Pyrolysis studies of some simple coal related aromatic methyl ethers

Abstract

Pyrolysis of the coal related model compounds o-, m-, and p-hydroxy and methoxyanisoles has been studied under inert atmosphere at reaction temperatures from 598 to 673 K, and for reaction times from 1 to 600 min. The thermal decomposition of all these anisoles takes place via two main primary pathways, namely by demethylation of the methoxyl groups, and by an intramolecular ipso substitution of the methoxyl groups via a spiranic oxiran intermediate. The demethoxylation under mild reaction conditions obviously takes place as a secondary reaction via the ipso substitution pathway. The demethylation of o-hydroxyanisole (guaiacol) is partly concerted on the basis of kinetics and of e.p.r. measurements of the residual spin concentration of the pyrolysis products. There is, however, no indication of a concerted mechanism for 0-methoxyanisole (veratrole). The apparent first order activation energy of all the anisoles studied is of the order 240 ± 20 kJ mol −1 corresponding to the average bond energy of the methyl CO bond in the aromatic methoxyl group.