Clean esterification of mandelic acid over Cs_2.5H_0.5PW₁₂O₄₀ supported on acid treated clay

Abstract

Several esters of mandelic acid are valuable precursors in a number of processes. Esterification is rampantly employed in the production of fragrances, flavors, plastics, pharmaceuticals and plasticizers. For instance, methyl mandelate is used as a precursor in the synthesis of pemoline, a CNS stimulant, and also plays a vital role in artificial flavoring and perfumes. Esters are normally produced by reaction of carboxylic acids and alcohols catalyzed by homogeneous mineral acids, which are fraught with contamination of the product and post-treatment pollution problems. A process for clean esterification of mandelic acid with methanol to produce methyl mandelate was developed by using novel solid acids such as Cs_2.5H_0.5PW₁₂O₄₀/K-10 clay, UDCaT-1 and sulfated zirconia. All of them are reusable and efficient catalysts. However, the activity of Cs_2.5H_0.5PW₁₂O₄₀/K-10 clay was superior to the rest. Cs_2.5H_0.5PW₁₂O₄₀/K-10 clay is a recyclable nano-catalyst. The effects of various parameters were studied to deduce the intrinsic kinetics of the reaction.