Camphor synthesis through the metal-doped phosphotungstic acid lacunar salts-catalyzed borneol green oxidation with hydrogen peroxide

Abstract

A new green oxidation procedure was developed using metal-doped cesium phosphotungstate lacunar salts as catalysts and hydrogen peroxide as oxidant for the conversion of borneol to camphor. A series of metal-doped cesium undecaphosphotungstate lacunar salt with general formulae Cs7-xPW11Mx+O39 (Mx+ = Zn2+, Cu2+, Fe3+, Co2+, Mn2+, and Cu2+) were synthesized and characterized by FT-IR, RAMAN, DRX analyses, and potentiometric titration. Among the salts evaluated, zinc-doped cesium undecaphosphotungstate was the most active and selective toward the camphor formation from borneol. Its highest activity was attributed to greater Lewis and Pearson acidity. The main reaction parameters were assessed. Based on experimental data, a reaction pathway was proposed. The borneol oxidation was carried out over a solid catalyst, providing camphor with a 95 % yield. This environmentally friendly route uses a green oxidant that gives water as a byproduct. The solid catalyst was easily recovered and reused without loss of activity.