O-ethyl phosphoramidic acids with sterically demanding N-substituents : useful precursors of ethyl metaphosphate on thermolysis

Kinetics of the thermal fragmentation of four N-substituted derivatives of O-ethyl phosphoramidic acids, (EtO-P(O)(NRR')(OH), were examined. When N contained either of the sterically demanding mesityl or 1-ada- mantyl groups, the reaction followed first-order kinetics, both in the absence and presence of an alcohol trapping reagent. In the former case, the product was a pyrophosphate (RR'N(EtO)(O)P-O-P(O)(OEt)OH). In the latter case, phosphorus was trapped as a dialkyl phosphate. Both reac- tions are therefore indicated to follow an elimination-addition mecha- nism, with ethyl metaphosphate as transient intermediate. The pyrophos- phate is derived from reaction of the metaphosphate with treacted phos- phoramidic acid