Theoretical and Experimental Chemistry, Vol. 36, No. 6, 2000 RATE AND EQUILIBRIUM OF ACETYL GROUP EXCHANGE BETWEEN PYRIDINES AND PYRIDINE N-OXIDES UDC 541.127:547.82 V. I. Rybachenko, 1 G. Schroeder, 2 K. Yu. Chotii, 1 V. V. Kovalenko, 1 B. Lenska, 2 and A. N. Red’ko 1 22 Acetyl group exchange reactions between N-acetoxypyridinium salts and 4-dimethylaminopyridine, 4-morpholinopyridine, and N-methylimidazole in acetonitrile at 298 K have been studied. The rate constants varied from 10 5 to 10 –4 L/mol·s, and the equilibrium constants ranged from 10 9 to 10 –9 . The rates and equilibrium constants of these reactions did not comply with the Brönsted equation. The kinetics of the acetyl exchange reactions are well described by a correlation equation containing squared terms. The acyl transfer reaction occupies one of the central places in chemistry and biochemistry [1]. Prediction of the reactivity of carbonyl containing compounds contains many problems and arouses considerable interest [2]. The basic method for the quantitative description of nucleophilic substitution reactions, as in many other reactions, is the analysis of the “rate–equilibrium” relation [2, 3]. Equilibrium constants for acyl transfer are known for a very restricted group of reactions [4]. The acid–base characteristics of the nucleophile or leaving group are usually changed. However the nature of the attacking atom and the nucleophilicity of the substituent correlate poorly with their basicities [2]. A typical example is pyridines – pyridine N-oxides [3]. As a result quantitative treatment of acyl transfers is limited as a rule by the sharply limited reaction series of compounds of a single type with variation of substituents in only one of the reactants [3, 5]. In this study we have obtained for the first time equilibrium and kinetic characteristics of the acetyl exchange reaction between acetoxypyridinium salts (AOPS) and 4-dimethylaminopyridine (Nu 8 ), 4-morpholinopyridine (Nu 9 ), and N-methylimidazole (Nu 6 ) in acetonitrile solution (Table 1): (1) CH 3 CONu i + ,X – + Nu j → CH 3 CONu j + ,X – + Nu i , where X = BPh 4 - , and Nu i and Nu j are 334 0040-5760/00/3606-0334$25.00 ©2000 Plenum Publishing Corporation ________ 1 L. M. Litvinenko Institute of Physical Organic and Coal Chemistry, National Academy of Sciences of Ukraine, 70 R. Luxemburg ul., 83114 Donetsk, Ukraine. 2 Faculty of Chemistry, Adam Mickiewicz University, 6 Grunwaldska Str., 60-780 Poznan, Poland. ____________________________________________________________________________________________________ Translated from Teoreticheskaya i Éksperimental’naya Khimiya, Vol. 36, No. 6, pp. 363-366, November-December 2000. Original article submitted June 30, 2000; revision submitted November 1, 2000. N O Cl 1 N O 2 N O CH 3 3 N O CH 2 CH 3 4 N O OCH 3 5 N N CH 3 6 N O CH 7 CH N(CH 3 ) 2 N N N(CH 3 ) 2 N 8 9 O