THE ELECTRON TRANSFER REACTIONS OF 3,7-BIS(DIMETHYLAMINE)PHENOTHIONIUM CHLORIDE (METHYLENE BLUE) WITH OXYANIONS IN AQUEOUS ACIDIC MEDIUM
THE ELECTRON TRANSFER REACTIONS OF 3,7-BIS(DIMETHYLAMINE)PHENOTHIONIUM CHLORIDE (METHYLENE BLUE) WITH OXYANIONS IN AQUEOUS ACIDIC MEDIUM
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Date
2007-09
Authors
ABDULAKEEM, Busari
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Abstract
The kinetics and mechanisms of the redox reactions of 3,7-bis
(dimethylamine)phenothionium chloride (MB+) with the oxyanions, BrO3
-, S2O8
2- and
SO3
2-, have been studied. The rate of the reaction is first order in each oxidant and
reductant concentrations for the three reactions. MB+ was oxidized by BrO3
- and S2O8
2-
and the order of reactivity is k2 (BrO3
-) k2 (S2O8
2-). The MB+- S2O8
2- reaction was Ag+
catalysed. SO3
2- reduced MB+. The rates of the redox reactions of SO3
2- an S2O8
2- with
MB+ show no acid dependence, while that with BrO3
- ion, showed acid independent and
a second order acid dependence. All the reactions are affected by change in ionic
strength. The stoichiometry is 2:3 for MB+: BrO3
- and 1:6 for MB+: S2O8
2-. The
stoichiometry for the MB+- SO3
2- could not be determined. The overall rate equation for
the three reactions can be represented as shown below:
For the MB+: BrO3
- reaction:
-1d[MB+] = k2[MB+][BrO3
-]
2 dt
where k2 = 10.16 0.29 dm3 mol-1 s-1, at [H+] = 0.20 mol dm-3 μ = 0.50 mol dm-3
(NaCI) and T = 29.0 1.00C.
For the Ag+ catalysed MB+: S2O8
2- reaction
-d[MB+] = k2[MB+][S2O8
2-][Ag+]
dt
where k2 = 0.37 0.03 dm3 mol s-1 at [H+] = 1.0 x 10-4 mol dm-3 μ = 0.10 mol dm-3
(NaNO3), [Ag+] = 5.0 x 10-3 mol dm-3 and T= 26.0 1.00C
For the MB+: SO3
2- reaction
-d[MB+] = k2[MB+][SO3
2-]
dt
where k2 = (3.02 0.22) x 10-3 dm3 mol-1 s-1 at [H+] = 1.0 x 10-3 mol dm3 μ = 0.10 mol
dm-3 (NaCI) and T = 25.0 1.00C
Free radicals were detected in the MB+ reactions with S2O8
2- and SO3
2-.
Spectroscopic investigation and kinetic evidence suggested the absence of short-lived
intermediate complex in all the systems studied.
The experimental results obtained for all the systems are in favour of the outersphere
mechanism.
Description
A THESIS SUBMITTED TO THE POSTGRADUATE
SCHOOL,
AHMADU BELLO UNIVERSITY, ZARIA
IN PARTIAL FULFILLMENT FOR THE AWARD OF
MASTER OF SCIENCE DEGREE IN INORGANIC CHEMISTRY.
DEPARTMENT OF CHEMISTRY
FACULTY OF SCIENCE
AHMADU BELLO UNIVERSITY, ZARIA, NIGERIA
SEPTEMBER, 2007
Keywords
ELECTRON TRANSFER REACTIONS,, DIMETHYLAMINE,, PHENOTHIONIUM CHLORIDE,, METHYLENE BLUE,, OXYANIONS,, AQUEOUS ACIDIC MEDIUM