ACID-CATALYZED HYDROLYSES OF WEAKLY BASIC PHOSPHATE ESTERS

The acid-catalyzed hydrolyses of p-nitrophenyl, 2,4-dinitrophenyl, bis-2,4-dinitrophenyl, and p-nitrophenyldiphenyl phosphate have been examined using hydrochloric, sulfuric, and perchloric acids in the range of 1-10 M. Plots of the first-order rate constant, kᴪ, against CH generally show maxima which are not caused by extensive protonation of the substrate. Addition of THF increases the rate of hydrolysis of 2,4-dinitrophenyl phosphate at low acidities and decreases it at high acidities, but the log A factors and the activation energies are only slightly sensitive to changes in acid concentration or solvent composition, except for hydrolysis of p-nitrophenyldiphenyl phosphate. The values of kH/kD are in the range of 0.7-1.land larger than generally found for A2 hydrolyses. These results suggest that proton transfers are partially rate limiting, and that initial-state effects are also important. The basicities of triphenyl and p-nitrophenyldiphenyl phosphates have been measured. © 1969, American Chemical Society. All rights reserved.