2,4,6 - Trichloro - 2,4,6 - triphenyltriphosphonitrile, and 2,4,6,8 - tetrachloro - 2,4,6,8 - tetraphenyl tetraphosphonitrile, of the respective formulae FORM:0992377/C2/1 and FORM:0992377/C2/2 where #f represents phenyl, are prepared by reacting phenyltetrachlorophosphorane with solid NH4Cl of particle size below 10m , in an inert solvent for the phosphorane, at 60-140 DEG C. Suitable solvents are hydrocarbons or halogenated hydrocarbons of boiling-point at least 60 DEG C. (e.g. n-heptane, CCl4, tetrachloroethylene, chlorobenzene, or chloropicrin) and preferred quantities of reactants are 0.1 to 1 mol. of NH4Cl/litre of solvent to less than 0.02 mols. of phosphorane/litre of solvent. The NH4Cl is suspended in the solvent, suitably by passing HCl and NH3 into it simultaneously, or passing in a smoke of NH4Cl in an inert gas (e.g. N2, argon or helium), to give a dispersion of particles of size between 1m and 10m . The phosphorane is suitably added to the refluxing suspension at such a rate as to maintain the desired reactant concentration. The trimer and tetramer formed may be separated by: (a) fractional crystallization from suitable solvent pairs (e.g. benzene-pentane or CHCl3-hexane), after purification of the reaction products by extraction at 60-140 DEG C. with a mixture of water and a solvent for the trimer and tetramer that itself has an aqueous solubility below 1% (e.g. n-heptane, hexane, pentane, CCl4, or benzene), when the water hydrolyses higher linear polymers to water-soluble products, and the trimer and tetramer are taken up in the non-aqueous phase; (b) by continuous extraction of the purified trimer-tetramer mixture with an aliphatic hydrocarbon of up to six contiguous carbon atoms, boiling below about 90 DEG C. (e.g. pentane, or hexane), when the trimer is extracted first. Cis and trans forms of the trimer may be separated by fractional crystallization from benzene, the cis form crystallizing first as a lesser soluble benzene adduct. Examples are given for the preparation of the trimer and tetramer in (1) chlorobenzene at various reaction temperatures; (2) chlorobenzene, using granular NH4Cl as a comparison; (3) heptane; also for purification of the reaction mixture by the above hydrolytic process; separation of the trimer-tetramer by (a) crystallization from chlorobenaene, followed by recrystallization from chloraform-pentane; (b) continuous extraction with pentane; separation of the cis and trans trimers by fractional crystallization from benzene. The cyclic polymers are useful for the preparation of thermally stable polymers by ammoniation and condensation at temperatures above 200 DEG C. Specification 981,821 is referred to.
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