Transfer of the dimethylcarbamoyl group from N-acyloxypyridinium salts to pyridines and from N-acylpyridinium salts to pyridine N-oxides was studied in acetonitrile. Equations relating the reaction rates and equilibria in the N3O and O3N acyl transfer series to the basicity of the nucleophile and leaving group were obtained. The reactions all are one-stage and occur by the forced concerted SN2 mechanism. The intersecting state model was used to obtain a modified Marcus equation that accounts for the asymmetry of the transition state with respect to reagents and products and allows uncontradictory analysis of the reaction mechanism.Previously we obtained kinetic and equilbrium data for reaction (1) of transfer of the dimethylcarbamoyl group from N-acylpyridinium salts to pyridines [1] and from N-acyloxypyridinium salts to pyridine N-The reaction mechanism was found out, and the reaction rate and equilibrium constants in these symmetrical reaction series were shown to adhere the Brønsted relation with b 0.5. At the same time, we found that the quality of reactivity predictions is much higher provided characteristics of identical reaction and the Marcus equation are used [2].In the present work we turned to unsymmetrical reactions (1) in which the carbamoyl group is transferred from N-acylpyridinium salts to peridine Noxides and, vice versa, from N-acyloxypyridinium salts to pyridine and substituted pyridines.In CH 3 CN we studied reactions of acylonium salts with nucleophiles (X = BPh 4 and Nu i , Nu j = Nu 1 3 Nu 20 ).The rate and equilibrium constants of reaction (1) in acetonitrile at 298 K are given in the table. The progress of reactions nos. 135,8,9, 14317, 20323, 36, 38, 40, and 53 was followed by UV spectroscopy at an optimal wavelength under pseudo-first-order reaction conditions at a tenfold or greater excess excess of acylonium salt or nucleophile. Reactions (41)3(44) were studied in a similar way by Fourier transform IR spectroscopy (FT-IR), following the decrease or increase of the intensity of absorption of acylonium salts in reactants and products, respectively.The corresponding n C=O values were as follows, cm !1 : 1797 (i = 5), 1789 (i = 6) 1787 (i = 7), and 1738 (i = 12). The rates of fast reactions nos. 6, 7, 18, 19, 24, 25, 31, 32, and 47352 were measured by the stoppedflow method. The second-order rate constants k 2 were calculated by Eq. (2) relating the apparent rate constants k ap (336 values) to the concentration of excess reagent by the least-squares method (k rev is the rate constant of the reverse reaction).(2) Treatment of kinetic data by Eq.(2) showed that k 2 >> k rev , whereas k rev~0 . Therefore, k rev values were not used in assessing the rate of the reverse reaction. The concentration of acylonium salts in acetonitrile in the kinetic experiments with IR monitoring was up to 10 !2 M and in the other cases it was not higher then 5 0 10 !3 M. Previously we showed [3] that under these conditions the dissociation degree of ionic dissociation of acylonium tetrafluoroborates in aceton...
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