Electrochemistry of Carbonium Ions in Acidic Media. 1. Triphenylmethyl Ion in Aluminum Chloride Containing Melts

Article abstract of DOI:10.1021/jo00346a019

The electrochemistry of the triphenylmethyl carbonium ion (1) has been studied in a room-temperature aluminum chloride containing melt.Formation of 1 is dependent on the acidity or pCl of a molten aluminum chloride/n-butylpyridinium chloride (1:1) binary mixture.The equilibrium constant for reaction 1 is 20.4 +/- 0.3 mol L^-1 at 40 deg C as determined by spectroscopic techniques.Formation of 1 from triphenylmethyl chloride is too slow to quantitatively determine a rate constant (k_f) by conventional electrochemical techniques.Cyclic voltammetric and controlled-potential coulometric data reveal that 1 is reduced in an one-electron process to a triphenylmethyl radical (2).Formation of 2 in the AlCl3 melt is verified by ESR spectroscopy.Dimerization of 2 produces an electrochemically oxidizable form of 1-(diphenylmethylene)-4-(triphenylmethyl)-2,5-cyclohexadiene (3); the rate constant for the dimerization of 2 is 1.33 +/- 0.08 * 10³ 1 mol^-1s^-1 at 40 deg C.Workup of an exhaustively electrolyzed solution of 1 in the melt produces <4-(diphenylmethyl)phenyl>triphenylmethane, which is the result of proton isomerization of 3.