Acetyl phenyl phosphate hydrolysis

The characteristic features of hydrolysis of diaryl phosphate monoanions (pronounced influence of leaving group on the rate of hydrolysis, k o/k = 1.6, and AS = —25 euu7y) also fail to support a metaphosphate mechanism118>. Hydrolysis of the acetyl phenyl phosphate monoanion is likewise far slower than that... 

For example, a number of studies have been made on the metal ion-catalyzed hydrolyses of acetyl phosphate and acetyl phenyl phosphate, " but the role of the metal ion in these processes remains uncertain. Investigations of catalysis by exchange labile metal ions e.g. Ca" and Mg") have yielded conflicting results and both the nature and distribution of the kinetically significant species, as well as the positions of bond cleavage, have yet to be determined unequivocally. Chelation, charge neutralization and attack by metal-bound hydroxide have variously been proposed as important factors in acyl phosphate hydrolysis. 

Buckingham, D. A., and C. R. Clark. 1981. Reactions of acyl phosphates. Base hydrolysis of [Co(NH3)jOP03COCH3] + and the metal hydroxide promoted hydrolysis of acetyl phenyl phosphate, Aust. J. Chem., 34 1769-1773. 

This conclusion agrees with other evidence for the same mechanisms (Di Sabato and Jencks, 1961). The volume of activation for the hydrolysis of acetyl phenyl phosphate mono-anion, which is —19 cm mole in water at 60°C (Di Sabato et al., 1962), is not indicative of mechanism as it can be interpreted in several ways. 

Tracer 0 studies have established that base hydrolysis of coordinated acetyl phosphate in the complex [(NH3)5Co-OP03COCH3] [ifcoH = 0.53 M s at 25°C and I = l.OM (NaC104)] occurs by exclusive carbon-oxygen bond fission. The hydrolysis of the acetyl phenyl phosphate monoanion is significantly catalyzed by the exchange-inert hydroxo complex [(NH3)sCoOH] ( MOH = 2.9 X 10 M s at 25 C) which operates by... 

A situation similar to that in acetyl phosphate is also encountered in benzoyl phosphate76 . Electron-attracting substituents on the phenyl ring accelerate the hydrolysis of the dianion (a linear relationship exists between log khydrol and the Hammett a constants with q = 1.2 and the linear log ki,j,drol./pKa relationship is the same as for the phosphoric monoaryl ester dianions65 . On the other hand, hydrolysis of the monoanion is influenced only slightly by substituents in the phenyl ring. These observations can also be rationalized in terms of the decomposition mechanism to the POf ion formulated for 116 and 117. 

The highly electrophilic character of the POf ion would suggest a very unselective phosphorylation behavior. For example, the ratio of alkyl phosphate to inorganic phosphate obtained in hydrolyses of phosphoric esters in water/alcohol mixtures should reflect the molar ratio of water and alcohol. This is indeed found in numerous cases, e.g. in the hydrolysis of phenyl and 4-nitrophenyl phosphate monoanions 97) or of 4-nitrophenyl phosphate dianions 65) at 100 °C in methanol/ water mixtures of various compositions, as also in the solvolysis of the acetyl phosphate dianion at 37 °C 97) or of phosphoenol pyruvate monoanions 82). Calculations of the free energy of the addition reactions of water and ethanol to the POf ion support the energetic similarity of the two reactions 98) (Table 4). 

The 1-phosphates of a- and /3-lactose have been synthesized by interacting silver diphenyl phosphate with hepta-O-acetyl-a-lactosyl bromide, with the elimination of silver bromide, followed by hydrogenolysis of the phenyl groups and fractional recrystallization of the barium salts. /3-Lactosyl phosphate is more readily hydrolyzed than the a anomcr in N hydrochloric acid at 37° (64% and 26% hydrolysis, respectively, after 80 minutes). 

Treatment of tetraacetyl a-glucosyl (CV) jind a-galactosyl bromides (p. 46) with silver diphenyl phosphate followed by hydrogenolysis of the phenyl residues and alkaline hydrolysis of the acetyl groups yields a-glucose (CVI)... 

---