Nucleophilic Reactions of Anions with Trimethyl Phosphate in the Gas Phase by Ion Cyclotron Resonance Spectroscopy

Article abstract of DOI:10.1021/ja00523a007

The gas-phase ion-molecule reactions of several negative ions (SF6^-, SF5^-, SO2F^-, F2^-, F^-, CF3Cl^-, Cl^-, CD3O^-, DNO^-, OH^-, and NH2^-) with trimethyl phosphate are investigated using ion cyclotron resonance techniques.Nucleophilic attack on OP(OCH3)3 occurs chiefly at carbon, resulting in displacement of O2P(OCH3)2^-.This behavior contrast with that observed in solution, where attack at phosphorus is favored for hard nucleophiles.This difference is ascribed to solvation energetics for the intermediates involved in the two reactions.The failure of SF6^- to transfer F^- to OP(OCH3)3 places an upper limit of 11 +/- 8 kcal/mol on the fluoride affinity of OP(OCH3)3.The significance of the results for the negative chemical ionization mass spectrometry of phosphorus esters is briefly discussed.