KINETICS AND MECHANISM OF RUTHENIUM(III) CATALYZED OXIDATION
73
Table 3. The values of K4, K5 and K6 calculated at different temperatures
Temperature, K
k
×
10–4, s–1
K
4, l/mol
K5
×
102, mol/l
K6 ×
10–3, l/mol
288
298
308
318
3.88
4.98
5.83
6.97
0.06 0.01
0.21 0.01
0.37 0.01
0.41 0.02
2.12 0.01
1.62 0.01
1.12 0.02
0.65 0.01
4.1 0.2
6.3 0.2
7.7 0.1
12.3 0.1
2. Rao, P.J.P., Sethuram, B., and Navaneeth Rao, T.,
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6. Ram, ReddyM.G., Sethuram, B., and Navaneeth
the reaction shows that these values mainly refer to the
rate limiting step supporting the fact that the reaction
before the rate determining step is fairly fast and
occurs with the low activation energy [34]. In the same
manner, K5 and K6 values were calculated at different
temperatures (Table 3), and the corresponding values
of the thermodynamic parameters are given in Table 2.
The moderate values of
mediate complex is more ordered than the reactants
[35]. The value of
S# within the range of radical reacꢀ
Δ
S# suggest that the interꢀ
Rao, T., Indian J. Chem., Sect. A, 1978, vol. 16, p. 331.
Δ
tion has been ascribed to the nature of electron pairing
and unpairing processes and to the loss of degrees of
freedom formerly available to the reactants upon the
formation of rigid transition state [36]. The observed
modest enthalpy of activation and relatively low value
of the entropy of activation as well as a higher rate conꢀ
stant of slow step indicate that the oxidation presumꢀ
ably occurs via innerꢀsphere mechanism. The concluꢀ
sion is supported by earlier observation [37]. The negꢀ
ligible effect of ionic strength explains the involvement
of neutral species in scheme. However, it is difficult to
interpret the effect of dielectric constant in view of
various ions involved. The catalyst ruthenium(III)
forms the complex with substrate, which enhances the
reducing property of substrate.
7. Karlin, K.D. and Gulineh, Y., Progress in Inorganic
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11. Karlin, K., Kaderli, S., and Zuberbuhler, A.D., Acc.
Chem. Res., 1997, vol. 30, p. 139.
12. Piere, J.L., Chem. Soc. Rev., 2000, vol. 29, p. 251.
13. Solomon, E.I., Chen, P., Metz, M., Lee, S.K., and
Palmer, A.E., Angew. Chem., Int. Ed. Engl., 2001,
vol. 40, p. 4570.
14. Halcrow, M.A., Angew. Chem., Int. Ed. Engl., 2001,
vol. 4, p. 816.
15. Peisach, J., Alsen, P., and Blumberg, W.E., The Bioꢀ
chemistry of Copper, New York: Academic, 1966, p. 49.
16. Meenakshisundaram, S. and Sathiyendiran, V., J. Chem.
Res., 2000, vol. 10, p. 458.
Among various species of DPC in alkaline
medium, monodiperiodatocuprate(III) (MPC)
(
Cu(H2IO6)(H2O)2) is considered as active species for
the reaction under study. The active species of rutheꢀ
nium(III) is found to be [RuH2O)5OH]2+. The cataꢀ
lytic constants and the activation parameters with refꢀ
erence to catalyst were computed. The results demonꢀ
strate that the role of pH in the reaction medium is
crucial. Rate constant of the slow step and other equiꢀ
librium constants involved in the mechanism evaluꢀ
ated, and activation parameters with respect to slow
step of the reaction were computed. The overall mechꢀ
anistic sequence described here is consistent with
product, mechanistic, and kinetic studies.
17. Kambo, N. and Upadhyaya, S.K., Transition Met.
Chem., 2000, vol. 25, p. 461.
18. Reddy, C.S. and Vijaykumar, T., Indian J. Chem., 1995,
vol. 34A, p. 615.
19. Murthy, C.P., Sethuram, B., and Navaneeth Rao, T.,
Z. Phys. Chem., 1981, vol. 262, p. 336.
20. Jeffery, G.H., Bassett, J., Mendham, J., and
Denny, R.C., Vogel’s Textbook of Quantitative Chemical
Analysis, New York: Longman, 1996, p. 455.
21. Panigrahi, G.P. and Misro, P.K., Indian J. Chem., 1978,
vol. 16A, p. 201.
22. Randrerath, K., Thin Layer Chromartography, New
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KINETICS AND CATALYSIS Vol. 53
No. 1
2012