1H NMR spectroscopic study of the tert-butyl chloride - Aluminum bromide cationic initiating system

Article abstract of DOI:10.1007/BF02494270

The interaction of tert-butyl chloride with aluminum bromide in methylene dibromide at -30 °C leads to the formation of two types of adducts, which give signals with δ 2.4 and 3.2 in the ¹H NMR spectra in addition to that of free alkyl halide. These signals are attributed to a polarized complex (PC) and ion pair (IP), respectively. An excess of AlBr₃ shifts the equilibria toward IP. The latter contains more AlBr₃ than the polarized complex. Based on the spectral data, we calculated the limiting values of some equilibrium constants. The ability of AlBr₃ to solvate counterions is consistent with the results of isobutylene polymerization under the action of the initiating Bu¹Cl-AlBr₃ system at different ratios of the starting concentrations [AlBr₃]₀/[Bu¹Cl]₀. An increase in this ratio results in both the acceleration of polymerization and an increase in the relative role of chain transfer reactions.