Kinetics and mechanism of ruthenium (III) catalyzed oxidation of ethanol by cerium (IV) in aqueous sulfuric acid media

✍ Scribed by Asim K. Das; Mahua Das

• Publisher: John Wiley and Sons
• Year: 1995
• Tongue: English
• Weight: 478 KB
• Volume: 27
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550270103

✦ Synopsis

The kinetics of oxidation of ethanol by cerium(1V) in presence of ruthenium(II1) (in the order of mol dm-3) in aqueous sulfuric acid media have been followed at different temperatures (25-40°C). The rate of disappearance of cerium(1V) in the title reaction increases sharply with increasing [CzH50H] to a value independent of [CzH50Hl over a large range (0.2-1.0 mol dm-3) in which the rate law conforms to:

where [Ru]T gives the total ruthenium(II1) concentration. The values of 10-3k, and are 3.6 2 0.1 dm3 mol-' s-l and 3.9 2 0.2 s-l, respectively, at 40°C, Z = 3.0 mol dm-3. The proposed mechanism involves the formation of ruthenium(II1)-substrate complex which undergoes oxidation a t the rate determining step by cerium(IV) to form ruthenium(1V)-substrate complex followed by the rapid red-ox decomposition giving rise to the catalyst and ethoxide radical which is oxidized by cerium(1V) rapidly. The mechanism is consistent with the existence of the complexes Ru"' . (CzH5OH) and Ru'" . (CzH50-I and both are kinetically active. The overall bisulphate dependence conforms to: k&sd = & R u ] ~/ { l + C[HS04-]} where A = 2.2 x lo4 dm3 mol-l s-l, C = 1.3 a t 40°C, [H'] = 0.5 mol dm-3, and Z = 3.0 mol dm-3. The observations are consistent with the Ce(S04)~ as the kinetically active species.