Gas-Phase Chemistry of Trimethyl Phosphite

Article abstract of DOI:10.1021/ja00334a009

The reactions of trimethyl phosphite, (CH3O)3P, with the nucleophiles H2N^-, CH3NH^-, (CH3)2N^-, HO^-, H(18)O^-, CH3O^-, CD3O^-, H^-, F^-, H2P^-, CH2=CH-CH2^- and (CH3)2C=C(CH3)CH2^- were investigated.Products, branching ratios, and reaction rate constants are reported.Reactions generally proceed through an ion-dipole complex -.(CH3O)3P>, to a phosphoranide anion intermediate, <(CH3O)3PZ^-> to displacement of methoxide to form a new ion-dipole complex -.(CH3O)2PZ>.If an additional acidic hydrogen is available on the nucleophile, the major products results from proton abstraction by methoxide: -(CH3O)2PYH> -> (CH3O)2PY^- + CH3OH.When the displacement of methoxide from phosphorus is sufficiently endothermic, a competing attack at carbon by the original nucleophile occurs: -(CH3O)3P> -> CH3YH + (CH3O)2PO^-.Nucleophiles without an additional acidic hydrogen reacts similarly, but the final reaction products result from (1) S_N2 reaction of methoxide, <(CH3O)2PZCH3O^-> -> Z(CH3O)PO^- + CH3OCH3, (2) S_N2 reaction of the original nucleophile, -(CH3O)3P> -> CH3Z + (CH3O)2PO^-, (3) stabilization of the phosphoranide intermediate to give the adduct Z(CH3O)3P^-, and (4) expulsion of methoxide from the ion-dipole complex.Reaction mechanisms are discussed in terms of the nature of the nucleophiles, the observed products, and the thermodynamics of the displacement reaction.