The phenoxaphosphinic acid ring system (I) was found to be remarkably stable. 2, 8- Dimethylphenoxaphosphinic acid was oxidized to the corresponding dicarboxy compound, and dinitro derivatives of both the dimethyl and the dicarboxy compounds were prepared. 2, 8-Dimethylphenothiaphosphinic acid was prepared by a variant of the Friedel-Crafts reaction in which p-tolyl sulfide and phosphorus trichloride were heated together in the ...
