Rate enhancement via micelle encapsulation for room temperature metal catalyzed Ce(IV) oxidation of formaldehyde to formic acid in aqueous medium at atmospheric pressure: A kinetic approach

Article abstract of DOI:10.1016/j.molliq.2013.07.003

Oxidation kinetics of formaldehyde by Ce(IV) in aqueous medium in the presence of surfactants has been carried out to observe the micellar effect on rate. The oxidation kinetics was studied by UV-VIS spectrophotometry. Three catalysts Cu(II), Cr(III), and Ag(I) are used. Both Cr(III) and Ag(I) are active catalysts for the formaldehyde oxidation in the presence and absence of anionic surfactants, but Cu(II) is not an effective catalyst in this reaction. There are no roles of hetero-aromatic N-bases: picolinic acid (PA), 2,2′-bipyridine (bipy) and 1,10-phenanthroline (phen) as rate enhancement agents rather they inhibit the oxidation reaction. The presence of micelles was found to accelerate the reaction rate and this effect has been explained by the partitioning of the reactants in micelle and also by considering the hydrophobic and electrostatic interactions between the surfactants and reactants. The effect of sodium dodecyl sulfate (SDS) on the rate also indicate that Ce(SO ₄)^{2 +} was the main reactive form of cerium(IV). The main product formic acid was identified by the NMR spectroscopy and spot test. The probable mechanism is proposed and rate constants are calculated. The combination of Cr(III) and SDS is the most suitable combination for the conversion of formaldehyde to formic acid.

Full text of DOI:10.1016/j.molliq.2013.07.003

Journal of Molecular Liquids 186 (2013) 122–130
Contents lists available at ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Rate enhancement via micelle encapsulation for room temperature
metal catalyzed Ce(IV) oxidation of formaldehyde to formic acid in
aqueous medium at atmospheric pressure: A kinetic approach
a
a,b
a
a,
Aniruddha Ghosh , Rumpa Saha , Pintu Sar , Bidyut Saha ⁎
a
Homogeneous Catalysis Laboratory, Department of Chemistry, The University of Burdwan, Golapbag, Burdwan Pin 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:
Oxidation kinetics of formaldehyde by Ce(IV) in aqueous medium in the presence of surfactants has been carried
out to observe the micellar effect on rate. The oxidation kinetics was studied by UV–VIS spectrophotometry. Three
catalysts Cu(II), Cr(III), and Ag(I) are used. Both Cr(III) and Ag(I) are active catalysts for the formaldehyde oxida-
tion in the presence and absence of anionic surfactants, but Cu(II) is not an effective catalyst in this reaction. There
are no roles of hetero-aromatic N-bases: picolinic acid (PA), 2,2′-bipyridine (bipy) and 1,10-phenanthroline
Received 21 May 2013
Received in revised form 2 July 2013
Accepted 4 July 2013
Available online 19 July 2013
(
phen) as rate enhancement agents rather they inhibit the oxidation reaction. The presence of micelles was
Keywords:
Formaldehyde
Ce(IV)
found to accelerate the reaction rate and this effect has been explained by the partitioning of the reactants in
micelle and also by considering the hydrophobic and electrostatic interactions between the surfactants and
reactants. The effect of sodium dodecyl sulfate (SDS) on the rate also indicate that Ce(SO
2
+
SDS
4
)
was the main
Cr(III)
Ag(I)
Cu(II)
reactive form of cerium(IV). The main product formic acid was identified by the NMR spectroscopy and spot
test. The probable mechanism is proposed and rate constants are calculated. The combination of Cr(III) and SDS
is the most suitable combination for the conversion of formaldehyde to formic acid.
©
2013 Elsevier B.V. All rights reserved.
1
. Introduction
and carcinogenic hexavalent chromium [5,6]. Cerium chemistry is
mainly dominated by the +3 and +4 oxidation states. Ce(IV) is a
recognized oxidizing agent in acid media which has the reduction
potential of the couple Ce(IV)/Ce(III): 1.40 V. Ce(IV) ion is quite stable
in water owing to its high over potential for water oxidation to oxygen,
though it is a strong oxidizing agent, and has well-established aqueous
chemistries [7]. Several sulfate and hydroxo complexes of Ce(IV) exists
Formaldehyde (HCHO) is a serious environmental pollutant and is
hazardous to health, while formic acid is an important organic com-
pound [1] widely used in the pharmaceutical, leather, and cellulose
industries; in the manufacture of pentaerythritol, latexes, etc. It is
industrially produced by the liquid phase oxidation of butane and
light naphtha (as a byproduct), by the direct hydrolysis of methyl
formate, acidolysis of formic acid salts, and by CO hydration [2]. Formic
acid plays an important role in deploying renewable energy sources. As
liquid fuel cell it is more promising, since the generated hydrogen can
deliver higher electrochemical power in conventional batteries [3].
The difficulty arises in oxidizing formaldehyde due to the fact that it
exists in hydrated form. Water is ubiquitous in environment, and the hy-
dration equilibrium [4] for formaldehyde, different from that of nearly all
+
2+
−
4−
such as Ce(SO
4
)
2
, Ce(SO
4
)
4 2 4 2 4 3 4
, Ce(SO ) , Ce(SO ) HSO , H Ce(SO )
+
and Ce(OH)
3
in sulfuric acid and sulfate media, but their roles have
not established much attention so far. The mechanism is quite compli-
cated due to the formation of different Ce(IV) complexes in the form
of active species [8]. Generally in the synthetic studies, use of transition
metal ions as catalysts under homogeneous conditions has not been
attended properly. Thus the use of proper catalyst in Ce(IV) oxidation
2 4
reaction in aqueous H SO media draws much attention in cerate
4
aldehydes and ketones, lies far to the right (Keq ~ 10 at 20 °C).
oxidimetry as well as in catalytic kinetic techniques of analysis [9].
The oxidation of organic compounds by Ce(IV) in aqueous sulfuric
acid is kinetically sluggish, and the process can be effectively catalyzed
by a variety of transition metal ions such as Cr(III), Ag(I), Mn(II), Ni(II)
and Cu(II), etc. [10]. Among the different transition metal ions, Cr(III),
Ag(I) and Cu(II) have been used as a catalyst here. The present oxida-
tion of formaldehyde by Ce(IV) in aqueous sulfuric acid media is a kinet-
ically sluggish reaction [11]. Formaldehyde oxidation by cerium(IV)
sulfate in aqueous sulfuric acid is an inner sphere reaction involving
Keq
⇌
HCHO þ H O
CH ðOHÞ :
2
2
2
Ce(IV) has been taken as a preferable oxidizing agent in the
present work as it is relatively nontoxic compared to the hazardous
⁎
Corresponding author. Fax: +91 342 2530452.
E-mail address: b_saha31@rediffmail.com (B. Saha).
4 2
the intermediate Ce(SO ) : HCHO complex. However, the selection of
0167-7322/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molliq.2013.07.003

A. Ghosh et al. / Journal of Molecular Liquids 186 (2013) 122–130
123
a suitable metal catalyst and oxidizing agent, along with systematically
tuned reaction conditions, can sketch an entry to the mild and well-
organized oxidative conversion of organic substrates. The lack of studies
on formaldehyde oxidation by Ce(IV) in the presence of surfactant has
encouraged us to study the kinetic behavior of the title reaction in
continuation of metal ion catalysis in oxidation reactions of substance
by Ce(IV).
The surfactant aggregation process or micellization is mainly an
entropy-driven process. When surfactant molecules are dissolved in
water, the hydrophobic part interrupts the hydrogen-bonded structure
of water, and free energy of the system increases. As a result surfactant
molecules accumulate at interfaces, so that their hydrophobic parts are
directed away from the water and resulting in the minimization of
free energy of the solution [12]. A micelle-encapsulated substrate expe-
riences a reaction environment unlike from bulk water, leading to a
kinetic medium effect.
were of analytical grade with 99.9% purity. Stock solutions of Picolinic
acid (A.R. Sigma-Aldrich, Mumbai, India), 2,2′-bipyridine (A.R. Merck,
Mumbai, India), 1,10-phenanthroline (A.R. Merck, Mumbai, India) and
surfactant sodium dodecyl sulfate (A.R. SRL, Mumbai, India) were
prepared by using the weighing balance (Sartorius BSA224S-CW) and
Digital Ultrasonic Cleaner CD 4820 instrument. Surfactant substrate
mixture solution and other mixture solution containing surfactants
were centrifuged to get a complete mixing through Centrifuge-Z206A
(Hermle Labortechnik GmbH).
2.2. Kinetic measurements
Under kinetic conditions [S]
T
≫ [Ce(IV)]
T
T
≫ [catalyst] , (here
S = substrate formaldehyde) the reaction was carried out at different
concentrations of metal catalyst keeping the concentration of other
reactants constant. All kinetic measurements were performed under
In a synthetic point of view it is more significant to develop an active,
economical and stable catalyst for formaldehyde oxidation processes by
metal ion. This new catalytic formic acid synthesis technology has some
advantages over the liquid or gas phase methods: it is technologically
simpler, environmentally friendly; the process needs only small capital
investments and micellar catalyst can be recycled.
The kinetics of bimolecular reactions has been monitored spectro-
photometrically under pseudo-first-order conditions. The decrease of
the absorption of Ce(IV) is followed with respect to time in the presence
of a more than 10-fold excess of formaldehyde.
pseudo first order conditions taking formaldehyde at least 15-fold
excess over Ce(IV) at a constant ionic strength (μ) of 1.5 mol dm−
3
.
The reaction was initiated by addition of thermally equilibrated
(30.0 ± 0.10) °C solution of Ce(IV), formaldehyde, all other catalysts,
containing the required quantity of sulfuric acid. All reaction rates
were determined by measuring the change of absorbance of oxidant
in a 1 cm quartz cuvette with a Shimadzu-3600 UV–VIS NIR spectro-
photometer fitted with a Shimadzu thermostatically controlled cell
block. The progress of the reaction was observed by monitoring the
decrease in the absorbance of Ce(IV) at its absorption maximum of
3
20 nm as a function of time [14]. The pseudo-first order rate constants,
2
. Experimental section
kobs, are calculated by plots of log[Ce(IV)] versus time. The first order
plots in almost all cases are linear up to 75% of completion of the reac-
2
.1. Materials
tion and the kobs values are reproducible [15] to within ± 5%.
In the present work, doubly distilled water was used for preparing
3. Results
the solutions in all cases. Formaldehyde (A.R. Merck, Mumbai, India)
was used as such that it was made pure by fractional distillation
and its concentration was obtained from density measurements. The
stock solution of formaldehyde was prepared by dissolving it up to
its solubility in cold water. The Ce(IV) stock solution was prepared by
The rate of disappearance of Ce(IV) in the title reaction was the first
T
order in [Ce(IV)] and the pseudo-first-order rate constants (kobs) are
evaluated as reported earlier [11]. The effect of the catalyst was investigat-
−
4
−3
ed at a certain concentration of formaldehyde (30 × 10 mol dm
under pseudo first order criteria [HCHO] ≫ [Ce(IV)] at room temper-
ature as presented in Table 1.
)
−
3
dissolving cerium(IV) ammonium sulfate (A.R. Merck) in 1 mol dm
T
T
sulfuric acid and was standardized against iron(II) ammonium sulfate
solution [13]. Other chemicals and reagents such as chromic sulfate,
silver nitrate, sulfuric acid, acrylonitrile, hydrated copper sulfate used
The reaction rate is not affected with Cu(II). Cr(III) and Ag(I)
showed the catalytic activity. Same type of results has been reported
Table 1
Pseudo-first order rate constant (kobs) and half life of the reaction in presence and absence of metal ion catalyst, hetero-aromatic bases and surfactant.
1
08 × [Metal ion] (mol dm−3
)
102 × [Surfactant]
105 × [HB]
(mol dm
106 × kobs
t
1/2
(h)
−
3
−3
(s−1)
(mol dm
)
)
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
9.17 ± 0.03
18.16 ± 0.02
20.41 ± 0.03
24.83 ± 0.05
42.33 ± 0.04
9.91 ± 0.03
10.13 ± 0.05
10.84 ± 0.06
15.73 ± 0.04
4.7 ± 0.02
708.1 ± 0.03
497.3 ± 0.03
895.0 ± 0.04
1258.0 ± 0.02
1662.0 ± 0.02
642.5 ± 0.04
650.8. ± 0.05
750.3 ± 0.03
920.0 ± 0.03
3.73 ± 0.03
4.89 ± 0.03
2.99 ± 0.05
21.0
10.6
9.43
7.75
4.54
19.42
19.0
17.76
12.23
37.76
0.27
0.387
0.215
0.153
0.116
0.3
Cr(III)
2
0
00
000
2
0
00
000
2
–
2
2
–
–
2
2
–
Ag(I)
–
2
2
–
–
–
Cu(II)
–
–
SDS
2
2
Cr(III)
2
0
00
000
2
0
00
000
2
2
SDS
2
2
Ag(I)
2
SDS
2
0.295
0.256
0.21
51.6
39.36
64.38
2
–
–
PA
bipy
phen
2
2
2
Ce(IV)]
T 2 4 T
= 2 × 10− mol dm−3, [H ] = 0.5 mol dm−3, [HCHO] = 30 × 10−4 mol dm−3, μ = 1.5 mol dm−3, temp = 30 °C. HB = hetero-aromatic bases: PA, bipy, phen.
SO
4
[

124
A. Ghosh et al. / Journal of Molecular Liquids 186 (2013) 122–130
for the Ce(IV) oxidation of organic carboxylic acids in aqueous sulfu-
ric acid [9].
in the band that were observed [21]. The band observed for free form-
aldehyde substrate was around 293 nm. This absorption band was
shifted to 415 nm and 580 nm for HCHO–Cr(III) mixture and
2
74 nm for HCHO–Ag(I) mixture.
3
.1. Product study and stoichiometry
The reaction stoichiometry was obtained by taking cerium(IV) in
3.3.2. Encapsulation of substrate by surfactant
large excess over the organic substrate to ensure its entire oxidation.
In this oxidation process total amount of cerium(IV) sulfate consumed
by 1 mol of formaldehyde was determined by individual reacting
species variation.
There are substantial evidences that those organic substrates
(formaldehyde) enjoying appreciable polar character are concentrated
predominantly much on the micellar surface. Being a polar molecule
formaldehyde that exists mostly at the micellar surface experiences
strong hydrophobic interactions between the molecule and the micelle
Under the kinetic conditions, the stoichiometry [11] conforms to:
(
SDS) [22]. The change in the absorption values are observed during
þ
2
CeðIVÞ þ HCHO þ H SO →2CeðIIIÞ þ HCOOH þ 2H :
measuring the scan absorption spectrum (interval of 1 min) of
formaldehyde–SDS mixture solution compared to the only formalde-
hyde solution. This indicates the encapsulation/incorporation (Fig. 4)
of formaldehyde within the SDS micelle. In this case the substrate form-
aldehyde is partitioned between water and micellar pseudo phase.
2
4
3
.2. Analysis of product and test of free radicals
The completion of the reaction was concluded by the absolute fading
−1
The pseudo-first-order rate constants (kobs, s ) are determined
of Ce(IV) color (yellow). Formic acid was identified as a main product
by spot test and NMR spectral analysis [16,17]. The stoichiometry of
Ce(IV):HCHO was found to be 2:1, the other product Ce(III) was also
detected by spot test [18]. The addition of acrylonitrile solution
from the slope of plots of ln(A320) against time (t) at wave length
3
20 nm; the rate datas are presented in Table 1. The half-life (t1/2)
values are directly calculated by using equation t1/2 = (ln2/kobs),
where ln2 = 0.693, kobs = pseudo-first-order rate constant. With an
increase in the concentration of the catalyst in the reaction mixture
the rate is also increased. It is cleared that the combination of SDS and
Cr(III) at its highest concentration accelerates the rate more compared
to the SDS–Ag(I) combination as given in Table 1. The above fact is
also depicted from the scanned absorption spectra observed for the
Cr(III) and Ag(I) catalyzed path in the presence of SDS (Fig. 2d and e).
The t1/2 value for SDS–Cr(III) combination path is minimum and the ob-
served rate is maximum. Almost 200 fold rate acceleration is achieved
by using SDS and Cr(III) as a combined catalyst compared to the
uncatalyzed reaction path.
(
40%, V/V) to the reaction mixture under the protection of nitrogen
gas has been carried out gently. A lot of white deposition was found,
indicating that the reaction system can initiate polymerization of
acrylonitrile [11,13,19]. The appearance of precipitate proves the gener-
ation of free radicals in the reaction. The characteristic H NMR signal
Supplementary file) of the purified product from the mixture also
1
(
confirmed that the oxidized product is formic acid [20].
3
3
5
.3. Spectrophotometric analysis of the reaction
.3.1. UV–VIS spectra
The reaction mixtures were scanned in the range over 200 nm–
00 nm in both the presence and absence of metal ion catalysts
3
.4. Dependence of rate on Ce(IV) and substrate concentration
[Cr(III), Ag(I), Cu(II)] and chelating agents (PA, bipy, phen) individually
The rate of the reactions was studied under varying concentrations
at regular time intervals to observe the gradual development of the
reaction intermediates (if any) and the product. The scanned spectra
indicate the gradual disappearance of Ce(IV) species and appearance
of Ce(III) species with changes in the absorbance values in a decreasing
way (Fig. 1). The same also appeared for micellar catalyzed reactions
in the presence and absence of metal ion catalysts (Fig. 2a, b, c, d, e).
In the presence of SDS and Cr(III), the scanned spectrum is monitored
within a very short time interval (15 s).
of Ce(IV), and plots of ln(A320) versus time were linear indicating a
first order dependence on Ce(IV) concentration. The rate of disappear-
ance of Ce(IV) in the present study was found to be first order on
Ce(IV) concentration and the pseudo-first-order rate constants (kobs
)
evaluated are given in Table 1.
T
The plot of kobs vs. [HCHO] first increases sharply as the substrate
concentration increases then levels off at a higher substrate concen-
tration as reported previously [11].
The formation of a complex between substrate and catalyst is
evidenced from UV–VIS spectra (Fig. 3) in which there were changes
3.5. Dependence of rate on catalyst concentration
The catalyst concentration has a high satisfactory result in the cata-
lyzed path over the uncatalyzed reaction path under the same experi-
mental and kinetic conditions. It is observed that both in the presence
and absence of SDS, with an increase in metal ion concentration the
rate of the reaction increased.
3.6. Dependence of Cr(III)
The pseudo-first-order rate constant (kobs) at fixed [HCHO]
T
concen-
−
4
−3
tration (30 × 10
mol dm ) increases [23] sharply with increasing
−
5
−8
−3
Cr(III) concentration (2 × 10
–2 × 10
mol dm ) but levels off
at higher values of Cr(III) concentration as evident from Table 1.
3.7. Dependence of Ag(I)
The reaction rates were measured with different Ag(I) concentra-
tions in the range of 2 × 10 –2 × 10 mol dm , keeping the con-
centration of other reactants constant (Table 1).
Fig. 1. Spectral changes observed during degradation of formaldehyde by Ce(IV) for
−
5
−8
−3
−
4
−3
−3
1
5 min time interval. [Ce(IV)]
T
= 2 × 10
mol dm
· [H
2
SO
4
] = 0.5 mol dm
,
= 30 × 10− mol dm , μ = 1.5 mol dm−3, temp = 30 °C.
4
−3
[HCHO]
T

A. Ghosh et al. / Journal of Molecular Liquids 186 (2013) 122–130
125
Fig. 2. a: Sequential scans of absorption spectra during the course of the Cr(III) catalyzed reaction of formaldehyde with Ce(IV) in sulfuric acid media for 5 min time interval with
4
−3
−4
−3
−5
−3
−3
−3
[
HCHO]
T
= 30 × 10− mol dm , [Ce(IV)]
T
= 2 × 10
mol dm , [Cr(III)]
T
= 2 × 10
mol dm , [H
2
SO
4
] = 0.5 mol dm , μ = 1.5 mol dm , temp = 30 °C. b: Sequential
= 30 ×
T T 2 4
= 2 × 10 mol dm , [Ag(I)] = 2 × 10 mol dm , [H SO ] = 0.5 mol dm , μ = 1.5 mol dm , temp = 30 °C. c: Sequential scans of absorption
scans of absorption spectra during the course of the Ag(I) catalyzed reaction of formaldehyde with Ce(IV) in sulfuric acid media for 5 min time interval with [HCHO]
T
−
4
−3
−4
−3
−5
−3
−3
−3
1
0
mol dm , [Ce(IV)]
−
4
−3
spectra during the course of the SDS catalyzed reaction of formaldehyde with Ce(IV) in sulfuric acid media for 1 min time interval with [HCHO]
T
= 30 × 10 mol dm
= 2 × 10− mol dm , [SDS]
= 2 × 10 mol dm , [H SO ] = 0.5 mol dm , μ = 1.5 mol dm , temp = 30 °C. d: Sequential scans of absorption spectra during the
T T 2 4
,
4
−3
−2
−3
−3
−3
[Ce(IV)]
course of the Cr(III) and SDS catalyzed reaction of formaldehyde with Ce(IV) in sulfuric acid media for 15 second time interval with [HCHO]
× 10 mol dm , [Cr(III)]
spectra during the course of the Ag(I) and SDS catalyzed reaction of formaldehyde with Ce(IV) in sulfuric acid media for 15 second time interval with [HCHO] = 30 × 10 mol dm
= 2 × 10− mol dm , [Ag(I)]
Ce(IV)] = 2 × 10 mol dm , [SDS] = 2 × 10 mol dm , [H SO ] = 0.5 mol dm , μ = 1.5 mol dm , temp = 30 °C.
T T T 2 4
T
= 30 × 10− mol dm , [Ce(IV)]
4
−3
T
=
−
4
−3
−5
−3
−2
−3
−3
−3
2
= 2 × 10 mol dm , [SDS] = 2 × 10 mol dm , [H SO ] = 0.5 mol dm , μ = 1.5 mol dm , temp = 30 °C. e: Sequential scans of absorption
T T 2 4
−
4
−3
T
,
4
−3
−5
−3
−2
−3
−3
−3
[
Thus the increase in the rate of formaldehyde oxidation with Ag(I) is
3.8. Dependence of Cu(II)
mainly due to the assembly of more number of radicals for initiating the
oxidation process [9]. It is also feasible that the Ag(II) intermediate can
directly initiate the reaction, since it is known to be a more powerful
oxidizing species compared to Ag(I). Similar observations that were
also made in Ag(I) catalyzed the grafting of acrylonitrile onto gum
arabic by Ce(IV)-system [24].
The reaction rates were measured with different Cu(II) concentra-
tion, keeping the concentration of other reactants constant and ob-
served that the oxidation reaction rate has not affected much with
Cu(II) (Table 1). Cr(III) and Ag(I) can show the catalytic action, but
Cu(II) cannot show any catalytic action in this reaction as cleared

126
A. Ghosh et al. / Journal of Molecular Liquids 186 (2013) 122–130
Fig. 3. Spectroscopic evidence for the complex formation between formaldehyde-
= 30 × 10− mol dm
4
−3
,
Cr(III) and formaldehyde-Ag(I) catalyst respectively. [HCHO]
T
temp = 30 °C. (a) UV–VIS spectra of formaldehyde only (λ = 293 nm), (b) UV–VIS
spectra (λ = 415 and 580 nm): of mixture of formaldehyde and Cr(III) catalyst
T
Fig. 5. Absorption spectrum of reaction mixture (after completion of reaction): [HCHO] =
−4
−3
−4
−3
−3
3
1
1
0 × 10 mol dm
,
[Ce(IV)]
T
= 2 × 10 mol dm
,
[H
2
SO
4
] = 0.5 mol dm
,
μ =
= 2 × 10− mol dm ; (c) UV–VIS spectra (λ = 274 nm) of mixture of
5
−3
[
Cr(III)]
T
−3
.5 mol dm , temp = 30 °C (a) uncatalyzed, (b) Ag(I) catalyzed: [Ag(I)] = 2 ×
T
5
−3
formaldehyde and Ag(III) catalyst; [Ag(I)]
T
= 2 × 10− mol dm
.
−5
−3
−5
−3
0
mol dm . (c) Cr(III) catalyzed: [Cr(III)]
T
= 2 × 10
mol dm
.
from Table 1. The same type of results has been previously reported
for the Ce(IV) oxidation of organic carboxylic acids in aqueous sulfu-
ric acid [9,13].
rate constants are calculated for kinetic traces at 320 nm. Cerium(IV)
in redox processes reacts as an outer-sphere or inner-sphere mecha-
nism in accordance with the type of the reductant [7,28].
When the reductant formaldehyde was present in excess over the
oxidant Ce(IV), the catalyst chromium(III) remained unchanged in all
cases, as observed by measuring the absorbance at 580 nm.
The absorption spectrum of Ce(IV) species found in aqueous sulfuric
acid solutions differs from that of Ce(III). There is one absorption band
near 320 nm (Fig. 5) for Ce(IV) complexes in the aqueous sulfuric acid
medium.
3
.9. Effect of hetero-aromatic N-bases on rate
The oxidation reaction was studied also in the presence of three
most well known representative chelating N-hetero-aromatic bases:
PA, bipy and phen separately. But the reaction rate was inhibited by
all the three chelating agents used. In this oxidation reaction there are
no effective contributions of the used nitrogen bases as rate enhancing
agents. The three bases have no enhancing activity on the rate of Ce(IV)
oxidation of formaldehyde rather they hinder the rate of oxidation to a
greater extent. Even though it was investigated that the three bases
promoted the rate of oxidation of organic substrate by Cr(VI) in some
earlier reports [25–27].
4.1. Mechanism of the reaction
An analysis of product analysis and spectroscopic results indicates
that formic acid was the main oxidized product, i.e., oxidation took
place at the aldehyde group (\CHO) of formaldehyde. The mechanism
of the reaction can be split into two parts: (i) uncatalyzed path and
4
. Discussion
(
ii) catalyzed path. Based on the investigation carried out by substrate,
The progress of the reaction of formaldehyde with cerium(IV) is
hydrogen ion, catalyst concentration variation the uncatalyzed and
catalyzed mechanistic schemes are proposed. The variation of substrate,
hydrogen ion and hetero-aromatic base concentrations are not shown
highly reflected by the observed changes in the electronic spectrum.
The reason for these changes is the disappearance of the intensive yel-
low colored cerium(IV), which is reduced to a pale green [7] cerium(III)
+
in this context. Depending on the substrate, H ion, and Ce(IV) concen-
(Fig. 5). In these experiments, the kinetic traces were scanned at
tration variation on the rate and from previous literature the following
3
20 nm wave length with respect to Ce(IV). The pseudo-first-order
H
H
H
H
K
Ce(IV)
Ce(IV) +
C
O
C
O
k
rds
e-transfer and deprotonation
H
.
C
+
O
+
H
+
Ce(III)
H
H
.
C
+
C
fast
C
O
+
Ce(IV)
Ce(III) +
O
H
H
H
+
C
H O
2
C
O
O
O
- H+
+
O
HO
H
Fig. 4. Spectral changes observed before and after mixing of surfactant (SDS) into
H
formaldehyde solution. (a) Absorption spectrum of pure formaldehyde solution,
4
−3
[
HCHO]
T
= 30 × 10− mol dm , (b) scanned absorption spectra of the formaldehyde–
Scheme 1. Oxidation of formaldehyde in absence of catalyst by Ce(IV) in aqueous acidic
media.
= 2 × 10− mol dm , temp = 30 °C.
2
−3
SDS mixture at 1 min time interval, [SDS]
T

A. Ghosh et al. / Journal of Molecular Liquids 186 (2013) 122–130
127
Ce4+ + SO 42 -
2+
O
O
C
Cu(II)
H
Ce SO4
Ce(SO4)2
HCHO
Cr(III)
Ce(IV)
H2O
Cu(II) +
H
C
C
O
Ce(III)+ Cu(II)
2
+
2-
H
H
H
HO
Ce SO4 + SO4
HCHO + Cr3+
(
Complex)
Scheme 4. Oxidation of formaldehyde in presence of Cu(II) by Ce(IV) in aqueous acidic
k1
HCHO Cr(III) Ce(SO4)2
+
Cr(IV) + Ce3+
media.
HCHO
k-1
k2
.
Cr3+ + HCHO
The rate law [9,11] comes from the variation of Ce(IV) concentra-
tion, HCHO concentration and H ion concentration. They are not
shown in the text. The rate law came out to be as:
HCHO Cr(IV)
+
Ce4+ + HCHO.
H O
H+
2
HCOOH + Ce3+
-
kK½CeðIVÞꢀ½HCHOꢀ
:
Scheme 2. Oxidation of formaldehyde in presence of Cr(III) catalyst by Ce(IV) in aqueous
acidic media.
kobs
¼
1
þ K½HCHOꢀ
The reaction is of first order with respect to the substrate in both
catalyzed and uncatalyzed paths.
All these indicate and point a probable way of association of oxidant,
substrate and catalyst in some pre-equilibrium steps [11].
mechanisms both in the presence and absence of metal ion catalysts are
proposed as in Schemes 1–4.
4.3. Mechanism of Cr(III) catalysis
4
.2. Uncatalyzed path
The proposed mechanism involves a redox reaction by participation
Cerium(IV) has a tendency to form complex with the organic sub-
strate, which then decomposes to a free radical in the primary step.
The next step which is the transfer of the electron from the radical
of Cr(III) which binds with the substrate to form an inner-sphere
complex [9,31,32]. The electron transfer occurs within the complex to
produce an intermediate, Cr(III) bound [33] to the formaldehyde ion
(
Scheme 1) to the metal ion initiates the breaking of C\H bond,
resulting in the formation of the organic product [29].
In aqueous H SO media, complexation of organic substrate with
(
Scheme 2) radical, which rapidly gets oxidized by Ce(IV). The free
radical generated through an inner-sphere electron transfer process is
bound to an inert Cr(III) center and as a result the radical is not readily
available in solution to progress the polymerization process of acryloni-
trile in the bulk. In fact, for the catalyzed reaction, polymerization of
acrylonitrile has been observed to proceed slowly than the uncatalyzed
reaction, i.e., in the absence of Cr(III).
2
4
Ce(IV)-sulfato species is a unusual process [30]. From UV spectral
results it is evident that formaldehyde combines with Ce(IV) to form a
complex. However, there is a possibility of weak association to form a
complex between the substrate and Ce(IV)-sulfato species as shown
in Scheme 1.
The above proposed mechanism and the rate law has been derived
+
[
9,11] by varying Cr(III), HCHO and H ion concentration (not shown
O
C
Ag(I)
in the manuscript).
O
C
K1
Ag(I)
+
kobs ¼ 2
k k ½CeðIVÞꢀ½CrðIIIÞꢀ½HCHOꢀ
:
1
2
H
H
H
H
fk ½CeðIIIÞꢀ þ k ½HCHOꢀg
−
1
2
O
C
Ag(I)
+
O
C
Ag(II)
The overall mechanism may therefore be simplified by the forma-
tion of chromium(IV) in a reversible equilibrium, which then forms a
complex with formaldehyde. The complex will then experience internal
oxidation–reduction in a rate-determining step to produce formalde-
hyde radical and regenerate the catalyst. Further reaction of formalde-
hyde with the oxidant in the fast step gives rise to the respective acid.
All these observations can be illustrated by considering the following
reaction mechanism involving an association of the Ce(IV), formal-
dehyde and catalyst Cr(III) in some preequilibrium steps before the
electron transfer step. Under the experimental conditions in aqueous
sulfuric acid media, the most important Ce(IV) species [23] are
k3
Ce(IV)
Ce(III)
+
H
O
k-3
H
H
H
O
C
Ag(II)
k4
.
H+
Ag(I) +
+
C
H
H
H
O
O
2
+,
−
Ce(SO
.4. Mechanism of Ag(I) catalysis
It is well established that Ag(I) forms adducts [9] with oxygen con-
4
)
4 2 4 3
Ce(SO ) and HCe(SO ) .
fast
.
C
+ Ce(IV)
+ Ce(III)
C
+
4
H
H
O
H
+
O
taining compounds [34]. The adduct initially formed between Ag(I)
and formaldehyde. This Ag(I)-adduct undergoes interaction with
Ce(IV) to yield another higher valent Ag(II)-adduct (Scheme 3). This
adduct formation is confirmed spectrophotometrically by the addition
of 2,2′-bipyridine in the reaction mixture which yields a brown orange
colored Ag(II)–bipyridine complex [13,35] with its characteristic
absorption maximum at 454 nm.
H
H O
2
C
O
C
C
O
+
- H+
H
HO
H
H
Scheme 3. Oxidation of formaldehyde in presence of Ag(I) catalyst by Ce(IV) in aqueous
acidic media.

128
A. Ghosh et al. / Journal of Molecular Liquids 186 (2013) 122–130
The rate law has been derived [9,11] by varying Ag(I), HCHO and
factor by which each of the reactant is assimilated into the micelles
from the bulk solution. A promotion in the overall rate would occur
when both reactants are preferentially located in the micelles
[37–40]. The presence of anionic micelle SDS in the reaction mixture
above its critical micelle concentration (CMC) increased the kobs value
significantly in comparison to the uncatalyzed reaction. Here it is
H+ ion concentration (not shown in the manuscript).
kobs ¼ k K ½CeðIVÞꢀ½AgðIÞꢀ½HCHOꢀ
3
1
4
.5. Mechanism of Cu(II) catalysis
Cu(II) has no catalytic effect in this oxidation reaction though it
can form complex (Scheme 4) with the substrate formaldehyde. The
reaction rate is not very much affected.
a
Ce(SO )2
+
4
+
2
4
H+
4
.6. Rate inhibition by N-hetero-aromatic bases
H+
H+
H+
H+
Generally the chelating agents such as PA, bipy and phen react with
the higher valent transition metal ions, e.g., Cr(VI). In acidic medium
Cr(VI) forms charged (cationic) metal–ligand complex which is the
main active oxidant [25–27,36] species responsible for speed up of the
oxidation process. But in our works the evidence for such type of active
oxidant formation, Ce(IV)–ligand complex by three chelating N-bases
H+
H+
H+
H+
H+
H+
H+
H+ H+
(
ligands) PA, bipy and phen, was not detected by UV–VIS spectropho-
tometry. There are three probable reasons behind the non-existence
of the Ce(IV)–N-base complex in the present system:
Ce(SO )2
+
4
➢
The formation of Ce(IV)–substrate complex (Schemes 1–3) prior to
the formation of Ce(IV)–N-base complex under the present kinetic
condition. Ce(IV) is relatively inert comparable to the Cr(VI) center.
The lack of tendency of Ce(IV) to accept electron from N-base li-
gands owing to its weak oxidizing property in comparison to Cr(VI).
Furthermore during the oxidation process the generated free radi-
cals that repel the non-bonding pair of electrons on N-base ligands
remain un-coordinated and uncomplexed with Ce(IV). This results
in Ce(IV) showing reluctance towards the acceptance of electrons
from the N-base ligands.
b
H
H
H
H
C
O
C
O
➢
➢
Ce(SO4)2+
Cr(III)
Cr(III)C
e
+
(
2
)
4
S
O
H+
(SO
H+
)
H+
e
C
H+
H+
H+
Cr(III)
Cr(III)
H+
H+
O
O
C
H+
C
So, the complexation of the N-base ligands with Ce(IV) is not so easy
H+
+
H
H
2
H+
)
4
a process. These chelating N-bases hinder the approaching of substrate
molecules (here HCHO) towards Ce(IV) to form a maximum number of
Ce(IV)–HCHO complexes and thus the reaction rate is inhibited in
presence of N-hetero-aromatic bases.
H
H
H+
H+ H+
O
4
e(S
2+
C
Cr(III)
O
Cr(III)
Ce(SO4)2+
H
O
C
C
H
4
.7. Reactive species of cerium(IV) sulfate
H
H
Cerium(IV) forms a number of complexes in sulfuric acid solution.
c
H
C
H
H
H
4
þ
−
2þ
þHþ
C
O
Ce þ HSO4
⇌
CeðSO Þ
4
ðActive speciesÞ
O
2þ
−
þ
Ce(SO )2+
CeðSO4Þ þ HSO4
⇌
CeðSO Þ þ H :
4
2
Ag(I)
4
Ag(I)
C
e
(
S
)
O
The equilibrium constant for the complex formation between
H+
O
H+
S
)
Ce(SO
media. In the present system, Ce(SO
thermodynamic activity for complex formation is much greater [11]
than that of Ce(SO . Hence, it is reasonable to consider K (formation
constant for the Ce(SO –HCHO complex) ≫ 8.2. From the hydrogen–
sulfate dependence, under the experimental conditions Ce(SO
4
)
2
and HCHO is 8.2 dm3 mol
−1
at 30 °C in aqueous H
2
SO
4
e
(
H+
C
H+
H+
H+
H+
H+
)2+ is kinetically active and its
4
Ag(I)
Ag(I)
O
C
O
C
)
4 2
1
H+
)
4 2
H+
2
+
)
4
)
has
H
H
H+
H+
H
H
O
H+ H+
S
(
been identified as kinetically active among the different sulfato-
cerium(IV) species. In aqueous-micellar media, the different sulfato
complexes of Ce(IV) are expected to be partitioned in different ways.
This partitioning behavior may be helpful to identify the kinetically
reactive species. In fact, the micellar effect can be imposed as a reliable
probe to identify the reactive species [30].
e
C
Ag(I)
O
Ag(I)
H
2+
Ce(SO4)
O
C
H
C
H
H
Scheme 5. (a): Schematic representation of partitioning of Ce(SO
HCHO and proton in anionic surfactant SDS (normal micelle) in aqueous medium.
)2+ (active species),
4
4
.8. Effect of the non-functional micellar catalyst on the reaction rate
2
+
(b): Schematic representation of partitioning of Ce(SO
4
)
(Active species), HCHO–
When micelles are present in the solution, bimolecular reactions
Cr(III) complex and proton in anionic surfactant SDS (normal micelle) in aqueous medium.
can occur at two regions, viz. at the micellar region and in the bulk
solution. The overall reaction rate is determined by the partitioning
2+
(
c): Schematic representation of partitioning of Ce(SO
4
)
(active species), HCHO–Ag(I)
complex and proton in anionic surfactant SDS (normal micelle) in aqueous medium.

A. Ghosh et al. / Journal of Molecular Liquids 186 (2013) 122–130
129
assumed that the substrate is distributed between water and micellar
phases; hence, the overall rate will be the sum of the rates in water
and in the micelles. Therefore catalytic effect occurs when both reac-
tants bind to the micelle and react to give the product. The CMC of
SDS has been found experimentally as 8.2 mM by conductometric
method by our group [25,41].
that is positively charged interacts electrostatically with this phase. In
spite of the existence of the hydrated form of formaldehyde maximum
in water it can also convert to the aldehyde form in the presence of polar
micelles. Nevertheless of this equilibrium, Ce(IV) and metal catalysts
[Cr(III) and Ag(I)] undergo association in complex formation with form-
aldehyde in both its hydrated and aldehyde form. The metal–substrate
complex is positively charged which is the active metal catalyst. There
is no doubt that a negatively charged (polar) SDS micelles concentrate
more on the surface of both the oxidant Ce(IV) and the active metal
catalyst because of strong electrostatic interaction. This is the actual
driving force of the oxidation process to be enhanced in SDS micellar
medium that acts as micellar catalyst [36,37,51,52]. It is really observed
that the reaction rate has been very much accelerated due to lowering
of the activation energy in the SDS micellar catalyzed path.
A comparison table (Table 2) is given explaining the selection of
choice of Ce(IV) and catalyst over the other oxidants used previously
in formaldehyde to formic acid conversion.
In comparison to the other oxidizing species and catalyst used
previously the Ce(IV) system in the presence of SDS micelle has
been taken as a preferable oxidant. Ce(IV) is relatively non hazardous
and it can speed up the reaction faster in the presence of SDS and
Cr(III) catalyst compared to the other metal ion oxidant as given in
Table 2.
4
.9. Partitioning of reactant in presence and absence of metal ion catalyst
The small H+ ions required for the reaction are predominantly
partitioned in the micellar pseudo-phase. The catalytic behavior of
SDS micelles (Table 1, Scheme 5a–c) indicates that the positively
2
+
charged species of cerium(IV), Ce(SO
4
)
, is the reactive species.
The negative polar head group of SDS may form an ion-pair with
the reactive and existing species of cerium(IV); due to strong coulombic
electrostatic attraction [42–45] as a result of which a large number of
oxidant species are encapsulated/incorporated into the small volume
preferably in the palisade layer of anionic micelles. SDS allows the
reaction in both the aqueous and micellar phases with a preferential
rate enhancement [46,47] in the micellar phase. Hence it leads to higher
local concentrations of both the reactants at the micelle-water inter-
phase compared with their stoichiometric concentrations. Thereby the
anionic surfactant SDS has been found to show the rate-acceleration
effect [47]. In the presence of SDS both the reactants formaldehyde
2
+
and Ce(SO
4
)
are preferably partitioned (Scheme 5a) in the stern
5. Conclusion
layer of SDS and consequently the rate is accelerated [41,48,49]. The
acceleration of rate is more pronounced when metal ion Cr(III) and
Ag(I) are introduced. In the Cr(III) and Ag(I) catalyzed path the
HCHO–Cr(III) (Scheme 5b) and HCHO–Ag(I) (Scheme 5c) complex is
also partitioned in the micelle–water interface. Electronic interaction
of these positively charged metal–substrate [Ce(IV)–HCHO] complexes
with the negatively charged hydrophilic head group of SDS operates
smoothly and the acceleration of rate is more pronounced when
Cerium(IV) oxidation of formaldehyde in acid medium is very
−
8
−3
sluggish in room temperature. Small amounts of (10
mol dm
)
Cr(III) and Ag(I) increase the reaction rate. The role of hydrogen ion
is vital in this reaction. Cu(II) has no effective catalytic contribution
to the enhancement of reaction rate. Rather it retards the rate of
oxidation process. The most well known hetero-aromatic N-bases
(chelating species) PA, bipy and phen also inhibit the rate of formal-
dehyde oxidation with Ce(IV). The oxidation takes place between
the positively charged species of cerium(IV) and hydrated form of the
formaldehyde. The oxidation reaction occurs through the formation of
an intermediate complex, which slowly undergoes uni-molecular
decomposition to yield a free radical. The free radical then reacts with
cerium(IV) species to give the product formic acid. The rate has been
dramatically enhanced in the presence of surfactant SDS. Almost 200
fold rate acceleration is achieved for formaldehyde to formic acid
conversion when combinations of SDS and Cr(III) are used compared
to the uncatalyzed reaction path. In the present oxidation system,
2
+
4
Cr(III) and Ag(I) are used. Again the kinetic contribution of Ce(SO )
is much important to detect the actual reactive Ce(IV) species [30].
The binding forces between the hydrophobic parts of the substrate
and SDS micelle may be employed to reduce the overall activation
energy needed for the reaction [50]. In the course of the reaction the
surfactant SDS is transiently modified through an interaction with the
substrate (formaldehyde) but is subsequently regenerated to its origi-
nal state. We may also note at this point that, generally, the substrate
formaldehyde is uncharged and, hence, will interact with the micellar
phase by virtue of its hydrophobic properties, and the reactive species
Table 2
A comparative result for oxidation of formaldehyde using different oxidants and catalysts.
Entry
Catalyst
[Reference]
Conditions
106
k
)
obs
Half life
(t1/2) [h]
−
1
(s
3
−2
mol dm−3, K
] = 1 × 10−3 mol dm−3
1
2
3
4
5
.
.
.
[NaOH] = 2.0 mol dm−
[53]
[54]
[55]
[56]
[57]
[HCHO] = 2 × 10
3
[Fe(CN)
6
−3
,
121.33
1.58
μ = 2.0 mol dm− , [NaOH] = 2.0 mol dm , T = 40 °C.
3
[TsOH] = 1.0 mol dm−
3
[HCHO] = 0.10 mol dm , [BIDC] = 1 × 10
−3
−3
mol dm−3,
1120.0
1240.0
611.0
0.172
0.155
0.315
0.207
TsOH] = 1.0 mol dm− , T = 35 °C.
3
[
[NaOH] = 0.1 mol dm−
3
3
[HCHO] = 0.1 mol dm , [Mo(CN)
−3
3−
] = 5 × 10
−4
mol dm−3
,
8
NaOH] = 0.1 mol dm− , μ = 0.10 mol dm , T = 25 °C.
3
−3
[
] = 0.5 mol dm−
[HCHO] = 0.0675 mol dm , [HClO
−3
] = 0.5 mol dm−3
Cr(VI)] = 1.2 × 10− mol dm−3, T = 25 °C.
[HCHO] = 500 ppmv, 0.334 g silver titanium oxide photo-catalyst
(Ag/TiO ) coated on glass sticks with 254 nm ultraviolet lamp (UVC),
T = 25 °C.
[HCHO] = 0.35 mol dm , [Ce(IV)] = 4.4 × 10
,
[HClO
4
4
3
[
.
Ag/TiO
2
glass-sticks
928.33
photocatalyst = 0.334 g.
2
6
−3
−3
mol dm−3,
6
.
.
[Ir(III)] = 6.0 × 10− mol dm−3
[11]
1450.0
1662.0
0.132
0.116
Ir(III)] = 6.0 × 10− mol dm [H
6
−3
−3
[
2
SO
4
] = 1.0 mol dm , T = 25 °C.
2
−3
−3
−3
−4
−3
7
[SDS] = 2.0 × 10− mol dm−3 and
Present work
[HCHO] = 3.0 × 10
[H ] = 0.5 mol dm , [Cr(III)] = 2.0 × 10
mol dm , [Ce(IV)] = 2.0 × 10
mol dm
,
Cr(III) = 2.0 × 10− mol dm
5
−3
+
−5
mol dm−3,
SDS] = 2.0 × 10− mol dm−3, μ = 1.5 mol dm , T = 30 °C.
2
−3
[
[SDS] = 2.0 × 10− mol dm and
2
−3
Present work
[HCHO] = 3.0 × 10
−3
−3
mol dm , [Ce(IV)] = 2.0 × 10
−3
−4
mol dm−3,
920.0
0.21
8.
Ag(I) = 2.0 × 10− mol dm
5
−3
[H ] = 0.5 mol dm , [Ag(I)] = 2.0 × 10
+
−5
mol dm−3,
SDS] = 2.0 × 10− mol dm , μ = 1.5 mol dm , T = 30 °C.
2
−3
−3
[
Here, BIDC = benzimidazolium dichromate.

130
A. Ghosh et al. / Journal of Molecular Liquids 186 (2013) 122–130
)2+ is a kinetically active oxidizing species which can effectively
Ce(SO
4
[23]
P.N. Saha, S.K. Mondal, D. Kar, M. Das, A.K. Das, R.K. Mohanty, Journal of Chemical
Research, Synopses (1997) 364–365.
24] G. Thota, P. Srinivas, ISRN Physical Chemistry (2012) 1–7.
[25] A. Ghosh, R. Saha, B. Saha, Journal of Industrial and Engineering Chemistry (2013),
http://dx.doi.org/10.1016/j.jiec.2013.03.028 (in press).
partitioned along with the substrate and HCHO–catalyst complex in the
micelle–water interphase to give rise to HCOOH. Considering the over-
all kinetic and catalytic behavior of Cr(III) and SDS it is confirmed that
combination of SDS and Cr(III) may be useful for the synthesis of formic
acid from formaldehyde.
[
[
26] A. Ghosh, R. Saha, S.K. Ghosh, K. Mukherjee, B. Saha, Spectrochimica Acta Part A
09 (2013) 55–67.
1
[27] A. Basu, S.K. Ghosh, R. Saha, A. Ghosh, T. Ghosh, K. Mukherjee, S.S. Bhattacharyya,
B. Saha, Tenside Surfactants Detergents 49 (2012) 481–487.
[
[
[
[
[
28] A.M.M. Doherty, D.M. Radcliffe, G. Stedman, Journal of the Chemical Society
Dalton Transactions (1999) 3311–3316.
29] P.K. Tandon, S.Z. Khanam, S.C. Yadav, R.C. Shukla, Transition Metal Chemistry 36
Acknowledgments
(
2011) 739–746.
30] A.K. Das, M. Islam, R. Bayen, International Journal of Chemical Kinetics 40 (2008)
45–453.
31] L.V. Nimbalkar, A.M. Chavan, G.S. Gokavi, Journal of Physical Organic Chemistry
1 (1998) 697–700.
Thanks are extended to UGC, New Delhi and CSIR, New Delhi for
providing financial help in the form of project and fellowship.
4
1
Appendix A. Supplementary data
32] P.K. Tandon, M. Srivastava, S. Kumar, S. Singh, Journal of Molecular Catalysis A:
Chemical 304 (2009) 101–106.
[33] Z. Yong-qing, L. Hong-mei, Y. Lin, Y. Guo-zhong, Chemical Research in Chinese
Supplementary data to this article can be found online at http://
dx.doi.org/10.1016/j.molliq.2013.07.003.
Universities 23 (2007) 333–338.
[
34] S.A. Chimatadar, T. Basavaraj, S.T. Nandibewoor, Inorganic Reaction Mechanisms
(2002) 209–219.
[35] M.B. Yadav, V. Devra, A. Rani, Indian Journal of Chemistry 49A (2010) 442–447.
4
References
[
36] K. Mukherjee, R. Saha, A. Ghosh, S.K. Ghosh, B. Saha, Journal of Molecular Liquids
[
[
[
[
1] M.T.S. Adrian, M.C.M. Isabel, M.Q.F. Rosa, J. Levec, Chemical Engineering Science
179 (2013) 1–6.
58 (2003) 963–970.
[37] B. Kumar, M.L. Satnami, K.K. Ghosh, K. Kuca, Journal of Physical Organic Chemistry
25 (2012) 864–871.
[38] N.J. Buurma, Annual Reports on the Progress of Chemistry Section B Organic
Chemistry 108 (2012) 316–333.
[39] F. Szabó, B. Pethő, Z. Gonda, Z. Novák, RSC Advances 3 (2013) 4903–4908.
[40] T. Dwars, E. Paetzold, Angewandte Chemie International Edition 44 (2005) 7174–7199.
[41] K. Mukherjee, R. Saha, A. Ghosh, S.K. Ghosh, B. Saha, Spectrochimica Acta Part A
101 (2013) 294–305.
[42] S.K. Ghosh, R. Saha, A. Ghosh, K. Mukherjee, B. Saha, Tenside Surfactants Deter-
gents 49 (2012) 370–375.
2] E.V. Danilevich, G.Y. Popova, I.A. Zolotarskii, A. Ermakova, T.V. Andrushkevich,
Catalysis in Industry 2 (2010) 320–328.
3] S.W. Ting, C. Hu, J.K. Pulleri, K.Y. Chan, Industrial and Engineering Chemistry
Research 51 (2012) 4861–4867.
4] O.A. Kholdeeva, M.N. Timofeeva, G.M. Maksimov, R.I. Maksimovskaya, W.A.
Neiwert, C.L. Hill, Inorganic Chemistry 44 (2005) 666–672.
[5] B. Saha, C. Orvig, Coordination Chemistry Reviews 254 (2010) 2959–2972.
[6] R. Saha, R. Nandi, B. Saha, Journal of Coordination Chemistry 64 (2011) 1782–1806.
[7] J. Wisniewska, G. Wrzeszcz, M. Kurzawa, R.V. Eldik, Dalton Transactions 41
(
2012) 1259–1267.
8] T. Sumathi, P. Shanmugasundaram, G. Chandramohan, Asian Journal of Chemistry 23
2011) 4385–4392.
9] A.K. Das, Coordination Chemistry Reviews 213 (2001) 307–325.
[43] S.K. Ghosh, R. Saha, K. Mukherjee, A. Ghosh, S.S. Bhattacharyya, B. Saha, Journal of
the Korean Chemical Society 56 (2012) 164–167.
[44] A. Ghosh, R. Saha, K. Mukherjee, S.K. Ghosh, S.S. Bhattacharyya, B. Saha, Journal of
[
[
(
Chemical Research 36 (2012) 347–350.
[
[
[
[
10] C. Zhang, F. Liu, Y. Zhai, H. Ariga, N. Yi, Y. Liu, K. Asakura, M.F. Stephanopoulos, H.
He, Angewandte Chemie International Edition 51 (2012) 9628–9632.
11] D. Kar, S.K. Mondal, M. Das, A.K. Das, Journal of Chemical Research, Synopses
[45] R. Saha, S.K. Ghosh, A. Ghosh, I. Saha, K. Mukherjee, A. Basu, B. Saha, Research on
Chemical Intermediates 39 (2013) 631–643.
[46] S.R.K. Minkler, B.H. Lipshutz, N. Krause, Angewandte Chemie 123 (2011)
7966–7969.
[47] G. Bianchini, A. Cavarzan, A. Scarso, G. Strukul, Green Chemistry 11 (2009)
1517–1520.
[48] A. Ghosh, R. Saha, K. Mukhejee, S.K. Ghosh, S.S. Bhattacharyya, S. Laskar, B. Saha,
International Journal of Chemical Kinetics 45 (2013) 175–186.
[49] S.K. Ghosh, A. Ghosh, R. Saha, B. Saha, Tenside Surfactants Detergents 49 (2012)
296–299.
(1998) 394–395.
12] P. Alexander, R. Kanicky, P.K.J. Shukla, D.O. Shahy, Journal of Colloid and Interface
Science 245 (2002) 1–15.
13] T. Sumathi, P. Shanmugasundaram, G. Chandramohan, Arabian Journal of Chemistry
4
(2011) 427–435.
[
[
14] M. Melichercik, L. Treindl, Chemical Papers 42 (1988) 433–438.
15] D.C. Bilehal, R.M. Kulkarni, S.T. Nandibewoor, Turkish Journal of Chemistry 27
(
2003) 695–702.
[50] C. Gitler, A. Ochoa-Solano, Journal of the American Chemical Society 90 (1968)
5004–5009.
[
16] M. Hassan, N.A. Alhemiary, A.S. Albadani, Arabian Journal for Science and
Engineering 37 (2012) 1263–1270.
[51] R. Saha, A. Ghosh, B. Saha, Chemical Engineering Science 99 (2013) 23–27.
[52] L. Kumar, T. Mahajan, D.D. Agarwal, Industrial and Engineering Chemistry
Research 51 (2012) 2227–2234.
[53] V.N. Singh, M.C. Gangwar, B.B.L. Saxena, M.P. Singh, Canadian Journal of Chemistry
47 (1969) 1051–1056.
[
[
17] F. Feigl, Spot Test in Organic Analysis, Elsevier Publishing Co., New York, 1956. 334.
18] Department of Chemistry, Hangzhou University, Handbook of Analytical Chemistry,
Chemical Industry Press, Beijing, 1982. 618.
[
[
[
[
19] Y. Zhai, H. Liu, B. Liu, Y. Liu, J. Xiao, W. Bai, Transition Metal Chemistry 32 (2007)
5
70–575.
20] R.J. Abraham, J.J. Byrne, L. Griffiths, M. Perez, Magnetic Resonance in Chemistry 44
2006) 491–509.
[54] P. Kumar, D. Panday, S. Kothari, Croatica Chemica Acta 84 (2011) 53–61.
[55] C.R. Dennis, I.M. Potgieter, S.S. Basson, Reaction Kinetics, Mechanisms and Catalysis
104 (2011) 1–7.
[56] T.J. Kemp, W.A. Waters, Proceedings of the Royal Society of London A 274 (1963)
480–499.
(
21] R.V. Hosahalli, A.P. Savanur, S.T. Nandibewoor, S.S. Chimadar, International
Journal of Chemical Kinetics 42 (2010) 440–452.
22] N. Sardar, M. Kamil, Industrial and Engineering Chemistry Research 51 (2012)
[57] J.L. Shie, C.H. Lee, C.S. Chiou, C.T. Chang, C.C. Chang, C.Y. Chang, Journal of Hazardous
Materials 155 (2008) 164–172.
1
227–1235.