KINETIC-STUDY OF THE THERMOLYSIS OF ANISOLE IN A HYDROGEN ATMOSPHERE

The gas-phase thermal decomposition of anisole diluted in a 10-fold excess of hydrogen has been studied at atmospheric pressure in a tubular flow reactor over the temperature range 793-1020 K. In the overall process the unimolecular decomposition PhOCH3 --> PhO. + CH3. (1) plays a prominent role. The rate constant k1 was separately determined between 790 and 875 K, employing a large (85-fold) excess of p-fluorotoluene as a carrier, and found to obey 10(15.3(+/-0.2)) exp[(-63.6(+/-0.7) kcal mol-1)/RT] (s-1). Methyl radicals formed in reaction 1 react with H-2 to generate highly reactive H-atoms. Induced decomposition of anisole also occurs, as the overall rate is about 1.2-1.5 times that in the toluene system. The major products are phenol and methane. Product composition and modeling studies show that the concentration of atomic hydrogen is 100 times higher when compared with the theoretical concentration in H-2. The exact origin of H in the product phenol is not clear, and if combination of H. with PhO. would totally account for it (reaction 14), this rate constant must be above 10(11.8) M-1 s-1. New reactions with H are advanced in order to fit product profiles through modeling with KINAL: H. + PhOCH3 --> (keto)phenol + CH3. for which k23 was set at 10(9.85) exp[(-5.4 kcal mol-1)/RT] (M-1 s-1). However extra CO was formed which is not due to decomposition of phenoxyl or reactions involving the side chain conversion of anisole. Its origin is as yet unclear, but intermediately formed ketophenol is advanced as a likely candidate.