Kinetic and mechanistic studies on the oxidative decolourisation of orange-II dye with alkaline chloramine-T

Article abstract of DOI:10.3184/174751915X14352295644456

The mono-azo dye, Orange-II (acid orange 7), is mainly used to dye materials like textiles, paper, leather and cosmetics. It is important to understand the kinetic and mechanistic aspects of the oxidative decolourisation of Orange-II dye. A simple, efficient and cost-effective oxidation method is developed for the reaction. A detailed kinetic study of the oxidative decolourisation of orange-II dye with chloramine-T (CAT) in alkaline medium at 308 K has been carried out spectrophotometrically at 486 nm. The reaction shows a first-order dependence of rate both on [CAT]_o and [Orange-II]_o and an inverse-fractional- order on [OH^-]. The reaction was studied at different temperatures and the thermodynamic parameters have been evaluated. The reaction was subjected to change in (i) ionic strength, (ii) p-toluenesulfonamide and (iii) chloride ions, and the effects of these on the reaction rate were determined. Oxidation products of Orange-II were characterised as 1,2-naphthaquinone and benzenesulfonic acid by GC-MS analysis. The observed kinetic results have been explained by a general mechanism to understand the elementary pathways of this redox system. The relevant kinetic modelling has been worked out.

Full text of DOI:10.3184/174751915X14352295644456

JOURNAL OF CHEMICAL RESEARCH 2015
VOL. 39 JUNE, 363–367
RESEARCH PAPER 363
Kinetic and mechanistic studies on the oxidative decolourisation of Orange-II
dye with alkaline chloramine-T
Nirmala Vaza*, A. S. Manjunathab and Puttaswamyb
aDepartment of Chemistry, Jyoti Nivas College Autonomous, Bangalore-560 095, India
bDepartment of Chemistry, Bangalore University, Central College Campus, Bangalore-560 001, India
The mono-azo dye, Orange-II (acid orange 7), is mainly used to dye materials like textiles, paper, leather and cosmetics. It is important to
understand the kinetic and mechanistic aspects of the oxidative decolourisation of Orange-II dye. A simple, efficient and cost-effective
oxidation method is developed for the reaction. A detailed kinetic study of the oxidative decolourisation of orange-II dye with chloramine-T
(CAT) in alkaline medium at 308 K has been carried out spectrophotometrically at 486 nm. The reaction shows a first-order dependence
of rate both on [CAT]o and [Orange-II]o and an inverse-fractional- order on [OH-]. The reaction was studied at different temperatures and the
thermodynamic parameters have been evaluated. The reaction was subjected to change in (i) ionic strength, (ii) p-toluenesulfonamide and
(iii) chloride ions, and the effects of these on the reaction rate were determined. Oxidation products of Orange-II were characterised as 1,2-
naphthaquinone and benzenesulfonic acid by GC-MS analysis. The observed kinetic results have been explained by a general mechanism
to understand the elementary pathways of this redox system. The relevant kinetic modelling has been worked out.
Keywords: Orange-II, chloramine-T, oxidative-decolourisation, kinetics, mechanism
Azo dyes constitute a large group of colourants and were used to
dye various materials. Orange-II (C.I. Acid orange 7) is a synthetic
mono-azo dye and it is chemically known as sodium 4-[(2E)-
2-(2-oxonaphthalen-1-ylidene)hydrazinyl]benzenesulfonate. It
is commonly used as a colourant in the textile, paper, leather,
cosmetics and food industries.1 Wastewater released from dyeing
industries in which Orange-II used is highly coloured and
hence leads to environmental and health problems.2 Oxidative
decolourisation is considered a simple and economic method for
the removal of dyestuffs from wastewater. The literature shows
that the oxidative decolourisation methods available for Orange-
II dye are quite limited.3-7 from their kinetic and mechanistic
aspects. The mechanism of oxidative decolourisation of Orange-
II by CAT in HClO4 medium has been investigated kinetically
and reported by our research group.8 But, to date, similar
investigations in alkaline medium are not available in the
literature. This aroused our interest to carry out a detailed kinetic
and mechanistic study of the oxidative decolourisation of Orange-
II with CAT in NaOH medium. It was also intended to compare
the present results with those obtained in acid medium.8 Hence,
in the present research we have developed a simple, efficient and
economic oxidative technique for decolourisation of Orange-II
dye with CAT in alkaline medium. The main target of the present
research was to explore the kinetic and mechanistic chemistry of
the oxidative decolourisation reaction of Orange-II-CAT redox
system in alkaline medium. We report here that the present redox
reaction in alkaline medium differs from the same redox reaction
studied in acid medium8 in some kinetic and mechanistic aspects.
The diverse nature of the chemistry of N-haloamines is a
consequence of their ability to act as source of species, such
as halonium cations, hypohalites and N-anions which act as
bases, nucleophiles and nitrinoids.1-9 They behave as mild
oxidants and are suitable for the limited oxidation of several
groups. Consequently, these reagents react with a wide
variety of functional groups effecting an array of molecular
transformations.9-13 Generally, monohaloamines undergo a two-
electron change while dihaloamines are four-electron oxidants.14
The reduction products are the respective sulfonamide and
NaCl or NaBr. The prominent member of this class, sodium
N-chloro-4-methyl benzenesulfonamide, commonly known as
chloramine-T (CAT), is a by-product of saccharin manufacture.
The N-Cl bond in CAT is highly polar and hence it is a fairly
strong electrophile. The redox potential of chloramine-T is
pH dependent and decreases with increase in the pH of the
medium.14 The nature of the active oxidising species of CAT
depends on the pH of the medium and the reaction conditions.
Chloramine-T is a source of positive halogen and this reagent
has been exploited as an oxidant for a variety of substrates
in both acidic and alkaline media. 10-13, 15-21. In addition to the
above facts, CAT is commercially available, inexpensive, water-
tolerant, non-toxic and easy to handle.12
The main focus of the present research work is two-fold: (i) to
establish the optimum conditions for the facile decolourisation
of Orange-II dye by the oxidation process and (ii) to study the
kinetics and mechanism of the oxidative decolourisation of
Orange-II with chloramine-T in alkaline medium. It was also
of interest to compare the present results with those obtained in
acid medium.8 This type of research could shed some light on
the chemical oxidation behaviour of Orange-II for the chemists
who are working in the field of environmental chemistry.
Experimental
Chloramine-T (Merck) was purified by the method of Morris et al.22.
An aqueous solution of CAT was prepared fresh whenever required,
standardised iodometrically and stored in brown bottles until further
use to prevent photochemical deterioration. The concentration of the
stock solution of CAT was determined periodically iodometrically.
Orange-II (Sigma) was used as received and an aqueous solution of the
desired strength of the dye was prepared afresh each time. All other
chemicals used were of analytical grade. Double-distilled water was
used throughout.
Kinetic procedure
Detailed kinetic runs were performed under pseudo-first-order
conditions of [CAT]o >>[Orange-II]o at 308 K in the presence of
NaOH. Kinetic measurements were carried out using a UV-Vis
spectrophotometer. A thermostatic water bath was used to maintain
the desired temperature with an accuracy of 0.1oC. Reactions
were carried out in glass stoppered pyrex boiling tubes whose outer
surface was coated black to eliminate any photochemical effects.
Chloramine-T, as well as the requisite amounts of Orange-II, NaOH
solutions and water (to keep the total volume constant for all the kinetic
runs) were taken in separate boiling tubes and were thermostatted for
about 30 min at 308 K. The reaction was initiated by the rapid addition
* Correspondent. E-mail: nirmavaz2005@yahoo.co.in

364 JOURNAL OF CHEMICAL RESEARCH 2015
pseudo-first-order rate constants (k’ s-1) obtained by these plots
were constant for the different initial concentrations of Orange-II
employed (Table 1), thus confirming the first-order dependence
of rate on [Orange-II]. Values of k’ increases with increase in
[CAT]o (Table 1). A plot of log k’ versus log[CAT] was linear (R2
= 0.9210) with a slope of unity, showing a first-order dependence
of rate on [CAT]o. Also, the second-order rate constants k” = k’/
[CAT] were fairly constant (Table 1), establishing a first-order
dependence of rate on [CAT]o. Furthermore, a plot of k’ versus
[CAT] was linear (R2 = 0.9875) passing through the origin
endorsing the first-order dependence of rate on [CAT]o and also
the intermediates formed are transient.
There was a decrease of rate with increase in [NaOH] (Table 1)
and a plot of log k’ versus log [NaOH] was linear (R2 = 0.9930)
with a negative slope of –0.33, indicating an inverse- fractional-
order dependence of rate on hydroxyl ion concentration. A graph
showing the decolourisation rate as a function of pH using the
present data (Table 1) and earlier data in acid medium.8 This is
illustrated in Fig. 1. Addition of the reduction product of CAT,
p-toluenesulfonamide (PTS: 5.0 × 10-4 M) did not affect the rate,
of a measured amount of oxidant to the stirred reaction mixture.
Immediately, a 4 mL aliquot of the reaction mixture was pipetted into
a cuvette placed in the spectrophotometer. Absorbance measurements
were made at 486 nm (λmax of the dye) for nearly three half-lives. The
absorbance readings at t = 0 and t = t are D0 and Dt. Plots of log Do/Dt
versus time were made to evaluate the pseudo-first-order rate constants
(k’ s-1) which were found reproducible within
5%. Regression
coefficients (R2) for all the linear plots were carried out on an fx-100 W
Scientific Calculator.
Reaction stoichiometry
Reaction mixtures containing varying ratios of CAT to Orange-II in
the presence of 1.0 x 10-3 M NaOH were equilibrated at 308 K for 24 h.
Determination of unreacted CAT by iodometry showed that one mole
of Orange-II consumed 1 mole of CAT. The observed stoichiometry
can be represented by Eqn (1):
OH
SO3H
N
N
H2O
TsNClNa +
(CAT)
+
Orange-II
Table 1 Effect of varying concentrations of CAT, Orange-II and NaOH on
the rate of reaction at 308 K
NaOH
103 [CAT]o
104 [Orange-II]o
103 [NaOH]
M
104 k’/s-1
O
O
M
0.5
1.0
2.0
4.0
8.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
M
1.0
1.0
1.0
1.0
1.0
0.5
1.0
2.0
4.0
8.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
0.1
0.5
1.0
2.0
6.0
1.29 (2.58)
2.50 (2.50)
4.82 (2.41)
9.42 (2.36)
18.9 (2.36)
5.05
4.82
4.95
4.84
4.80
SO3H
+
+ TsNH2
+
N2
+
NaCl
(1)
1,2- naphthoquinone
benzenesulfonic acid
-
(Here Ts = CH3C6H4SO2 )
Product analysis
The reaction mixture in the stoichiometric ratio under stirred condition
was allowed to progress for 24 h at 308 K. After completion of the
reaction (monitored by TLC), the reaction products were neutralised
with acid and the products were extracted twice with diethyl ether. The
organic products were subjected to spot tests and chromatographic
analysis (TLC technique), which revealed the formation of oxidation
products, namely 1,2-naphthoquinone and benzenesulfonic acid. These
were separated by column chromatography and confirmed by GC–MS
analysis. The mass spectra showed a molecular ion peak at 158 amu and
158 amu, clearly confirming 1,2-naphthoquinone and benzenesulfonic
acid, respectively. Furthermore, it was noted that there was no reaction
between 1, 2-naphthoquinone or benzenesulfonic acid with CAT under
the present set of experimental conditions.
11.1
6.32
4.82
3.75
2.88
The values in parentheses refer to second-order rate constants. (k// dm3 mol-1 s-1).
1.4
Alkaline medium
Acid medium
1.2
1.0
0.8
0.6
0.4
The reduction product of CAT, p-toluenesulfonamide (PTS or TsNH2),
was extracted with ethyl acetate and detected by paper chromatography.17
Benzyl alcohol saturated with water was used as the solvent with 0.5%
vanillin in 1% HCl solution in ethanol as spray reagent (Rf = 0.905).
Nitrogen was identified by the conventional test.
Results
Decolourisation of Orange-II was performed efficiently by the
oxidation process using CAT as an oxidant. This redox system is
most efficient in alkaline medium. In the course of this research,
the optimum conditions for the facile oxidative decolourisation of
Orange-II were established. The kinetics of oxidation of Orange-
II with CAT was investigated at several initial concentrations of
the reactants in alkaline medium.
2
4
6
8
10
12
Under pseudo-first-order conditions in which [CAT]o >>
[Orange-II]o, and at constant [NaOH] and temperature (308 K ),
plots of log [absorbance] versus time were linear (R2 > 0.9990),
indicating a first-order dependence of rate on [Orange-II]. The
pH
Fig. 1 Plot of log k’ versus pH. Experimental conditions are as in Table 1
and ref. 8.

JOURNAL OF CHEMICAL RESEARCH 2015 365
Table 2 Effect of varying temperature on the rate of reaction and
activation parameters for the oxidation of Orange-II by CAT in alkaline
medium
OH
O
N
N
SO3H
N
NH
SO3H
Temperature/K
298
104 k’/s-1
1.97
(hydrazone)
(azo)
303
3.49
308
4.82
For dyes where the hydroxyl group is ortho to the azo link, the
aqueous solution favours the hydrazone form. In the present
case, the hydrazone form of Orange-II is involved in the
reaction.
313
318
8.92
13.42
74.90
72.30
75.70
–93.90
9.20
Ea /kJ mol-1
ΔH≠ /kJ mol-1
ΔG≠ /kJ mol-1
ΔS≠ /J K-1 mol-1
Log A
In view of the above facts, Scheme 1 can be formulated for
the oxidative decolourisation of Orange-II with CAT in alkaline
medium to account the experimental results. In Scheme 1, an
initialequilibriumstep(step(i))involveshydrolysisoftheanionic
form of CAT, TsNCl-, forming the conjugate acid TsNHCl in a
OH--retarding step. In the next slow and rate-determining step,
a lone pair of electrons present on the nitrogen atom of the
imine group of Orange-II attacks the chlorine of the conjugate
acid, forming an intermediate complex (X) with the elimination
of p-toluenesulfonamide (TsNH2). This intermediate complex
by several fast steps (step(iii)), in the presence of a molecule
of H2O, yields the ultimate products, 1,2-naphthoquinone and
benzenesulfonic acid with the elimination of HCl and N2.
The rate law for Scheme 1 can be deduced as follows:
If [CAT]t represents the total effective concentration of CAT,
then
[CAT]o=2.0 x 10-3 M; [Orange-II]o =1.0 x 10-4 M; [NaOH] = 1.0 x 10-3 M.
which inferred that PTS is not involved in a pre-equilibrium step
with the oxidant. Similarly, addition of NaCl (5.0 × 10-4 M) had no
significant effect on the rate, indicating that neither inter-halogen
nor free chlorine was formed during the reaction sequence.
The ionic strength of the medium was varied by adding 0.2
M NaClO4 solution to the reaction system. There was no effect
of it on the rate of reaction and hence no attempt was made to
keep the ionic strength constant for the kinetic runs. The effect of
temperature on the rate was studied by conducting the kinetic runs
at different temperatures (298–318K). From the linear Arrhenius
plot of log k’ versus 1/T (R2 = 0.9926), values of the activation
parameters were computed. All these results are summarised
in Table 2. Addition of an aqueous solution of acrylamide to
the reaction mixture did not initiate any polymerisation. This
confirms the absence of free radical species in the reaction
mixture.
[CAT]t = [TsNCl-] + [TsNHCl]
(2)
By substituting for [TsNCl-] from equilibrium (i) of Scheme 1 in
Eqn (2) and solving for [TsNHCl], one obtains
[
K
]
1 [CAT]t
H2O
Discussion
[TsNHCl]
=
(3)
[OH-]
[
]
+ K1 H2O
There is a special interest for studying chloramine-T reaction
mechanisms, as it behaves both as oxidising and chlorinating
agent for a variety of a substances in both acidic and alkaline
medium.15-21 An aqueous solution of CAT behaves as a strong
electrolyte and depending on the pH of the medium, it furnishes
different types of reactive species. Morris et al.22, Bishop and
Jennings,23 Hardy and Johnston24, and Pryde and Soper25 have
shown the existence of several equilibria in acid and alkaline
solutions of CAT. The possible oxidising species in acidified
CAT solutions are TsNHCl, TsNCl2, HOCl and possibly
H2O+Cl, and in alkaline solutions TsNHCl, HOCl, TsNCl- and
OCl-. From these four possible oxidising species of CAT in
alkaline medium, the most reactive species in the present study
will be decided from the observed kinetic results.
From the slow/rate-determining step of Scheme 1,
Rate = k2[TsNHCl] [Orange-II]
(4)
Substituting for [TsNHCl] from Eqn (3) into Eqn (4), yields the
following rate law:
K1k2 [CAT]t [Orange-II] [H2O]
(5)
Rate =
[OH-] + K1 [H2O]
Rate law (5) is in good agreement with the observed
experimental results.
Since rate = k’ [CAT]t, rate law (5) can be transformed as,
Hardy and Johnston24 have reported that there could be
a considerable concentration of TsNHCl even in alkaline
CAT solutions. If HOCl is primarily involved, a first-order
retardation of rate by the added PTS is expected, but no such
effect was noticed. Several researchers have observed the
retarding influence of OH- ions on the rate of CAT reactions
with a number of substrates26-29 and suggested that the reaction
in weakly alkaline solution of CAT is due to the formation of
the conjugate acid TsNHCl from TsNCl- in a OH--retarding step.
In the present study, an inverse-fractional-order dependence
of rate on [OH-], and the lack of effect on the ratio of added
PTS clearly indicate that TsNHCl is the most effective reactive
species.
K1k2
[Orange-II][H2O]
k/
=
(6)
(7)
[OH-]
+ K1
[H2O]
[OH-]
1
1
=
+
k/
K1k2[Orange-II][H2O]
[Orange-II]
k2
The validity of this rate law was verified by plotting 1 / k’ versus
[OH-] which was found to be linear (R2 = 0.9890).
The influence of a charged species on the rate of reaction
is known as the salt effect [30]. The primary salt effect is the
influence of electrolyte concentration on the rate of reaction,
whereas the secondary salt effect is the actual change in the
Azo dyes containing hydroxyl group conjugated to azo group
exhibit azo-hydrazone tautomerism as shown below.

366 JOURNAL OF CHEMICAL RESEARCH 2015
K1
TsNHCl + OH-
H
i) TsNCl- + H2O
Fast
O
O
Cl
N
SO3H
N
..
N
SO3H
N
k2
TsNHCl +
ii)
(CAT)
slow and rds
(Orange-II)
+ TsNH2
(complex)
O
Cl
H
N
O
Cl
N
SO3H
N
N
SO3H
k3
Fast
iii)
H
O
(complex)
..
H2O
- HCl
O
H
N
O
+
SO3H
N
1,2-naphthoquinone
-N2
SO3H
benzenesulfonic acid
Scheme 1 A detailed mechanistic interpretation for the oxidative decolourisation of Orange-II dye with CAT in alkaline medium.
concentration of the reaction ions resulting from the addition of
the electrolytes. For primary salt effect, Bronsted has given a
relation between the reaction rate (k) and the ionic strength (I)
in a reaction involving ions of charges ZA and ZB and later on it
was modified by Bjerrum as,
energy of activation and enthalpy of activation indicate that the
transition state is highly solvated. The large negative entropy of
activation accounts for the formation of the compact activated
complex with fewer degrees of freedom. The experimental
observation shows that there is no effect of p-toluensulfonamide,
chloride ions and ionic strength on the reaction rate which also
substantiates the proposed mechanism and the derived rate law.
Oxidative decolourisation of Orange-II with CAT in acid
medium8 differs from that in alkaline medium from the
following aspects: (i) It is interesting to note that although
the decolourisation kinetic orders are the same (first-order)
with respect to each [CAT] and [Orange-II ] in both acid and
alkaline media, but the order on [OH-] (inverse-fractional-
order) is somewhat different from that on [H+] (fractional-
order), (ii) The energy of activation reveals that the rate of
decolourisation of Orange-II with CAT is faster in acid medium
(Ea = 71.7 kJ mol-1) compared to alkaline medium (Ea = 74.9
kJ mol-1). (iii) The oxidation products of Orange-II-CAT redox
reaction in acid medium are benzene and 1,2-napthoquinone,
whereas in alkaline medium they are 1,2-naphthoquinone and
benzenesulfonic acid. (iv) In acid medium, the azo form of
log k = log k0 + 1.018 ZAZB√I
(8)
Here k and k0 are the rate constants at ionic strength I (of an inert
salt) and at infinitely dilute concentration (I=0), respectively.
Acccording to this equation, a plot of log k versus √I is a
straight line with a slope equal to 1.018 ZAZB. In the present
investigation, variation of ionic strength of the medium by
adding NaClO4 (0.2 M) solution did not alter the rate, indicating
that one of the reactant species is non-electrolytic as shown in
step (ii) of Scheme 1. Hence, the observed ionic strength effect
is consistent with the Bronsted–Bjerrum concept30 and the
proposed Scheme 1.
The proposed mechanism is also supported by the moderate
values of energy of activation and other thermodynamic
parameters. The fairly high positive values of Gibbs free

JOURNAL OF CHEMICAL RESEARCH 2015 367
5
6
7
8
J. Jun, S. Xueting, S. Chao and Y. Shiying, Chem. Eng. J., 2013, 232, 259.
F.J. Poblete, P. Corrochano and B. Cabanas, Phys. Org. Chem., 2009, 22, 546.
A. Azam, M. Yasser and A. Hamid, Sep. Purif. Technol., 2005, 43, 143.
J.P. Shubha, M. Dinamani, K. Vinutha and Puttaswamy, IJLTEMAS., 2014,
3, 140.
Orange-II has been considered as the reactive substrate species
whereas in alkaline medium hydrogen form was considered, and
(v) The rate law in acid medium is, rate = K1k2 [CAT] [Orange-
II] [H+] / 1+ K1[H+] whereas it takes the form rate = K1k2[CAT]
[Orange-II][H2O] / [OH-] + K1 [H2O] in alkaline medium. Due
to its simplicity and cost-effectiveness, this method can be
adopted to decolourise Orange-II dye.
9
M.M. Campbell and G. Johnson, Chem. Rev., 1978, 78, 65.
10 K.K. Banerji, B. Jayaram and D.S. Mahadevappa, J. Sci. Ind. Res., 1987, 46,
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Conclusions
12 A. Geethanjali, Synlett., 2005, 18, 2857.
For the oxidative decolourisation of Orange-II with chloramine-T in
alkaline medium, the experimental rate law obtained is: –d[CAT]/
13 R.V. Jagadeesh and Puttaswamy, Chloramine-T second update. encyclopedia
of reagents for organic synthesis. Wiley Interscience, Chichester, 2013.
14 A.R.V. Murthy and B.S. Rao, Proc. Ind. Acad. Sci., 1952, 35, 69.
15 D.S. Mahadevappa, K. S. Rangappa, N.M.M. Gowda and B.T. Gowda, J.
Phy. Chem., 1981, 85, 3651.
16 N. Kambo and S.K. Upadhyay, Indian J. Chem., 2004, 43A, 1210.
17 Puttaswamy, R.V. Jagadeesh, N. Vaz and A. Radakrishna, J. Mole. Catal. A:
Chem., 2005, 229, 211.
dt = k [CAT]o [Orange-II]o [NaOH]-0.33
.
1,2-naphthaquinone and
benzenesulfonic acid were identified as the oxidation products
of Orange-II by GC-MS data. Activation parameters were
evaluated. The observed results have been explained by a plausible
mechanism and the related rate law has been deduced. The present
redox system developed is simple, effective and inexpensive for the
decolourisation of Orange-II dye.
18 Puttaswamy, N. Vaz and R.V. Jagadeesh, Chinese. J. Chem., 2008, 26, 536.
19 K.N. Vinod, Puttaswamy and K.N. Ninge Gowda, Inorg. Chim. Acta, 2009,
362, 2044.
20 N. Vaz, L. Parashuram, A.S. Manjunatha and Puttaswamy, J. Appl. Chem,
2014, 3, 2157.
21 Puttaswamy, S. Dakshayani and A.S. Manjunatha, J. Catalyst Catalysis,
2014, 1, 39.
22 J.C. Morris, J.A. Salazar and M.A. Wineman, J. Am. Chem. Soc., 1948, 70,
2036.
NV gratefully acknowledges the financial assistance from
UGC – New Delhi under the Major Research Project Scheme
(F. No. 39-842/2010) and also wishes to thank the Principal and
Management of Jyoti Nivas College for the encouragement.
Received 9 November 2014; accepted 29 April 2015
Paper 1503438 doi: 10.3184/174751915X14352295644456
Published online: 27 June 2015
23 E. Bishop and V.J. Jennings, Talanta, 1958, 1, 197.
24 F.F. Hardy and J.P. Johnston, J. Chem Soc. Perkin Trans 2, 1973, 742.
25 B.G. Pryde and F.G. Soper, J. Chem. Soc., 1931, 1510.
26 S.P. Mushran, R. Sanehi and M.C. Agarwal, Naturforsch., 1972, 27(B), 1161.
27 D.S. Mahadevappa, M.B. Jadhav and H.M. K. Naidu, Int. J. Chem. Kinet.,
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28 K.N. Vinod, Puttaswamy and K.N.N. Gowda, Ind. Eng. Chem. Res., 2010,
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29 A. Sukhdev and Puttaswamy, Synth. React. Inorg. Metal-org. Nano-Metal
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