Photochemical Synthesis of Lactic Acid Esters at Ambient Temperature Employing Sulfonically Fuctionalized N/W-Doped Nano-semiconductor.

Abstract

Appreciating the wide array of applications of lactic acid esters in the flavoring industry as well as in cosmetic and pharmaceutical industries, respectively, their clean and green synthesis gain immense importance. Therefore, traditional ester synthesis processes, involving high-temperature requirements, need to be replaced. A photochemical route has been adopted where visible light illumination was used as the major driving force to synthesize lactic acid esters. This process involves the application of sulfonically functionalized nitrogen/tungsten-doped nanotitania as photocatalysts. These functionalized catalysts efficiently and repeatedly catalyzed the esterification of lactic acid at ambient temperature. The photo-activity of these catalysts is attributed to the presence of a large number of active sulfonate sites on its surface. As per the proposed photochemical mechanism, illumination initiates the electron discharge from the conduction band, which migrates toward absorbed lactic acid through sulfonate sites forming lactic acid radical. This radical in turn attracts the alcohol molecules producing the desired ester. Reaction parameters were optimized to maximize the product yield. The economic validity of the photocatalyst was specked by repetitive experiments, and both the catalysts were found to be efficient even after five reusability cycles. The development of these catalysts can completely replace commercial ester synthesis strategies.