Phosphorylation of Phenols with cyclo-Triphosphate

Abstract

Phosphorylation of phenols (phenol, catechol, resorcinol, hydroquinone, cresols, hydroxybenzoic acids, and nitrophenols) with inorganic sodium cyclo-triphosphate hexahydrate (P_3m), Na₃P₃O₉·6H₂O, was carried out under various reaction conditions (pH, temperature, and molar ratio). (1)The main products of these reations were triphosphate derivatives of phenols produced by phosphorylation of a hydroxyl group. Reaction of catechol with P_3m gave a five-membered cyclic phosphate formed by an intramolecular cyclization of a triphosphate derivative. (2)The optimum conditions for phosphorylation were found to be pH 12, and a molar ratio of P_3m : phenols=1 : 5. (3)The pK_a values of phenols strongly affected the reaction rate and yield. The reactivity of phenols increased with an increase in their pK_a values. A hydroxyl group on phenols with a pK_a value of more than 8 would be reactive with P_3m. (4)The reactivity of ortho-substituted phenols was less than those of meta- and para-substituted phenols, owing to the steric hinderance of ortho-substituents. (5)The mechanism of the reaction in the phosphorylation of phenols with P_3m is discussed.