MECHANISM OF THE PHOSPHORYLATION REACTION OF 2-HALOALKYLPHOSPHONIC ACIDS

2-Haloalkylphosphonic acids require aqueous solutions of suitable pH t o react as phosphorylating agents. Reaction rates are slow at pH<pK1, moderate at pK1<pH<pK2 (monoanion) and fast at pH>pK2(dianion). The an d products in water are phosphoric acid (major) and 2-hydroxyalkyl- an d vinylphosphonic acids (minor). The dianion is stable in non-aqueous solutions. The order of reactivity is bromo>chloro>>fluoro. Dehydrohal ogenation is the major pathway with mono- and diesters. In contrast, 2 -chloroethylphosphonothioic acid dianion is stable even at pH 13. Thes e findings are consistent with a mechanism involving a bimolecular pro cess rather than an SN1 pathway via a metaphosphate intermediate.