Journal of the Chemical Society. Perkin transactions II p. 1463 - 1466 (1994)
Update date:2022-08-11
Topics:
Lee, Won Heui
Maskill, H.
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 (KRCl = 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.
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