The Rate of Isomerization of sec-Butyltoluene Catalyzed by Anhydrous Aluminum Chloride

Abstract

The rate of isomerization of sec-butyltoluene (SBT) catalyzed by anhydrous aluminum chloride was studied in dilute toluene solution. Experimental conditions such as stirring speed, catalyst concentration, and so on, were chosen to avoid occurrence of the two phase system and the side reactions such as disproportionation.
The reaction kinetics was investigated as a pseudo-first order triangular system. Best fit values of the six rate constants were estimated by the Gauss-Newton method.
The Arrhenius plots of the rate constants gave concave curves, each of which was approximated by two straight lines. From this behavior of the rate constants, it was concluded that the mechanism of the isomerization of SBT was dependent on. reaction temperature. That is, at relatively lower temperature (2030° C) the isomerization occurs by the intramolecular 1, 2- shift mechanism and at higher temperature (35-50° C) by a competitive intermolecular alkyl transfer mechanism in which both, the !one through generating of sec-butyl cation from the protonated SBT and the other through carbonium ion chan alkylation-dealkylation, take place simultaneously.
The rate constants were re-estimated taking into account the above mechanism. The Arrhenius equations were then determined as follows:
k0=1.188x 10'9 exp (-29.67 x 10 I RT) min-1 for 20° C to 50° C; k 5.167x 109 exp (-7.783 x 1O^2-/R T), k0, =2.541x 1O^2- exp (092 x 1O^2-/R T) min-1 for 20° C to 30° C and kmp= 6.933 X 1017 exp (-27.48 x 108/R T) km =5.135 x 1019 exp (-30.41 x 108/R 71) min-1 for 35° C to 50° C.
The equilibrium constants, ICO₃ and Kom were independent of reaction temperature and K0=0.0667, 0.4410 and 34.00.