In view of the rapid reaction of secondary phosphines with sulfur,'it seemed reasonable that the expected dithiophosphinic acid I (in equilibrium with its ammonium salt) was indeed formed initially but rapidly equilibrated with the cyclic intermediate I1 through intramolecular addition of sulfhydryl to the cyano group. Intermediate 11, which is a cyclic anhydride, might then be attacked by hydroxide either at the imide carbon atom yielding I11 or at the ...
