Solketal synthesis from glycerol and acetone in the presence of metal salts: A Lewis or Brønsted acid catalyzed reaction?

Abstract

In this paper, several commercial transition metal salts were tested in acetalization reactions of glycerol with acetone to produce solketal (i.e., 2,2-dimethyl-1,3-dioxolan-4-yl)methanol). Among the salts assessed, Fe(NO3)3 9⋅H2O exhibited the highest catalytic activity, virtually converting all the glycerol to solketal, with 95% selectivity in short reaction time (ca. 30 min). Ferric nitrate is inexpensive, commercially available, non-corrosive and water-tolerant Lewis acid catalyst. Although soluble, it was easily recovered through a liquid-liquid extraction process followed by the drying of the aqueous phase and reused without loss activity or selectivity. The performance of Fe(NO3)3 was compared to other Lewis and Brønsted acid catalysts. Insights on the reaction mechanism were performed aiming to verify the effect of H+ ions generated by hydrolysis of metal catalysts throughout the reactions. This process described herein is an attractive option to the Brønsted acid-catalyzed routes because it is non-corrosive, avoids products neutralization steps and allow an easy recovery and reuse of catalyst.