KINETICS OF OXIDATION OF PANTOTHENIC ACID
209
activation parameters. The fairly high positive values
of ꢀH= and ꢀG= indicate that the transition state is
highly solvated, while large negative value of ꢀS= sug-
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a fewer degrees of freedom.
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It was thought worthwhile to compare the reactivity
of PA by CAT in the absence of osmium tetroxide cat-
alyst under the identical experimental conditions. The
reaction was carried out at different temperatures (303–
323 K) and from the Arrhenius plot of log kꢁ vs. 1/T
(r = 0.9885), values of the activation parameters for the
uncatalyzed reaction were calculated. These data are
presented in Table IV. Further, it has been pointed out
by Moelwyn-Hughes [28] that in presence of the cat-
alyst, the uncatalyzed and catalyzed reactions proceed
simultaneously.
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k1 = ko + KC[catalyst]x
(16)
Here k1 is the observed pseudo-first-order rate constant
in the presence of OsO4 catalyst, ko is the pseudo-first-
order rate constant for the uncatalyzed reaction (in the
absence of OsO4 catalyst), KC is the catalytic constant,
and x is the order of the reaction with respect to OsO4
and is found to be 0.74 in the present study. The values
of KC were calculated at different temperatures using
the equation
KC = (k1 − ko)/[OsO4]0.74
(17)
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These values were found to vary for different tempera-
tures. Further, the plots of log KC vs. 1/T were found to
be linear (r = 0.9858) and values of activation param-
eters were computed. All these results are summarized
in Table IV. It was found that OsO4 catalyzed reaction
is about sevenfold faster than the uncatalyzed reaction.
This is confirmed by the observed activation parame-
ters. Hence, the observed rate of oxidation obtained in
presence of OsO4 catalyst justifies the facile oxidation
of PA by CAT in alkaline medium.
In conclusion, the stoichiometry and products of ox-
idation of PA by CAT in acid and alkaline media is
same, but their kinetic patterns are different. It was
also found that OsO4 was an efficient catalyst for the
oxidation of PA by CAT in alkaline medium.
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