Kinetics of micellar effect of non-ionic surfactant on oxidative degradation of ciprofloxacin

Article abstract of DOI:10.14233/ajchem.2020.22343

Oxidative degradation kinetics of leading fluoroquinolone family drug ciprofloxacin (CIP) by chloramine-T (CAT) in TX-100 micelle media was studied spectrophotometrically at 275 nm and 298 K. In pseudo-first-order conditions the rate constant (kobs) decreased regularly with increasing [TX-100]. To understand the self-organizing activities of TX-100, CMC values in varying reaction conditions had been evaluated. The role of non-ionic surfactant in the oxidative degradation process of ciprofloxacin by chlorinating agent chloramine-T is explained in terms of mathematical model explained by Menger-Portnoy. The reaction showed first to zero order dependence on [CAT] and fractional order on [CIP]. Increasing [H⁺] decreased the rate of reaction. The effect of ionic strength and solvent polarity of the medium in reaction conditions were studied. The effects of added salts [HSO4Na], [KCl], [KNO3] and [K2SO4] had also been studied. The stoichiometry of the reaction determined was 1:2 and the oxidation products were identified by LC-EI-MS. The analysis of degradation product of ciprofloxacin evidently reveals that the piperazine moiety is active site for oxidation in the reaction. Activation parameters were studied to propose appropriate mechanism for the reaction.

Full text of DOI:10.14233/ajchem.2020.22343

Asian Journal of Chemistry; Vol. 32, No. 2 (2020), 359-368
A
SIAN
J
OURNAL OF HEMISTRY
C
https://doi.org/10.14233/ajchem.2020.22343
Kinetics of Micellar Effect of Non-Ionic Surfactant on Oxidative Degradation of Ciprofloxacin
1
2,*
3
4
1
AJAYA KUMAR SINGH , ALPA SHRIVASTAVA , DILIP R. SHRIVASTAVA , RAJMANI PATEL and NEERJA SACHDEV
1Department of Chemistry, Government Vishwanath Yadav Tamaskar Postgraduate Autonomous College, Durg-491001, India
2Department of Chemistry, Indira Gandhi Government Arts, Commerce and Science College, Vaishali Nagar, Bhilai, Durg-490020, India
3Department of Chemistry, Dr. Khoobchand Baghel Government Arts and Science Postgraduate Autonomous College, Bhilai-490020, India
4Department of Chemistry, Hemchand Yadav University, Durg-491001, India
*Corresponding author: E-mail: alpashubhe@yahoo.com
Received: 19 July 2019;
Accepted: 7 October 2019;
Published online: 30 December 2019;
AJC-19727
Oxidative degradation kinetics of leading fluoroquinolone family drug ciprofloxacin (CIP) by chloramine-T (CAT) in TX-100 micelle
media was studied spectrophotometrically at 275 nm and 298 K. In pseudo-first-order conditions the rate constant (kobs) decreased
regularly with increasing [TX-100]. To understand the self-organizing activities of TX-100, CMC values in varying reaction conditions
had been evaluated. The role of non-ionic surfactant in the oxidative degradation process of ciprofloxacin by chlorinating agent chloramine-
T is explained in terms of mathematical model explained by Menger-Portnoy. The reaction showed first to zero order dependence on
[CAT] and fractional order on [CIP]. Increasing [H+] decreased the rate of reaction. The effect of ionic strength and solvent polarity of the
medium in reaction conditions were studied. The effects of added salts [HSO4Na], [KCl], [KNO3] and [K2SO4] had also been studied. The
stoichiometry of the reaction determined was 1:2 and the oxidation products were identified by LC-EI-MS. The analysis of degradation
product of ciprofloxacin evidently reveals that the piperazine moiety is active site for oxidation in the reaction.Activation parameters were
studied to propose appropriate mechanism for the reaction.
Keywords: Ciprofloxacin, Chloramine-T, Triton X-100, Oxidative degradation, Micelle.
(Triton X-100) has been found to show typical detergent
properties thus may solubilize the lipid bilayer membrane by
integration into the cell membrane. In micelle environment
polyoxyethylene chains of TX-100 stay outside the core and
move freely in solvent and stabilize interface [8]. In this way
it may show toxic effects to some aquatic species [11]. TX-100
has a hydrophilic polyethylene oxide group (on average it has
9.5 ethylene oxide units) and a hydrocarbon lipophilic or
hydrophobic group. The hydrocarbon group is a 4-(1,1,3,3-
tetramethylbutyl)-phenyl group. It is related to the pluronic
range of detergents. The pluronics are triblock copolymers of
ethylene oxide and propylene oxide. The part formed from
ethylene oxide is more hydrophilic than the part from propylene
oxide. Triton X-100 is very viscous at room temperature and
is thus easiest to use after being gently warmed [12].
INTRODUCTION
Surfactants have significant physical adsorption properties
that may involve entropic effect, charge-charge interactions,
associations of hydrophobic groups, solvency and hydrogen
bonding effects. Therefore surfactants have been used as solu-
bilizers [1] and surface modifiers frequently during past 2-3
decades. Based on their applications in various fields non-ionics
are the second largest class after the anionic surfactants [2].
Non-ionic surfactants exhibit strong affinity for hydroxylated
surfaces and their adsorption on solid surfaces is affected by
hydrophobic interactions.Apart from their compatibility with
other surfactants these also show peculiar temperature behaviour.
In comparison to respective ionic counterparts, non-ionic
surfactants have much less sensitivity to pH and ionic strength
of medium [3-6]. Widespread use of non-ionic surfactants [7-
10] has drawn environmental concern for assessment of their
bio-degradability and toxicity. In aquatic environment TX-100
Present study reports the kinetic investigation of effect of
TX-100 on degradation of ciprofloxacin by chloramine-T in
aqueous medium. We have reported the effects of cationic
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360 Singh et al.
Asian J. Chem.
(CTAB) and anionic (SDS) surfactants on the oxidative degra-
dation of two frequently used fluoroquinolone family drugs
(ciprofloxacin and norfloxacin) by common chlorinating agent
chloramine-T [13-15]. Present investigation reveals the effect
of non-ionic surfactant TX-100 on oxidation of ciprofloxacin.
Studies have been reported showing varying quantities
of ciprofloxacin in aquatic environment as well as in effluents
of WWTPs (wastewater treatment plants) [16,17]. Chlorine
based disinfectants are most frequent disinfection agents used
during wastewater treatment processes [18,19], chloramine-T
is one among such disinfectant. Present study aims to find the
kinetics and mechanism of oxidation reaction of ciprofloxacin
by chloramine-T in the presence of TX-100.
triple distilled water. The stock solution of chloramine-T (LOBA
Chemie) was stored in dark coloured bottle and its strength
was checked iodometrically [20]. Ciprofloxacin (SigmaAldrich)
stock solution was prepared by dissolving known amount of
its hydrochloric salt and was stored in amber coloured bottle
to prevent any photochemical degradation.
Determination of CMC:To determine the self-organizing
activities of TX-100, CMC values have been determined. In
the presence of reactants at required temperature the CMC of
TX-100 was measured conductometrically (Systronics conduc-
tometer 304 at 298.0 0.2 K). The calibration of conductometer
was done with 0.01 M KCl solution. The breakpoint of nearly
straight line in the plots of equivalent conductivity vs. [TX-100]
gave the CMC values which are indicative of micelle formation
(Fig. 1, Table-1).
EXPERIMENTAL
Kinetic measurements:All reactant solutions were placed
in the thermostatic water bath for 30 min in order to attain a
temperature of 298 0.2 K. The kinetics of the reaction was
studied taking the requisite amounts of ciprofloxacin, TX-100,
Solutions were prepared using analytical grade reagents
without further purification. 1/100 stock solution of TX-100
(Merck) was prepared by dissolving its requisite quantity in
0.7
0.6
0.5
0.4
0.3
0.50
0.45
0.40
0.35
0.30
0.25
TX-100 + CAT
0.2
TX-100 + H2O
0.20
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
[TX-100] × 10–3 mol dm–3
0.0
0.1
0.2
0.3
0.4
0.5
0.6
[TX-100] × 10–3 mol dm–3
0.40
0.35
0.30
0.25
0.20
0.34
0.32
0.30
0.28
0.26
0.24
0.22
0.20
0.18
TX-100 + CIP
TX-100 + HClO4
0.00
0.17
0.34
0.51
0.68
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45
[TX-100] × 10–3 mol dm–3
[TX-100] × 10–3 mol dm–3
Fig. 1. Plots of equivalent conductivity vs. [surfactant] with different reactants

Vol. 32, No. 2 (2020)
Kinetics of Micellar Effect of Non-Ionic Surfactant on Oxidative Degradation of Ciprofloxacin 361
while keeping all other concentrations and conditions constant,
TABLE-1
CMC VALUES OF TX-100 IN DIFFERENT
EXPERIMENTAL CONDITIONS
gave the reaction order with respect to the particular reagent.
The experiments were carried out in duplicate where the rate
constants were found to be reproducible and well within 4 %
error.
Solution
Water + TX-100
Water + TX-100 + Chloramine-T
Water + TX-100 + Ciprofloxacin
Water + TX-100 + H2SO4
CMC (× 10-3) (mol dm-3)
0.4 (0.3-0.9)a
0.30
The reaction was monitored with respect to ciprofloxacin
at 275 nm wavelength. Disappearance of ciprofloxacin can be
seen in the time scan of the reaction mixture. The spectral
changes occurring during the typical kinetic runs at each
minute for the oxidation of ciprofloxacin by chloramine-T in
TX-100 micelle media were recorded in the region of 220 to
360 nm. There is a continuous decrease of absorbance at 275
nm which clearly indicates disappearance of ciprofloxacin with
the progress of the reaction.
0.18
0.10
T = 298 K; [CIP] = 3 × 10-5 mol dm-3; [CAT] = 3 × 10-4 mol dm-3;
[HClO4] = 2 × 10-4 mol dm-3
aLiterature value given in parentheses [[RReeff.. 2211]]
HClO4 and chloramine-T in a black coated reaction vessel that
was kept in the thermostatic water bath at 298 0.2 K. Reaction
initiation time was taken when half of the required volume of
thermally equilibrated chloramine-T was added to the reaction
system. The kinetics of the reaction was followed spectrophoto-
metrically at 275 nm by measuring the absorbance (A), at
constant intervals of time, on a UV-visible spectrophotometer
Varian Cary 50 Bio, using 10 mm quartz cuvette and under
pseudo 1st order condition where [CIP] << [CAT]. The slope
of the plot of logA versus time (min) gave the pseudo 1st order
rate constants (kobs) (Fig. 2). Kinetic plots were linear for more
than four half-lives whereA is taken up to 75 % completion of
the reaction. The slope of log kobs versus log (concentration),
In all the kinetic measurements, the chloramine-T was
used in excess (≥ 10-fold) relative to the ciprofloxacin, to
ensure pseudo-first order condition. The observed rate cons-
tants were evaluated from the linear plots of log (absorbance)
against time record upto 5 min only (which was giving fairly
straight line) but the reaction was monitored upto ≈ 75 %
completion of the reaction.
Stoichiometry and product analysis: The stoichiometric
analysis of different sets of reaction mixtures containing chlor-
amine-T, sulphuric acid and surfactant with excess quantity
1.25
1.25
[CAT] = 2 × 10–4 mol dm–3
1.20
1.20
[CAT] = 1 × 10–4 mol dm–3
y = -0.041x + 1.077
y = -0.045x + 1.081
1.15
1.15
1.10
1.05
1.00
0.95
1.10
1.05
1.00
0.95
-1.0 -0.5 0.0
0.5
1.0
1.5
2.0
2.5
3.0
-1.0 -0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Time (min)
Time (min)
1.20
1.20
1.15
1.10
1.05
1.00
0.95
[CAT] = 3 × 10–4 mol dm–3
y = -0.039x + 1.073
[CAT] = 4 × 10–4 mol dm–3
y = -0.036x + 1.069
1.15
1.10
1.05
1.00
0.0
0.5
1.0
1.5
2.0
-1.0 -0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Time (min)
Time (min)
Fig. 2. Plots of log absorbance vs. time

362 Singh et al.
Asian J. Chem.
330.0075
of ciprofloxacin were kept at 298 K. Determination of uncon-
sumed ciprofloxacin in each set gave the idea that one mole of
ciprofloxacin was consumed for the oxidation of two mole of
chloramine-T (Table-2). For the identification of oxidation
products of ciprofloxacin, excess of chloramine-T over cipro-
floxacin was allowed to react in the presence of sulphuric acid.
The reduced product of oxidant chloramine-T i.e., p-toluene
sulphonamide (PTS) was initially characterized by TLC [22].
Finally the main oxidation product of ciprofloxacin that corres-
ponds to full dealkylation of the piperazine ring (i.e., the -NH2
product) and other products were isolated and confirmed by
GC-MS analysis (Fig. 3) in which the reaction mixture was
extracted with diethyl ether. The ether layer was concentrated
by slow evaporation before analyzing with GC-MS, JEOL-
JMS (Mate-MS system, Japan).Analysis of ciprofloxacin reac-
tion indicated the presence of main products with molecular
ions of m/z 364 (yield 5 %), 351 (yield 10 %), 295 (yield 15
%), 263 (yield 55 %) and 193 (yield 40 %), respectively. The
molecular ion of ciprofloxacin is m/z 330. The m/z 351 corres-
ponds to N-oxide product. The m/z 364 corresponds to M+ 35
products with respect to ciprofloxacin. The full dealkylation
of the piperazine ring produced the m/z 263 (i.e., the -NH2
product) with highest intensity. This product was also identified
previously as oxidation product [23] and photo degradation
product of ciprofloxacin [24]. The m/z 295 may correspond to
the chlorinated product of fully dealkylation product (i.e., m/z
263). The oxidation product of ciprofloxacin was also charac-
terized by FT-IR spectral studies. IR (KBr, ν, cm-1): 1560m (-
NH2), 1621s (C=O), 3059s (NH), 3500s (OH).
100
m/z
0
140 160 180 200 220 240 260 280 300 320 340 360
Fig. 3. LC-ESI-MS-MS spectra of oxidation products of ciprofloxacin
On the basis of stoichiometric and product analysis formu-
lated stoichiometric equation is given in Scheme-I.
RESULTS AND DISCUSSION
To obtain the rate constants as functions of [CAT], [CIP]
and [HClO4], pseudo-first-order conditions were maintained
in each kinetic run. First to zero-order-rate is observed with
respect to [CAT], whereas fractional-order-rates are determined
in both [CIP] and [HClO4]. The additives have been found to
put composite effects (catalytic and inhibition).Arrhenius and
Eyring equations are found valid for the reaction over a range
of temperatures and different activation parameters have been
evaluated.A probable reaction mechanism, in agreement with
the observed kinetic results, has been proposed and discussed.
Influence of changes in the surfactant concentrations on the
observed rate constant is also investigated and the reaction
followed the same type of kinetic behaviour in micellar media.
Pseudo-first-order rate constant (kobs) is found to show a regular
decrease with increasing [TX-100]. Role of non-ionic surfac-
tant TX-100 is explained in terms of the mathematical mode.
Effect of variation of chloramine-T: To find out the order
of the reaction with respect to [CAT], the rate constant was
TABLE-2
STOICHIOMETRIC RESULTS OF OXIDATION OF
CIPROFLOXACIN BY CHLORAMINE-T AT 298 K
[CAT] × 103 (mol dm-3)
Ciprofloxacin ×
102 (mol dm-3)
No. of
equivalence
Initial
20.00
40.00
60.00
Final
16.00
31.87
47.79
Consumed
4.06
8.16
12.30
2.00
4.00
6.00
1:2.03
1:2.04
1:2.05
O
O
CH3
F
Piperazine moiety
OH
2
4H2O
+
+
N
N
Pyridone moiety
HN
SO2Na·NCl
N-Chloro-4-methylbenzenesulfonamide,
sodium salt (CAT)
1-Cyclopropyl-6-fluoro-4-oxo-7-piperazin-1-yl
quinoline-3carboxylic acid (CIP)
O
O
CH3
F
OH
2
2NaCl
2CH3COOH
NH3
+
+
+
+
H2N
N
Pyridone moiety
SO2·NH2
-Toluenesulphonamide (PTS)
p
(Oxidation product of CIP)
Scheme-I

Vol. 32, No. 2 (2020)
Kinetics of Micellar Effect of Non-Ionic Surfactant on Oxidative Degradation of Ciprofloxacin 363
determined at different initial concentrations of chloramine-T
ranging from 2.0 to 8.0 × 10-4 mol dm-3. The concentrations of
ciprofloxacin (3.0 × 10-3 mol dm-3), HClO4 (2.0 × 10-4 mol dm-3)
and temperature (298 K) were kept constant. Pseudo-first-order
rate constant (kobs), obtained at different [CAT] are shown in
Table-3. The result shows that the rate constant decreases with
increasing [CAT]. The decrease in rate constant may be due to
the retardation influence of the reduced product PTS. The rate
of reaction was found to show first to zero order dependence
(Fig. 4) to [CAT].
kinetic experiments at different concentrations of ciprofloxacin
keeping the [CAT] = 3.0 × 10-4 mol dm-3, [HClO4] = 2.0 × 10-4
mol dm-3 and temperature = 298 K constant. The kobs values
are summarized in Table-4 (Fig. 5). The rate constant increased
with [CAT]. The plot of rate constant versus [CIP] is nonlinear
passing through the origin. The linear plot between log kobs
versus log [CIP] yield slope equal to 0.13, indicating fractional-
order in [CIP]. The first order dependence of reaction on
ciprofloxacin is further supported by the parallel plots of log
absorbance versus time for the varying concentrations of
ciprofloxacin (Fig. 6).
11
10
9
2.3
3.36
y = 0.130x + 2.629
2.2
3.34
2.1
3.32
8
2.0
3.30
7
1.9
3.28
6
1.8
3.26
5
1.7
3.24
4
0.5 1.0 1.5 2.0 2.5 3.0 3.5
[CIP] × 105 mol dm–3
4.6 4.8 5.0 5.2 5.4 5.6
5 + log [CIP]
2
3
4
5
6
7
8
[CAT] × 104 mol dm–3
Fig. 5. Effect of ciprofloxacin on the observed rate constant
Fig. 4. Effect of oxidant chloramine-T on observed rate constant and rate
of the reaction
Effect of variation of acid: To study the effect of variation
of [HClO4] on the rate constant, the reaction was monitored in
varying concentrations of HClO4 (1 × 10-4 to 10 × 10-4 mol
Effect of variation of ciprofloxacin: The dependence of
the rate constant on [CIP] was determined by carrying out the
TABLE-3
EFFECT OF OXIDANT ON RATE CONSTANT FOR THE TX-100 MEDIATED OXIDATION OF CIPROFLOXACIN BY CHLORAMINE-T
Absorbance at 275 nm wavelength with respect to variation of [CAT] (× 104 mol dm-3)
Time (min)
2.0
2.5
3.0
4.0
5.0
6.0
8.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
1.056
0.992
0.932
0.867
0.812
0.765
0.711
0.660
0.617
0.576
0.538
0.519
0.482
0.458
0.431
0.418
0.402
0.389
0.365
0.342
0.324
0.312
2.26
1.043
0.987
0.926
0.862
0.807
0.755
0.708
0.662
0.611
0.576
0.534
0.51
0.472
0.448
0.425
0.411
0.396
0.381
0.357
0.338
0.316
0.302
2.25
1.037
0.971
0.911
0.858
0.807
0.752
0.702
0.657
0.616
0.572
0.536
0.503
0.465
0.441
0.419
0.405
0.391
0.374
0.357
0.332
0.312
0.296
2.20
1.039
0.968
0.911
0.858
0.807
0.767
0.723
0.682
0.643
0.611
0.573
0.492
0.459
0.435
0.415
0.400
0.387
0.368
0.351
0.326
0.305
0.286
1.93
1.053
0.995
0.935
0.889
0.846
0.809
0.769
0.732
0.697
0.665
0.632
0.492
0.463
0.441
0.428
0.412
0.392
0.375
0.358
0.332
0.318
0.297
1.68
1.068
1.015
0.961
0.918
0.881
0.839
0.798
0.762
0.728
0.698
0.666
0.623
0.583
0.561
0.544
0.518
0.489
0.462
0.455
0.427
0.411
0.388
1.54
1.068
1.015
0.961
0.918
0.881
0.839
0.798
0.762
0.728
0.698
0.666
0.623
0.583
0.561
0.544
0.518
0.489
0.462
0.455
0.427
0.411
0.388
1.36
8.5
9.0
9.5
10.0
20.0
kobs × 103 s-1
-dc/dt
2.53
3.14
3.69
4.31
4.69
5.16
6.11
T = 298 K; [CIP] = 3.0 × 10-5 mol dm-3; [H+] = 2.0 × 10-4 mol dm-3; [TX-100] = 1.2 × 10-3 mol dm-3

364 Singh et al.
Asian J. Chem.
TABLE-4
TABLE-5
EFFECT OF SUBSTRATE CIPROFLOXACIN
ON TX-100 MEDIATED OXIDATION OF
CIPROFLOXACIN BY CHLORAMINE-T
EFFECT OF VARIATION OF ACID ON THE RATE CONSTANT
Absorbance at 275 nm wavelength with
respect to variation of [HClO4] (× 104 mol dm-3)
Time (min)
Absorbance at 275 nm wavelength with
1.0
2.0
4.0
6.0
8.0
10
respect to variation of [CIP] (× 105 mol dm-3)
Time (min)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
1.569
1.557
1.545
1.536
1.525
1.513
1.501
1.489
1.481
1.469
1.458
1.441
1.435
1.415
1.404
1.387
1.371
1.362
1.355
1.341
1.325
1.276
1.115
0.855
0.622
0.472
2.42
1.562
1.553
1.544
1.533
1.525
1.514
1.503
1.492
1.483
1.473
1.462
1.438
1.425
1.412
1.403
1.381
1.369
1.359
1.351
1.337
1.325
1.269
1.100
0.841
0.612
0.432
2.19
1.564
1.555
1.543
1.533
1.524
1.514
1.505
1.495
1.485
1.477
1.468
1.438
1.425
1.412
1.403
1.381
1.369
1.359
1.351
1.337
1.325
1.269
1.100
0.841
0.612
0.432
1.88
1.543
1.535
1.527
1.521
1.514
1.508
1.502
1.495
1.487
1.481
1.475
1.445
1.432
1.418
1.408
1.387
1.373
1.367
1.354
1.343
1.335
1.114
0.987
0.862
0.655
0.511
1.47
1.530
1.525
1.520
1.515
1.509
1.505
1.500
1.495
1.491
1.487
1.482
1.458
1.442
1.426
1.413
1.391
1.377
1.369
1.357
1.342
1.337
1.107
0.993
0.835
0.662
0.532
1.05
1.521
1.517
1.513
1.509
1.504
1.499
1.495
1.491
1.487
1.484
1.48
1.463
1.456
1.432
1.419
1.409
1.382
1.375
1.363
1.348
1.332
0.949
0.799
0.632
0.554
0.469
0.92
0.5
1.0
2.0
2.5
3.0
3.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
0.999
0.949
0.901
0.851
0.807
0.767
0.723
0.689
0.659
0.624
0.591
0.492
0.455
0.431
0.409
0.396
0.387
0.365
0.351
0.325
0.305
0.279
1.74
1.026
0.968
0.911
0.861
0.813
0.767
0.723
0.682
0.643
0.611
0.573
0.492
0.459
0.435
0.415
0.4
0.381
0.364
0.347
0.321
0.305
0.278
1.92
1.035
0.971
0.911
0.858
0.807
0.752
0.702
0.657
0.622
0.581
0.545
0.503
0.461
0.437
0.415
0.392
0.378
0.362
0.348
0.321
0.302
0.284
2.10
1.057
0.971
0.911
0.858
0.807
0.752
0.702
0.657
0.622
0.581
0.545
0.514
0.476
0.451
0.428
0.416
0.391
0.378
0.351
0.333
0.311
0.289
2.15
1.067
0.999
0.939
0.867
0.812
0.765
0.711
0.668
0.631
0.587
0.551
0.519
0.482
0.458
0.431
0.418
0.402
0.389
0.365
0.342
0.324
0.312
2.20
1.098
1.028
0.959
0.897
0.835
0.783
0.728
0.683
0.642
0.599
0.556
0.457
0.415
0.371
0.356
0.332
0.315
0.288
0.259
0.234
0.211
0.186
2.25
8.5
9.0
9.5
8.5
9.0
9.5
10.0
15.0
20.0
25.0
30.0
35.0
kobs × 103 s-1
10.0
20.0
kobs × 103 s-1
T = 298 K; [CIP] = 3.0 × 10-5 mol dm-3; [H+] = 2.0 × 10-4 mol dm-3;
[TX-100] = 1.2 × 10-3 mol dm-3
T = 298 K; [CIP] = 3.0 × 10-5 mol dm-3; [CAT] = 3.0 × 10-4 mol dm-3;
[TX-100] = 1.2 × 10-3 mol dm-3
[CIP] × 105
mol dm–3
1.04
3.4
3.3
3.2
3.1
3.0
2.9
1.02
0.5
1.0
2.0
1.00
2.5
3.0
0.98
3.5
0.96
0.94
0.0
0.2
0.4
0.6
Time (min–1)
Fig. 6. First order plots of log absorbance versus time
0.8
1.0
1.2
1.4
1.6
4.0
4.2
4.4
4 + log [HClO4]
Fig. 7. Plots of log kobs versus log [acid]
4.6
4.8
5.0
dm-3, keeping other experimental conditions constant. Regular
decrease in rate constant is reported with the increasing [HClO4]
(Table-5, Fig. 7).
Effect of additives: The rate constant did not show measu-
rable change with increasing dielectric constant of the medium.
Addition of PTS in the reaction mixture showed that the rate
of reaction decreased with increasing [PTS] (Table-7). A plot
of observed rate constant versus [PTS] has been shown in Fig.
9a.Variations of ionic strength of the medium [K2SO4], [KNO3]
and [KCl] did not bring about any significant change in the
values of observed rate constants under the constant experi-
mental conditions (Table-8). The rate constant was found to
Effect of TX-100:The effect of TX-100 concentration on
the reaction was studied at constant [CAT] (3.0 × 10-4 mol dm-3),
[CIP] (3.0 × 10-5 mol dm-3), [HClO4] (2.0 × 10-4 mol dm-3) and
temperature (298 K) (Table-6). The results show that as the
[TX-100] increases, the rate constant show regular decrease
and towards higher concentration tending to achieve a constant
value. From Fig. 8, it can be concluded that the TX-100 put
retardation effect on the oxidative transformation of drug cipro-
floxacin by chloramine-T in acidic conditions.

Vol. 32, No. 2 (2020)
Kinetics of Micellar Effect of Non-Ionic Surfactant on Oxidative Degradation of Ciprofloxacin 365
TABLE-6
EFFECT OF INCREASING CONCENTRATION OF TX-100 ON OXIDATION OF CIPROFLOXACIN BY CHLORAMINES-T
Absorbance at 275 nm wavelength with respect to
variation of [TX-100] (× 103 mol dm-3)
Absorbance at 275 nm wavelength with respect to
variation of [TX-100] (× 103 mol dm-3)
Time
(min)
Time
(min)
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
0.00
0.16
0.33
0.50
0.66
0.83
1.00
1.16
1.33
1.50
1.66
1.83
2.00
2.16
2.33
2.50
5.00
–
0.460 0.432 0.466 0.487 0.485 0.495 0.482
0.427 0.403 0.429 0.461 0.461 0.468 0.467
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
8.5
9.0
9.5
10.0
0.395 0.384
0.41
0.428 0.435 0.444 0.449
0.372 0.359 0.391 0.409 0.409 0.415 0.429
0.345 0.337 0.368 0.389 0.389 0.396 0.413
0.322 0.315 0.347 0.362 0.378 0.381 0.393
0.303 0.294 0.321 0.348 0.354 0.365 0.375
0.283 0.276 0.307 0.331 0.339 0.349 0.360
0.269 0.261 0.288 0.316 0.325 0.331 0.354
0.254 0.245 0.271 0.295 0.308 0.325 0.333
0.239 0.231 0.254 0.284 0.295 0.316 0.325
0.228
0.22
0.245 0.273 0.283 0.301 0.313
0.214 0.206 0.234 0.261 0.275 0.291 0.303
0.202 0.202 0.231 0.257 0.255 0.278 0.288
0.191 0.189 0.217 0.242 0.238 0.263 0.275
0.178 0.172 0.207 0.231 0.223 0.246 0.261
0.065 0.066 0.078 0.081 0.083 0.098 0.126
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
kobs
×
6.30
6.23
5.80
4.75
4.36
3.90
3.55
kobs
×
3.20
2.80
2.58
2.35
2.20
2.20
2.20
103 (s-1)
103 (s-1)
T = 298 K; [CIP] = 3.0 × 10-5 mol dm-3; [H+] = 2.0 × 10-4 mol dm-3; [CAT] = 3.0 × 10-4 mol dm-3
7
6
5
4
3
2
TABLE-7
EFFECTS OF [ACETIC ACID], [PTS]
AND [HCOONa] ON REACTION RATE
Acetic acid ×
104 (mol dm-3)
[PTS] × 104
[HSO4Na] ×
kobs × 103 (s-1)
(mol dm-3)
104 (mol dm-3)
5
10
20
30
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
0
1
2
4
6
8
10
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
0
1
2
4
6
8
10
2.23
2.22
2.24
2.22
2.21
1.55
0.48
0.46
0.46
0.44
0.45
2.21
1.96
1.43
0.95
0.78
0.77
0.66
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
[TX-100] × 103 mol dm–3
–
Fig. 8. Effect of TX-100 on the pseudo first order rate constants
T = 298 K; [CIP] = 3.0 × 10-5 mol dm-3; [CAT] = 3.0 × 10-4 mol dm-3;
[HClO4] = 2.0 × 10-4 mol dm-3; [TX-100] = 2.0 × 10-3 mol dm-3
different activation parameters. The value of rate constants at
different temperatures is summarized in Table-9 along with
the activation parameters. The activation energy (Ea) was calcu-
lated from the slope ofArrhenius plot (Fig. 10a). To determine
whether the reaction mechanism is associative or dissociative,
the entropy of activation is needed, which can be evaluated
from an Eyring plot (Fig. 10b). A large negative value of ∆S#
indicates an associative reaction and a large positive value of
∆S# indicates a dissociative reaction [26]. Using Eyring equa-
tion the calculated values of ∆H# is 31.21 kJ mol-1 and ∆S# is
-71.22 JK-1 mol-1. Thus, an inner sphere mechanism, with both
reactants binding in the transition state, occurs.
decrease with the increasing [HSO4Na] (Fig. 9b). This may be
due to the fact that electrolytes decrease the CMC and increase
the aggregation number of ionic micelle [25] may be due to
the increased screening by counter ions and thereby decrease
the effective charge density of the micelle.
Activation parameters for the uncatalyzed and TX-100
catalyzed oxidative transformation of ciprofloxacin by chlor-
amine-T in acidic conditions.
A series of kinetic runs were carried out at different tempe-
ratures with fixed [CAT] = 2.0 × 10-4 mol dm-3, [CIP] = 2.0 ×
10-5 mol dm-3 and [HClO4] = 2.0 × 10-4 mol dm-3 to find the

366 Singh et al.
Asian J. Chem.
TABLE-8
EFFECTS OF [KCl], [KNO3] AND [K2SO4] ON REACTION RATE
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
[KCl] × 104
[KNO3] × 104
[K2SO4] × 104
kobs × 103 (s-1)
(a)
(b)
(mol dm-3)
(mol dm-3)
(mol dm-3)
1.0
2.0
3.0
4.0
5.0
6.0
8.0
10.0
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
1.0
2.0
3.0
4.0
5.0
6.0
8.0
10
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
2.22
2.21
2.22
2.22
2.22
2.21
2.21
2.21
2.19
2.19
2.30
2.11
2.29
2.56
2.65
2.33
2.20
2.19
2.15
2.19
-2
0
2
4
6
8
10 12
0
2
4
6
8
10
[PTS] × 104 mol dm–3
[NaHSO4] × 104 mol dm–3
Fig. 9. Effect of reduced product of oxidant chloramine-T and added
electrolyte
1.0
3.0
6.0
10
–
–
–
The effect of TX-100 concentration on the reaction was
also studied at constant [CAT] = 2.0 × 10-4 mol dm-3, [CIP] =
2.0 × 10-5 mol dm-3 and [HClO4] = 2.0 × 10-4 mol dm-3 and
temperature (35 °C), taking fixed [TX-100] = 1.2 × 10-3 mol
dm-3. To confirm whether mechanism of the oxidation of
oxidative transformation of ciprofloxacin by chloramine-T in
both aqueous as well as micellar media is similar, different
experiments were performed as a function of [CIP], [CAT]
and [HClO4] in the presence of [TX-100] (1.2 × 10-3 mol dm-3)
at 298 K temperature (Table-9). The behaviour with respect
to [CIP], [CAT] and [HClO4] was similar to that in the aqueous
medium, which shows that reaction mechanism in the presence
ofTX-100 remains the same as that in the homogeneous aqueous
medium. The effect of temperature on the reaction rate in micellar
media was also studied. The activation parameters (Ea, ∆H#,
∆S# and ∆G#), evaluated by using Arrhenius and Eyring
equations, show that TX-100 micelles act as catalyst providing
a new reaction path with lower Ea (aqueous > TX-100).
TX-100 catalyzed oxidative transformation of ciproflo-
xacin by chloramine-T.
T = 298 K; [CIP] = 3.0 × 10-5 mol dm-3; [CAT] = 3.0 × 10-4 mol dm-3;
[HClO4] = 2.0 × 10-4 mol dm-3; [TX-100] = 1.2 × 10-3 mol dm-3
TABLE-9
TEMPERATURE EFFECT AND ACTIVATION PARAMETERS
FOR UNCATALYZED AND TX-100 CATALYZED REACTIONS
OF OXIDATION OF CIPROFLOXACIN BY CHLORAMINE-T
Without TX-100
kobs × 103 (s-1)
With TX-100
kobs × 103 (s-1)
Parameter
293K
298 K
0.63
0.72
1.49
2.12
303K
1.03
2.73
308K
1.25
3.30
Ea (kJ mol-1)
∆ H# (kJ mol-1)
∆ S# (JK mol-1)
∆ G# (kJ mol-1)
33.89
36.39
-62.88
18.77
37.22
39.73
-43.69
13.06
[CIP] = 2.0 × 10-5 mol dm-3; [CAT] = 2.0 × 10-4 mol dm-3; [H2SO4] =
2.0 × 10-4 mol dm-3; [CTAB] = 3.5 × 10-3 mol dm-3
4.20
1.70
4.15
Arrhenius plots
Eyring plots
1.65
4.10
1.60
(b)
4.05
(a)
1.55
4.00
1.50
3.95
Y = - 17.70x + 7.120
Y = - 19.01x + 7.032
Y = - 20.75x + 8.034
1.45
1.40
1.35
1.30
1.25
1.20
1.15
1.10
3.90
Y = - 19.44x + 7.122
3.85
3.80
3.75
3.70
3.65
3.60
3.55
0.318 0.320 0.3220.324 0.326 0.328 0.3300.332 0.334 0.336
0.318 0.320 0.322 0.324 0.326 0.328 0.330 0.332 0.334 0.336
10–2/T K–1
10–2/T K–1
Fig. 10.Effect of temperature on the pseudo-first-order rate constant for TX-100 catalyzed oxidation of ciprofloxacin by chloramine-T in
acidic medium

Vol. 32, No. 2 (2020)
Kinetics of Micellar Effect of Non-Ionic Surfactant on Oxidative Degradation of Ciprofloxacin 367
Menger-Portnoy model: The Menger-Portnoy model
[27] considers the partitioning of only one reactant between
the micellar and aqueous phase (Scheme-II).
To verify the applicability of Menger-Portnoys model to
the kinetic data obtained for the TX-100 catalyzed oxidation
of ciprofloxacin by chloramine-T in acidic conditions, a graph
is plotted between 1/kobs and C. Linear plot obtained (Fig. 11)
confirms the retardation influence of TX-100 on the title
reaction. The calculated value of binding constant KA has been
found to be 2.6.
kw
(CIP)w
KA
(CAT)w
(CAT)m
Product
Product
+
+
km
CONFLICT OF INTEREST
(CIP)m
Scheme-II
The authors declare that there is no conflict of interests
regarding the publication of this article.
Based on Scheme-II following rate law can be proposed:
kmKAC + kw
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