Monoalkyl phosphates, alkaline hydrolysis

Although alkaline hydrolysis of monoalkyl or monoaryl phosphates is ordinarily very difficult, 2,4-dinitrophenyl phosphate, 2,4-(N02)2CaH30P03H2, does react with aqueous base, and with cleavage at the phosphorus-oxygen bond. Suggest an explanation for this. 

As the acidity of the solution is increased, the rate of hydrolysis of monoalkyl phosphates, ROPO(OH>2, rises from essentially zero in alkaline solution, and passes through a maximum at the point (moderate acidity, pH about 4) where the concentration of monoanion, R0P0(0H)(0 ), is greatest. Cleavage is at the phosphorus-oxygen bond. 

Monoalkyl phosphates are very stable to alkali. The dianion R—0 —PO3 " is predominant in alkaline solution and the stability appears to be due to electrostatic repulsion to attack by 0H . The neutral triesters (R0)3 P0 are readily hydrolyzed by alkali to the diesters (R0)2 = P02 . No inversion or migration has been detected during alkaline hydrolysis so that the affected bond is probably P-0. Neighboring groups such as OH (as in glycol phosphate or glycerolphosphate) increase stability while NH2 (as in aminoethyl phosphate) decreases it ° ° . 

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See also in sourсe #XX -- [ ]

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