Multinuclear nuclear magnetic resonance study of the interaction of some phosphorus(V) compounds with inorganic acids. The protonating abilities of HNO3, MeSO3H, and HPO2F2 towards the phosphoryl group

Abstract

The influence of protonation upon ³¹P and ¹⁷O n.m.r. parameters of the phosphoryl compounds POCl₃ and HPO₂F₂ has been investigated. For POCl₃, δ(¹⁷O) and ¹J(P–O) decrease whereas δ(³¹P) increases with increasing protonation of the phosphoryl group. For HPO₂F₂ the changes in δ(¹⁷O) and δ(³¹P) were less informative although ¹J(P–F) appears to increase smoothly with increasing protonation. The same trend in ¹J(P–F) is observed for solutions of Na₂PO₃F in some inorganic acids (MeSO₃H, CF₃CO₂H, HNO₃, HSO₃Cl, and 25 oleum). The POCl₃ results indicate that the ability of HNO₃ to protonate the phosphoryl group is significantly greater than would be anticipated on the basis of Hammett acidity-function measurements, whereas the protonating ability of MeSO₃H is as anticipated on the basis of its Hammett function and that of HPO₂F₂ is lower than those of HNO₃ and MeSO₃H, comparable with that of liquid HCl. The values of δ(³¹P) of POBr₃ in HNO₃, MeSO₃H, and HPO₂F₂ are in agreement with the above conclusions.