Patent GB-675372-A (GB)
Title: Improvements in or relating to 2, 3-difluoro-1, 3, butadiene, its polymers and copolymers and the preparation thereof
IPC: C07C17/20
Filed: 1950-01-02
Abstract: 2,3 - Difluoro - 1,3 - butadiene may be polymerized alone or with other polymerizable ethylenically unsaturated comonomers in free radial or ionic systems.  The polymers and copolymers may be treated with curing agents to effect cross linking.  Many comonomers for copolymerization are specified, representative being vinyl chloride and acetate, vinyl ethyl ether, vinyl methyl ketone, styrene, acrylic acids, esters, nitriles and amides thereof, maleic anhydride, dimethyl fumarate, b -cyanoacrylic acid, vinylidene chloride, isobutene, butadiene, chloroprene, 2-chloro-3-fluoro-1,3-butadiene (made in the preparation of 2,3-difluoro-1,3-butadiene (see Group IV (b)), 2,3-dimethyl-1,3-butadiene and piperylene.  In examples (1) and (2) polymerization is effected in the presence of water, potassium persulphate and mixed lauryl and myristyl sodium sulphates to give a non-fusible product insoluble in CCl4, CHCl3 and methyl ethyl ketone and also in (2) copolymers are prepared in a similar fashion with vinyl and vinylidene chlorides, acrylonitrile and 2,3 - dichloro - 1,3 - butadiene.  The homopolymers are tough, extensible and have good tensile strength and the copolymers largely retain the characteristics of the polymerized comonomer depending on the relative quantities of comonomer and 2,3-difluoro-1,3-butadiene taken.ALSO:2,3-Dichloro-1,3-butadiene is reacted with chlorine to give 1,2,2,3,3,4-hexachlorobutane which is fluorinated to replace at least one of the chlorine atoms at each of the 2- and 3-positions thereof, and the resultant polychloropolyfluorobutane is dehalogenated to give 2,3-difluoro-1,3-butadiene.  Chlorination is preferably effected in an inert solvent, e.g. carbon tetrachloride, chloroform, ethylene dichloride, acetylene tetrachloride and hexachlorobutadiene, in the presence of a chlorination catalyst such as stannic, ferric and antimony penta-chloride.  Fluorination may be effected with hydrogen fluoride with a fluorination catalyst such as mercuric or antimony penta-fluoride at 0-120 DEG  C., preferably about 50 DEG  C., under pressure to maintain a liquid phase reaction. Some monofluoro substituted product is obtained which on dehalogenation yields 2-chloro-3-fluoro-1,3-butadiene so that if a pure difluorobutadiene is required the 1,2,3,4-tetrachloro-2,3-difluoro-butane should be isolated from the fluorination reaction mass, e.g. by filtration or distillation, before dehalogenation.  Dehalogenation is effected by heating with Zn, Mg, Fe, Ca, Ba, Sr or Al, preferably in a polar solvent, e.g. methanol or formamide.  In examples: (1) 2,3-dichloro-1,3-butadiene in carbon tetrachloride is treated with chlorine in the presence of stannic chloride, the hexachlorobutane thus obtained being treated in an autoclave with hydrogen fluoride in the presence of mercuric oxide and the fluorinated product isolated by distillation is dehalogenated by heating with zinc dust in ethanol; (2) is as (1) except that a pure 1,2,3,4-tetrachloro-2,3-difluoro-butane is isolated before dehalogenation which is effected in methanol not ethanol.