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 Ogroups; 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. Methyl ethylene phosphate, 1, undergoes hydrolysis 101 23456 7***times as rapidly as does trimethyl phosphate. In dilute acid solution, the products are both those of ring opening and of exocyclic cleavage.1-4 to the region where/is proportional to (OH-).

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This hydrolysis almost certainly proceeds by way of the same cation, A, CsH&H=G--C(CH3)3, which is required for the oxidative rearrangement. Therefore, if this intermediate were formed, the oxygen atom originally present in the carbinol would appear in the t-butyl alcohol. None does. Therefore the rearrangement does not occur.On the basis of the present work alone, no distinction can be made between an oxidative process producing a carbonium ion and one producing a radical. The work of Lansbury, et al.,1° coupled with that here reported, makes the carbonium ion sequence of eq. 6 quite probable.The general base catalysis of the mutarotation of glucose and the general acid catalysis of the inversion of menthone are subject to steric hindrance; 2,6-lutidine is a poorer catalyst than would be expected considering its ionization constant by factors of 25 and about 10, respectively. The hydrolysis of methyl ethylene phosphate is catalyzed by heterocyclic bases with a solvent deuterium isotope effect, ka,o/kD,o, of about 2 ; 2,6-lutidine is again a poorer catalyst than anticipated by a factor of ten. These data suggest: (1) that the hydrolysis of methyl ethylene phosphate is subject to general base, rather than to nucleophilic, catalysis; and (2) that general base and general acid catalysis are moderately sensitive to steric hindrance.

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