A kinetic study of isotopic exchange reactions between lanthanide ions and lanthanide polyaminopolycarboxylic acid complex ions—I isotopic exchange reactions of Ce(III) with Ce(HEDTA), Ce(EDTA) −, Ce(DCTA) − and Ce(DTPA) 2−

Abstract

The rates and mechanisms of the isotopic exchange reactions of Ce(III) ions with Ce(HEDTA); Ce(EDTA) −; Ce(DCTA) − and Ce(DTPA) 2− complex ions have been investigated. The rate equations and the experimentally determined rate constants at 20°C, μ = 0·1 and acetate buffer concentration of 10 −2 M are as follows: • Rate = k 1[H +][Ce(HEDTA)]; where k 1 = 23·1 × 10 4 l.mole −1 min −1 • Rate = k 2[H +][Ce(EDTA) −]; where k 2 = 9·4 × 10 4 l.mole −1min −1 • Rate = k 3[H +][Ce(DCTA) −] + k 4[Ce(DCTA) −] + k 5[C(III)][Ce(DCTA) −] where k 3 = 3·9 × 10 3 l.mole −1min −1; k 4 = 4·2 × 10 −3min −1 and k 5 = 5·6l.mole −1min −1 • Rate = k 6[Ce(DTPA) 2−][H +] 2 + k 7[Ce(III)][Ce(DTPA) 2−] where k 6 = 3·0 × 10 8 l. −2 mole −2 min −1 and k 7 = 1·6 l.mole −1min −1 The mechanisms of the exchange reactions of the multidentate chelates are discussed in terms of the lability of the carboxylic acid groups. The exchange reactions are catalysed by acetate ions and the effects of increased acetate concentration on the various terms of the rate equations have been examined. Activation energies have been determined.