Trimeric Phenylphosphonitrile Bromides

Submitted by PIERO NANNELLI, SHU-KUNG CHU,t BALDEV MANUAS,t and THERALD MOELLER  

Partial ammonolysis of phosphorus(V) chloride or bromide and of monoalkyl- or -aryl-substituted dichloro- or dibromophos-phines in the presence of chlorine or bromine is a general method for the synthesis, respectively, of the corresponding simple or substituted phosphonitrile halides. This type of reaction may yield either cyclic or linear poljuners, depending upon the temperature, solvent, reaction time, and/or reagent ratio. 

The reaction flask is then placed in an oil bath, the temperature of which is raised to 170-180 over a 3- to 4-hour period. The reaction mixture is stirred at this temperature until the evolution of hydrogen bromide ceases (24r-48 hoxms). The unreacted ammoniiun bromide is removed by filtration through sintered glass while the mixture is still hot, and washed wdth a few milliliters of fresh dry bromobenzene. The combined filtrate and washings are transferred to a 1-1. single-necked flask arranged for vacuum distillation and placed in an oil bath. An 

The dark viscous residue is e. tracted in the flask with five successive 300-ml. volumes of boiling dry n-heptane.f Each e.xtract is stored separately in a refrigerator at ca. 3°. On standing, these solutions deposit crude crystalline product and, possibly, an oily material that slowly solidifies under n-heptane. Complete crystallization may require scratching the inner walls of the containers and storage for a week. 

Purification of the combined crude product is effected by two to three recrystallizations from n-heptane, with activated charcoal added initially to remove color. Dissolution in n-heptane is slow and requires both boiling with tw o to three times the volume of solvent required to dissolve the material from the original mother liquor and manual stirring to break up lumps. Recrystallization is also slow and requires storage of the solutions for 2-3 days in a refrigerator. The product obtained melts at ca. 145° and is, substantially, a mixture of the tw o crystalline modifications of the trans isomer. Yield, based upon phenyldibromophosphine, 39 g. (34.5%). Anal. Calcd. for [NP(C6H6)Br] C, 35.67 H, 2.49 N, 6.93 P, 15.33 Br, 39.57 mol. wt., 606. Found C, 35.97 H, 2.47 N, 6.94 P, 15.25 Br, 39.31 mol. wt., 621. 

---