Carbon kinetic isotope effects on the hydrolysis of aryl carbonates

Abstract

Carbon kinetic isotope effects on the hydrolysis of aryl carbonates in 1:1 (v/v) dioxane-water at 25°C at various pHs were used to calculate isotope effects on the reactions with hydroxide ion and with water. For diphenyl carbonate k OH 12 /k OH 13 =1.0482 and k w 12 /k w 13 =1.0509. For bis (p-methoxyphenyl)carbonate k OH 12 /k OH 13 =1.0493 and k w 12 /k w 13 =1.0518. For bis(p-nitrophenyl)carbonate k OH 12 /K OH 13 =1.0476. The small change in the isotope effect with substituent group fro both alkaline and neutral hydrolysis is in contrast to the large substituent effect on the rate constants for both reactions. The nearly constant isotope effect indicates that transition-state structures are similar for all substrates