Dissociation kinetics of the solvated electron species in methylamine and methylamine–ammonia mixtures

Abstract

Y. HARIMA, H. KURIHARA, Y. NISHIKI, S. AOYAGUI, K. TOKUDA, and H. MATSUDA. Can. J. Chem. 60, 445 (1982). Potential-sweep voltammetric and potential-step chronoamperometric experiments were made at -50°C with solvated electrons in methylamine containing LiC1, KI, or CsI. The dissociation rate constants of the ion pairs, (M+.e,-), M being alkali metal and e,-free solvated electron. were greater than lo3 s ' . The pseudo-first-order rate constant of the dissociation of K into the one-electron species, e , and (K',e,-) in rapid equilibrium, was determined as 40s-I by chronoamperometry with 0.5 M KI solutions. The formation constants of K-from the one-electron species determined by chronoamperometry and voltammetry were 4.5 x lo4 M-I and 5.6 x lo4 M-', respectively. An addition of a small amount of ammonia to methylamine caused a decrease in the formation constant of K and an increase in its dissociation rate constant. The appendix deals with a theoretical treatment of chronoamperograms for an electrode process preceded by the dissociation of a dimer. The boundary value problem was solved by the explicit finite difference method and the analytical method which was based on the concept of reaction layer. Chem. 60,445 (1982). Operant 8 -5O0C, on a procede a des experiences voltammetriques a variation lineaire de potentiel et chronoamperometriques a saut de potentiel avec des electrons solvates dans de la methylamine contenant du LiCL, du KI ou du CsI. Les constantes de vitesse de dissociation des paires d'ions, (M+.e,-), M etant le metal alcalin et e , I'electron solvate libre, sont plus grandes que lo3 s l . On a etabli que la constante de vitesse de dissociation de pseudo premier ordre de K en especes mono-electroniques, e,-et (M+.e,-) en Cquilibre rapide, est Cgale a 40 s-I, en faisant appel a la chronoamperometrie sur des solutions a 0.5 M de KI. Les constantes de formation de K-, telles que determinees par chronoamperometrie et voltammetrie, sont respectivement egales 84.5 x 104 M-' et 5.6 x 104 M 1 . L'addition de petites quantites d'ammoniac a la methylamine a provoque un accroissement de la vitesse de dissociation de l'espece bi-electronique et une decroissance de sa constante de formation. L'appendice presente un traitement theorique des chronoamperogrammes pour un processus d'electrode qui est procede par la dissociation d'un dimere. On a resolu le probleme de la valeur aux limites par la methode de la difference finie explicite et la methode analytique qui est basee sur le concept de la couche de reaction.[Traduit par le journal] Introduction (M+.e,-), and alkali metal anion, (M+.2eSp) or M-. Since Hart and Boag (I) in 1963 revealed the In Our electrochemical experiments e , and presence of solvated electrons in water by generat-(M+.es-) were recognized as species having one ing them with pulse radiolysis and detecting them excess electron, and M-, two excess electrons. with spectroscopy, this technique has developed were termed the One-and the two-electron quickly as a powerful tool to investigate solvated ...