Cyclization of citronellal to p-menthane-3,8-diols in water and carbon dioxide?

Green Chemistry Pub Date: 2009-06-03 DOI: 10.1039/B823297K

Abstract

A clean process has been developed for the synthesis of p-menthane-3,8-diols from cyclization of citronellal in CO2–H2O medium without any additives. With the addition of CO2, the reaction rate could be enhanced about 6 times for the cyclization of citronellal in H2O, because CO2 dissolved into water and formed carbonic acid inducing an increase of the acidity. Although, the reaction conversion in CO2–H2O is slightly lower compared to that obtained with sulfuric acid as catalyst, CO2–H2O could replace the sulfuric acid at a relative higher reaction temperature. The reaction kinetics studies showed that the hydration of isopulegols to p-menthane-3,8-diols is a reversible reaction. The equilibrium constant and the maximum equilibrium yield obtained in CO2–H2O at a range of CO2 pressures are similar to that with sulfuric acid catalyst.

Graphical abstract: Cyclization of citronellal to p-menthane-3,8-diols in water and carbon dioxide
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