KINETICS AND MECHANISMS OF THE OXIDATION OF NICOTINIC ACID, L-CYSTEIC ACID, L-ASPARTIC ACID AND L-TRYPTOPHAN BY PERMANGANATE ION IN AQUEOUS ACIDIC MEDIUM
KINETICS AND MECHANISMS OF THE OXIDATION OF NICOTINIC ACID, L-CYSTEIC ACID, L-ASPARTIC ACID AND L-TRYPTOPHAN BY PERMANGANATE ION IN AQUEOUS ACIDIC MEDIUM
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Date
2012-12
Authors
ANWETING, IDONGESIT BASSEY
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Abstract
The kinetics and mechanisms of oxidation of nicotinic acid, L – cysteic acid, L –
aspartic acid and L– tryptophan have been investigated in aqueous acidic medium at
28.0±1.0oC, I = 0.5 mol dm-3 (Na2SO4), [H+] = 0.1mol dm-3 (H2SO4) for nicotinic acid and L
– tryptophan, for L – cysteic acid, the reaction was studied at 27.0±1.0oC, I = 0.5 mol dm-3
(Na2SO4), [H+] = 0.1mol dm-3 (H2SO4). For L – aspartic acid, the reaction was studied at
29.0±1.0oC, I = 1.0 mol dm-3 (Na2SO4) and [H+] = 0.2mol dm-3 (H2SO4). The stoichiometry is
1:1 (oxidant: reductant) for MnO4
- – nicotinic acid and L – tryptophan systems, and 2:5
(oxidant: reductant) for MnO4
- – L – cysteic acid and L – aspartic acid systems. The rate of
reaction is first order with respect to all the reductants and oxidant and second orders overall
in all the systems investigated. The rate of reaction showed dependence on acid
concentrations. The reactions conform to the following rate laws:
−
[MnO
] = k[MnO
][nicotinic acid]
where k = (1.72 ± 0.015) × 10-1 dm3mol-1s-1 at 28.0±1.0oC, I = 0.5 mol dm-3 and [H+] =
0.1mol dm-3,
−
[MnO
] = k[MnO
][L − cysteic acid]
where k = (5.49 ± 0.07) × 10-1dm3mol-1s-1at 27.0±1.0oC, I = 0.5 mol dm-3 and [H+] =
0.1mol dm-3 ,
−
[MnO
] = k[MnO
][L − aspartic acid]
where k =(3.50 ± 0.06) ×10-2 dm3mol-1s-1 at 29.0±1.0oC, I = 1.0 mol dm-3 and [H+] =
0.2mol dm-3,
−
[MnO
] = k[MnO
][L − tryptophan]
where k= (8.75 ± 0.14) × 10-2 dm3mol-1s-1,at 28.0±1.0oC, I = 0.5 mol dm-3 and [H+] =
0.1mol dm-3 .
The rate of reaction displayed negative salt effect for MnO4
- – nicotinic acid, L –cysteic acid
and L – tryptophan systems, whereas positive salt effect was displayed for MnO4
-–L–
aspartic acid system. The reactions were sensitive to changes in the dielectric constant of the
medium for the reactions involving nicotinic acid, L – aspartic acid and L – tryptophan.
Added anions and cations were found to catalysed the reactions for all the systems. The
Description
A THESIS SUBMITTED TO THE SCHOOL OF POSTGRDUATE STUDIES,
AHMADU BELLO UNIVERSITY, ZARIA, NIGERIA, IN PARTIAL FULFILMENT
OF THE REQUIREMENTS FOR THE AWARD OF MASTER OF SCIENCE
DEGREE IN INORGANIC CHEMISTRY
Keywords
KINETICS, MECHANISMS, OXIDATION, NICOTINIC ACID, PERMANGANATE ION, L-CYSTEIC ACID, AQUEOUS ACIDIC MEDIUM, L-TRYPTOPHAN