J. Electroanal. Chem., 102 (1979) 117--126 117 © Elsevier Sequoia S.A., Lausanne -- Printed in The Netherlands THE PROPERTIES OF THE ION ASSOCIATES OF BENZOPHENONE IN DMF ANDRZEJ LASIA Institute of Fundamental Problems of Chemistry, University of Warsaw, ul. Pasteura 1, 02-093 Warsaw (Poland) (Received 16th October 1978; in revised form llth December 1978) ABSTRACT The properties of the ion associates of benzophenone (BP) free radicals with Na ÷ and Li ÷ have been investigated polarographically in dimethylformamide. It was found that BP = forms ion pairs with Na ÷ (Kas s = 69 M -1 ) and two types of associates with Li÷: BP~...Li+(Kass,1 = 330 M -1 ) and BP~...(Li+)2(Kass,2 = 2900 M -2). The influence of temperature on the equilibria was also discussed. The ion associates with Li ÷ disappear in a disproportionation reaction; the mechanism and kinetics of that reaction were studied. It was found that the main contribu- tion to the overall kinetics are made by the pairs (a) BPT...Li + + BP~...Li ÷, (b) BP ~ + BP~...(Li+)2, (c) BP~...Li + + BP~...(Li+)2. INTRODUCTION Electrochemical reduction of organic molecules in non-aqueous solvents is often complicated by the formation of ion pairs with cations of the supporting electrolyte [1--14]. It was found that free radicals can associate with the sup- porting electrolyte cations forming not only ion pairs RL..Me ÷ but also triple ions (R~):...Me "+ [6,7] and RL..(Me+)2 [8,11,12,14,15]. Ion associates were examined by several methods and electrochemical methods were found to be very attractive in studying stoichiometry and kinetics of those species. The equilibrium constants and the stoichiometry of the association can be obtained from the shift of reversible half-wave potentials in the positive direc- tion with increase of the cation concentration [1,6]. Ion pairs are often unstable and disappear mainly in dimerization [ 16--21] and disproportionation [21--24] processes. Detailed investigations of the mech- anism of such processes show [ 18--24] the following parallel reaction pathways: kl 2R ~ -~ k2 -- + R'...Me + R ~ -* k3 2 R~...Me ÷ -~ products (1) (2) (3) From the dependence of the observed effective rate constant (kerr) on the con- centration of metal cations the real rate constants kl, k2 and k3 can be obtained. In the present paper a detailed study of the association of benzophenone