KINETICS AND MECHANISMS OF OXIDATION OF SOME ALKALOIDS (CAFFEINE, IMIDAZOLE, THEOBROMINE AND THEOPHYLLINE) BY PERMANGANATE ION IN AQUEOUS ACIDIC MEDIUM
KINETICS AND MECHANISMS OF OXIDATION OF SOME ALKALOIDS (CAFFEINE, IMIDAZOLE, THEOBROMINE AND THEOPHYLLINE) BY PERMANGANATE ION IN AQUEOUS ACIDIC MEDIUM
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Date
2012-10
Authors
JONES, FRANK
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Abstract
The kinetics of the redox reactions of caffeine (CAF), imidazole (IDZ), theobromine (TB) and
theophylline(TP) have been studied in aqueous acid medium. Stoichiometries of the reactions,
determined by the mole ratio method were observed to be 1:1(CAF- MnO
and TP −
MnO
) and 1:2 (IDZ- MnO
and TB- MnO
) systems respectively. The rate of the reactions
showed two parallel acid pathways, the acid dependent and the acid independent pathway for all
the systems studied. The kinetic results showed first order dependence with respect to
permanganate ion and reductants (CAF, IDZ, TB, TP) concentrations respectively. The reactions
obey second order kinetics with the following general rate laws. – d[MnO4
–]/dt =k2[MnO
][S]
where (S = CAF, IDZ, TB or TP) with k2 (CAF) = 4.0 × 10–2 ± 0.02mol dm–3, k2 (IDZ) = 9.1
× 10–2 ± 0.1 mol dm–3, k2 (TB) = 9.2 × 10–2 ± 0.02 mol dm–3 and k2 (TP) = 5.4 × 10–1 ± 0.2 mol
dm–3 Spectroscopic studies and Michaelis-Menten plots showed no evidence of the formation of
intermediate complex in all the systems. Free radical were also not observed. Added ions
(HCOO─, CO3
2 ─Mg2+ and Ca2+) were observed to catalyze the reactions.The outer-sphere
mechanism is proposed for these reactions .
Description
A THESIS SUBMITTED TO THE
POSTGRADUATE SCHOOL,
AHMADU BELLO UNIVERSITY, ZARIA
NIGERIA
IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR
THE AWARD OF MASTER OF SCIENCE IN INORGANIC
CHEMISTRY
Keywords
KINETICS, MECHANISMS, OXIDATION, ALKALOIDS