Patent GB-746508-A (GB)
Title: Improvements in the production of vinylidene cyanide and homologues thereof
Inventor: ARDIS ALAN EDRIC
Filed: 1953-09-21
Abstract: Homo- and inter-polymers of vinylidene cyanide and its homologues are prepared in the presence of a gaseous diluent or liquid diluent gaseous at the temperature employed, which is inert towards the polymerization products.  The vinylidine cyanide may be flash-distilled to free it from solid matter and then polymerized, any carboxylic acids and the liquid diluent present having no disadvantageous effect on the polymerization, or vinylidene cyanide crude distillate may be poured into water whereby the cyanide auto polymerizes.  Inert diluents specified are benzene, toluene, xylenes, mono-, di- and tri-chlorobenzenes, nitrogen, hydrogen, helium, methane, ethane and propane. Specifications 653,468, 677,825 and 746,507 are referred to.ALSO:Vinylidene cyanides having the general formula R1CH=C(CN)2, wherein R1 is hydrogen or an alkyl radical having 1 to 4 carbon atoms are prepared by pyrolyzing a diacyl cyanide of the structure <FORM:0746508/IV(a)/1> wherein R is an aliphatic acyloxy radical and R1 is as defined above, at a temperature of 400 DEG  to 750 DEG  C. in the presence of a gaseous diluent or liquid diluent gaseous at the temperatures employed, the diluents being inert towards the diacyl cyanide and end products. The inert diluent increases the stability of the crude pyrolysis product and enables the pyrolysis to be effected at ordinary pressures with increased yields.  Suitable diluents are liquid aromatic hydrocarbons or their halo-derivatives, e.g. benzene, toluene, xylenes, mono-, di- and tri-chlorbenzenes, and inert gases such as nitrogen, hydrogen, helium, methane, ethane and propane; generally, 8 to 12 mols. of diluent are used per mol. of diacyl cyanide.  Preferably, the diacyl cyanide is mixed with an inert liquid diluent, the mixture vaporized and the vapours passed through a heated pyrolysis tube which may be of brass, stainless steel or glass. The pyrolysis products comprising a vinylidene cyanide and a carboxylic acid are then condensed in a quench system, for example, as described in Specification 746,507.  The condensate may be flash distilled to obtain a crude vinylidene cyanide containing carboxylic acid and inert diluent which may be polymerized without further purification.  However, a purified vinylidene cyanide may be obtained from the crude product by distillation, crystallization from toluene or other like solvent, condensation with a diolefine such as butadiene or cyclopentadiene forming a solid substituted cyclohexane with the monomeric vinylidene cyanide which is pyrolysed at temperatures above about 400 DEG  C. to yield pure monomeric vinylidene cyanide, or finally, autopolymerization of the crude vinylidene cyanide compound, e.g. by pouring the monomeric product into water and decomposing the polymer to monomer, suitably at 170 DEG  to 250 DEG  C., as described in Specification 677,825.  Examples describe the pyrolysis of 1-acetoxy-1,1-dicyano ethane to vinylidene cyanide and 1-propionoxy-1,1-dicyano ethane to methyl vinylidene cyanide at atmospheric or reduced pressure.  In like manner there may be pyrolyzed 1-propionoxy-1,1 - dicyano propane, 1 - acetoxy - 1,1 - dicyano butane, 1 - butyroxy - 1,1 - dicyano butane and 1-valeryloxy-1,1-dicyano ethane.  Specification 653,468 also is referred to.