โ Scribed by Donovan A. Dixon; Novelette P. Sadler; Tara P. Dasgupta
No coin nor oath required. For personal study only.
The kinetics of oxidation of L-ascorbic acid (H2A) by the mononuclear complex [Co(NH3)5(OH2)] (C103) 3 have been studied spectrophotometrically at 490nm. The mechanism involves single one-electron transfers involving the pentaamminehydroxo complex and the ascorbate anions (HA-and A 2 ), subsequent formation ofascorbate radicals and > 90% Co". The appropriate rate law in the 7.00 ~< pH ~< 8.40 and 0.005 ~< [AT] ~< 0.05 tool din-3 ranges, has been established as:
The rate is slower at lower pH as the less important reaction k 1 (ROH 3+ + HA-~ products) becomes dominant, where R is (NH3)5Co m. The more significant rate constant k 4 (ROH2+ + A 2-,products) was calculated at 25.7~ as (2.7 + 0.5) x 102din 3mol ls-l, with A/4 ~ = 105 4-11 kJ tool-1 and AS # = 93 _+ 45 J tool -1 K-1 and iron(II), play no part in the reaction of #-peroxo-bis[pentaamminecobalt(III)] in acid! This additional factor made this study an interesting prospect, as other anomalies could be forthcoming from reaction with this mononuclear system.
Experimental
The materials were of analytical or reagent grade and were used as received. The purity of L-ascorbic acid was determined iodometrically (~'~).
The complex was synthesized from Co(NO3)2-6H20, (NH4)zCO 3 and concentrated aqueous ammonia as reported in the literature (15). U.v.-vis.: 2max (rim) 510; e (din 3 mol-1 cm-1) 92.9 [Lit.( ): fi~max (rim) 510; e (din 3 mol-1 cm-1) 93].
๐ SIMILAR VOLUMES
## Abstract The mechanism by which an excess of iron(II) ion reacts with aqueous chlorine dioxide to produce iron(III) ion and chloride ion has been determined. The reaction proceeds via the formation of chlorite ion, which in turn reacts with additional iron(II) to produce the observed products. T