Conversion of triose sugars with alcohols to alkyl lactates catalyzed by Bronsted acid tin ion-exchanged montmorillonite

We describe the Bronsted acid catalysis of tin ion-exchanged montmorillonite (Sn-Mont), which is easily prepared by the ion-exchange of naturally occurring sodium montmorillonite (Na-Mont) with an aqueous tin tetrachloride solution, for the conversion of two trioses, i.e., dihydroxyacetone (DHA) and glyceraldehyde (GLA), in alcohols to afford the corresponding alkyl lactates. For the conversion of DHA with methanol, the product distribution closely depends on the substrate concentrations, reaction temperatures, and reaction times. Under the optimized reaction conditions, an almost quantitative yield of methyl lactate is obtained with the production of water as the exclusive side-product. Additionally, the montmorillonite catalyst is easily recovered from the reaction mixture by filtration, and reused without any loss in activity. Sn-Mont also demonstrates a high activity for the conversion of DHA with higher alcohols, such as EtOH, nPrOH, and nBuOH, to the corresponding alkyl lactates in 89-93% yields. (C) 2011 Elsevier B.V. All rights reserved.