N.m.r. study of the protonation of phosphine, hypophosphorous acid and orthophosphorous acid

The PH+4 ion was identified by phosphorus and proton magnetic resonance in the strong acids H2O ˙ BF3 and CH3OH ˙ BF3 at room temperature, and by proton magnetic resonance in concentrated sulphuric acid at low temperatures. The P—H coupling constant was insensitive to changes in the conditions. The protonation of H2PO(OH) and HPO(OH)2 in aqueous sulphuric acid was studied by measuring J(P—H) as a function of the acid concentration. The results are not consistent with the scales of Hammett function derived for other types of base, although the various scales are related by "linear free-energy relationships".