Process for preparing halogenated diaryl hydrogen phosphates

In the method for preparing a halogenated diaryl hydrogen phosphate which comprises reacting a halogenated phenol with a phosphorus oxyhalide in the presence of a catalyst and an inert organic solvent, the phenol being employed in excess of 2 moles per mole of oxyhalide, to form intermediate reaction product mixture consisting of diaryl phosphorohalidate, triaryl phosphate, and a minor proportion of monoaryl phosphorodihalidate, and then effecting hydrolysis of intermediate reaction product with water to form a final product mixture mixture of diaryl hydrogen phosphate, triaryl phosphate, and a minor proportion of monoaryl dihydrogen phosphate, the improvement for substantially avoiding coproduction of triaryl phosphate in the final product mixture which comprises:

• employing as the halogenated phenol a 2,6-dihalophenol having the halogens in its 2 and 6 ring positions selected independently from the group consisting of bromine and iodine, and
• effecting the hydrolysis in the presence of inert organic hydrolysis solvent at a pH between about 1 and 9 and a temperature between about 20.degree. and 100.degree. C. for a time between about 15 minutes and 18 hours to form bis(2,6-dihalophenyl) hydrogen phosphate having in admixture therewith only a minor proportion of tris(2,6-dihalophenyl)phosphate and 2,6-dihalophenyl dihydrogen phosphate.