Wacker PdCl 2–CuCl 2 catalytic oxidation process: Oxidation of limonene

Abstract

Wacker oxidation of limonene, using PdCl 2/CuCl 2/O 2 in glacial AcOH at 302 K with a 24 h reaction time, yielded cis-carvyl acetate, trans-carvyl acetate, trans-carveol, carvone and α-terpinyl acetate. Oxidation of limonene was also carried out in t-butanol using PdCl 2/CuCl 2/ t-butyl hydroperoxide (molar ratio 1:2:360): the yields of oxidation products were higher in the presence of added chloride ion: conversion rates of about 80% after 36 h reaction time were observed at ratios of [PdCl] 2]:[LiCl] = 1:4. t-Butylperoxy products resulted in the PdCl 2/CuCl 2/ t-butyl hydroperoxide oxidations from η 3-allyl-palladium intermediates. Generally, allylic oxidation was the predominant reaction. The reaction products were generally identified from their mass spectra and retention indices obtained using HRGC–MS.