Mechanistic investigation of the oxidation of vitamin B1 with sodium N-chlorobenzenesulfonamide in presence of ruthenium(III) catalyst in hydrochloric acid medium: A kinetic approach

Article abstract of DOI:10.1007/s00706-008-0909-1

The oxidative cleavage of vitamin B₁ (thiamine hydrochloride, THM) with sodium N-chlorobenzenesulfonamide (chloramine-B, CAB) has been kinetically investigated in HCl medium in presence of ruthenium(III) catalyst at 308 K. The oxidation reaction follows the rate law, -d[CAB]/dt = k [CAB] [Ru(III)] [H⁺] [THM]^a [Cl^-]^b, where a and b are less than unity. Variation of ionic strength of the medium and addition of the reaction product, benzenesulfonamide (BSA) had no significant effect on the reaction rate. The change in relative permittivity of the medium affected by changing the solvent composition with acetonitrile has been studied. The stoichiometry of the reaction was found to be 1:1, and N-[(4-amino-2- methylpyrimidine-5-yl)methyl]benzensulfonamide and 2-(4-methylthiazol-5-yl) ethanol were identified as the oxidation products of vitamin B₁. The reaction constants involved in the mechanism were computed. The reaction was studied at different temperatures and the overall activation parameters have been evaluated. C₆H₅SO₂NHCl has been postulated as the reactive oxidizing species. The observed results have been explained by plausible mechanisms and the relative rate laws have been deduced.

Full text of DOI:10.1007/s00706-008-0909-1

Monatsh Chem 139, 1203–1210 (2008)
DOI 10.1007/s00706-008-0909-1
Printed in The Netherlands
Mechanistic investigation of the oxidation of vitamin B1 with sodium
N-chlorobenzenesulfonamide in presence of ruthenium(III) catalyst
in hydrochloric acid medium: a kinetic approach
Kikkeri N. Mohana, Ningegowda Prasad, Kuriya M. L. Rai
Department of Studies in Chemistry, University of Mysore, Manasagangotri, Mysore, India
Received 14 November 2007; Accepted 5 February 2008; Published online 12 May 2008
# Springer-Verlag 2008
Keywords Vitamin B1; Chloramine-B; Ruthenium(III) catal-
ysis; Oxidation kinetics.
Abstract The oxidative cleavage of vitamin B1 (thi-
amine hydrochloride, THM) with sodium N-chloro-
benzenesulfonamide (chloramine-B, CAB) has been
kinetically investigated in HCl medium in presence
of ruthenium(III) catalyst at 308 K. The oxidation
reaction follows the rate law, ꢀd[CAB]=dt ¼ k [CAB]
[Ru(III)] [Hþ] [THM]a [Clꢀ]b, where a and b are less
than unity. Variation of ionic strength of the medium
and addition of the reaction product, benzenesulfon-
amide (BSA) had no significant effect on the reaction
rate. The change in relative permittivity of the medi-
um affected by changing the solvent composition with
acetonitrile has been studied. The stoichiometry of
the reaction was found to be 1:1, and N-[(4-amino-
2-methylpyrimidine-5-yl)methyl]benzensulfonamide
and 2-(4-methylthiazol-5-yl)ethanol were identified as
the oxidation products of vitamin B1. The reaction
constants involved in the mechanism were computed.
The reaction was studied at different temperatures and
the overall activation parameters have been evaluated.
C6H5SO2NHCl has been postulated as the reactive
oxidizing species. The observed results have been
explained by plausible mechanisms and the relative
rate laws have been deduced.
Introduction
Vitamin B1 (thiamine, THM) was the first member
of vitamin B complex to be isolated and identified as
vitamin. Vitamin B1 occurs in the outer coats of
the seeds of many plants including cereal grains.
Thiamine is fundamentally associated with carbohy-
drate metabolism. It is phosphorylated in the body to
the active coenzyme, thiamine pyrophosphate that
functions as co-carboxylase for various reactions in
carbohydrate metabolism including the transketolase
reaction in the direct oxidative pathway of glucose
metabolism [1]. Thiamine might also serve as a mod-
ulator of neuromuscular transmission. It binds to
isolated nicotinic cholinergic receptors, and neuro-
transmission is impaired by pyrithiamine, a thiamine
antimetabolite [2]. In thiamine deficiency, the oxida-
tion of ꢀ-keto acid is impaired, resulting in an in-
crease in the concentration of pyruvate in blood. The
requirement of thiamine is related to metabolic rate
and is greatest when carbohydrate is a source of en-
Correspondence: Kikkeri Narasimhasetty Mohana, Depart-
ment of Studies in Chemistry, University of Mysore,
Manasagangotri, Mysore 570 006, India. E-mail: knmsvp@
yahoo.com
Vitamin B1 (THM)

1204
K. N. Mohana et al.
Table 1 Effect of varying concentrations of reactants and acid
on the reaction rate at 308 K [RuCl3] ¼ 4ꢃ10ꢀ4 mol dmꢀ3
ergy [3]. The oxidation kinetics and mechanism of
vitamin B1 are thus important to the process in vitro.
The chemistry of N-halogeno compounds contain-
ing the halogen in the þ1 oxidation state has re-
ceived considerable attention. The most prominent
member of this group is chloramine-T (CAT), which
is a byproduct in the manufacture of saccharin. It is
well known as an analytical reagent for determining
diverse substrates, and the mechanistic aspects of
these reactions have been documented [4–6]. The
benzene analogue chloramine-B (C6H5SO2NClNa ꢁ
1.5 H2O, CAB) is also important and received consid-
erable attention as an oxidimetric reagent [7–9]. Con-
ductometric studies of the interaction of CAB with
some metal ion solutions [10] and photolysis of aque-
ous solution of CAB have been reported [11].
After reviewing the literature, we found that there
was no information available on the oxidation kinet-
ics of THM with any oxidant. However, oxidation
of THM with alkaline potassium ferricyanide [12],
hypoiodide [13], and chlorite [14] showed the for-
mation of an intense blue fluorescent compound,
thiochrome. In view of varied nature of N-halo-
amines and extensive biological importance of vitamin
B1, it was felt important and interesting to investigate
the oxidative behavior of CAB towards vitamin B1.
The reaction of vitamin B1 with CAB in presence of
HCl medium without a catalyst was found to be slug-
gish, but the reaction was found to be facile in the
presence of micro-amounts of ruthenium(III) catalyst.
Therefore the present paper reports the results of the
investigation on the mechanistic and kinetic aspects of
oxidation of vitamin B1 with CAB in the presence of
HCl and ruthenium(III) catalyst. The objectives of
the present investigation are to (i) elucidate the re-
action mechanism in the biological system, (ii) put
forward appropriate rate law, (iii) ascertain the reac-
tive species, and (iv) identify the oxidation products.
,
ꢁ ¼ 0.2 mol dmꢀ3
104½CABꢄ
103½THMꢄ
102½HClꢄ
104kobs
sꢀ1
mol dmꢀ3
mol dmꢀ3
mol dmꢀ3
3.0
5.0
7.0
8.0
9.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
8.0
8.0
8.0
8.0
8.0
6.0
10.0
12.0
14.0
8.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
4.0
6.0
7.0
8.0
5.0
5.0
4.11
4.09
3.97
3.99
4.13
3.61
4.39
4.72
5.18
2.71
5.95
7.45
9.44
4.10
3.98
8.0
8.0
8.0
8.0
ꢅ
5.0
5.0
ꢅꢅ
8.0
ꢅ
In presence of benzensulfonamide
At ionic strength 0.5 mol dmꢀ3
ꢅꢅ
stants, kobs obtained at 308 K are listed in Table 1.
Under similar experimental conditions, an increase
in [THM]0 increased the rate. Plot of logkobs versus
log[THM] was linear (r ¼ 0.998) with a slope of 0.45
indicating a fractional-order dependence on [THM]0.
Effect of varying [HCl] and [Ru(III)] on the rate
At constant [CAB]0, [THM]0, [RuCl3], and tempera-
ture, the reaction rate increased with increasing
Table 2 Effect of varying Hþ, Clꢀ, and RuCl3 concentrations
on the reaction rate at 308 K [CAB]0 ¼ 5ꢃ10ꢀ4 mol dmꢀ3
,
[THM] ¼ 8ꢃ10ꢀ3 mol dmꢀ3, ꢁ ¼ 0.2 mol dmꢀ3
102½Hþꢄ
102½Clꢀꢄ
104½RuCl3ꢄ
104kobs
sꢀ1
mol dmꢀ3
mol dmꢀ3
mol dmꢀ3
4.0
5.0
6.0
7.0
8.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
15.0
15.0
15.0
15.0
15.0
5.0
7.0
9.0
10.0
11.0
5.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.8
2.0
3.0
5.0
6.0
6.06
7.52
9.08
10.76
12.11
4.09
5.53
6.83
7.29
7.77
2.01
2.99
5.26
6.45
Results and discussion
Effect of varying reactant concentrations on the rate
The reaction was performed in the presence of RuCl3
catalyst and HCl under pseudo-first-order conditions
([PYX]0 ꢂ [CAB]0). Plots of log[CAB] versus time
were linear (r>0.991). The linearity of these plots,
together with the constancy of slope for various
[CAB]0, indicates a first-order dependence of the re-
action rate on [CAB]. The pseudo-first-order rate con-
5.0
5.0
5.0

Mechanistic investigation of the oxidation of vitamin B1
1205
of Clꢀ in the form of NaCl keeping [Hþ] constant
(0.05moldmꢀ3) increases the reaction rate (Table 2).
From a plot of logkobs versus log[Clꢀ] (Fig. 2; r ¼
0.996), the order with respect to [Clꢀ] is found to be
0.82.
Effect of added benzenesulfonamide on the rate
The addition of reduced product, benzenesulfona-
mide had no effect on the rate, indicating that it is
not involved in the pre-equilibrium step prior to the
rate-determining step.
Effect of varying ionic strength and relative
permittivity of the medium
Fig. 1 Plot of 4 þ log(kobs=sꢀ1) versus 5 þ log{[Ru(III)]=
mol dmꢀ3} at [CAB] ¼ 5ꢃ10ꢀ4, [THM] ¼ 8ꢃ10ꢀ3, [HCl] ¼
0.05, and [Ru(III)] ¼ 4ꢃ10ꢀ4 mol dmꢀ3
The reaction rate remained unaffected by varying ion-
ic strength of the medium through addition of sodium
perchlorate (0.2–0.5 mol dmꢀ3). The dielectric per-
mittivity of the medium was varied by adding dif-
ferent proportions of CH3CN (0–20%, v=v), but no
significant change in the rate was observed when in-
creasing the CH3CN content in the reaction mixture.
The values of relative permittivity were computed
from the values of the pure liquids [15].
Effect of temperature on the rate
The reaction was studied at different temperatures
(303–321 K) (Table 3), keeping other experimental
conditions constant. From the Arrhenius plot of
log kobs versus 1=T (r ¼ 0.998), activation energy
and other thermodynamic parameters were found to
Fig. 2 Plot of 4 þ log(kobs=sꢀ1
10ꢀ4, [THM] ¼ 8ꢃ10ꢀ3 and [Ru(III)] ¼ 4ꢃ10ꢀ4mol dmꢀ3
)
versus 2 þ log{[Hþ]=
¼
be Ea ¼ 95.69 kJ ꢁ molꢀ1, Á H0 ¼ 93.11 kJ ꢁ molꢀ1,
mol dmꢀ3} and 2 þ log{[Clꢀ]=mol dmꢀ3} at [CAB] ¼ 5ꢃ
¼ 0
and Á S ¼ ꢀ7.88 J ꢁ Kꢀ1 ꢁ molꢀ1.
[HCl] (Table 1). A plot of log kobs versus log[HCl]
was linear (r ¼ 0.997) with a slope of 1.83. The rate
increased with increasing [RuCl3] (Table 2). Plot of
log kobs versus log[Ru(III)] (Fig. 1; r ¼ 0.999) was
linear with a slope equal to 1.02, confirming first-
order dependence on [Ru(III)].
Table 3 Effect of temperature and solvent composition on
the reaction rate ½CABꢄ0 ¼ 5ꢃ10ꢀ4 mol dmꢀ3, ½THMꢄ0 ¼
8ꢃ10ꢀ3 molꢀd3mꢀ3, ½HClꢄ ¼ 0:05 mol dmꢀ3, ½RuCl3ꢄ ¼ 4ꢃ
10ꢀ4 mol dm , ꢁ ¼ 0.2 mol dmꢀ3
Temperature=K
CH3CN=%, (v=v)
104kobs=sꢀ1
303
308
313
318
321
308
308
308
308
–
–
–
–
–
2.16
4.09
7.30
13.01
18.28
4.01
3.98
4.12
3.96
Effect of varying [Hþ] and [Clꢀ] on the rate
At constant [Clꢀ] ¼ 0.15mol dmꢀ3 maintained with
NaCl, increase in the concentration of Hþ using HCl
increased the rate (Table 2). A plot of logkobs versus
log[Hþ] was linear (Fig. 2; r ¼ 0.997) with unit slope
indicating first-order dependence on [Hþ]. Addition
5
10
15
20

1206
K. N. Mohana et al.
Test for free radicals
and [RuCl(H2O)5]2þ do not exist in aqueous solu-
tions of RuCl3, however, other studies [24–26] have
shown that the following ligand substitution equilib-
rium exists in acidic solutions.
The addition of the reaction mixture to aqueous ac-
rylamide monomer solution did not initiate polymer-
ization indicating the absence of in situ formation of
free radical species in the reaction sequence.
3ꢀ
RuCl3 ꢁ xH2O þ 3HCl ꢀ! ½RuCl6ꢄ þ xH2O þ 3Hþ
3ꢀ
2ꢀ
ꢀ*
)ꢀ
½RuCl6ꢄ þ H2O
½RuCl5ðH2OÞꢄ þ Clꢀ
ð6Þ
Postulated mechanism
Singh et al. [27, 28] have employed the above equi-
librium in the ruthenium(III)-catalyzed oxidation of
primary alcohols with bromamine-T and ethylene gly-
cols with N-bromocetamide in HClO4 medium. In the
present studies, increasing effect of added chloride
ion on the rate suggests that [RuCl6]3ꢀ is the more
likely catalyzing species [23, 26] which interacts with
the oxidants to form a complex intermediate.
Further, UV-spectral measurements showed that a
sharp absorption band was noticed at 220 nm for
RuCl3, 224 nm for CAB solution, and 216 nm for
THM in presence of 0.5 mol dmꢀ3 HCl. A mixture
of CAB and RuCl3 solution in the presence of HCl
showed an absorption band at 268 nm, while for a
mixture of THM and RuCl3 solution an absorption
band was noticed at 214 nm. The spectral evidence
showed that complex formation takes place only be-
tween RuCl3 and oxidant. Based on the preceding
discussion, a detailed mechanistic interpretation
(Scheme 1) for the Ru(III)-catalyzed THM-CAB re-
action in acid medium has been proposed to substan-
tiate the observed kinetics.
Bishop and Jennings [16], Morris et al. [17], and
Higuchi and co-workers [18] have shown the
existence of similar equilibria in acid and alkaline
solutions of metal salts of N-haloarenesulfonamides.
Chloramine-B, an analogue to chloramine-T, behaves
as a strong electrolyte in aqueous solutions and fur-
nishes different types of reactive species in acidic
solutions. To confirm this hypothesis, conductometric
and pH titrations between aqueous solutions of CAB
and HCl were performed. The conductometric behav-
ior of CAB is identical with that of CAT [19, 20],
while the pH titration curves observed are similar to
those noted by Morris et al. [17]. The possible equi-
libria in acidified CAB solutions are,
RNClNa
RNClꢀ þ Naþ
ð1Þ
ð2Þ
ð3Þ
ð4Þ
ð5Þ
ꢀ*
)ꢀ
RNClꢀ þ H
RNHCl
þ ꢀ*
)ꢀ
ꢀ*
RNHCl þ H2O
RNH2 þ HOCl
)ꢀ
ꢀ*
2RNHCl
RNH2 þ RNCl2
)ꢀ
þ
þ ꢀ*
HOCl þ H
H2O Cl
)ꢀ
From Scheme 1,
where R is C6H5SO2.
rate ¼ k3½Xꢄ½Subꢄ
Applying steady state conditions to X, then
ð7Þ
ð8Þ
Therefore the possible oxidizing species in acid
solution of CAB are the free acid (RNHCl), RNCl2,
HOCl, and H2OClþ. The involvement of RNCl2
in the mechanism leads to a second-order rate law
and negative effect of RNH2 according to Eq. (4),
which is contrary to the experimental observations.
If HOCl were the primary oxidizing species, a
first-order retardation of the rate by the added
RNH2 would be expected. However, no such effect
is noticed. Hardy and Johnston [21] have deter-
mined the pH dependent relative concentrations
of the species present in acidified bromamine-B
solutions of comparable molarities indicating that
C6H4SO2NHBr is the likely oxidizing species in ac-
id medium.
k2½RNHClꢄ½RuðIIIÞꢄ ꢀ k ½Xꢄ ꢀ k3½Xꢄ½Subꢄ ¼ 0
ꢀ2
From step (i) of Scheme 1,
½RNHClꢄ
K1 ¼
½RNClꢀꢄ½Hþꢄ
Electronic spectral studies by Cady and Connick
[22] and Connick and Fine [23] have shown that
the octahedral complexes such as [RuCl5(H2O)]2ꢀ,
[RuCl4(H2O)2]ꢀ, [RuCl3(H2O)3], [RuCl2(H2O)4]þ,
Scheme 1

Mechanistic investigation of the oxidation of vitamin B1
substituting in Eq. (8), it can be shown that
1207
K1k2½RNClꢀ½Hþꢄ½RuðIIIÞꢄ
½Xꢄ ¼
ð9Þ
k
ꢀ2 þ k3½Subꢄ
Since the iodometric titre corresponds to both
CAB and RNClꢀ, and CAB is consumed in the for-
mation of RNClꢀ, it is reasonable to assume that
[RNClꢀ] ¼ [CAB], on substituting Eq. (9) in Eq. (7),
the following rate law (Eq. (10)) is obtained.
K1k2k3½CABꢄ½Hþꢄ½RuðIIIÞꢄ½Subꢄ
Scheme 2
rate ¼
ð10Þ
k
ꢀ2 þ k3½Subꢄ
The rate law (Eq. (10)) is in complete agree-
ment with the experimental results. Since rate ¼
kobs½CABꢄ, Eq. (10) can be transformed into Eqs. (11)
and (12).
Applying steady state approximation for X, it can be
shown that
K1k6½RNClꢀꢄ½Hþ½C2ꢄ
½Xꢄ ¼
ð14Þ
K1k2k3½Hþꢄ½RuðIIIÞꢄ½Subꢄ
k
ꢀ6 þ k7½Subꢄ
kobs
¼
¼
ð11Þ
k
ꢀ2 þ k3½Subꢄ
If [Ru(III)]t represents the total concentration of
Ru(III), then
1
k
ꢀ2
kobs K1k2k3½Subꢄ½Hþꢄ½RuðIIIÞꢄ
½RuðIIIÞꢄt ¼ ½C1ꢄ þ ½C2ꢄ
By substituting for [C1] from equilibrium step (i) of
ð15Þ
1
þ
ð12Þ
K1k2½Hþꢄ½RuðIIIÞꢄ
Scheme 2 in Eq. (15), one obtains
Based on Eq. (12), a plot of 1=kobs versus 1=[Sub]
at standard concentrations of [Hþ] and [Ru(III)], was
found to be linear (Fig. 3; r ¼ 0.985) and the value of
K1k2 was calculated from the intercept of the plot
(K1k2 ¼ 36.1).
½C2ꢄ½H2Oꢄ
½RuðIIIÞꢄt ¼
þ ½C2ꢄ
K5½Clꢀꢄ
or
K5½RuðIIIÞꢄ ½Clꢀꢄ
t
½C2ꢄ ¼
ð16Þ
In the presence of chloride ion at constant [Hþ],
Scheme 2 is proposed for the reaction mechanism.
From slow step of Scheme 2,
½H2Oꢄ þ K5½Clꢀꢄ
By substituting Eq. (16) in Eq. (14), Eq. (17) is
obtained.
rate ¼ k7½Xꢄ½Subꢄ
ð13Þ
K1K5k6½RNClꢀꢄ½Hþꢄ½RuðIIIÞꢄ ½Clꢀꢄ
t
½Xꢄ ¼
ð17Þ
fkꢀ6 þ k7½Subꢄgf½H2Oꢄ þ K5½Clꢀꢄg
By substituting Eq. (17) in Eq. (13), the following
rate law is obtained.
K1K5k6k7½CABꢄ½Hþꢄ½RuðIIIÞꢄ ½Clꢀꢄ½Subꢄ
fkꢀ6 þ k7½Subꢄgf½H2Oꢄ þtK5½Clꢀꢄg
rate ¼
ð18Þ
The rate expression (Eq. (18)) clearly demon-
strates the fractional-order dependence of rate on
[Clꢀ] and [Sub], and is in good agreement with the
experimental results.
In Schemes 1 and 2, Sub represents the substrate,
X and X0 represent the complex intermediate species
whose structures are shown in Scheme 3, where a
detailed mechanism of Ru(III)-catalyzed oxidation
of THM with CAB in HCl medium is illustrated.
An initial equilibrium involves protonation of
RNClꢀ forming an active oxidizing species of CAB
Fig. 3 Plot of sꢀ1=kobs versus mol dmꢀ3=[THM] at standard
concentrations of Hþ and RuCl3

1208
K. N. Mohana et al.
Scheme 3
(RNHCl). In the next step, the oxygen atom of the
oxidant is coordinated to the metal center of the
active catalyst species, [RuCl6]3ꢀ to form a loosely
bound metal complex, X (step (i) in Scheme 3)
trapped in a solvent cage. This is similar to an asso-
ciative interchange mechanism involving a fast pre-
equilibrium in a ligand substitution reaction of metal
complexes. Then follows nucleophilic attack of the
sulfonamide nitrogen on the methylene group of
thiamine to form intermediate X0, Y and releasing
[RuCl6]3ꢀ (step (ii) of Scheme 3). Then reorganiza-
tion of the intermediate (X0) to form products with
the release of chlorine.
Laidler [29] and Amis [30] have described the
effect of solvent composition on the reaction kinet-
ics. For limiting case of zero angle of approach be-
tween two dipoles or an ion-dipole system, Amis
[30] has shown that a plot of log kobs versus 1=D

Mechanistic investigation of the oxidation of vitamin B1
1209
Kinetic measurements
gives a straight line with a positive slope for a reac-
tion involving a positive ion and a dipole and a neg-
ative slope for a negative ion-dipole or dipole–dipole
interactions. In the present investigations, variation
of dielectric permittivity of the medium does not
affect the rate supports the proposed mechanisms.
The reduction product of the oxidant, benzenesulfo-
namide did not influence the rate showing that it is
not involved in any pre-equilibrium. The proposed
mechanism is also supported by the values of energy
of activation and other activation parameters. The
fairly high positive values of Gibb’s free energy of
activation and enthalpy of activation indicate that the
transition state is highly solvated, while the high
negative value of entropy of activation accounts for
the formation of a compact transition state in which
several degrees of freedom are lost.
Mixtures containing requisite amounts of the THM, RuCl3,
HCl, and NaClO4 were taken in stoppered Pyrex glass tubes
whose outer surfaces were coated black. Required amount
of water was added to maintain a constant total volume. The
tube was thermostated in a water bath set at a given tem-
perature (308 ꢆ 0.1 K). To this solution, a measured amount
of pre-equilibrated CAB solution was added to give a known
concentration. The progress of the reaction was monitored
iodometrically for two half-lives by withdrawing aliquots of
the reaction mixture at regular time intervals. Under pseu-
do-first-order conditions, rate constants k0obs were reproduc-
ible within ꢆ3%. Regression analysis of the experimental
data to obtain regression coefficient, r, was performed using
MS Excel.
Stoichiometry and product analysis
Reaction mixtures containing various ratios of THM and CAB
were equilibrated in the presence of 0.05mol dmꢀ3 HCl
and 5ꢃ10ꢀ4 mol dmꢀ3 RuCl3 catalysts at 308 K for 48h.
Iodometric estimation of unconsumed CAB in the mixture
revealed that one mole of CAB was consumed per mole of
THM. Accordingly, the following stoichiometric equation can
be formulated,
Conclusions
Oxidative cleavage of vitamin B1 with chloramine-
B in hydrochloric acid medium using a RuCl3
catalyst has been studied. The stoichiometry of
the reaction was found to be 1:1 and the oxidation
products of THM were identified by spectral stud-
ies. Oxidation of THM with CAB in acid medium
will become facile in presence of micro-quantities
of ruthenium(III) catalyst. C6H5SO2NHCl was found
to be the reactive oxidizing species. Activation pa-
rameters were computed from the Arrhenius plot.
The observed results have been explained by plausi-
ble mechanisms and the related rate laws have been
deduced.
C12H17N4ClOS þ RNClNa þ HCl
ꢀ! C12H14N4SO2 þ C6H9NSO þ NaCl þ Cl2 ð19Þ
where R ¼ C6H5SO2.
The products in the reaction mixture were extracted several
times with diethyl ether. The combined ether extract was
evaporated and subjected to the column chromatography on
silica gel (60–200 mesh) using gradient elusion (chloroform).
After initial separation, the products were further purified
by recrystallization. The oxidation products of THM were
detected by conventional spot tests [32], and identified as
N-[(4-amino-2-methylpyrimidine-5-yl)methyl] benzensulfon-
amide (X00) and 2-(4-methylthiazol-5-yl)-ethanol (Y) by 1H
NMR spectral studies. X00 (D2O): ꢂ ¼ 2.3 (s, 3H, CH3), 7.7 (s,
H, Ar–H), 7.5–8.0 (bm, 5H, Ar–H), 3.8 (s, 2H, NH2) ppm; Y
(CDCl3): ꢂ ¼ 2.5 (s, 3H, CH3), 3.9 (t, 2H, CH2), 2.8 (t, 2H,
1
CH2), 8.5 (s, H, Ar–H). H NMR spectra were recorded on a
Experimental
BRUKER 400MHz spectrometer using D2O=CDCl3 as sol-
vent and TMS as internal reference.
Materials
Chloramine-B was prepared and purified by the method de-
scribed earlier [31]. An aqueous solution of the compound was
standardized iodometrically and preserved in brown bottles to
prevent its photochemical deterioration. Vitamin B1 (Himedia)
was used as received. An aqueous solution of the compound
was prepared freshly each time. A solution of RuCl3 (Arora
Mathey) in a solution of hydrochloric acid was used as cata-
lyst. The final concentrations of HCl and RuCl3 were
1.0ꢃ10ꢀ2 and 8.86ꢃ10ꢀ3 mol dmꢀ3. Allowance was made
for the amount of HCl present in catalyst solution while pre-
paring for kinetic runs. All other chemicals used were of
accepted grades of purity. Ionic strength of the reaction mix-
ture was kept constant with a concentrated solution of NaClO4
(Merck). Doubly distilled water was used for the preparation
of aqueous solutions.
Acknowledgements
The authors are thankful to University of Mysore, Mysore, for
financial support.
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