Isotopic exchanges in the treatment of cyclopentane or cyclohexane with some deuterated or tritiated acids

Abstract

The exchange between the H atoms of cyclopentane (3) or cyclohexane (4) and the labeled acid protons of CF3SO3D (2-d), [3H]CF3SO3H (2-t), [3H]H2SO4 (1-t), or ZnCl2−[3H]HCl (5-t) has been investigated. Results from the treatment of 3 or 4 with 2-d at 0° or 20 °C, respectively, gave rise to polydeuterated cycloalkanes, indicating that all H atoms of 3 or 4 could be involved in the exchange. The rates of incorporation of the T-label into the hydrocarbon layer from the tritiated acids were found to be directly related to acid strength. After treatment of 3 or 4 with 2-t, quenching of the acid layer and analysis by isotope dilution showed the presence of cyclopentanol or cyclohexanol. A carbocationic chain mechanism for the exchange, as well as the mechanism for the formation of the cycloalkyl cation from the cycloalkane, are discussed.