Solar-driven aromatic aldehydes: green production from mandelic acid derivatives by a Co(ii)/C₃N₄ combined catalyst in aqueous media

Abstract

According to the requirements for sustainable development, reclaiming fine chemicals from wastewater under mild conditions is an extremely significant line of research.

Telescoped Two-Step Continuous-Flow Synthesis of Vanillin

“…Over 99% of vanillin is produced through chemical synthesis; among this synthetic vanillin, 85% is derived from a two-step synthesis (as shown in Scheme ) using guaiacol ( 2 ) and glyoxylate ( 3 ) as starting materials . The base-mediated electrophilic aromatic substitution (S E Ar) reaction of 2 with 3 to prepare the vanillylmandelic acid intermediate ( 4a ), , followed by transition-metal-mediated or -catalyzed aerobic oxidative decarboxylation, − results in vanillin. This method continues to be a leading and sustainable route for vanillin synthesis because the two starting substrates can be supplied from petrochemicals and biomass feedstocks. , This synthesis method that is performed using a conventional batch process, despite the demand for increased production, has suffered from three problems: low production efficiency, high environmental impact, and heavy workload.…”

“…In the first reaction process, the Cannizzaro reaction of 3 with strong bases (disproportionation of aldehydes to carboxylic acids and alcohols) decreases the yield of 4a (Scheme b) . In addition, in the second reaction process, the overoxidation of vanillin results in undesired vanillic acid ( 5 ) or oligo-vanillin products, reducing the yield and purity of the vanillin (Scheme c). − The conventional batch process performs these reactions at lower temperatures over a longer period of time to prevent a decrease in yield caused by such side reactions. These methods can improve yields; however, they reduce productivity substantially.…”