Kinetics and mechanism of the thermal decomposition of the thiosulphatopentaamminecobalt(III) ion in dilute aqueous acid

Abstract

ANTHONY MARTIN NEWTON. Can. J . Chem. 64, 31 1 (1986).In acetic acid -sodium acetate buffer of pH 5.6 (25°C) the C O ( N H~)~S~O , + ion undergoes redox decomposition rather than aquation. First-order kinetic are observed and the reaction products c o 2 + , NH3, and S4O6'-are due to internal reduction of Co(II1) by coordinated S2032-. In dilute perchloric acid of pH <4 the rate is retarded, first-order plots are not linear, and S4062-is not a major product of the reaction. It is proposed that, in dilute HClO,, protonation of C O ( N H~)~S~O~+ depletes the concentration of the reactive complex and that decomposition of coordinated HS2O3-occurs. Conversion of 0-bonded ~~0 2 -to S-bonded ~~0 2 -in the reactive complex is also considered.ANTHONY MARTIN NEWTON. Can. J. Chem. 64, 311 (1986) Dans un tampon d'acide acitique -acetate de sodium, a pH 5,6 et a 25OC, l'ion C O ( N H~)~S~O~+ subit plutBt une reaction d'oxydo-reduction qu'une reaction d'aquation. On observe une cinktique du premier ordre et les produits de la reaction, soit le co2+, le NH3 et le S4062-, proviennent de la reduction interne du Co(II1) par l'ion S2O3'-coordonnk. L'acide perchlorique diluk, pH <4, retarde la vitesse alors que les courbes d'ordre un ne sont pas lineaires et que I'ion S4O6'-n'est pas un produit majoritaire de la reaction. On pense que, en presence de HC104 dilut, la protonation de l'ion C O ( N H~)~S~O~+ diminue la concentration du complexe reactif et que I'ion coordonte HS2O3-se decompose. On considere tgalement la transformation de l'ion S203'-lie par I'oxyg&ne en l'ion ~2 0 3~-lie par le soufre dans le complexe rtactif.[Traduit par le journal] i

Kinetics and mechanism of the anation of (??)-hydroxo(tetraethylenepentamine)cobalt(III) by thiosulfate, the base hydrolysis of the (sulfur-bonded) thiosulfato(tetraethylenepentamine)-cobalt(III) and photochemistry of oxygen and sulfur-bonded thiosulfato complexes

“…However, in acid medium, the complex decomposes instead of undergoing aqua- tion (14). The sulfur-bonded Co(tetren)S20 2, however, does not undergo aquation or decomposition in acid media ( Figure 3) but undergoes base hydrolysis in an alkaline medium ([OH ]r = 0-1-0.4moldm-3) 9…”