepared by the fluorination of 1,1,1-trichloroethane. Such a multi-step process is typical for vinylidene fluoride preparation. A one-step process for converting vinylidene chloride, a readily available material, to vinylidene fluoride by gas phase reaction with HF using chromium salts or a combination of Alf.sub.3 and a "activator" selected from La(NO.sub.3).sub.3, NH.sub.4 VO.sub.3, and SnC1.sub.2 has been disclosed in U.S. Pat. No. 3,600,450. Unsatisfactory results were reported when Alf.sub.3 was impregnated with metals such as cadmium, chromium, iron, manganese, molybdenum, nickel, zinc, or zirconium. Another process for catalytically converting vinylidene chloride is disclosed in U.S. Pat. No. 4,147,733 using an alumina based catalyst coated with Cr.sub.2 O.sub.3 and NiO. This process uses highly corrosive aqueous HF as the fluorinating agent.
This invention provides a process for the one-step gas phase conversion of vinylidene chloride to vinylidene fluoride using anhydrous Alf.sub.3, or a combination of Alf.sub.3 with certain transition metals, as catalyst. These catalysts which have theretofore not been considered useful for such conversions are effective when oxygen is added to the reactant mixture.