Development of an efficient ruthenium catalyzed synthetic process and mechanism for the facile conversion of benzothiazoles to orthanilic acids

Article abstract of DOI:10.1016/j.molcata.2010.06.006

Ruthenium-Schiff base complex catalyzed efficient protocol has been developed for the synthesis of orthanilic acids from benzothiazoles in good to excellent yields using N-haloamines. Hexa-coordinated ruthenium complex with Schiff base and triphenylphosphine ligands has been prepared and its catalytic function was invented for the synthesis of orthanilic acids. The synthetic process utilizes our efficient method for the selective and preferential oxidation of thiazole ring of benzothiazoles using N-haloamines without effecting phenyl ring. The detailed catalytic, mechanistic and kinetic investigations have been made for the synthetic reactions. Solvent isotope studies have been made in H₂O-D₂O and the reactions were carried out at different temperatures. Under the identical set of conditions, the kinetics of catalyzed reactions has been compared with uncatalyzed reactions and found that the catalyzed reactions are 9-11 folds faster. The catalytic constants (K_C) have been calculated for each N-haloamine at different temperatures and the values of activation parameters with respect to the catalyst have been evaluated. Spectroscopic evidence for the formation of 1:1 complex between N-haloamine and ruthenium has been obtained. The observed results have been explained by a plausible mechanism and the related rate law has been deduced.

Full text of DOI:10.1016/j.molcata.2010.06.006

Journal of Molecular Catalysis A: Chemical 328 (2010) 99–107
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Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Development of an efficient ruthenium catalyzed synthetic process and
mechanism for the facile conversion of benzothiazoles to orthanilic acids
R.V. Jagadeesh∗, P. Karthikeyan, P. Nithya, Y. Sree Sandhya, S. Sudhaker Reddy, P. Pradeep Kumar Reddy,
M. Vinod Kumar, K.T. Prabhu Charan, R. Narender, P.R. Bhagat
Division of Organic Chemistry, School of Advanced Sciences, Vellore Institute of Technology University, VIT University Campus, Vellore 632014, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Ruthenium–Schiff base complex catalyzed efficient protocol has been developed for the synthesis of
orthanilic acids from benzothiazoles in good to excellent yields using N-haloamines. Hexa-coordinated
ruthenium complex with Schiff base and triphenylphosphine ligands has been prepared and its catalytic
function was invented for the synthesis of orthanilic acids. The synthetic process utilizes our efficient
method for the selective and preferential oxidation of thiazole ring of benzothiazoles using N-haloamines
without effecting phenyl ring. The detailed catalytic, mechanistic and kinetic investigations have been
made for the synthetic reactions. Solvent isotope studies have been made in H2O–D2O and the reactions
were carried out at different temperatures. Under the identical set of conditions, the kinetics of catalyzed
reactions has been compared with uncatalyzed reactions and found that the catalyzed reactions are
9–11 folds faster. The catalytic constants (KC) have been calculated for each N-haloamine at different
temperatures and the values of activation parameters with respect to the catalyst have been evaluated.
Spectroscopic evidence for the formation of 1:1 complex between N-haloamine and ruthenium has been
obtained. The observed results have been explained by a plausible mechanism and the related rate law
has been deduced.
Received 10 March 2010
Received in revised form 2 June 2010
Accepted 4 June 2010
Available online 11 June 2010
Keywords:
Ruthenium catalysis
Synthetic process
Benzothiazoles and orthanilic acids
Reaction mechanism
N-haloamines
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
Synthesis of organic molecules using oxidation process plays a
central role in organic chemistry both at laboratory and industrial
The synthesis of orthanilic acids is an important task due to their
valuable applications in both laboratory and industry. The impor-
tance of orthanilic acids resides in their widespread uses in the
syntheses of various organic dyes [1], and their potential uses as
reagents for the synthesis of pharmaceutically active heterocyclic
compounds. The amide and sulfamoyl derivatives of orthanilic
acids with certain related substitutes have significant medicinal
importance such as sulfa drugs and salidiuretic active agents [2,3].
One of the most relevant methods for the synthesis of orthanilic
acids involves the reduction of o-nitrobenzenesulfonyl chloride or
oxidation of di-o-nitrophenyl disulfide [4]. However, there was not
much attention paid towards the synthesis of these compounds by
alternative methods other than the nitro group reductions or sul-
fide/thiol group oxidations. Hence, we felt it would be keen interest
to investigate the alternative method for the synthesis of orthanilic
acids. In this regard, we have developed an easy and selective syn-
thetic process by the oxidation of benzothiazoles at thiazole ring to
produce orthanilic acids in good to excellent yields.
level. Selective oxidation processes are important in synthesis of
organic compounds, biomolecules and pharmaceuticals, because
these reactions create new functional groups or modify existing
functional groups in a molecule [5,6]. Several methods are avail-
able for the synthesis and oxidation of organic molecules using
different oxidants ranging from metal oxidants to atmospheric
O2. However, still there is a need for developing environmentally
friendly methodologies and introduction of safe, cost-effective and
stable reagents for the synthesis of organic molecules via oxida-
tion process. The development of new processes for the selective
oxidations with environmentally friendly oxidants has potential
practical applications in organic synthesis. In this regard, a large
group of compounds entitled sodium N-haloarenesulfonamidates
(organic haloamines) are widely used in fine organic synthesis
[7]. The sodium N-haloarenesulfonamidates (Fig. 1; henceforth
abbreviated as N-haloamines) are the new class of oxidants and
reagents with polarizable N–X bond, which attracts the attention
of chemists in recent times. These compounds are the precur-
sors of halonium cations, hypohalite species, and N-anions capable
of acting both as bases and as nucleophiles [8]. These com-
pounds resemble hypohalites in their oxidative behaviour and,
even though less familiar, they are more stable than hypohalites
∗
Corresponding author. Tel.: +91 9731989352.
E-mail address: rvjdeesh@gmail.com (R.V. Jagadeesh).
1381-1169/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2010.06.006

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8900 spectrometer. MS data was obtained on 17A Shimadzu gas
chromatograph with a QP-5050A Shimadzu mass spectrometer.
Chloramine-T (E-Merck) and chloramine-B (Fluka) were purified
by the method of Morris et al. [10] and Verger and Perlin [16],
respectively. Benzothiazoles (Lancaster, Sigma–Aldrich and Fuka)
were acceptable grade of purity and used as received. A solution of
benzothiazole by aqueous acetonitrile (1:1 water:acetonitrile) was
employed for the kinetic study. Solvent isotope studies were made
with D2O (99.4%) supplied by Bhabha Atomic Research Center,
Mumbai, India. Reagent grade chemicals and doubly distilled water
were used throughout. Bromamine-T and bromamine-B were pre-
pared by the literature procedures [17,18] and the solutions of these
were prepared in 1:1 ratio of acetonitrile:water and standardized
by iodometric procedure and preserved in brown bottles to prevent
photochemical deterioration.
Fig. 1. Structure of N-haloamines.
Scheme 1. Ruthenium catalyzed synthesis of orthanilic acids from benzothiazoles.
[9,10]. Consequently, these reagents react with a wide range
of functional groups effecting an array of molecular transfor-
mations [7,8]. The prominent members of N-haloamine class of
compounds are chloramine-T (p-CH3C6H4SO2NClNa.3H2O or CAT),
chloramine-B (C6H5SO2NClNa.1.5H2O or CAB) and the correspond-
ing bromine analogues bromamine-T (p-CH3C6H4SO2NBrNa.3H2O
or BAT) and bromamine-B (C6H5SO2NBrNa.1.5H2O or BAB). Sodium
N-haloarenesulfonamidates, due to their versatile properties have
proved to be valuable reagents for a variety of functional group
transformations [7–13]. N-haloamines act as good oxidants and
reagents both in alkaline and acidic media, and have been widely
used for the oxidation and synthesis of variety of organic and
biomolecules [7–13].
Ruthenium has various valences (0–8) and therefore, numerous
useful catalytic reactions for organic synthesis have been explored
[11–15] using ruthenium. Metal complexes of ruthenium contain-
ing nitrogen and oxygen donor ligands are found to be effective
catalysts for oxidation, reduction, hydrolysis, and other organic
transformations [11–15]. In the present work, we have prepared
a ruthenium complex with group of three tridentate O,N,N donor
ligand along with triphenyl phosphine. The ligand is abbreviated in
general as L and it has three potential donor sites, viz., phenolate
oxygen, azomethine nitrogen and amine nitrogen. Although many
catalytic applications of ruthenium towards the oxidation and syn-
thesis of various organic molecules have been reported [11–15], a
literature survey shows there are no kinetic investigations made
on the synthetic reactions of benzothiazoles particularly involving
ruthenium as a homogeneous catalyst.
The wide range of applications of orthanilic acids, the use-
fulness of ruthenium catalyst in organic reactions and versatile
properties of N-haloamines, instigate us to carryout the title reac-
tion. By keeping above points in mind, we reported herein a new
and simple method for the preparation of orthanilic acids from
benzothiazoles using N-haloamines and ruthenium complex cat-
alyst (Scheme 1). The objectives of the present study are to: (i)
prepare hex-coordinated ruthenium–Schiff base complex and to
explore its application as catalyst system, (ii) develop an efficient
synthetic process for the facile conversion of benzothiazoles to
orthanilic acids, (iii) elucidate a plausible mechanism and to deduce
an appropriate rate law, (iv) ascertain the various reactive species,
(v) assess the relative rates of oxidation of benzothiazoles towards
N-haloamines, (vi) find the catalytic efficiency of ruthenium and
to compare the reactivity with that under uncatalyzed oxidation
and (vii) study the solvent isotope using D2O. The present method
developed for the synthesis of orthanilic acids from benzothiazoles
offers many advantages including high conversion, short reaction
times and the involvement of non-toxic reagents.
2.2. Preparation of catalyst
The Schiff base ligand was prepared by the reaction
between pyrrole-2-aldehyde and 2-aminophenol. Ethanolic solu-
tions of pyrrole-2-aldehyde (0.01 mol; 20 mL) and 2-aminophenol
(0.01 mol; 20 mL) were mixed and refluxed for about 4 h. The reac-
tion mixture was evaporated to a small volume and left to cool.
The resulting Schiff base ligand was precipitated on cooling and
then was filtered off, washed with ethanol and recrystallized from
ethanol. The purity of the Schiff base ligand was monitored on TLC
using eluants 1:1 ethyl acetate and petroleum ether and separated
by column chromatography (yield = 90%).
(1)
The ligand was characterized by IR spectral analysis. IR spectra
of Schiff base showed a strong band around 1580–1600 cm−1 for
the free azomethine (–CH N–) group. In the ruthenium complex,
this band is shifted to the region 1522–1543 cm−1, indicating the
coordination of the Schiff base through the azomethine nitrogen
[19]. Further the ligand was characterized by mass spectral analysis.
The starting complex [RuCl3(PPh3)3] was prepared according to
the reported literature procedure [20]. The ruthenium complex was
prepared by the reaction between [RuCl3(PPh3)3] and Schiff base.
The mixture (1:1 ratio) of [RuCl3(PPh3)3] (0.1 mmol) and Schiff base
ligand (0.1 mmol) in 20 mL benzene was heated under reflux for 5 h.
After completion of the reaction, the reaction mixture was concen-
trated and cooled to room temperature followed by the addition of
ether. The solid complex was removed by filtration, washed with
petroleum ether, recrystallized from CH2Cl2 and dried in vacuum.
The yield of the complex is found to be around 75%.
(2)
2. Experimental
The ruthenium complex was characterized spectroscopically as
follows:
2.1. Materials
Melting points were determined on X-4 apparatus and were
uncorrected. IR spectra were obtained using Shimadzu FTIR-
IR spectra of Schiff base showed
a strong band around
1580–1600 cm−1 for the free azomethine (–CH N–) group and this

R.V. Jagadeesh et al. / Journal of Molecular Catalysis A: Chemical 328 (2010) 99–107
101
Table 1
Ruthenium catalyzed synthesis of orthanilic acids from benzothiazoles.
Entry Sustrate
Product
Reaction time Yield (%) mp (◦C)
(h min)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
IS
5.00
4.30
4.20
5.30
4.0
95
96
96
94
96
95
92
92
96
95
90
90
96
94
96
95
92
92
96
95
90
293 (300)
6-OMe
6-OH
6-Br
6-CH3
6-C1
5-OMe
5-OH
5-Br
5-CH3
5-C1
315 (314–318)
255 (257)
253 (350)
172 (170)
291 (289)
315 (320)
357 (355)
297 (298–300)
230 (228)
275 (278)
343 (340)
330 (328)
317 (318)
272 (275)
191 (189)
218 (220)
153 (151)
241 (239)
190 (187)
247 (245
Fig. 2. Structure of [RuCl(PPh3)2Cl].
5.30
5.35
5.30
4.20
4.35
5.45
6.00
4.30
5.35
4.10
5.35
5.40
5.35
4.25
4.40
5.50
band was shifted to the region 1522–1543 cm−1 in metal complex,
indicatingthatone of thecoordination is throughazomethinenitro-
gen [19] of Schiff base. Strong band was observed in the region
1270–1300 cm−1 for free Schiff base has been assigned to pheno-
lic C–O stretching. After the complexation, this band was shifted to
higher frequency region 1290–1330 cm1, indicates that other coor-
dination is through phenolic oxygen atom [21]. The characteristic
absorption band for secondary amine N–H stretching is observed
in the region 3300–3000 cm−1. But this band was absent in the
complex indicating that the one more coordination site is tertiary
nitrogen atom of pyrrole ring to the metal ion [22]. The other char-
acteristic bands due to triphenylphosphine were also present in
the expected region, and hence these are attributable to the coor-
dinated N,N,O-donor ligand (L). Elemental analysis of the complex
6-COOH
6-F
5-COOH
5-F
6-NH2
6-OAc
6-NO2
5-SO3H
5-OH
5-Br
5-CH3
5-C1
5-COOH
5-F
5-NH2
5-OAc
5-NO2
4-SO3H
4-OH
4-Br
4-CH3
4-C1
4-COOH
4-F
19
20
21
5-NH2
5-OAc
5-NO2
4-NH2
4-OAc
4-NO2
Melting points (mp) given in parenthesis refer to authetinc sample.
C47H38N2OP2ClRu was also made and the percentage of carbon,
hydrogen and nitrogen was found to be 66.5, 4.45 and 3.30 respec-
tively.
2.4. Procedure for the synthesis of orthanilic acids
To a stirred solution of benzothiazoles (10 mmol), bromamine-
B (50 mmol) in alkaline acetonitrile/water (1:1) mixture (20 mL),
catalyst (2 mmol) was added and the mixture was heated at 313 K
for 4–6 h. After completion of the reaction, the reduction product
of N-haloamine, p-toluenesulfonamide (PTS) or benzenesulfon-
amide (BSA) was extracted with ethyl acetate and identified by TLC
and confirmed by mass spectral analysis. The aqueous part of the
reaction mixture was neutralized with acid followed by solvent
evaporation under reduced pressure. The residue was dissolved
in dichloromethane and the dichloromethane layer was washed
twice with water and then dried over sodium sulfate. The sol-
vent was evaporated under reduced pressure and the residue thus
obtained was purified by passing through a short silica gel column
using dichloromethane as eluent. Evaporation of the solvent yields
orthanilic acids around 95%. The products were identified by TLC
and mp by comparing with authentic samples. Further, the com-
pounds were confirmed by mass spectral analysis. The reaction
times and yields are given in Table 1. Alternatively, after extracting
out p-toluenesulfonamide, the aqueous layer was neutralized with
acid and the orthanilic acids are estimated as their zinc orthanilates.
The procedure for the estimation is as follows: to the reaction mix-
ture, calculated volume of 1 mol dm−3 HCl was added, followed by
10 mL of pH 5.0 buffer and 10 mL of 1% zinc chloride. The precipi-
tate formed was filtered, dried at 105–110 ◦C and the recovery of
(C6H7SO3N)2 Zn was found be around 95%.
The electronic spectrum of ruthenium complex showed charge
transfer bands [23]. Due to the relatively high oxidizing proper-
ꢀ
ties of ruthenium, the charge transfer bands of type L y → t2g are
prominent in the lower energy region. The electronic spectrum of
the complex is showed in the 360 nm region.
Magnetic susceptibility measurements show that the complex
[RuCl(PPh3)2L] is diamagnetic, which corresponds to the +3 state
of ruthenium (low-spin d6, S = 0). 1H NMR spectra of the complex
showed broad signal within 7.03–7.60 ppm due to the coordi-
nated PPh3 ligands. The signal observed at 5.82 ppm for azomethine
proton for the coordinated N,N,O-donor ligand (L). The expected
aromatic proton signals for the coordinated ligand have been
observed within 5.5–6.6 ppm.
Based on the above spectroscopic data the complex is hexa-
coordinated and the ligand is coordinated to the metal centre,
via pyrrole N–H and phenolic O–H protons, as a dianionic triden-
tate N,N,O-donor. Two triphenylphosphines and a chloride are also
coordinated to the metal centre in an octahedral fashion as shown
in Fig. 2.
2.3. Reaction stoichiometry
Reaction mixtures containing varying ratios of N-haloamines to
benzothiazole in the presence of 1.0 × 10−3 mol dm−2 NaOH and
1.0 × 10−6 catalyst were equilibrated at 313 K for 24 h. Determina-
tion of unreacted N-haloamine amount in reaction mixture showed
that 1 mol of benzothiazole consumed 5 mol of N-haloamine, con-
firming the following stoichiometry:
2.5. Kinetic measurements
The detailed kinetic experiments were made with respect
to conversion of benzothiazole to orthanilic acid with four N-
(3)

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R.V. Jagadeesh et al. / Journal of Molecular Catalysis A: Chemical 328 (2010) 99–107
Table 2
haloamines as model reaction. The reactions were carried out
under pseudo first-order conditions with a known excess of
[benzothiazole]o over [N-haloamines]o at 313 K. The reactions were
carried out in stoppered Pyrex boiling tubes whose outer surfaces
were coated black to eliminate photochemical effects. For each run,
requisite amounts of solutions of benzothiazole, NaOH, catalyst
and aqueous acetonitrile (1:1 water:acetonitrile) (to keep the total
volume constant for all runs) were introduced in to the tube and
thermostated at 313 K until thermal equilibrium was attained. A
measured amount of N-haloamines solution, also thermostated at
the same temperature, was rapidly added with stirring to the mix-
ture in the tube. The progress of the reaction was monitored by the
iodometric determination of unreacted N-haloamines in aliquots
(5 mL each) of the reaction mixture withdrawn at different inter-
vals of time. The course of the reaction was studied for at least two
half-lives. The pseudo first-order rate constants (kꢀ) calculated from
the linear plots of log [N-haloamine] vs. time were reproducible
within 5%.
Effect of varying reactant concentrations on the reaction rate at 313 K.
103 [N-haloamine] 102 [Benzothiazole]
104 kꢀ s−1
(mol dm−3
)
(mol dm−3
)
CAT
CAB
BAT
26.2
26.8
26.6
26.5
26.4
BAB
54.6
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
0.5
1.0
2.0
4.0
8.0
8.61
8.80
8.50
8.70
8.30
2.11
4.31
8.50
17.1
34.4
16.4
16.7
16.5
16.3
16.2
4.12
8.31
16.5
54.2
54.5
54.8
54.2
13.8
27.8
54.5
6.45
13.3
26.6
53.1
33.2
67.1
110
225
107
[NaOH] = 1.0 × 10−2 mol dm−3; [ruthenium] = 1.0 × 10−6 mol dm−3
.
3. Results
3.1. Synthesis of anthranilic acids
Synthesis of orthanilic acids from benzothiazoles was achieved
using catalytic amounts of ruthenium in acetonitrile/water (1:1)
at 313 K by N-haloamines with 1:5 benzothiazoles:N-haloamines
ratio in the presence of alkali. The products and the yields
were summarized in Table 1. In general substrates contain-
ing electron-donating moieties found to be more reactive and
required shorter reaction times compared to substrates contain-
ing electron-withdrawing groups. The synthetic process proceeds
with the formation of 2-benzothiazolones and 2-aminothiophenols
as the two intermediates. Benzothiazoles first utilize 1 mol of
N-haloamine to form 2-2-benzothiazolones followed by the for-
mation of 2-aminothiophenol by utilizing one more mole of
N-haloamine. So formed 2-aminothiophenols consume another
3 mol of N-haloamine to yield ultimate and desired compounds,
orthanilic acid. The detailed mechanism for the reactions is
depicted in Scheme 3.
The reactions were studied in various solvents (acetonitrile, 1,2-
dichloromethane, ethanol, and acetonitrile/water (1:1) mixture).
The mixture of acetonitrile/water (1:1) was found to be the best
solvent system. The reactions were found to be highly dependent
upon pH of the system. To evaluate the effect of pH, the reactions
were carried out under similar experimental conditions at differ-
ent pH’s using NaOH. At neutral pH, the oxidation reactions were
found to be very slow, however the reaction rates increase with
increasing in pH (addition of NaOH). This behavior of the reaction is
attributed to the dissociation of N-haloamines in aqueous medium
by furnishing different reactive species. This behaviour of dissoci-
ation of N-haloamines is well explained in discussion part. Due to
the increase of rate in the presence of NaOH, the reactions were
carried out at 1.0 × 10−2 mol dm−3 NaOH.
Fig. 3. Plots of log kꢀ vs. log [benzothiazole].
Table 3
Effect of varying NaOH and ruthenium concentrations on the reaction rate at 313 K.
102 [NaOH]
106 [Ruthenium)
104 kꢀ s−1
(mol dm−3
)
(mol dm−3
)
CAT
CAB
8.62
13.2
16.5
22.5
30.5
6.00
9.65
16.5
26.5
42.6
BAT
BAB
28.5
0.25
0.5
1.0
2.0
4.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
0.25
0.5
1.0
2.0
4.0
4.47
6.75
8.50
11.6
15.5
3.03
4.85
8.50
13.4
21.5
14.1
21.2
26.6
36.6
48.8
43.2
54.4
74.6
99.3
19.4
31.1
54.4
86.0
9.45
15.2
26.6
42.4
67.9
137
[N-haloamine]o = 2.0 × 10−3 mol dm−3; [benzothiazole]o = 2.0 × 10−2 mol dm−3
.
vs. time is linear (r > 0.9910) indicating a first-order dependence
of rate on [N-haloamine]o. The values of pseudo first-order rate
constants (kꢀ) are given in Table 2. Further, the values of kꢀ are
unaffected with variation of [N-haloamine]o, confirming first-order
dependence on [N-haloamine]o. Under the similar experimental
conditions, an increase in [benzothiazole]o led to an increase in
the kꢀ values (Table 2). Plots of log kꢀ vs. log [benzothiazole] were
linear (Fig. 3; r > 0.9908) with unit slopes, showing a first-order
dependence of the rate on [benzothiazole]o. Further, plots of kꢀ vs.
[benzothiazole] were linear (r > 0.9980) passing through the origin,
confirming the first-order dependence on [benzothiazole]o. Fur-
thermore, the second-order rate constants kꢀꢀ = kꢀ/[benzothiazole]o
are nearly the same for all the cases establishing a first-order depen-
dence on the [benzothiazole]o (values are not shown).
3.2. Kinetics of synthesis of orthanilic acid from benzothiazole
The kinetics of synthesis of orthanilic acid from benzothiazole by
CAT, CAB, BAT, and BAB (henceforth abbreviated as N-haloamine)
has been investigated at several initial concentrations of the reac-
tants in the presence of NaOH and micro-quantity of ruthenium
catalyst at 313 K. It has been observed that the similar kinetic
behavior was observed with all the four N-haloamines under the
identical experimental conditions.
The rate of the reaction increases with increase in [NaOH]
(Table 3) and plots of log kꢀ vs. log [NaOH] were linear (Fig. 4;
r > 0.9904) with positive slopes (0.4–0.45), indicating fractional-
order dependence of rate on [NaOH]. Further, the rate of the
With the benzothiazole in excess, at constant [NaOH], [ruthe-
nium], [benzothiazole]o and temperature, plot of log [N-haloamine]

R.V. Jagadeesh et al. / Journal of Molecular Catalysis A: Chemical 328 (2010) 99–107
103
Fig. 4. Plots of log kꢀ vs. log [NaOH].
Fig. 6. Plots of log kꢀ vs. 1/D.
Table 5
Solvent isotope studies for the synthesis of orthanilic acid by CAT and BAB in
H2O–D2O mixtures at 313 K.
1/2
(kꢀo/kꢀn
)
Atom fraction of deuterium (n)
kꢀn s−1
CAT
BAB
CAT
BAB
0.00
0.25
0.50
0.75
0.95
8.50
9.62
10.5
11.2
11.9
54.4
60.3
65.7
70.2
75.5
1.0
1.0
0.94
0.90
0.87
0.84
0.96
0.92
0.89
0.86
Fig. 5. Plots of log kꢀ vs. log [catalyst].
[N-haloamine]o = 2.0 × 10−3 mol dm−3
;
[benzothiazole]o = 2.0 × 10−2 mol dm−3
;
[NaOH] = 1.0 × 10−2 mol dm−3; [ruthenium] = 1.0 × 10−6 mol dm−3
.
reaction increases with increasing [ruthenium] (Table 3) and a plot
of log kꢀ vs. log [ruthenium] is linear (Fig. 5; r > 0.9911) with slopes
less than unity (0.71) indicating a fractional-order dependence of
rate on [ruthenium]. Addition of p-toluenesulfonamide (PTS) or
benzenesulfonamide (BSA), a reduction product of N-haloamines,
(1.0 × 10−3–4 × 10−3 mol dm−3), to the reaction mixture did not
affect the rate significantly. This indicates that neither PTS nor BSA
is involved in any step prior to the rate-limiting step in the scheme
proposed.
The effect of ionic strength (I) of the medium on the rate was
studied in a range of 0.10–0.50 mol dm−3 using NaClO4 solution,
keeping the other experimental conditions constant. The rate was
found to be unaffected with the addition of NaClO4. Rate studies
were carried out in H2O–MeOH mixtures having different com-
positions (0–30% (v/v)), thereby varying the dielectric constant of
the solvent medium. The rate was found to decrease with increase
in MeOH content (Table 4) and plots of log kꢀ vs. 1/D were linear
(Fig. 6; r > 0.9901) with negative slopes. Blank experiments per-
formed with MeOH indicate that there was no oxidation of MeOH
by any of the four N-haloamines under the selected experimental
conditions.
formal solvent isotope effect ratio kꢀ (H2O)/kꢀ (D2O) = 0.71 and 0.72
for these two N-haloamines. Solvent isotope studies were made
using H2O–D2O mixtures for CAT and BAB (Table 5). The effect of
the temperature on the rate was studied by performing the kinetic
experiments at various temperatures (303–323 K), keeping other
experimental conditions constant. From the linear Arrhenius plots
of log kꢀ vs. 1/T (r > 0.9921), the values of activation parameters (Ea,
ꢀH =/ , ꢀG =/ , ꢀS =/ ) for the overall reaction were evaluated. These
data are summarized in Table 6.
At experimental conditions the addition of NaCl or NaBr
(1.0 × 10−3 to 4.0 × 10−3 mol dm−3) did not alter the rate of the
reaction. These results indicate that there is no role for halide ions
in the reaction. The addition of the reaction mixtures to aqueous
acrylamide monomer solutions, kept in the dark, did not initiate
polymerization, confirming the absence of any free radical species
Table 6
Temperature dependence and values of composite activation parameters for the
synthesis of orthanilic acid by N-haloamines in the presence and absence of ruthe-
nium catalyst.
Rate studies in D2O medium for CAT and BAB revealed
that kꢀ (H2O) = 8.5 × 10−4 s−1 and 54.4 × 10−4 s−1
,
and kꢀ
Temperature
(K)
104 kꢀ s−1
(D2O) = 11.9 × 10−4 s−1 and 75.5 × 10−4 s−1 respectively. The
CAT
CAB
6.25 (0.45)
BAT
BAB
303
308
313
318
323
2.90a (0.20)b
5.51 (0.34)
8.50 (0.80)
12.0 (1.44)
19.0 (2.10)
71.1 (96.2)
68.5 (93.6)
79.0 (90.0)
12.5 (1.00)
27.0 (2.30)
42.0 (4.00)
54.0 (5.2)
65.0 (8.0)
93.0 (12.5)
44.7 (62.8)
42.2 (60.2)
77.0 (84.0)
Table 4
10.5 (0.92)
16.5 (1.65)
20.0 (2.45)
33.0 (4.20)
62.8 (87.9)
60.0 (85.3)
78.5 (87.0)
15.8 (1.69)
26.6 (2.65)
35.0 (4.00)
48.0 (6.10)
52.7 (71.1)
50.0 (68.5)
78.0 (85.0)
Effect of varying dielectric constant (D) of the medium on the rate of the reaction at
313 K.
% [MeOH] (v/v)
D
104 kꢀ s−1
Ea (kJ mol−1
)
CAT
CAB
BAT
BAB
ꢀH =/ (kJ mol−1
ꢀG =/ (kJ mol−1
)
)
0.0
10.0
20.0
30.0
76.73
72.37
67.48
62.71
8.50
7.36
6.63
5.83
16.5
15.3
13.7
11.4
26.6
23.8
21.5
18.2
54.4
50.4
44.0
37.7
ꢀS =/ (J K−1 mol−1) −25.2 (−1.04) −57.5 (−4.18) −93.5 (−15.6) −124 (−20.9)
Values in parentheses refer in the absence of ruthenium catalyst.
a
[N-haloamine]o = 2.0 × 10−3 mol dm−3; [benzothiazole]o = 2.0 × 10−2 mol dm−3
;
[N-haloamine]o = 2.0 × 10−3 mol dm−3
;
[benzothiazole]o = 2.0 × 10−2 mol dm−3
;
[NaOH] = 1.0 × 10−2 mol dm−3; [ruthenium] = 1.0 × 10−6 mol dm−3
.
[NaOH] = 1.0 × 10−2 mol dm−3; [ruthenium] = 1.0 × 10−6 mol dm−3
.
b
Experimental conditions are the same as ‘a’ without ruthenium catalyst.

104
R.V. Jagadeesh et al. / Journal of Molecular Catalysis A: Chemical 328 (2010) 99–107
generated in the reaction sequence. The control experiments were
also performed under similar reaction conditions without the N-
haloamines.
4. Discussion
4.1. Reactive species of N-haloamines
Investigations of Morris et al. [10], Bishop and Jennings [9], Pryde
and Soper [24] and Hardy and Johnston [25] have shown the exis-
tence of similar equilibria of N-metallo-N-arylhalosulfonamides
(N-haloamines) in aqueous media. Depending on the pH, N-
haloamines exhibits the different equilibria in aqueous solutions
[10,9,24,25].
Scheme 2. General mechanistic scheme for the synthesis of orthanilic acids from
benzothiazoles.
In alkaline solutions of N-haloamines, RNX2 does not exists, and
the possible oxidizing species are RNX− and OX− anions, which
could be transformed into more reactive species RNHX and HOX,
during the course of the reaction in alkali retarding steps. Sev-
eral workers have observed the retarding effect of OH− ions on
the rate of haloamines with a number of substrates [26–28] and
have suggested that the reactivity of weakly alkaline solutions of
haloamines is due to the formation of the conjugate acid RNHX from
RNX− in OH− retarding step (RNX− + H2O ꢀ RNHX + OH−). But in
the present investigations, the OH− ions increases the rate of the
reaction clearly indicates RNX− as the reactive oxidizing species
(RNHX + OH− ꢀ RNX− + H2O). In earlier work [11–13], the posi-
tive influence of OH− ion on the rate of haloamine reactions with
a number of compounds have been observed and suggested RNX−
as the reactive oxidizing species. In the present investigations, the
rate of the reaction is accelerated by OH− ions clearly indicates that
the anion RNX− is the most likely reactive species of N-haloamines
involved in the oxidative conversion of benzothiazoles to orthanilic
acids.
of metal species and ꢀA is the absorbance difference between
ruthenium–CAT mixture and ruthenium alone. Eq. (6) is valid when
[S] is much higher than [M]Total. According to Eq. (6), a plot of 1/ꢀA
vs. 1/[S] or 1/[S]2 should be linear with an intercept in case of 1:1
or 1:2 type of complex formation between M and S. The ratio of
intercept to slope of this linear plot gives the value of K.
Ruthenium complex in aqueous alkaline acetonitrile medium
containing CAT showed an absorption peak at 345 nm (ꢁmax for the
complex). The complex formation studies were made at this ꢁmax of
345 nm. In a set of experiments, the solutions were prepared by tak-
ing different amounts of CAT (0.5 × 10−3 to 8 × 10−3 mol dm−3) at
constant amounts of ruthenium (1.0 × 10−6 mol dm−3) and NaOH
(0.01 mol dm−3) at 313 K. The absorbance of these solutions was
measured at 345 nm. The absorbance of ruthenium in alkaline
medium is also measured at same wavelength (345 nm). The dif-
ference of these absorbance (with and without CAT) gave the
differential absorbance, ꢀA. A plot of 1/ꢀA vs. 1/[CAT] was linear
(r = 0.9900) with an intercept suggesting the formation of 1:1 com-
plex between ruthenium–CAT. Further, the plot of log (1/ꢀA) vs. log
(1/[CAT]) was also linear (r = 0.9871). From the slope and intercept
of the plot 1/ꢀA vs. 1/[CAT], the value of the formation constant, K,
of the complex was deduced and found to be 5.21 × 102.
4.2. Reactive species of ruthenium complex
Under the experimental conditions, [OH−] ꢁ [ruthenium] and
the fact that [OH−] increases the rate, ruthenium is mostly present
as the hydroxylated species, [Ru(OH)(PPh3)2(L)] and its formation
is given in the following equilibrium:
4.4. Reaction scheme and rate law
Based on the above discussion and the observed kinetic
results, the general mechanism (Scheme 2) has been proposed
for the ruthenium complex catalyzed synthesis of orthanilic acids
from benzothiazoles using N-haloamines in alkaline medium. In
Scheme 2, Y and Yꢀ represent the intermediate species whose
structures are shown in Scheme 3. The detailed mechanism for
the ruthenium catalyzed oxidative conversion of benzothiazoles is
depicted in Scheme 3. Based on Scheme 3, following rate law was
derived and which is consistent with all the experimental results.
[RuCl3(PPh3)2(L)] + OH− ꢀ [Ru(OH)(PPh3)2(L)] + Cl−
(4)
Hrdroxylated species of ruthenium has been postulated as the
reactive species in alkaline medium for the synthesis of orthanilic
acids from benzothiazoles.
4.3. Evidence showing complex formation between ruthenium
and CAT
K6K7k8[N-haloamine]t[Benzothiazole][Ruthenium][OH−]
The existence of complex between ruthenium and CAT was
evidenced from the UV–visible spectra of both ruthenium and
ruthenium–CAT mixture, in which a shift of ruthenium from 360 to
345 nm was observed, indicating the formation of a complex.
The complex formation between metal ion ruthenium and CAT
was given by the following equilibrium (Eq. (5)):
Rate =
[H2O] + K1[OH−] + K1K2[Pt(IV)][OH−]
(7)
Scheme 3 and the rate law (7) are consistent with the observed
experimental results and supported by the following facts:
K
M + n Sꢁ(MSn)
(5)
4.5. Effect of dielectric permittivity
Here, M and MSn are two metal species with different extinction
coefficients. For the equilibrium (12), Ardon [29] has derived the
following relation (Eq. (6)):
A decrease of reaction rate with a decrease in D (increase in
MeOH content) of the medium supports the proposed mechanism.
Amis and Jaffe [30] have shown that
1/ꢀA = 1/[S]n{1/ꢀE[MTotal]K} + 1/ꢀE[MTotal
]
(6)
log kDꢀ = log kꢀ + Zeꢂ/2.303 kTr2
D
(8)
where, K is the formation constant of the complex, [S] is the con-
centration of CAT, ꢀE is the difference in extinction coefficient
between two metal species, [M]Total is the total concentration
where kꢀ is the rate constant in a medium of infinite dielectric
constant and kꢀD is the rate constant as function of dielectric con-

R.V. Jagadeesh et al. / Journal of Molecular Catalysis A: Chemical 328 (2010) 99–107
105
Scheme 3. Detailed mechanism for the ruthenium catalyzed synthesis of orthanilic acids.
stant D, Ze is the charge on the ion, ꢂ is the dipole moment of the
dipole, k is the Boltzmann constant, T is the absolute temperature
and r is the distance of approach between the ion and dipole. Eq.
(18) predicts a linear relation between log kꢀ vs. 1/D (r > 0.9901). The
slope of the line should be negative for a reaction between a nega-
tive ion and a dipole or between two dipoles, while a positive slope
is obtained for positive ion–dipole reactions. In the present inves-
tigations, plots of log kꢀ vs. 1/D were linear with negative slopes
(r > 0.9901) supporting the participation of negative ion and dipole
in the rate-limiting step (Scheme 3).
H2O–D2O mixtures could throw light on the nature of the transition
state [32,33]. The dependence of rate constant kꢀn on n, the atom
fraction of deuterium in a solvent mixture, is given [33] by Eq. (22):
TS
RS
koꢀ /knꢀ = ꢃ(1 − n + n˚i)/ꢃ(1 − n + n˚j)
(9)
where ˚i and ˚j are isotopic fractionation factors for isotopi-
cally exchangeable hydrogen sites in the transition state (TS) and
reactant state (RS) respectively and kꢀo is the rate constant in pure
H2O. If the reaction proceeds through a single transition state [33],
then the Eq. (9) takes the form given in Eq. (10):
(koꢀ /knꢀ )1/2 = [1 + n(˚j − 1)]
(10)
4.6. Effect of solvent isotope
It is interesting to note that the rates in D2O medium are faster
than that in H2O. Since the OD− is a stronger base than OH− by
a factor of 2–3, the solvent isotope effect of this magnitude is
expected [31]. However, the observed inverse solvent isotope effect
kꢀ (D2O)/kꢀ (H2O) of 1.40 for CAT and 1.38 for BAB (Table 5) and the
normal kinetic isotope effect kꢀOH−/kꢀOD− < 1 could counter-balance
the solvent isotope effect, which can be attributed to the fractional-
order dependence of rate on [OH−]. The solvent isotope studies in
From Eq. (20), a plot of (kꢀo/kꢀn)1/2 vs. n should be linear. It is
observed that such a plot is linear (Fig. 7; r > 0.9915) with a slope
of (˚j − 1) = −0.16 and −0.14, giving values of 0.84 and 0.86 for
the fractionation factor in the cases of CAT and BAB respectively.
Considering the diversity of the procedure employed, it is reason-
able to assume that there is an agreement between the n values
obtained. Further, a comparison with the standard plots [34] clearly
implies the involvement of a single or H–D exchange during the

106
R.V. Jagadeesh et al. / Journal of Molecular Catalysis A: Chemical 328 (2010) 99–107
Table 7
Values of catalytic constant (KC) at different temperatures and activation parameters
calculated using KC values.
Temperature
(K)
KC
CAT
CAB
3.67
6.10
9.38
11.1
18.2
62.0
59.0
66.0
−24.6
BAT
7.27
8.95
15.1
19.2
26.5
54.4
51.8
64.5
−41.0
BAB
15.6
303
308
313
318
323
1.80
3.26
4.87
6.68
10.7
68.6
66.0
24.0
31.1
36.0
50.9
44.7
42.0
63.0
−60.0
Ea (kJ mol−1
)
ꢀH =/ (kJ mol−1
ꢀG =/ (kJ mol−1
)
)
67.0
−3.89
ꢀS =/ (J K−1 mol−1
)
Fig. 7. Kinetc isotope studies plots.
[N-haloamine]o = 2.0 × 10−3 mol dm−3
;
[benzothiazole]o = 2.0 × 10−2 mol dm−3
;
[NaOH] = 1.0 × 10−2 mol dm−3; [ruthenium] = 1.0 × 10−6 mol dm−3
.
reaction sequence. The participation of OH− ion in the formation of
transition state is thus inferred.
4.9. Catalytic activity
Moelwyn-Hughes [36] has derived the following equation relat-
ing both catalyzed and uncatalyzed reactions:
4.7. Activation parameters in the presence of ruthenium catalyst
k1 = ko + KC[catalyst]x
(11)
The reactions were carried out at range of temperatures
(303–313 K) and the energy of activations (Ea) for each reaction
has been calculated from the linear Arrhenius plots of log kꢀ vs.
in which k1 is the observed pseudo first-order rate constant
obtained in the presence of ruthenium catalyst, ko is the pseudo
first-order constant for the uncatalyzed reaction, KC is the catalytic
constant and x is the order of the reaction with respect to ruthe-
nium. In the present investigations, ‘x’ values for the standard run
were found to be 0.71. Then the value of KC is calculated using the
Eq. (11). The values of KC have been evaluated for each N-haloamine
at different temperatures (303–323 K) and KC was found to vary
with temperature (Table 7). Further, plots of log KC vs. 1/T were
linear (r > 0.9901) and the values of energy of activation and other
activation parameters for the catalyst were computed.
1/T (r > 0.9921). The values of other activation parameters (ꢀH =/
,
ꢀG =/ , ꢀS =/ ) for the overall reaction were also evaluated. These
data are summarized in Table 6. The values of ꢀH =/ and ꢀS =/
for the oxidation of benzothiazole with all the four N-haloamines
are linearly related (r = 0.9916), with an isokinetic temperature
of ˇ = 370 K, indicating that a common mechanism operates in
the synthesis of orthanilic acid of benzothiazole by all the said
four N-haloamines. Further, the genuine nature of the isokinetic
relationship was verified by the Exner criterion [35] by plot-
ting log kꢀ(303 K) vs. log kꢀ(313 K); this plot is linear (r = 0.9906). The
value of ˇ was calculated from the equation ˇ = T1(1 − q)/(T1/T2) − q
where q is the slope of the Exner plot and T2 > T1. The value of ˇ
was found to be 365 K. The values of ˇ evaluated from both the
plots are much higher than the temperature range used in the
present work (313 K). This indicates a common enthalpy-controlled
pathway for all the reactions. The high positive values of the
free energy of activation and of the enthalpy of activation sug-
gest that the transition state is highly solvated, while the high
negative entropy of activation indicates the formation of rigid asso-
ciated transition states. The values of ꢀG =/ are almost the same
in the cases of all the N-haloamines, suggesting that the oxida-
tion of benzothiazole by N-haloamines proceeds by a common
mechanism.
4.10. Comparison of reactivity values of N-haloamines
Under identical experimental conditions, the rates are found to
be higher with bromamines compared to chloramines by a fac-
tor of 3 (Table 2) and to follow the order: BAB > BAT > CAB > CAT.
This is attributable to the difference in electrophilicities of the
halo cations Br+ and Cl+ involved in the oxidation process and
is also related to the ease with which these species are gener-
ated in reactions. In these reactions, the electronegativity values
of Br+ and Cl+ play a vital role. Bromine has the electronegativity of
2.7, while chlorine has a higher value of 2.8. As the electroneg-
ativity increases, the electropositive nature decreases, since the
halo cations are the reactive species in these oxidation reactions
and the electropositive nature is Br > Cl. This may also be due
to the moderate differences in the van der Waal’s radii of the
bromine and chlorine. Therefore, the reactivity of bromamines
is greater than that of chloramines. This is consistent with the
observed order of reactivity: BAB > BAT > CAB > CAT in the present
work. Hence, it can be generalized that bromamines are stronger
oxidants compared to chloramines. A similar behaviour has been
reported [37,38] in the oxidation of several other substrates using
N-haloamines.
Further, the observed oxidation rates are lower in BAT and in
CAT compared to the rates in BAB and in CAB, the ratios kꢀ (BAB)/kꢀ
(BAT) and kꢀ (CAB)/kꢀ (CAT) were found to be around 2. This indi-
cates the participation of a –CH3 group in CAT and BAT, which
exerts a strong inductive effect in enriching the electron density
at the polar N–X bond, thereby reducing the electrophilicity of the
X atom. This explains why the reactivity of benzenesulfonamide
derivatives is higher than that of toluenesulfonamide derivatives
of N-haloamines. It also substantiates the observed overall reac-
4.8. Activation parameters in the absence of ruthenium
It was felt reasonable to compare the reactivity of these four
N-haloamines towards benzothiazole in the absence of ruthenium
catalyst under identical set of experimental conditions in order to
evaluate the catalytic efficiency of ruthenium. The reactions were
studied at different temperatures (303–323 K) in absence of Ruthe-
nium. From the plots of log kꢀ vs. 1/T (r > 0.9902), we evaluated the
activation parameters for the uncatalyzed reactions (Table 6). The
ruthenium complex catalyzed reactions were found to be 9–11
times faster and thus the observed results justify the need of a
catalyst for a facile conversion of benzothiazoles by the chosen
N-haloamines in alkaline medium. The catalyst ruthenium forms
a complex (Y) with N-haloamines, which increases the oxidizing
property of chosen N-haloamines than without ruthenium.

R.V. Jagadeesh et al. / Journal of Molecular Catalysis A: Chemical 328 (2010) 99–107
107
tivity of BAB > BAT > CAB > CAT towards the oxidative conversion of
benzothiazoles in the present work.
[7] E. Kolvari, A.G. Choghamarani, P. Salehi, F. Shirini, M.A. Zolfigol, J. Iran. Chem.
Soc. 4 (2007) 126–174.
[8] M.M. Campbell, G. Johnson, Chem. Rev. 78 (1978) 65–79.
[9] E. Bishop, V.J. Jennings, Talanta 1 (1958) 197–199.
5. Conclusions
[10] J.C. Morris, J.A. Salazar, M.A. Wineman, J. Am. Chem. Soc. 70 (1948)
2036–2041.
[11] R.V. Jagadeesh, Puttaswamy, J. Phys. Org. Chem. 21 (2008) 844–858.
[12] C.H. Vinod Kumar, K.N. Shivananda, R.V. Jagadeesh, C. Naga Raju, J. Mol. Catal.
A: Chem. 311 (2009) 23–28.
[13] C.H. Vinod Kumar, R.V. Jagadeesh, K.N. Shivananda, Y. Sree Sandhya, C. Naga
Raju, Ind. Eng. Chem. Res. 49 (2010) 1550–1560.
Ruthenium complex catalyzed synthesis of orthanilic acids
was achieved efficiently using N-haloamines in the presence of
alkali. Hexa-coordinated ruthenium–Schiff base complex was pre-
pared and it has been used as the catalyst for the facile synthesis
of orthanilic acids. Catalyzed synthetic reactions undergo with
similar oxidation mechanism and follow the identical kinetic
behaviour. Catalyzed reactions showed rates 9–11 fold faster than
the uncatalyzed reactions. The present method developed for
the synthesis of orthanilic acids from benzothiazoles offers many
advantages including high conversion, short reaction times and
the involvement of non-toxic reagents. It can be concluded that
ruthenium–Schiff base complex acts as an efficient catalyst for the
selective oxidative conversion of benzothiazoles to orthanilic acids
by N-haloamines in alkaline medium.
[14] K.R. Bhat, K. Jyothi, B. Thimme Gowda, Oxid. Commun. 25 (2002) 117–124, and
references therein.
[15] F.A. Cotton, G. Wilkinson, C.A. Murillo, M. Bochmann, Advanced Inorganic
Chemistry, 6th ed., John Wiley and Sons Inc., New York, 1999.
[16] J. Verger, C. Perlin, Chem. Abstr. 66 (1967) 79665–79666.
[17] C.G.R. Nair, R.L. Kumari, P. Indrasenan, Talanta 25 (1978) 525–527.
[18] M.S. Ahmed, D.S. Mahadevappa, Talanta 27 (1980) 669–670.
[19] B. Khera, A.K. Sharma, N.K. Kaushik, Polyhedron 2 (1983) 1177.
[20] J. Chatt, G. Leigh, D.M.P. Mingos, R.J. Paske, J. Chem. Soc. A (1968) 2636.
[21] R. Karvembu, S. Hemalatha, R. Prabhakaran, K. Natarajan, Inorg. Chem. Com-
mun. 5 (2002) 487.
[22] D.M. Boghaei, S. Mohebi, J. Mol. Cat. A: Chem. 179 (2002) 41.
[23] A.B.P. Lever, Electronic Spectra of dn ions in Inorganic Electronic Spectroscopy,
2nd edn., Elsevier, New York, 1984, 376.
[24] B.G. Pryde, F.G. Soper, J. Chem. Soc. (1931) 1512–1514.
[25] F.F. Hardy, J.P. Johnston, J. Chem. Soc., Perkin Trans. 2 (1973) 742–745.
[26] D.S. Mahadevappa, K.S. Rangappa, N.M.M. Gowda, B.T. Gowda, Int. J. Chem.
Kinet. 14 (1982) 1183–1197.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.molcata.2010.06.006.
[27] R.V. Puttaswamy, Jagadeesh, Int. J. Chem. Kinet. 38 (2006) 48–56.
[28] R.V. Puttaswamy, Jagadeesh, Cent. Eur. J. Chem. 3 (3) (2005) 482–501.
[29] M. Ardon, J. Chem. Soc. (1957) 1811–1815.
[30] E.S. Amis, G. Jaffe, J. Chem. Phys. 10 (1942) 598–601.
[31] C.J. Collins, N.S. Bowman, Isotope Effects in Chemical Reactions, Van Nostrand
Reinhold, New York, 1970, p. 267.
References
[32] W.J. Albery, M.H. Devics, J. Chem. Soc., Faraday Trans. 68 (1972)
167–190.
[1] R.Q. Brewster, W.E. MeEwen, Organic Chemistry, 3rd ed., Prentice Hall, Engle-
wood Cliffs, NJ, 1961.
[2] K. Sturm, R. Muschaweck, M. Hropot, J. Med. Chem. 26 (1983) 1174–1187.
[3] R.T. Morrison, R.N. Boyd, Organic Chemistry, 3rd ed., Prentice Hall of India, New
Delhi, 1981, p. 761.
[4] E. Wertheim, Org. Syn. Coll. vol. 2 (1943) 471.
[5] M. Hudlicky, Oxidations in Organic Chemistry, American Chemicals Society,
Washington, DC, 1990, 838.
[6] G.A. Russel, Selective Oxidation Process, American Chemical Society, Washing-
ton, DC, 1965, 112.
[33] G. Gopalakrishnan, J.L. Hogg, J. Org. Chem. 50 (1985) 1206–1209.
[34] N.S. Isaacs, Physical Organic Chemistry, Wiley, New York, 1987, p. 275.
[35] O. Exner, Chem. Commun. (2000) 1655–1656, and references therein.
[36] E.A. Moelwyn-Hughes, Kinetics of Reaction in Solutions, Oxford University
Press, London, 1947, pp. 297–299.
[37] K.S. Rangappa, H. Ramachandra, D.S. Mahadevappa, N.M. Made Gowda, Int. J.
Chem. Kinet. 28 (1996) 265–274.
[38] K.S. Rangappa, J. Indian Chem. Soc. 81 (2004) 1025–1030.