Organic carbonates. Part XII. The alkaline hydrolysis of highly branched ethylene and trimethylene carbonates

Abstract

The rates of hydrolysis of four highly branched ethylene carbonates (Ia)–(Id), and eleven trimethylene carbonates (IIa)–(IIk) in alkali-metal hydroxide at several temperatures have been measured by means of: (1) direct titrimetry, (2) conductometry, (3) pH-stat method, (4) the flow method, and (5) nonaqueous titration of carbon dioxide liberated (after acidification) during the reaction. The rates are not affected by added salts but the reaction exhibits a solvent-effect. The first stage of reaction is two to five orders of magnitude faster than the second stage (decarboxylation) and the ratio k_OH/k_CO2 depends both on ring-size and substitution. With a [substrate] : [base] ratio greater than 3 the rates (k_OH) of all cyclic carbonates can advantageously be measured by means of conductometry. Plots of –log k_OH/T from various techniques against 1/RT values give a straight line for each substrate attesting to the reliability of the methods and data presented.