Molar Absorptivity and pKR+ of the 4,4'-Dimethoxytrityl Carbenium Ion in Methanolic Water, and its Equilibrium with Chloride Ion

Article abstract of DOI:10.1039/P29940001463

The 4,4'-dimethoxytrityl carbenium ion has been generated in 80:20 (v/v) water-methanol containing perchloric acid in a rapid reaction from 4,4'-dimethoxytrityl alcohol and in a slower reaction from 4,4'-dimethoxytritylamine.The pK_<*> (-0.95; K_<*>=8.98) and molar absorptivity (ε_<*>=297 000) of the cation have been measured directly under equilibrium conditions in this highly aqueous medium at ionic strength = 1.0 mol dm^-3 by a convenient spectrophotometric method at 25 deg C.In addition, the pK_<*> has been measured at other temperatures, which allows the determination of the standard enthalpy (ΔH^<*> = -11.4 kJ mol^-1) and entropy (ΔS^<*> = -20 J K^-1 mol^-1) of the reaction of the cation with the solvent, and at other ionic strengths.The equilibrium constant for the formation of 4,4'-dimethoxytrityl chloride from the cation and chloride has also been measured in the same medium (K_RCl = 8.20 at 25.0 deg C, ionic strength = 1.0 mol dm^-3) by generating the cation from the alcohol and perchloric acid in the presence of 0.10 mol dm^-3 sodium chloride.

Full text of DOI:10.1039/P29940001463

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