An environmentally benign process to synthesize vanillin and other substituted phenyl aldehydes using natural phenylpropenes.

Abstract

The limited vanillin (3a) production from plant sources requires identifying some renewable and sustainable approaches for its synthesis. This study aimed to develop an efficient, eco-friendly process for synthesizing vanillin (3a) from eugenol (1a) and eugenol-rich essential oils. The chemical methodology for vanillin (3a) synthesis involved base-mediated isomerization of eugenol (1a) to isoeugenol (2a), followed by OsO₄/NaIO₄ mediated oxidation of isoeugenol to vanillin (3a) using different additives such 1,4-diazabicyclo[2.2.2]octane (DABCO) and substituted pyridines in reusable environment-friendly solvents. Use of 2,6-dimethylpyridine and 2,6-dimethylpyridine N-oxide as additives in the oxidation step offered a significantly higher product yield (vanillin 3a, 70 %). The process synthesized vanillin (3a) irrespective of the cis/ trans stereochemistry of isoeugenol (2a). The peculiarity of the method relates to converting eugenol (1a) to vanillin (3a) without phenolic group protection, which offers step economy. Besides efficient vanillin (3a) synthesis, the process's general implications involve converting other naturally occurring phenylpropenes or phenylpropenes-enriched oils to the corresponding phenyl aldehydes (59-82 % yield).