KINETICS OF GALLIUM CHLORIDE CATALYZED METHYLATION OF TOLUENE AND XYLENES IN EXCESS METHYL CHLORIDE . PARTIAL RATE FACTORS FOR METHYLATION REACTION

Kinetic studies have been made of the gallium chloride catalyzed methylation of toluene and m-xylene in excess methyl chloride at –35.6°. These reactions were found to follow kinetics similar to that of the benzene reaction, the rate expression being – d[ArH]/dt = K3[GaCl3]o2[ArH]. Product xylene isomerization was observed in the toluene reaction. The rate constants decrease markedly with increasing reaction time from their zero-time values of k3·toluene = 7.9 × 10−4 and k3,m·m-xylene = 6 × 10−3 l.2 mol−2 min−1. It is shown that disproportionation cannot be the sole cause of this effect. Catalytic inhibition due to σ-complex formation is also considered. Partial rate factors mf 1.8, pf 9.4, and of 8.3 are calculated from the extrapolated zero-time rate constants and isomer distribution of the benzene and toluene reactions. Zero-time rate constants and isomer distributions are predicted for the polymethylbenzenes, and are found to be in excellent agreement with those determined for the m-xylene reaction. © 1969, American Chemical Society. All rights reserved.