Electrochemical study of the methylcyclopentane oxidation in anhydrous hydrogen fluoride and HF_SbF5 superacid solutions

Abstract

The electrochemical study of methylcyclopentane (MCPH) oxidation in anhydrous hydrogen fluoride and related superacid media leads to determination of the standard potentials of the MCPH redox couples and to the establishment of the potential acidity diagram of MCPH. Fromtthese results the oxidation by H+ ion of MCPH into the carbenium ion MCP+ is observed in acidic media: pH<6 or R(H)<−21.9 (pH values are reported on the acidity scale in HF, pH=0 for a molar solution of SbF5, and the acidity levels are referred to H2O by means of an R(H) function: for pH=0, R(H) is −27.9). In HF−SbF5 mixtures, pH<2.3 or R(H) <−25.6, the protonation of MCPH to form the carbonium ion MCPH2+ has to be taken into account and the acidity constant is determined. In basic media, pH>8.1 or R(H)>−19.8, condensation reactions are enhanced through a radical oxidation state; the disproportionation constant of the dimer (MCP)2 is determined. Moreover, in the most acidic media, pH<2 or R(H)<−25.9, evidence for the cracking of MCPH through the protolysis of a C−C bond is shown.