Investigation and development of novel synthetic approaches for synthesis of euxanthone and derived dyes

Abstract

The historical dye Indian yellow, derived from euxanthic acid formed from 1,7-dihydroxyxanthone (euxanthone) and methyl (tri-O-acetyl-α-d-glucopyranosyl bromide) uronate, has significantly influenced the art world due to its vibrant color and unique production process. Studying Indian yellow is important for its historical relevance and impact on various art forms, as well as the challenges in its synthetic production. Herein, this work investigates the synthesis of the two main components, a novel method for obtaining euxanthone, and attempts to produce euxanthic acid and Indian yellow. All key intermediates and desired compounds have successfully been synthesized with good to high isolated yields, and characterized using different analytical and spectroscopic techniques. A proposed mechanism for euxanthone synthesis via 2,6,2',5'-tetramethoxybenzophenone formation is also offered. During this process, 2,7-dihydroxyxanthone has also been synthesized, revealing an equilibration reaction that produced three isomeric tetramethoxybenzophenones, confirmed by both GC/MS and NMR. Following the synthesis of euxanthone and clarification of the equilibration, the production of Indian yellow via euxanthic acid formation has further been explored.