PH-PRODUCT AND PH-RATE PROFILES FOR HYDROLYSIS OF METHYL ETHYLENE PHOSPHATE . RATE-LIMITING PSEUDOROTATION

The hydrolysis of methyl ethylene phosphate in dilute acid solution has previously been shown to occur both with ring opening and with cleavage of the exocyclic methyl group, whereas the methyl ester of propylphostonic acid reacts under these conditions only with ring opening. These facts had been correlated with the theory that hydrolysis of the exocyclic methoxyl group takes place only after pseudorotation about the central phosphorus atom. The complete pH-product profile for the hydrolysis of methyl ethylene phosphate is shown in Figure 3 and explained in the text. The drop in the percentage of exocyclic cleavage in strongly acid solution may be correlated with rate-limiting pseudorotation; the rise in the percentage of exocyclic cleavage in strong alkali may be correlated with the ionization of both the hydroxyl groups in the pentacovalent intermediate so as to produce two O- groups; according to theory, these should occupy equatorial positions, and so the ionization could force a pseudorotation that promotes exocyclic cleavage. The kinetic equations for the over-all process exhibit unusual features that are discussed. © 1969, American Chemical Society. All rights reserved.