The cleavage of the arylOCH 3 bond using anisole as a model compound

Abstract

The thermal decomposition of anisole as a prototype of the aryl-methyl-ether linkage of lignin and coals has been studied under supercritical conditions using tetralin as hydrogen donor solvent. The effect of homogenous Lewis acid catalysts have also been studied under the same conditions. The main reaction products are phenol, benzene, toluene and cresols. At high tetralin to anisole ratios the selectivity to phenol is almost 80% with little or no cresol production. This selective conversion can be carried out rapidly and cleanly at high temperature (> 450 ° C). Kinetic studies were undertaken using pyrolytic, donor solvent hydrogenolytic and Lewis acid catalysed regimes in the temperature range 400–500 °C. The kinetics of anisole decomposition in a large excess of tetralin have been found to be in good agreement with those published in the literature. The Lewis acid catalysts lower the activation energy relative to the pyrolytic and hydrogenolytic cases. The kinetic studies and their mechanistic interpretation lead to a mechanism involving surprisingly few radical species: methyl, phenoxy, phenoxymethyl and phenyl radicals. In the presence of FeCl 3, the selectivity towards phenols and cresols is enhanced, though a side reaction leads to polymerization at low (400–420 °C) temperatures. It is concluded that the aryl-O-methyl ether linkage in anisole can easily be broken at high temperatures, 450–500 °C, in supercritical hydrogen donor solvent to give phenol in high yield and selectivity.