The Synthesis and Mechanistic Considerations of a Series of Ammonium Monosubstituted H‐Phosphonate Salts

Abstract

A series of ammonium monosubstituted H‐phosphonate salts were synthesized by combining H‐phosphonate diesters with amines in the absence of solvent at 80 °C. Variation of the ester substituent and amine produced a range of ionic liquids with low melting points. The products and by‐products were analyzed by spectroscopic and spectrometric techniques in order to get a better mechanistic picture of the dealkylation and formal dearylation observed. For dialkyl H‐phosphonate diesters, (RO)2P(O)H (R=alkyl), the reaction proceeds via direct dealkylation with the reactivity increasing in the order R=iPr<Et<Me corresponding to DFT calculated activation enthalpies of 22.6, 20.8, and 17.9 kcal mol−1. For the diphenyl H‐phosphonate diesters, (PhO)2P(O)H, the dearylation was found to proceed via phenol‐assisted formation of a 5‐coordinate intermediate, (PhO)3PH(OH), from which P(OPh)3 and water were eliminated. The presence of an equivalent of water then facilitated the formation of P(OH)2OPh and the amine, R'NH2, subsequently abstracted a proton from it to yield [(PhO)PH(O)O]‐[R'NH3]+.

The Step‐Wise Synthesis of Oligomeric Phosphoramidates

“…A possible mechanism that explains the formation of the P−O−P by‐product, is through nucleophilic attack on the α‐carbon of the OMe group of N−P−N by the amine resulting in an ionic intermediate [61] ( I , Scheme 5). This α‐attack is not possible in the case of the N−P−N compounds with P(OPh) derivatives and thus the amine substituted by‐product is not observed in this case.…”