A Strategy for the Synthesis of 1,2-Dichlorotetrafluorocyclobutene from Hexachlorobutadiene and Its Reaction Pathway

In this paper, a novel strategy for the preparation of 1,2-dichlorotetrafluorocyclobutene (DTB) was proposed via a catalytic gas-phase process of fluorination using hexachlorobutadiene (HCBD) and anhydrous HF. In order to search for suitable catalysts and reveal the reaction pathway for this synthetic route, a series of studies were carried out. First, CrO_x/ZnO catalysts with different promoters (Ni, Cu, In, Al) were prepared by a precipitate method and the optimum reaction conditions were investigated. The highest activity was achieved on the Cr–Ni–Zn catalyst, whose yield of DTB reached 90% by a multiple cycle reaction. Second, the effects of different promoters on the properties of catalysts were studied by Brunauer–Emmett–Teller (BET) surface area analysis, scanning electron microscopy (SEM), X-ray diffraction (XRD), temperature-programmed desorption in ammonia (NH₃-TPD), and X-ray photoelectron spectroscopy (XPS). It was found that the Cr–Ni–Zn catalyst showed the excellent catalytic performances with more CrO_xF_y species, higher oxygen concentration, and widely distributed acid strength on its surface. Third, combining experimental results with theoretical calculations, a reaction pathway has been proposed. This study offers an economic synthetic route for DTB from HCBD, which is a valuable and promising method for industrial production.