Theoretical and Experimental Chemistry, Vol. 37, No. 4, 2001 RATE AND EQUILIBRIUM CONSTANTS FOR REACTIONS TRANSFERRING A DIMETHYLCARBAMOYL GROUP BETWEEN PYRIDINES UDC 541.127:547.82 V. I. Rybachenko, 1 G. Schroeder, 2 K. Yu. Chotii, 1 V. V. Kovalenko, 1 and K. Eitner 2 We have studied 18 reactions, including four identity reactions, involving transfer of a dimethylcarbamoyl group with N-acylpyridinium bonds to pyridine and its 4-substituted derivatives in acetonitrile solutions at 298 K. The rate constants k ij varied within the range 0.4 to 10 –6 L/mol×s; the equilibrium constants K ij varied from 10 7 to 10 –5 . The rate and equilibrium for exchange of carbamoyl groups are described satisfactorily by the Brönsted equation. We have shown that all the reactions occur according to a forced concerted S N 2 mechanism. The structure of the transition state and its position on the reaction coordinate for identity transfer are considered using a More O’Ferrall–Jencks diagram. Earlier [1, 2] we obtained the kinetic characteristics of some reactions involving transfer of a dimethylcarbamoyl group from the corresponding N-,O-acylonium salts to pyridines and N-oxides of pyridines in CH 3 CN solutions. However, structural constraints in putting together reaction series and especially lack of data on the equilibrium have made correlation analysis and prediction of reactivity difficult. With the aim of further studying the mechanism of these reactions and determining the structure of the transition state, in this work we have studied symmetric reactions of acyl transfer only between acylpyridinium salts and pyridines (Nu), including identity reactions (when Nu i = Nu j ): (1) Me 2 NCONu i + ,X – + Nu j ↔ Me 2 NCONu j + ,X – + Nu i , where X = BPh 4 - and Nu i , Nu j = 230 0040-5760/01/3704-0230$25.00 ©2001 Plenum Publishing Corporation ________ 1 L. M. Litvinenko Institute of Physical Organic and Coal Chemistry, National Academy of Sciences of Ukraine, 70 R. Luxemburg Vul., 83114 Donets’k, Ukraine. 2 Chemistry Department, Adam Mickiewicz University, 6 Grunwaldska Str., 60-780 Poznan, Poland. ___________________________________________________________________________________________________ Translated from Teoreticheskaya i Éksperimental’naya Khimiya, Vol. 37, No. 4, pp. 231-235, July-August, 2001. Original article submitted May 30, 2001. N (CH 3 ) 2 N H 3 C N N N O N Nu1 Nu2 Nu3 Nu4 N N (CH 3 ) 2 N CH 3 O N Nu5 Nu6 Nu7