Electrophilic Aromatic Substitution. 9. A Kinetic Study of the Friedel-Crafts Isopropylation Reaction in Nitromethane

Article abstract of DOI:10.1021/jo00359a038

The kinetics of the aluminum chloride catalyzed reaction between isopropyl chloride and benzene or toluene were determined in solvent nitromethane by using vacuum-line techniques.The reaction at 25 deg C was first order in isopropyl chloride and in aromatic hydrocarbon and first order in initial catalyst concentration.Noncompetitive results are k_T/k_B = 2.0 +/- 0.7 with the following toluene product isomer distribution: percent ortho, 45.3 +/- 1.5; percent meta, 22.7 +/- 1.1; percent para, 32.0 +/- 1.0.For competitive runs k_T/k_B was 2.3 +/- 0.1 with the same isomer distribution.Rate constants at 25, 15, 0, -15, and -27 deg C yielded E_a = 78 +/- 4 kJ/mol, ΔH^<*> = 76 +/- 4 kJ/mol, Δ^<*> = -13 +/- 14 J/mol deg.The results are consistent with a ? complex-like transition state and a predominantly ionic mechanism.