Isotope Effect on Dehydration Reaction of 2-Methy1-3- pheny1-2-propanol with Anhydrous Aluminum Bromide

Abstract

Kinetic isotope effect on the dehydration reaction of 2-methyl-3-pheny1-2-propanol (MPP) with anhydrous aluminum bromide was examined. The ratios of the first-order specific rate constants of 2-methyl-d₃-3-phenylpropan-1, 1, 1-d₃-2-ol (MPP-d₆) and of 2-methyl-3-phenylpropan3, 3-d₂-2-ol (MPP-d₂) to that of MPP were k (MPP) (MPP-d₆) = 1.2 and k (MPP) (MPP-d₂) =1.5, respectively. Activation parameters for the d ehydration reaction of MPP-d₂ were found to be E_a= 53.5 kJ/mol, ΔS_??_165.6 J/deg. /mol and ΔG_??_ = 110.4 kJ/mol. The hydrogen bromide-catalyst addition complex is suggested to add to 1, 1-dimethyl-2-phenylethoxyaluminum dibromide to form an unstable intermediate, which then eliminate leaving group-O-AlBr₂.