Effect of CHAPS and CPC micelles on Ir(III) catalyzed Ce(IV) oxidation of aliphatic alcohols at room temperature and pressure

Article abstract of DOI:10.1016/j.molliq.2014.03.037

Kinetics of cerium(IV) oxidation of aliphatic alcohols: ethanol, propanol, propan-2-ol, 1-butanol and 2-butanol were studied at 30 °C in the presence and absence of surfactants in acidic medium. The reaction was studied under pseudo-first-order conditions

Full text of DOI:10.1016/j.molliq.2014.03.037

Journal of Molecular Liquids 196 (2014) 223–237
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Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Effect of CHAPS and CPC micelles on Ir(III) catalyzed Ce(IV) oxidation
of aliphatic alcohols at room temperature and pressure
Aniruddha Ghosh a, Rumpa Saha a,b, Bidyut Saha a,1
a
Homogeneous Catalysis Laboratory, Department of Chemistry, The University of Burdwan, Golapbag, Burdwan 713104, WB, India
K. G. Engineering Institute, Bishnupur, Bankura, WB, India
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Kinetics of cerium(IV) oxidation of aliphatic alcohols: ethanol, propanol, propan-2-ol, 1-butanol and 2-butanol
were studied at 30 °C in the presence and absence of surfactants in acidic medium. The reaction was studied
under pseudo-first-order conditions, [alcohol]T ≫ [Ce(IV)]T. Ir(III)-salt used as catalyst had a significant effect
on reaction rate. Cationic surfactant CPC (N-cetylpyridinium chloride) inhibits the reaction rate but zwitterionic
surfactant CHAPS (3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate) catalyzes the oxidation re-
action significantly. CMC value of CHAPS was determined by a spectrofluorometer. The reaction rate increased
with increase in the acid concentration of the medium. NMR and FTIR spectra confirmed the oxidized products.
The aggregation of surfactants in the reaction condition was studied through Scanning Electron Microscope
(SEM) and Transmission Electron Microscope (TEM). Dynamic light scattering (DLS) was used to characterize
the shape changes of the aggregates. The variations of the reaction rates for the different alcohols in the presence
of surfactants and metal ion catalyst are discussed qualitatively in terms of Berezin's model, nature of surfactants,
and charge of surfactants. Ir(III) in association with CHAPS micellar catalyst exhibited ~500–2000 fold rate en-
hancements compared to the uncatalyzed reaction path.
Received 7 February 2014
Received in revised form 11 March 2014
Accepted 27 March 2014
Available online 8 April 2014
Keywords:
Alcohols
Ce(IV)
Ir(III)
CPC
CHAPS
Berezin's model
© 2014 Elsevier B.V. All rights reserved.
1. Introduction
transition metals such as Cr(III), Ag(I), Ir(III), Pd(III), Ru(III), Os(VIII),
and Mn(II) [13–15]. It is previously reported that a variety of
Selective oxidation of alcohols to carbonyl compounds is one of the
most important transformations in industrial chemistry. Aldehydes
and ketones are precursors for many drugs, vitamins, fragrances and it
opens up the possibility of using renewable biomass-derived feed
stocks. The synthesis of carbonyl compounds is generally carried out
in environmentally harmful organic solvents at high temperature and
pressure by using stoichiometric oxygen donors (such as chromate
and permanganate) producing large amount of wastes [1,2]. The oxida-
tion of alcohols to aldehydes or ketones [3–6] has been traditionally
based on the use of stoichiometric amounts of higher valent toxic tran-
sition metal oxidants, which renders the catalytic reaction expensive
and unattractive from an environmental point of view [7–10] in both
the laboratories and industries.
Cerium chemistry is a very broad area of considerable attention
through the recent years, resulting in substantial advance both in the
synthetic and mechanistic categories. Cerium(IV) is a well known oxi-
dant [11] in acidic media having reduction potential 1.44 V of the couple
Ce(IV)/Ce(III) in H2SO4 medium and is stable only in a high acid concen-
tration [12]. Most of the cerium(IV) oxidation reactions are catalyzed by
transition-metal-catalyzed transformations can be carried out within
micellar media [16]. The potential of iridium(III) chloride as a homoge-
neous catalyst was best recognized when it was used in an acidic medi-
um for oxidation of a range of alcohols to aldehydes, ketones or
carboxylic acids proceeds in good yield. The Iridium(III) catalyzed
oxidation of aliphatic and substituted alcohols, diols and aromatic com-
pounds by cerium(IV) in an acidic medium has been investigated early
[17,18]. To discover the effect of iridium(III) chloride in catalyzing the
oxidation of aliphatic alcohols, we have studied the oxidation of ethanol,
propanol, propan-2-ol, butanol and 2-butanol in the presence of
iridium(III) chloride by cerium(IV) in an aqueous sulfuric acid medium.
However, so far it was not investigated the influence of the metal cata-
lyst on the reaction rates of oxidation reaction in micellar solutions.
Most of the organic substrates are often poorly soluble in water. Mi-
cellar systems are often used to overcome the solubility problems of the
organic reactants [19,20]. Recently, great attention has been paid to the
development of organic reactions in water [21]. Compared with other
organic solvents, water is the most abundant “greenest” solvent
among all solvents, it is ubiquitous on the earth as well as being a
clean, and easy-to-handle [1]. The advantage of using micellar solution
as catalyst, avoiding large amounts of organic solvents and the micellar
catalyst can be recycled by simple techniques [22]. In addition to the
avoidance of organic solvents and the recycling of the aqueous medium,
E-mail addresses: aniruddhachem27@gmail.com (A. Ghosh), b_saha31@rediffmail.com
(B. Saha).
1
Tel.: +91 9476341691 (mobile), +91 342 2533913 (O); fax: +91 342 2530452 (O).
http://dx.doi.org/10.1016/j.molliq.2014.03.037
0167-7322/© 2014 Elsevier B.V. All rights reserved.

224
A. Ghosh et al. / Journal of Molecular Liquids 196 (2014) 223–237
the valuable micellar catalyst offers an additional benefit of facile reac-
tion monitoring of room temperature reactions [23]. Nowadays the ef-
fect of micellar catalysis on reaction kinetics is growing popularly [6,
24–29]. Micellar catalysis [30] represents a viable solution to solubiliza-
tion problems; in fact, surfactant aggregation driven by the hydrophobic
effect ensures the formation of apolar nano-environments where both
substrates as well as catalysts can be efficiently dissolved and interact
with higher local concentrations [31,32]. It is to mention here that the
most suitable surfactants are still selected for capable of solubilizing
all species of proteins is 3-[(3-cholamidopropyl)dimethylammonio]-1-
propanesulfonate (CHAPS). It has many applications in various fields
of biological, medical, and pharmaceutical sciences [33]. CHAPS is a
zwitterionic derivative of cholic acid having combined properties of
both sulfobetaine type detergents and bile salts. It is frequently used
in membrane protein isolation, surface modifier for specific protein ad-
sorption, protein solubilization, purification, and denaturation [34]. But
no such experiment was performed about the catalytic efficiency of
CHAPS in kinetics. We have thus taken a more precise and detail exper-
imental effort on the catalyzing properties of non-toxic [35] surfactant
CHAPS over the N-cetylpyridinium chloride (CPC) in oxidation kinetics.
The important aim of this study was to determine the effects of
structural variations of alcohols and effect of various surfactants on
the rate of oxidation by Ce(IV). Besides that the other objectives
were to find out the main kinetically reactive species (Scheme 1),
main oxidation product, deduce the rate law and probable reaction
site in the presence of catalyst.
used were of the highest purity available commercially. The stock solu-
tion of Ce(IV) was obtained by dissolving cerium(IV) ammonium sulfate
in 1 mol dm−3 sulfuric acid and was standardized with iron (II) ammo-
nium sulfate solution using ferroin as an external indicator [18,36].
Cerium(IV) solution was always made up and stored in a black coated
flask to prevent photochemical reaction. A solution of iridium(III) chlo-
ride was prepared by dissolving the sample in a minimum amount of
concentrated hydrochloric acid. Conductivity water was used through-
out the study.
2.2. Instrumentation
The weighing balance (Sartorius BSA224S-CW), sonicator (Digital
Ultrasonic Cleaner CD 4820), centrifuge (Z206A, Hermle Labortechnik
GmbH), UV–vis NIR spectrophotometer (UV-VIS-NIR-3600, SHIMADZU),
stopped flow spectrophotometer (SX20 Stopped-Flow Spectrometer),
DLS instrument (Malvern Zetasizer Nano ZS-90 instrument), optical
microscope (LEICA DM 1000), SEM (S530 HITACHI SEM) instrument
using IB 2 ion coater, HR-TEM microscope (JEOL JEM 2100), FTIR spectro-
photometer (RX1, Perkin-Elmer), 1H NMR (400 MHz, Bruker Ascend)
and spectrofluorometer (LS 55, Perkin-Elmer) were used for various
purpose of experiments.
2.3. Kinetic measurements
Reaction mixtures containing the known quantities of the substrate
(i.e., ethanol, propanol, propan-2-ol, 1-butanol and 2-butanol), and
acid under the kinetic conditions, [alcohol]T ≫ 10[Ce(IV)]T were
thermostated at 30 °C ( 0.1 °C). The reaction was initiated by mixing
the requisite amounts of the oxidant and catalyst [surfactant or Ir(III)
in particular case] with the reaction mixture. All kinetic measurements
were made at an ionic strength of 2.0 mol dm−3 at 30.0 0.1 °C. The
progress of the reaction was followed by monitoring the decrease in ab-
sorbance of cerium(IV) at 320 nm [37] by the use of a UV–vis spectro-
photometer equipped with 1 cm quartz cells in a thermostated cell
holder and a Temperature Control System. The surfactant CHAPS was
used above the critical micelle concentrations (6.3 mM at 303 K) [35]
in all experiments to make sure of the existence of micellar aggregates
in solution. The pseudo-first-order rate constants (kobs, s−1) were
2. Experimental
2.1. Materials and methods
2.1.1. Chemicals
Ethanol (SRL, AR, Mumbai, India), propanol (SRL, AR, Mumbai, India),
propan-2-ol (SRL, AR, Mumbai, India), 1-butanol (SRL, AR, Mumbai,
India), 2-butanol (SRL, AR, Mumbai, India), N-cetylpyridinium chloride
(CPC) (SRL, AR, Mumbai, India), CHAPS (SRL, AR, Mumbai, India),
H2SO4 (E. Merck, AR), Na2SO4 (E. Merck, AR), HCl (E. Merck, AR), pyrene
(SRL, AR, Mumbai, India), iridium(III) chloride (SRL, AR, Mumbai, India),
cerium(IV) ammonium sulfate (E. Merck, AR) and all other chemicals
R
C
O
R
OH
R
CPC/CHAPS micelle
Ir(III) salt
Ce(III) 2H+
+
2
+
2
or
Ce(IV) H SO
+
+
C
2
4
R
R
H
+ ve
ve head group
/
C
O
when R = H
Ce(SO4)2+
Ce(SO4)+
H
Ce(SO4)2
3
Ce(SO4)3
Ce(SO4)2
Scheme 1. A probable scheme for the main reactive species involved in the oxidation in micellar media.

A. Ghosh et al. / Journal of Molecular Liquids 196 (2014) 223–237
225
calculated from the linear plots of -ln(A320) versus time at 320 nm
wavelength (Fig. 1), (where A320 = Absorbance of Ce(IV) at 320 nm
wavelength). All the first order plots were linear, with a correlation co-
efficient of 0.993–0.999. The results were reproducible within an accu-
propionaldehyde, and butanal were obtained from the oxidation of eth-
anol, propanol and 1-butanol respectively. Again the ketones: acetone
and 2-butanone were the main products of oxidation of propan-2-ol
and 2-butanol. Qualitative identifications of the carbonyl products of
cerium(IV) oxidation reactions were performed with the formation of
yellow or yellow orange colored 2,4-dinitrophenyl hydrazone deriva-
tives directly by addition of 2,4-dinitrophenyl hydrazine in the reaction
mixtures [39,40]. The hydrazone precipitate was filtered off and was
weighed out after proper drying. The hydrazones were recrystallized
to determine the melting points. The melting points were matched
with the earlier reports [41,42]. The crystalline 2,4-DNP derivatives
were thoroughly mixed with KBr, pressed into a form of disk (pellet),
to record FTIR spectrum and compared with spectra of the derivatives
of known aldehydes/ketones (supplementary data). Thus, we may safe-
ly conclude that carbonyl compound is the main oxidation product. The
spectra of the derivatives of the reaction products were sufficiently dif-
ferent to permit reasonably positive identification of the products [43].
racy of
2.5%. The pseudo-first-order rate constants of the present
oxidation reactions were measured also in the presence of CPC, CHAPS
and Ir(III). The possibility of decomposition of the surfactants CPC and
CHAPS by Ce(IV) has been investigated and the rate of decomposition
has been found negligible [38]. Values of the rate constants for the
alcohol-Ce(IV) reactions determined from the slopes of the appropriate
plots are presented in Table 1. The t1/2 values are directly calculated in
Table 1 by using the relation t1/2 = (ln2 / kobs), where ln2 = 0.693,
kobs = pseudo-first-order rate constant in s−1
.
2.4. Fluorimetry
Fluorescence measurements were performed in a spectrofluorome-
ter using a quartz cell of path length 1 cm at 30 0.1 °C with an excita-
tion and emission slit width of 3.0 nm and 2.5 nm respectively and a
scan speed of 500 nm min−1. Pyrene was used as the fluorescence
probe. A series of surfactant solutions were prepared for fluorescence
intensities measurement following the procedure used in spectro-
photometry. The solutions were excited at 334 nm, and the emission
spectra were recorded in the range 360–450 nm. The fluorescence in-
tensities of the peaks at ~372 nm (I1) and ~383 (I3) were extracted
from the spectra, and the I3/I1 value vs. surfactant CHAPS concentration
was used for CMC determination. The CMC was found around 6.3 mM
from the plot of fluorescence intensity versus CHAPS concentration
(Supplementary data).
2.5.1. Stoichiometry
Stoichiometry of the reaction was evaluated by taking cerium(IV) in
large excess over the organic substrate to ensure its complete oxidation.
Different reaction mixtures with different sets of concentration of reac-
tants, where [Ce(IV)] was used in excess over [substrate] at constant
ionic strength and acidity were kept for 24 h at 303 K in an inert atmo-
sphere. The results indicated that 2 mol of Ce(IV) was consumed (Fig. 2)
per mol of substrate, (i.e. 2:1). In all cases it was assumed that 1 mol of
carbonyl product is formed per 2 mol of cerium(IV) reduced by aliphatic
alcohols. The calculation of the yield of product from the weight of 2,4-
dinitrophenylhydrazone formed requires a knowledge of the reaction
product and stoichiometry.
2.5. Product analysis and stoichiometry
In our experimental condition the concentration of Ce(IV) was kept
less than the concentration of alcohols but in the stoichiometric study, a
known excess of Ce(IV) was allowed to react completely with a mixed
amount of alcohols at 30 °C. After completion of the reaction, the corre-
sponding oxidized products aldehydes and ketones (carbonyl com-
pound) were efficiently separated by fractional distillation [5,6]. The
1H NMR spectra (Supplementary file) of the product carbonyl com-
pound in CDCl3 solvent were obtained on an NMR spectrophotometer
operating at 400 MHz frequency. In this study the products ethanal,
2.6. Test for free radical intermediates
The intervention of free radicals was examined as follows. The reac-
tion mixture, to which a known quantity of acrylonitrile scavenger had
been added initially, was kept in an inert atmosphere for 2 h. Upon di-
luting the reaction mixture with methanol, white precipitate was
formed, indicating the presence of free radical intervention in the reac-
tion. The formation of free radicals was confirmed by acrylonitrile poly-
merization [36,44].
Fig. 1. Representative first-order plot for Ce(IV) oxidation of 2-butanol in CHAPS catalyzed path and propanol in Ir(III) mediated CHAPS catalyzed path. [Ce(IV)]T = 2 × 10−4 mol dm−3
[CHAPS]T = 8 × 10−3 mol dm−3, [H2SO4]T = 0.5 mol dm−3, μ = [H2SO4 + Na2SO4] = 2.0 mol dm−3, Temp = 30 °C. (a) [2-butanol]T = 2 × 10−3 mol dm−3; (b) [propanol]T = 2 ×
10−3 mol dm−3, [Ir(III)]T = 2 × 10−6 mol dm−3
,
.

226
A. Ghosh et al. / Journal of Molecular Liquids 196 (2014) 223–237
Table 1
Effect of Ir(III), CPC and CHAPS micellar catalyst on pseudo-first-order rate constant and half-life for the Ce(IV) oxidation of alcohols.
Substrate
106 × metal catalyst
103 × micellar catalyst
106 × kobs (s−1
)
Half-life (t1/2) (h)
(mol dm−3
)
(mol dm−3
)
Ethanol
30.500
22.160
6.184
11.870
21.660
4.594
4.731
5.342
5.659
5.246
4.353
4.231
13.150
10.004
8.545
7.569
7.311
6.039
5.015
6.114
6.669
7.155
8.805
6.898
4.967
4.892
14.250
7.455
6.965
5.214
6.931
6.484
6.747
9.468
6.941
6.639
6.267
8.257
7.476
7.356
84.160
72.830
135.60
89.80
78.50
277.0
237.20
403.70
556.7
1732.0
22,800.0
12,200.0
13,200.0
12,000.0
15,500.0
0.02
6.310
8.680
31.120
16.217
8.887
Propanol
Propan-2-ol
1-Butanol
2-Butanol
Ethanol
0.04
0.06
0.05
0.01
0.09
0.05
0.08
0.07
0.03
0.06
0.05
0.05
0.08
0.06
0.05
0.06
0.07
0.04
0.01
0.01
0.03
0.05
0.04
0.05
0.05
0.06
0.01
0.03
0.03
0.04
0.01
0.02
0.02
0.06
0.04
0.03
0.07
0.02
0.02
0.01
0.06
0.05
0.04
0.05
0.06
0.03
0.03
0.01
0.02
0.08
0.05
0.07
0.07
0.09
–
–
–
CPC
0.4
0.6
0.8
1.0
1.2
1.4
1.5
0.4
0.6
0.8
1.0
1.2
1.4
1.5
0.4
0.6
0.8
1.0
1.2
1.4
1.5
0.4
0.6
0.8
1.0
1.2
1.4
1.5
0.4
0.6
0.8
1.0
1.2
1.4
1.5
41.897
40.689
36.038
34.0160
36.690
44.210
45.497
14.638
19.240
22.527
25.430
26.330
31.870
38.380
31.480
28.860
26.900
21.860
27.900
38.7581
39.349
13.510
25.821
27.640
36.920
27.770
29.690
28.530
20.330
27.730
29.0
30.710
23.310
25.750
26.170
2.287
2.640
1.420
2.140
2.450
0.690
0.810
0.470
0.340
Propanol
–
–
–
–
CPC
CPC
CPC
CPC
Propan-2-ol
1-Butanol
2-Butanol
Ethanol
Ir(III)
2
–
2
–
Propanol
Propan-2-ol
1-Butanol
2-Butanol
Ethanol
Propanol
Propan-2-ol
1-Butanol
2-Butanol
Ethanol
–
CHAPS
CHAPS
8
8
0.110
Ir(III)
30.40 s
56.90 s
52.60 s
58.0 s
Propanol
Propan-2-ol
1-Butanol
2-Butanol
44.50 s
[Ce(IV)]T = 2 × 10−4 mol dm−3, [CPC]T = 1.1 × 10−3 mol dm−3, [H2SO4]T = 0.5 mol dm−3, [alcohol]T = 2 × 10−3 mol dm−3, μ = 2.0 mol dm−3, Temp = 30 °C.
2.7. Determination of the size of aggregates by dynamic light scattering (DLS)
was performed to obtain micelle/vesicle size and morphology on a
DLS instrument with a capillary cell. Size measurements were per-
formed at a 90° angle in triplicate. DLS analyzes the velocity distribution
of particle movement by measuring dynamic fluctuations of light
The hydrodynamic diameters (Dh) of CPC micelles with and without
reactants were determined by DLS experiment. DLS characterization
R
C
or
O
2
OH
R
R
R
2H+
+
2
Ce(III)+
+
C
Ce(IV)+ H2SO4
R
H
O
C
H
when R = H
Fig. 2. Conversion of alcohol to corresponding carbonyl compound by Ce(IV) at 30 °C.

A. Ghosh et al. / Journal of Molecular Liquids 196 (2014) 223–237
227
Fig. 3. (a) to (c) Different views of TEM images showing micelles formed by CPC in aqueous medium, [CPC]T = 1.5 × 10−3 mol dm−3. (d) to (f) Different views of TEM images of the re-
action mixture showing the interaction of Ce(IV) by CPC micelles in the aqueous acidic medium. [CPC]T = 1.5 × 10−3 mol dm−3, [Ce(IV)]T = 2 × 10−4 mol dm−3, [H+] = 0.5 mol dm−3
,
μ = 2.0 mol dm−3, Temp = 30 °C.
scattering intensity caused by the Brownian-motion of the particle. The
light scattering study was done with CPC surfactant by taking concen-
tration above its CMC value in an acidic medium.
bi-layer structure. Most of the micelles appear to be bent rather than
straight cylinders. It has been known for many years that aggregates
with different morphologies can form in small molecule surfactant sys-
tems. The addition of reactants changes the morphologies of the aggre-
gates from bi-layers or cylinders to spheres. At [CHAPS] N CMC, the
broken rock-type materials of large size appeared in the SEM picture.
In this concentration of CHAPS in the medium, the formation of particles
of varied geometries and patterns was observed as below:
2.8. High resolution transmission electron microscope (HR-TEM) images of
CPC micelle
The HR-TEM investigation was done at 20 kV acceleration voltage
using a lacey carbon coated Cu grid of 300 mess size. Samples were pre-
pared by placing sample mixture drops directly on the copper grids
using a micropipette. The reactants including the surfactant present in
the aqueous mixture were allowed to settle. TEM pictures (Fig. 3) are
presented which illustrate the multiple morphologies of the aggregates
made from the surfactant CPC. Also, the micrograph suggests a relatively
narrow size distribution of the cylindrical micelle diameters, but a wide-
ly variable length. With the addition of reactants, the morphology
changes at some extent may be due to the accumulation of a small
amount of reactant at the micellar surface.
3. Results
3.1. Spectrophotometric study of the reaction
3.1.1. UV–vis spectra
The ceric(IV) ion, is a facile oxidant of organic compounds such as al-
cohol. In that case, ethanol, propanol and 1-butanol, are oxidized into
ethanal, propionaldehyde and 1-butanal respectively, itself susceptible
to further oxidation to corresponding acids. Due to the excess concen-
tration of alcohol present in solution as compared to ceric(IV), it is ex-
pected that the ceric(IV) ion will be totally reduced to Ce(III) at the
end of reaction. Indeed, solutions of Ce(IV) salts are yellow in the pres-
ence of alcohol, whereas solutions of Ce(III) salts are colorless [45]. The
progress of the oxidation of alcohols with cerium(IV) in the presence
and absence of surfactant and Ir(III) (Fig. 5, 6, 7) is reflected by marked
changes [46] in the electronic spectrum of certain time intervals. The
2.9. Scanning electron microscope (SEM) images of CHAPS micelle
SEM analysis was done by placing a drop of CHAPS solution on a foil
paper. Then it was air dried, coated with gold, and was observed under a
Scanning Electron Microscope. The SEM picture (Fig. 4) of pure CHAPS
looked like rod-like or cylindrical particles. This also looked like a
Fig. 4. (a) to (c) Different views of SEM images showing micelles formed by CHAPS in aqueous medium. [CHAPS]T = 8.0 × 10−3 mol dm−3
.

228
A. Ghosh et al. / Journal of Molecular Liquids 196 (2014) 223–237
Fig. 5. Sequential scans of absorption spectra during the course of the uncatalyzed reaction of alcohol with Ce(IV) in sulfuric acid media for 5 min time interval, with [Ce(IV)]T = 2.0 ×
10−4 mol dm−3, [H2SO4]T = 0.5 mol dm−3, μ = [H2SO4 + Na2SO4] = 2.0 mol dm−3, Temp = 30 °C. (a) [ethanol]T = 2.0 × 10−3 mol dm−3, (b) [2-butanol]T = 2.0 × 10−3 mol dm−3
.
scanned absorption spectra of the different set of reaction mixtures
were taken for both in the presence and absence of surfactant and
Ir(III) (Figs. 6, 7). Replicate scans of the spectra during the course of
the reaction showed a decrease in the absorbance only, with no evi-
dence of any shift in the peaks (Figs. 5, 6 and 7).
on acid concentration used. The absorbance maximum at 320 nm due
to the electronic transitions of the cerium(IV) complexes. The color of
Ce(IV) compounds in presence of anion in aqueous medium is due to
the LMCT bands. The absorption spectrum of Ce(IV) species in aqueous
sulfuric acid solution differs from that of Ce(III) species[14]. However,
Ce(III) complexes produced after completion of reaction have an ab-
sorption band near 250 nm (Fig. 8). The reason for these changes is
The spectra presented in Figs. 5 to 7 reveal one absorption band of
cerium(IV) at 320 nm with a molar absorption coefficient depending
Fig. 6. Sequential scans of absorption spectra during the course of the Ir(III) catalyzed reaction of alcohol with Ce(IV) in sulfuric acid media. [Ce(IV)]T = 2 × 10−4 mol dm−3, [H2SO4]T
0.5 mol dm−3, [Ir(III)]T = 2 × 10−6 mol dm−3, μ = [H2SO4 + Na2SO4] = 2.0 mol dm−3, Temp = 30 °C. (a) [propan-2-ol] = 2.0 × 10−3 mol dm−3, Interval time 2 min, (b) [1-butanol]T
2.0 × 10−3 mol dm−3, Interval time 2 min, (c) [2-butanol]T = 2.0 × 10−3 mol dm−3, Interval time 2 min.
=
=

A. Ghosh et al. / Journal of Molecular Liquids 196 (2014) 223–237
229
Fig. 7. Sequential scans of absorption spectra during the course of the CHAPS catalyzed reaction of alcohol with Ce(IV) in sulfuric acid media. [Ce(IV)]T = 2 × 10−4 mol dm−3, [H2SO4]T
0.5 mol dm−3, [CHAPS]T = 8 × 10−3 mol dm−3, μ = [H2SO4 + Na2SO4] = 2.0 mol dm−3, Temp = 30 °C. (a) [ethanol]T = 2.0 × 10−3 mol dm−3, Interval time 3 min; (b) [1-butanol]T
2.0 × 10−3 mol dm−3, Interval time 30 s, (c) [2-butanol]T = 2.0 × 10−3 mol dm−3, Interval time 1 min.
=
=
the disappearance of the intensive yellow colored cerium(IV), which is
reduced to a pale green cerium(III). Cerium(III) complexes, under con-
ditions used in this work, are practically transparent in visible spectral
region and exhibit only less intensive absorption bands at 295, 254,
241, 223 and 212 nm respectively in UV region. In contrast,
with cerium(III) the lowest energy electronic absorption bands in the
UV regions corresponding to the 4fn → 4fn−1d1 transition. The electron-
ic spectrum of Ce(III) is corresponding to a single transition between
2F5/2 (ground state) and 2F7/2
.
3.2. Dependence on [Ce(IV)]
The oxidation reaction of the alcohols is of first order in [Ce(IV)] in
the absence and presence of surfactant as indicated by the linearity of
a plot of −ln(A320) versus time (t) (Fig. 1) [47].
3.3. Dependence on [H2SO4]
The reaction was carried out at a various initial concentration of sul-
furic acid at a fixed CPC concentration as in Table 2. It was observed that
the rate of oxidation reaction of each alcohol increased with an increas-
ing sulfuric acid concentration (Fig. 9). The plots of kobs versus [H+
]
(Fig. 9) for the aliphatic alcohols are found to be linear in nature. This in-
dicates that the reaction order with respect to [H+] is first. From the hy-
drogen ion dependence on rate constants for the various aliphatic
alcohols it is clear that the rate is increased with the increasing concen-
tration of H+. The half-life value (Table 2) of the corresponding reaction
decreases in usual way.
Fig. 8. Absorption spectra of Ce(III) solution from Ce(IV) after completion of the
uncatalyzed reaction at 30 °C. [Ce(IV)]T = 2 × 10−4 mol dm−3, [H2SO4]T = 0.5 mol dm−3
,
μ = [H2SO4 + Na2SO4] = 2.0 mol dm−3, [alcohol]T = 2.0 × 10−3 mol dm−3. (a) ethanol,
(b) propanol, (c) propan-2-ol, (d) 1-butanol, (e) 2-butanol.

230
A. Ghosh et al. / Journal of Molecular Liquids 196 (2014) 223–237
Table 2
determining step to give Ce(III) and free radical (C2) so as to participate
at the faster steps to yield the carbonyl product. The free radical generat-
ed during the reaction was evident from the acrylonitrile polymerization
test [36,44,47,48]. The effects of structural variations of alcohols were in-
vestigated in our present system and in most cases everything except the
alcohol was kept constant and thus the cerium(IV) species should be the
same for all alcohols [50]. The rate law of the uncatalyzed reaction path
[12,51] has been expressed as:
Effect of hydrogen ion concentration on reaction rate for different alcohol oxidation by
Ce(IV).
Substrate
Ethanol
H
+ (mol dm−3
)
106 × kobs (s−1
)
Half-life (t1/2) (h)
0.5
1
1.5
2
2.5
0.5
1
1.5
2
2.5
0.5
1
1.5
2
2.5
0.5
1
1.5
2
5.659
9.376
9.538
10.622
12.290
7.311
8.123
9.489
11.074
12.10
8.392
12.430
13.670
14.80
17.110
6.931
9.60
0.01
0.05
0.03
0.02
0.06
0.03
0.03
0.04
0.05
0.01
0.02
0.05
0.06
0.05
0.03
0.05
0.06
0.02
0.04
0.04
0.01
0.02
0.06
0.03
0.05
34.0
20.530
20.180
18.120
15.660
26.330
23.70
20.280
17.380
15.90
22.930
15.480
14.080
13.0
11.250
27.770
20.0
19.70
17.150
16.30
23.30
16.30
14.80
13.270
12.50
Â
Ã
Propanol
kK RR0C HOH
kobs
¼
:
1 þ K½RR0C HOHꢀ
Propan-2-ol
1-Butanol
2-Butanol
4.2. Reaction mechanism of iridium(III) catalysis
It is known that IrCl3 in hydrochloric acid medium gives IrCl63−
species. During the oxidation of alcohols to carbonyl compounds,
[IrCl5H2O]2− has been considered as the reactive species of Ir(III)-
catalyst in our present kinetic study [19]. The possibility of the associa-
tion of alcohol and Ir(III) leading to a certain interaction between
alcohol and Ir(III) in the first pre-equilibrium step (Scheme 3), was de-
tected by UV–vis absorption spectra of different alcohol-Ir(III) mixture
solutions. The UV–vis spectrum of the mixing solution is distinctly dif-
ferent from those of the individual alcohols and Ir(III) solution (supple-
mentary data) [19]. Spectral evidence suggesting that 1:1 type complex
formation between alcohol and Ir(III) in the first equilibrium step. The
second equilibrium probably involves the outer-sphere association
(C3) of the alcohol and Ir(III) catalyst followed by the electron transfer
leading to the complex (C4) which may be Ce(III)·(alcohol)·Ir(IV). Sub-
sequently electron transfer occurs within the complex to give Ir(III) and
the free radical which is rapidly oxidized by Ce(IV) at a fast step. Thus
the oxidation of alcohol occurs through the Ir(III)/Ir(IV) catalytic cycle
[52]. The reaction mechanism involving an association of the oxidant,
substrate and catalyst in some pre-equilibrium steps before the electron
transfer step [18,53,54]. The rate expression [53,55] of the Ir(III)-cata-
lyzed reaction pathway has been expressed as follows:
9.770
11.220
11.80
8.257
11.80
13.0
2.5
0.5
1
1.5
2
14.50
15.40
2.5
[Ce(IV)]T = 2 × 10−4 mol dm−3, [CPC]T = 1.1 × 10−3 mol dm−3, [alcohol]T = 2 ×
10−3 mol dm−3, Temp = 30 °C.
4. Discussion
4.1. Reaction mechanism of uncatalyzed path
In the uncatalyzed path the proposed mechanism involves the forma-
tion of complex in a reversible manner to form [Ce(IV)-S] (S = alcohol)
complex followed by a slow redox decomposition (Scheme 2) giving rise
to aldoxide radical which is rapidly oxidized by Ce(IV). An example of
this type was the oxidation of DMSO by Ce(IV) [48] which involves a re-
versible rapid complex formation between them with a kinetic proof
yielding the final products in the rate determining step. Cerium(IV)
forms 1:1 complexes of the type [ROH.Ce(IV)]4+ with the alcohols [12,
49] by the elimination of cerium(III) and H+ ions. Here the complex
[Ce(IV)-alcohol] (C1) may undergo deprotonation with the transfer of
single electron from the substrate to Ce(IV)-sulfato species at the rate-
Â
Ã
k1K1K2 RR0CHOH ½IrðIIIÞꢀ
kobs
¼
:
1 þ K1½RR0CHOHꢀð1 þ K2½IrðIIIÞꢀÞ
4.3. Dependence of rate constant on structural variation of alcohols
It is believed that the amount of covalent bonding between rare
earth ions and electronegative atoms is quite small since high energy;
diffuse orbitals (4f, 5d, 6s, or 6p) would have to be involved in the bond-
ing. The paucity of stable complexes of rare earth metal ions supports
the postulate of weak electrostatic bonding rather than stronger cova-
lent bonding [50]. Several factors must be considered in attempting to
rationalize the changes in the observed rate constants for the alcohol
oxidation with changes in the alcohol structures. These are electronic ef-
fect, steric effect, size of cerium(IV)-alcohol and Ir(III)-alcohol com-
plexes and the location of the reactants in the nano-reactor (micellar
surface). The relative rates of chromic acid oxidation of many stereo iso-
meric pairs of alcohols have been reported previously [50]. In general,
the more sterically crowded alcohol oxidizes at a faster rate in aqueous
solvent. The steric factor mainly arises from the step up (Scheme 4) of
a single \CH2 group from ethanol to propanol and then butanol
(Scheme 4). In fact, a trend in rate constant of the Ce(IV) oxidation of
different alcohol was observed. It does seem to exist as the crowded al-
cohol in the Ce(IV)-alcohol complex for more sterically hindered alco-
hol of a pair of alcohols of comparable polar nature is greater than that
for the less crowded alcohol. Although sometimes discrepancy have
been also observed. Such was reflected from our study by the kobs for
ethanol (3.05 × 10−5 s−1) and propanol (2.216 × 10−5 s−1), propan-
2-ol (0.6184 × 10−5 s−1) and 1-butanol (1.187 × 10−5 s−1), and
Fig. 9. Dependence of kobs on [H+] for the Ce(IV) oxidation of alcohol in the presence
of constant CPC concentration in aqueous H2SO4 media at 30 °C. [Ce(VI)]T = 2 ×
10−4 mol dm−3, =2 × 10−3 mol dm−3, [CPC]T = 1.1 × 10−3 mol dm−3. a for [ethanol]t
2 × 10−3 mol dm−3, b for [propanol]T = 2 × 10−3 mol dm−3, c for [propan-2-ol]t
2 × 10−3 mol dm−3, d for [1-butanol]t = 2 × 10−3 mol dm−3, e for [2-butanol]T
=
=
=
2 × 10−3 mol dm−3
.

A. Ghosh et al. / Journal of Molecular Liquids 196 (2014) 223–237
231
H
Ce(IV)
O
OH
H
R
R
R
R
K
C
C
Ce(IV)
+
H
(C1)
k (rds)
e- transfer and deprotonation
H
O
R
.
+ H+
+ Ce(III)
C
R
(C2)
fast
H
O
H
O
R
R
+
R
R
.
C
C
Ce(IV)
H
Ce(III) +
+
O
R
R
R
R
R
+
C
or
O
O
C
C
H+
=
H
= H
when R
R or R
CH3, CH3CH2
Scheme 2. Oxidation of aliphatic alcohol by Ce(IV) in the absence of catalyst in aqueous acidic media.
2-butanol (2.166 × 10−5 s−1) [48]. Therefore, ethanol and propanol
were oxidized at a faster rate (Table 1) in comparison to propan-2-ol,
1-butanol, and 2-butanol in the uncatalyzed path. Again, propan-2-ol
and 1-butanol were oxidized at a more faster rate compared to the eth-
anol, propanol, and 2-butanol in Ir(III) catalyzed path. The trend is
slightly discontinued here. But in the case of CHAPS and CHAPS-Ir(III)
systems the larger oxidation rate constants were obtained (Table 1)
for more sterically hindered alcohols over less sterically hindered
alcohols. The magnitude of the rate constants for the Ce(IV)-oxidation
of alcohols with different chain length is different.
bile salt derivative is fully removed from contact with water molecules
[57]. All these effects strongly explain that CHAPS increases in both
the affinity of cerium(IV) and Ir(III) reactive species to react with alco-
hol consequently increases the velocity of reaction in micelles.
4.5. Micellar effect on reaction rate
The surfactant concentration presents higher than the critical mi-
celle concentration (cmc) in water results in the formation of micelles
[58] consisting of a hydrophobic core and a hydrophilic head groups.
In the case of oxidation of all the alcohols, the cationic surfactant
N-cetylpyridinium chloride (CPC) has been found (Fig. 11b) to retard
the rate and the rate levels off at a higher CPC concentration. However
the most characteristic zwitter-ionic surfactant CHAPS has been found
to accelerate the rate process.
4.4. Structural difference between CPC and CHAPS surfactants
The head groups of zwitterionic (or amphoteric) detergents are hy-
drophilic and contain both positive and negative charges in equal num-
bers, resulting in zero net charge. Thus, 3-[(3-cholamidopropyl)
dimethylammonio]-1-propanesulfonate, better known as CHAPS be-
haves differently from N-cetylpyridinium chloride (CPC: containing a
pyridinium moiety and cetyl group) because of the presence of OH
groups in the CHAPS molecule, it possibly interacts with the aliphatic
alcohols through conformation changes of the amphiphile [40]. The
zwitterionic amphiphile CHAPS (Fig. 11a) interacts fairly by way of hy-
drogen bonding and hydrophobic interaction. Its hydrophobic group is
the same as that of cholic acid, i.e., a trihydroxy bile acid. During aggre-
gate formation, the hydrophobic faces are considered to contact with
each other, while the hydrophilic ones remain exposed to the aqueous
environment [56]. Therefore, the nonpolar part of CHAPS micelle cannot
be simply ascribed as a methyl group along with the number of methy-
lene groups like a classical surfactant tail (here CPC, Fig. 11b). During
micellization only a very small part of the cholesterol-like skeleton of
4.5.1. Rate accelerating effect by CHAPS
The oxidation reaction rates observed (Table 1) in CHAPS micellar
media can differ from those observed in conventional media. This is
accounted for the solubilization as well as in the orientation of the reac-
tants, reduction of their effective concentrations through their segrega-
tion in different ‘compartments’ within the bulk medium. The faster
oxidation rate is attributed to the higher reactant concentration within
CHAPS micelles, the changes in the polarity and physicochemical prop-
erties of the medium [59,60].
The zwitterionic micellar surface of CHAPS attracts the cationic spe-
cies Ce(SO4)2+ and Ir(III)-alcohol positive complex due to electrostatic
or coulombic interactions. Again the hydrophobic interactions [61]
can bring about the incorporation of the reactants (substrate) into mi-
celles. Thus, overall increment of rate occurs due to the increased

232
A. Ghosh et al. / Journal of Molecular Liquids 196 (2014) 223–237
k K K [
][Ir(III)]
RRCH
OH
1 2
1
kobs
=
[
1 + K RRCH ](
OH
1 +K2 [Ir(III)] )
1
H
Ir(III)
O
OH
H
R
R
R
K1
C
C
Ir(III) +
H
R
(C3)
H
H
Ir(III)
O
Ir(IV)
O
R
R
K2
R
C
Ce(III)
+
Ce(IV)
+
C
H
R
H
(C4)
k1
rds
O
H
R
R
.
H+
C
+ Ir(III)
+
O
O
H
+
H
R
R
.
+
C
C
+ Ce(III)
Ce(IV)
H+
R
R
R
R
R
or
O
O
C
C
H
when
=
H
R
R or R
=
CH3, CH3CH2
Scheme 3. Oxidation of aliphatic alcohol by Ce(IV) in the presence of Ir(III) catalyst in aqueous acidic media.
concentration of both alcohol and Ce(SO4)2+/Ir(III)-complex in the
Stern layer (Scheme 5) of micelle [62]. Reactants in the close vicinity
of the hydrophobic parts respond to the changes of properties in medi-
um by showing enhanced reaction rate [63]. Moreover, it should be
noted that the different hydrophobic alkyl chain length of the five differ-
ent alcohols is also expected to affect the partitioning effects
(Scheme 5a) and hence, the extent of the accelerating effects of the mi-
celle. Micellar catalysis by CHAPS was found to be more sensitive to-
wards Ir(III)-salt [64]. The incorporation of metal-substrate complex
into the micelles of CHAPS enhances almost kilo fold rate acceleration
for different alcohol oxidation. Based on electrostatic [4–6,13,15,
26–29] considerations, the reactive species Ce(SO4)2+ (presence of pos-
itive charge cloud around it) and the substrate alcohol (presence of elec-
tron cloud around on it) come closer to the zwitter-ionic CHAPS micellar
surface (containing a sulfobetaine group), which increases the local mo-
larities in the Stern layer [65]. Addition of Ir(III)-salt caused neutraliza-
tion of micellar surface charge (Scheme 5b), consequently catalyzed the
reaction by virtue of increased concentration of reactants in the Stern
layer [65].
4.5.2. Rate retarding effect by CPC
The inhibiting effect of CPC micelles is related to the different posi-
tions of the localization of substrate and oxidant in cationic micelles.
The rate data presented in Table 1 clearly reveals that the rate decreased
with increase in concentration of CPC. This indicates that there is a
charge development in the transition state involving a more polar acti-
vated complex [66] than in the reactants. From the plot of kobs versus
CPC concentration the rate constant value at the maxima or minima is
smaller than the rate constant value [67] in bulk water. This maxima
or minima point is the CMC value of CPC ranging from ~1.0 to 1.2 mM
for different alcohols. Addition of CPC leads to a slight increase in the re-
action rate after which further addition of CPC inhibits the observed rate
constant kobs value up to the minimum (Fig. 10a to e). In this path, CPC
restricts the positively charged alcohol-Ce(IV)-sulfate complex in an
aqueous phase and thus the accumulated neutral substrate in the micel-
lar phase (Stern layer) cannot participate in the reaction [4,6,26]. The
plot of kobs versus [CPC] (Fig. 10, Table 1) shows a continuous decrease
Scheme 4. Structural variation of the representative aliphatic alcohols.

A. Ghosh et al. / Journal of Molecular Liquids 196 (2014) 223–237
233
Fig. 10. Influence of the surfactant CPC on the kobs for the Ce(IV) oxidation of alcohol in aqueous H2SO4 media at 30 °C. [Ce(VI)]T = 2 × 10−4 mol dm−3, [H2SO4]T = 0.5 mol dm−3, μ =
[H2SO4 + Na2SO4] = 2.0 mol dm−3. For (a) [ethanol]T = 2 × 10−3 mol dm−3, (b) [propanol]T = 2 × 10−3 mol dm−3, (c) [propan-2-ol]T = 2 × 10−3 mol dm−3, (d) [1-butanol]T = 2 ×
10−3 mol dm−3, (e) [2-butanol]T = 2 × 10−3 mol dm−3
.
in rate up to the concentration of CPC used. Positive hydrophilic
groups of CPC micelles directed towards the exterior of the micelle
which strongly repels (Scheme 6) the approaching reactive species
Ce(SO4)2+ in an aqueous acidic medium. Hence relative lowering of
the local concentration of the reactants in the micellar phase which
results observed decreases in rate constants [38].
The catalytic effect is more pronounced in the presence of CHAPS in
comparison to CPC. Hence the rate of reaction is increased by the addi-
tion of both CHAPS and Ir(III) metal catalyst. The experimental data in
Table 1 describes the half life (t1/2) values of the alcohol oxidation reac-
tion by Ce(IV) gradually decreases upon addition of Ir(III) and CHAPS
micellar catalyst. The decrease in t1/2 value becomes more severe
when combined effect of CHAPS micelle and Ir(III) catalysts has come
into play.
4.6. The kinetic model to explain the micellar effects
Micellar catalysis generally depends on the interactions of the mi-
celle with the substrate (s) and the intermediate complex. This is an
enormously complicated problem because a number of different inter-
actions are concerned including those associated with the head groups
of the surfactant, different segments of the alkyl chain and the counter-
ions. By considering the Berezin's model, a solution above the CMC may
be regarded as a two-phase system (Scheme 7), consisting of an aque-
ous phase and a micellar pseudophase. A quantitative model for a bimo-
lecular reaction occurring only in the aqueous (kW path) and micellar
(kM path) phase [38] has been given as:
4.7. Optical micrographs for micelle
The optical micrographs are taken for the substrate–surfactant mix-
tures at 10:1 ratio in 100× magnification in an optical microscope. The
images (Fig. 12) represent the evidence of micelle formation in the
aqueous medium. The formation of micelles in association with the al-
cohols in aqueous medium was clearly identified from optical images.
4.8. DLS explanation of micellar aggregate
It was found from the plot (Fig. 13) that, in the case of CPC the size or
diameter of micelle changes when alcohol and Ce(IV) are added into the
micellar medium. The plot informs us about the changes in micellar di-
ameter when reactants are present in the reaction medium. This is also
evident from the SEM images (Fig. 4) of CPC micelle. The changes in size
or diameter of the micelle help us to understand that an interaction
RorR0 ¼ −H; −CH3; −CH3CH2
W = aqueous medium, M = CPC/CHAPS micellar medium, S =
substrate (alcohol), O = oxidant.

234
A. Ghosh et al. / Journal of Molecular Liquids 196 (2014) 223–237
Scheme 6. Schematic model showing probable location of reactants for the cationic micel-
lar mediated oxidation reaction between [Ce(IV)] complex and alcohol.
Fig. 11. (a) Molecular structure of surfactant CHAPS; (b) Molecular structure of surfactant
CPC.
occurs between the substrate (alcohol) and Ce(IV) with the "stern
layer" of CPC micelle. The overall charge of CPC micelle is cationic, there-
fore positive Ce(IV) species that interacts less with the aggregates and
alcohol molecules reside in the “stern layer” of the micelle. The size of
CPC was 5.6 nm as found in the plot. Upon the interaction of oxidant
and substrate with the outer surface of the aggregates the diameter of
the CPC micelle increases from 5.6 nm to 7.6 nm and 6.61 nm respec-
tively corresponding to Ce(IV) and alcohol (propanol) system.
Scheme 5. Schematic model showing probable location of reactants for the zwitter-ionic micellar mediated oxidation reaction between (a) [Ce(IV)] species, alcohol and proton; (b)
[Ce(IV)], Ir(III)-alcohol and proton.

A. Ghosh et al. / Journal of Molecular Liquids 196 (2014) 223–237
235
R or R
H
CH3, CH3CH2
=
,
W = aqueous medium, M = CPC/CHAPS micellar medium, S = substrate (alcohol), O = oxidant
Scheme 7. Partitioning of the oxidant and substrate between the aqueous and micellar pseudo phase.
CeðSO4Þ− þ SO24−
⇌
CeðSO4Þ3
K2 ¼ 5:5
3−
0
4.9. Reactive species of cerium(IV)
ð3Þ
ð4Þ
ð5Þ
2
Both Ce(III) and Ce(IV) ions are reported to form a number of com-
plexes in sulfuric acid media (Eqs. (1) to (4)) depending upon the con-
centrations of H+, HSO4−, and SO42−. The stepwise equilibria of Ce(III)–
sulfato and Ce(IV)–sulfato species, and the corresponding formation
constants [14] are as follows:
Ce4þ þ HSO−4
⇌
CeðSO4Þ2þ þ Hþ K1 ¼ 3500
0
CeðSO4Þ2þ þ HSO−4
⇌
CeðSO4Þ þ Hþ K2
0
¼ 200
2
2
CeðSO4Þ þ SO24−
⇌
CeðSO4Þ 3− þ Hþ K2 ¼ 20
0
ð6Þ
ð7Þ
Ce3þ þ SO24−
⇌
CeðSO4Þþ K1 ¼ 43
0
2
3
ð1Þ
HSO−4
⇌
SO42− þ Hþ:
CeðSO4Þþ þ SO24−
⇌
CeðSO4Þ− K2 ¼ 5
0
ð2Þ
2
Fig. 12. Optical micrograph images of mixtures of alcohol and surfactants in water: (a) 1-butanol:CHAPS = 10:1 (b) propan-2-ol:CPC = 10:1.
Fig. 13. (a) Variation of particle size distribution of CPC (1.1 mM) micelles/vesicles determined by dynamic light scattering (DLS). The average particle sizes for only (■) CPC is 5.6 nm and
ceric(IV) incorporated ( ) CPC is 7.6 nm. [Ce(IV)] = 2 × 10−4 mol dm−3, μ = 2 mol dm−3. (b) The average particle sizes for only (■) CPC is 5.6 nm and propanol incorporated ( ) CPC is
6.61 nm. [propanol] = 2 × 10−3 mol dm−3
.

236
A. Ghosh et al. / Journal of Molecular Liquids 196 (2014) 223–237
Table 3
Acknowledgment
The enhancement in rate of oxidation for different alcohol catalyzed by CHAPS-Ir(III)
system compared to the uncatalyzed reaction.
Thanks to UGC [(Grant- F. No. 33-495/2007 (SR)], New Delhi and
CSIR [(Grant- 01(2463)/11/EMR-II)], New Delhi for providing financial
help in the form of project and fellowship.
104 × substrate
Catalyst (mol dm−3
)
Enhancement
in rate
(mol dm−3
)
Ethanol
Propanol
Propan-2-ol
1-Butanol
2-Butanol
20
20
20
20
20
CHAPS = 8 × 10−3 and
Ir(III) = 2 × 10−6
747 fold
549 fold
2130 fold
1013 fold
719 fold
Appendix A. Supplementary data
Supplementary data to this article can be found online at http://dx.
doi.org/10.1016/j.molliq.2014.03.037.
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H
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alcohol oxidation.
The pseudo-first-order rate constants of the oxidation reaction be-
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N
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The overall key analysis of our present work comparing to the
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