The uncatalysed and copper(II) promoted hydrolysis of 4-nitrophenyl glycinate
Abstract
The uncatalysed hydrolysis of 4-nitrophenyl glycinate has been studied over a range of pH at I= 0.1 mol dm–3(KNO3) and 35 °C. The ionization equilibrium of 4-nitrophenyl glycinate can be represented as in (i) where the pK is ca. 7.1 at 25 °C. Rate constants have been obtained for both NH3CH2[graphic omitted]H4NO2-4 [graphic omitted] NH2C[graphic omitted]CO2C6H4NO2-4 + H+(i) water and base hydrolysis of the species L and HL+. For the species L, kOH= 2.3 × 102 dm3 mol–1 s–1 and kH2O= 6.1 × 10–5 dm3 mol–1 s–1 while for HL+, kOH= 3.8 × 105 dm3 mol–1 s–1 and kH2O= 2.3 × 10–6 dm3 mol–1 s–1 at 35 °C. The hydrolysis of the ester is strongly promoted by copper(II), and under the experimental conditions employed, it has been shown that the metal-ion promotion involves the steps (ii) and (iii) with KM= 2.7 × 102 dm3 mol–1 and kOH= 6.6 × 106 Cu2++ L[graphic omitted][CuL]2+(ii), [CuL]2–+ OH– [graphic omitted] Products (iii) dm3 mol–1 s–1 at 35 °C. Base hydrolysis of [CuL]2+ is ca. 3 × 104 times faster than for L and some 18 times faster than for HL+ at 35 °C. Possible mechanisms for these reactions are considered.