Equilibrium CH-acidity of organophosphorus compounds - Communication 1. Influence of the solvent on the CH-acidity of phosphine oxides and phosphine sulfides

Article abstract of DOI:10.1007/BF00922118

1. The equilibrium CH-acidity (pK) of phosphine oxides and phosphine sulfides of analogous structure was determined in diglyme (DG) and in DMSO by the method of transmetallation. The acidity of the phosphine sulfides is almost unchanged from one solvent to another. The acidity of phosphine oxides in relatively nonpolar DG is three to five orders of magnitude higher than in DMSO, on account of the coordination of the phosphoryl group of the carbanions with the alkali metal cation in DG. The ionic dissociation constants of Li-substituted phosphine oxides in DG are two to three orders of magnitude lower than for phosphine sulfides. The distance between ions in ion pairs in Li-substituted phosphine oxides is reduced. 2. For an estimation of the acidifying effect of phosphinyl and thiophosphinyl groups, we used the pK in DMSO. Thiophosphinyl substituents negligibly exceed phosphinyl groups in their summary acidifying effect. 3. The introduction of (C₆H₅)₂PO and (C₆H₅)₂PS groups as substituants into diphenylmethane and fluorene increases the acidity of the latter by ～8 units of pK.