KINETICS AND REACTION-MECHANISMS OF COPPER(I) COMPLEXES WITH ALIPHATIC FREE-RADICALS IN AQUEOUS-SOLUTIONS - A PULSE-RADIOLYSIS STUDY

The reactions (Cu(I)L + . R --> LCu(II)-R and the mechanism of decomposition of the transient complexes LCu(II)-R were studied using the pulse-radiolysis technique (L(1) = H2O, L(2) = 2,5,8,11-tetramethyl-2,5,8,11-tetraazadodecane; . R = . CH3, . CH2COOH, . CH(CH3)COOH, .-CH2CH2COOH.) The kinetics of formation of the transient complexes obey pseudo-first-order rate laws. The rate constants measured for these reactions are in the range (2-4) x 10(9) M(-1) s(-1) for L(1) and 6 x 10(6)-1 x 10(8) M(-1) s(-1) for L(2). The mechanisms of decomposition of the transient complexes depend on the nature of R and L as follows: 1. For R = CH3 ethane is the final product. The kinetics of its formation obey second-order rate laws. Free methyl radicals are not intermediates in these processes. 2. For R = CH2CH2COOH the transient complexes decompose via an analogous mechanism to that of R = CH3 for L(1) and via homolysis of the copper-carbon a bond for L(2). 3. For R = CH2COOH and CH(CH3)-COOH the transient complexes decompose via heterolysis of the copper-carbon a bonds forming Cu(II)L. The effect of the nature of R and L on the kinetics of these reactions is discussed.