RATES AND EQUILIBRIA FOR THE ADDITION OF METHOXIDE ION TO 2,6-DIPHENYL-DIPHENYLPYRLIUM AND 4-METHOXY-2,6-DIPHENYLPYRYLIUM CATIONS

The reactions of addition of MeO to the title cations, 1 and 2, respectively, have been studied spectrophotometrically in MeOH. Owing to the high reactivity of these cations, buffers have been used for the kinetic measurements. The system Et3N/Et3NH+ has been found suitable because of the low reactivity of Et3N toward the substrates. Rate and equilibrium constants for the addition to position 4 of 1 and to positions 2 and 4 of 2 have been determined or estimated at 25°C. The equilibria are well shifted toward the adducts, much more than in the additions of MeO to N-substituted pyridinium cations. The lower rate of addition to the methoxy-bearing position of 2 with respect to that of addition to the hydrogen-bearing position of 1 is discussed in terms of electronic and other structural effects and also in comparison with related data for the addition to the trinitrobenzene and dinitrothiophene systems. © 1979, American Chemical Society. All rights reserved.