Continuous process for the production of phosphonitrilic chlorides

#This invention relates to a process for the preparation of polymeric phosphonitrilic chlorides. More particularly, the invention relates to a novel, continuous process for the production of polymeric phosphonitrilic chlorides by the ammonia-phosphorus pentachloride reaction under constant process conditions.

#Polymeric phosphonitrilic chlorides, particularly the lower molecular weight predominantly cyclic phosphonitrilic chloride oligomers of the general formula (PNCl.sub.2)n, n being an integer of at least 3, are generally prepared by the reaction of either ammonia or ammonium chloride with phosphorus pentachloride. In some cases, these reactants may be formed in situ.

#Representative prior art processes are described, for example, in U.S. Pat. No. 3,359,080, issued Dec. 19, 1967 to Ridgway et al, wherein elemental chlorine, PCl.sub.3 and NH.sub.4 Cl are reacted in an inert solvent; U.S. Pat. No. 3,462,247, issued Aug. 19, 1969 to Paddock et al wherein a metallic salt is used to catalyze the PCl.sub.5 - NH.sub.4 Cl reaction; U.S. Pat. No. 3,656,916 to Schiedermaier et al wherein PCl.sub.5 and NH.sub.3 are reacted in an inert solvent, the ammonia being added under controlled rates of addition; U.S. Pat. No. 3,658,487, issued Apr. 25, 1972 to Wunsch et al wherein chlorine, ammonia and phosphorus are reacted in an inert chlorinated hydrocarbon solvent; U.S. Pat. No. 3,669,633, issued June 13, 1972 to Beinfest et al wherein PCl.sub.3 and Cl.sub.2 are used to form PCl.sub.5 in situ; and U.S. Pat. No. 3,780,162, issued Dec. 18, 1973 to Bergeron et al wherein ammonia and PCl.sub.5 are reacted under pressure in the presence of hydrogen chloride, which serves as a reactant to produce ammonium chloride in situ. Wunsch et al further discuss the PCl.sub.5 -NH.sub.3 reaction and the P.sub.3 NCl.sub.12 intermediate formed therein in Chem.-Zeitung 94, (21) 832 1970.

#The invention is further illustrated by the following examples which are not to be considered as limitative of its scope. Percentages are by weight, except where otherwise indicated.

#In the continuous process, there are used two stirred reactors containing reaction mixtures maintained at such overflow levels that the hold time in each is about 3 hours (hold time is the time needed to fill the reactor to said level at the constant rate of feed used in the process). The PCl.sub.5 is fed, at a constant rate, as a hot (115.degree. C) solution in o-dichlorobenzene solvent (DCB) containing about 1.25 moles of PCl.sub.5 per liter, into the bottom of the first reactor. A stream of gaseous ammonia is fed into the lower part of the first reactor just above the path of the tip of the stirrer blade, at a constant rate such as to provide about 1.05 to 1.10 mole NH.sub.3 per mole of PCl.sub.5 fed into the first reactor. The reactor temperature is kept in the range of 115.degree. to 119.degree. C; pressure is substantially atmospheric. After the initial filling period, the level of reaction mixture in the first reactor is maintained by pumping a slurry of excess reaction mixture comprising PCl.sub.5 -NH.sub.3 intermediate, NH.sub.4 Cl and any unreacted PCl.sub.5 to the second reactor kept in the range of 135.degree. to 140.degree. C. No ammonia is introduced into the second reactor. The level in the second reactor (after its initial filling period, for example, after three hours of continuous transfer) is also maintained by pumping excess mixture to a product collector. By-product HCl gas from both reactors is collected in aqueous caustic scrubbers. The crude product is checked periodically for insolubles which are almost exclusively NH.sub.4 Cl, for product polymeric phosphonitrilic chloride content, and for the percent of linear fraction (hexane insolubles) in the product.

#A sample of product was filtered and then stripped of DCB in vacuo to obtain a product that contained 89.2% hexane soluble cyclic oligomers. The linear (hexane-insoluble) fraction was a yellow oil. The cyclic portion was analyzed by gas chromatography. Molecular distribution of the cyclic portion was as follows: