Dimethyl phosphate anion, attack

P-O bond fission is the usual mode of attack by nucleophiles on phosphodiesters, although there are exceptions. The labile diester methyl-2,4-dinitrophenyl phosphate shows significant amounts of attack at aromatic carbon (nucleophilic aromatic substitution, with loss of methyl phosphate) in competition with attack at phosphorus, most notably with hydroxide and with primary amines.46 Due to the small size of the methyl group it is sterically susceptible to nucleophilic attack in phosphate esters the hydrolysis of the dimethyl phosphate anion occurs almost exclusively by C-O bond fission.4 With larger or less labile leaving groups, even... 

A similar effect controls the rate of attack of hydroxide ion on an ester. The attack of hydroxide ion on an electrically neutral ester, such as trimethyl phosphate, involves many interactions. The attack of hydroxide ion on an ester-anion, such as dimethyl phosphate anion, presumably involves the same interactions, plus an additional electrostatic interaction between the hydroxide ion and the residual negative charge on the phosphate anion. (Figure 5.)... 

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