Kinetics and thermodynamics of the decarboxylation of 1,2-glycerol carbonate to produce glycidol: computational insights†
The kinetics and thermodynamics of the decarboxylation of 1,2-glycerol carbonate to yield glycidol were studied using “chemically accurate” quantum chemical calculations. Both base- and acid-catalyzed reactions were examined, as were the potential reactions that yield the 3-hydroxyoxetane isomer. Under all conditions, glycidol was the preferred product. While the free energy barrier for the alkoxide form of 1,2-glycerol carbonate to form the epoxide ring is low, the rate-determining step of the overall reaction is the loss of carbon dioxide from the resultant carbonate anion (ca. 21.7 kcal mol−1). Protonation of 1,2-glycerol carbonate is expected to be difficult, but decarboxylation henceforth is exergonic, and the free energy barrier is lower (12.3 kcal mol−1). Calculations also indicate that oligomerization of 1,2-glycerol carbonate (ΔG = 4.9 kcal mol−1), followed by degradation to glycidol, is unlikely on thermodynamic grounds.