Ru(III) catalysed oxidation of 2-propanol by Cr(VI) in micellar media

Article abstract of DOI:10.1016/j.molliq.2019.111247

Acetone, the simplest ketone of abundant useful is produced from 2-propanol by oxidation with hexavalent Cr(VI) sluggishly under pseudo 1st order reaction condition. The rate is enhanced considerably using Ru(III) metal salt solution at ppm level as a cat

Full text of DOI:10.1016/j.molliq.2019.111247

Accepted Manuscript
Ru(III) catalysed oxidation of 2-propanol by Cr(VI) in micellar
media
Suman Chowdhury, Atanu Rakshit, Animesh Acharjee,
Aniruddha Ghosh, Kalachand Mahali, Bidyut Saha
PII:
S0167-7322(19)32013-6
https://doi.org/10.1016/j.molliq.2019.111247
111247
DOI:
Article Number:
Reference:
MOLLIQ 111247
To appear in:
Journal of Molecular Liquids
Received date:
Revised date:
Accepted date:
8 April 2019
24 June 2019
26 June 2019
Please cite this article as: S. Chowdhury, A. Rakshit, A. Acharjee, et al., Ru(III) catalysed
oxidation of 2-propanol by Cr(VI) in micellar media, Journal of Molecular Liquids,
https://doi.org/10.1016/j.molliq.2019.111247
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ACCEPTED MANUSCRIPT
Ru(III) catalyzed oxidation of 2-propanol by Cr(VI) in
micellar media
1
1
1,2
3
Suman Chowdhury , Atanu Rakshit , Animesh Acharjee , Aniruddha Ghosh , Kalachand
Mahali and Bidyut Saha1*
3
1Homogeneous Catalysis Laboratory, Department of Chemistry, The University of Burdwan,
Burdwan 713104, WB, India
2Department of Chemistry, Hooghly Mohsin College, Chinsurah, WB, India
3Department of Chemistry, University of Kalyani, Kalyani, 741235, WB, India
*
9
Corresponding author, E-mail Id: b_saha31@rediffmail.com (B. Saha) Mobile: +91
476341691
Abstract
Acetone, the simplest ketone of abundant useful is produced from 2-propanol by oxidation with
st
hexavalent Cr(VI) sluggishly under pseudo 1 order reaction condition. The rate is enhanced
considerably using Ru(III) metal salt solution at ppm level as a catalyst. Additional rate
enhancement, is obtained in SDS micellar media, is reflected in rapid reduction of peak height of
absorbance curve of the oxidant Cr(VI) at λmax = 440 nm. The product, acetone is confirmed by
1
IR spectrum of 2, 4- DNP derivative and H-NMR study of acetone.
Keywords
2
-Propanol oxidation, Ru(III) metal catalysis, SDS micellar medium, ionic interaction.

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Abbreviations:
CMC – Critical Micelle Concentration
SDS – Sodium dodecylsulphate
CPC – Cetylpyridinium chloride
2
,4-DNP – 2,4-Dinitrophenylhydrazine
RDS – Rate Determining Step

ACCEPTED MANUSCRIPT
1
. Introduction
Synthetic organic reaction is a key process and one of the most important parts of organic
chemistry causing prosperity in biological and industrial issues of human being. Oxidation of
alcohol by higher valent metal ions being an organic reaction imparts the role of representative
on behalf of whole synthetic organic reactions. But like other synthetic organic processes
oxidation of alcohols by metal ions is also associated with ‘non-greener’ approach. So, some
greener approach is deeply solicited and mostly welcome. All the chemical processes in nature
(spontaneous or non-spontaneous) are honoured with the title ‘green’ as they are
thermodynamically irreversible requiring no external energy, hazardless due to involvement of
non-toxic, non-volatile solvents[1]. In this connection, using of non-aqueous and toxic solvents
in synthetic organic reactions is a ‘non-green’ process. So, in search of some greener approach a
way out has been revealed from the undiscovered treasury of chemistry where a non-organic
solvent, water, medium has been used to oxidise alcohol by Cr(VI) at ambient temperature in
homogeneous medium, achieved by using different surfactants. Surfactants are chemical species
having both hydrophilic and hydrophobic moieties. Therefore organic and inorganic species get
trapped in the aggregation of surfactants termed as ‘micelle’ which elevates the emulsifying
character of the medium [2-5]. In the present age surfactants, their characterisation, impacts
upon various reaction, Physicochemistry of Mixed Micellization, Thermodynamics of
aggregation, micellar behaviour in different media etc. are very wide field of research [6-11].
In this paper, the rate of oxidation of 2-propanol by Cr(VI) metal ion has been studied
spectrophotometrically in micellar media and in presence of Ru(III) metal ion as a catalyst at
3
0ºC. There may arise a big question about the greener approach where the toxic and
carcinogenic metal ion, Cr(VI) is used [12]. But, it is to be mentioned here that after the
oxidation of 2-propanol to acetone Cr(VI) is also reduced to trivalent chromium, Cr(III) which
being non-toxic to human health suppresses the initial toxicity. Even, Cr(III) is used as a
supplementary nutritive food object [13-14]. Though, there are many Cr(VI) sources e.g. PDC
(pyridinium dichromate), PCC (pyridinium chlorochromate), IDC (imidazolium dichromate)
available in market, potassium dichromate has been chosen here mainly for its greater solubility
in aqueous solvent where those one are scarcely soluble in water but organic solvent [12,15].
Choosing of 2-propanol as an alcohol lies in the large scale production of the corresponding
simplest ketone, acetone, which is very important as a precursor in the preparation of organic
derivatives and higher homologues of acetone for industrial and biological purposes including its
numerous uses as polar, aprotic solvent in laboratory [16-20]. The rate of oxidation of 2-

ACCEPTED MANUSCRIPT
propanol by Cr(VI) is quite slow. So, the rate enhancement is truly demanding. Here the rate
enhancement is achieved by using different surfactants which also make nano shaped
environment or nano reactor in the reaction medium [15, 21]. As already mentioned, there is
another chemical species Ru(III) metal ion, we have used for some additional rate enhancement
which is the main attraction of this research paper and has been discussed below in details. Rate
enhancement of 2-propanol oxidation by Cr(VI) by heteroaromatic bases in micellar media is
already reported [21]. But, the rate of the reaction is never reported in presence of any metal ion.
Beside that, there is some additional advantage of using metal salt for catalytic purposes over
hetero aromatic bases as promoter discerning the reusability and easy separation of metal salts
catalyst after one successful use of it [22-28] and the trace amount of metal salt which is too
small in concentration in contrast to the heterogeneous base promoters in the reaction mixtures
(about 1000 times smaller) making the metal salt superior as a catalyst to the heteroaromatic
promoter [29-32]. Therefore, our experiment is seemed to be exclusive in this regard.
2
. Experimental
2
.1. Materials and reagents :- 2-propanol (AR, Qualigens), K
2
Cr
2
O
7
(99.9 %, AR, BDH,
India), H SO (98%, AR, Merck, India), HCl (E. Merck, AR), sodium dodecylsulfate ( >90%,
2
4
AR, Merck, India), N-cetylpyridinium chloride (98.0 %, AR, SRL, India), Triton X-100 (98%,
AR, HIMEDIA, India), Ruthenium (III) chloride trihydrate pure (AR, SRL, Mumbai, India),
deuterium oxide (D
2
O) (99.9%, AR, Sigma-Aldrich, USA), chloroform-d (CDCl ) (99.8%, AR,
3
Sigma-Aldrich, USA). A solution of Ru(III) was prepared dissolving the salt in minimum
amount of concentrated hydrochloric acid and for the preparation of all solutions throughout the
experiments double distilled water was used. A methanolic solution of 2,4-DNP was prepared
for derivatization of acetone for IR experiment. All the chemicals were used as received without
further purification.
2
.2. Procedures and kinetic measurements
st
Every kinetic measurements were done keeping the reaction condition pseudo 1 order where
the 2-propanol was taken 20 times of the concentration of potassium dichromate acidified with
0
.5(M) H
2
SO . All the reactions were performed at thermostated condition at 30ºC (± 0.1ºC)
4
individually. In every oxidation reaction the concentration of the substrate and oxidant were
-3
-4
maintained at 4×10 (M) and 2×10 (M) respectively in 0.5(M) acidic medium made by H
2
SO
4
i.e at pH < 1 in presence and absence of varying concentration of surfactants (SDS, CPC and
-6
TX-100) above CMC and Ru(III) salt solution with the concentrations of order 10 (M). At pH <
-
1
hexavalent chromium remains mainly in the form of HCrO
4
in the aquous medium [32].

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Double beam UV-visible spectrophotometer [UV-Vis 1800 and UV-Vis 2450 (SHIMADZU)]
fitted with temperature controller was used to record one of the maximum absorbances (λmax) of
-1
-1
Cr(VI) at 440nm ( calculated absorption coefficient = 15630 L mol cm ) at 5 minutes time
interval to monitor the onward movement of the reactions. Sartorius BSA 224S-CW balance and
Digital Ultrasonic Cleaner CD 4820 Sonicator was used to prepare all the reaction solutions. For
1
various structural analysis IR spectra were recorded using Perkin Elmer Spectrum 2 and H-
NMR was recorded by Bruker Ascend 400 MHz spectrometer.
2
.3.
Product analysis and stoichiometry
Appearance of pale blue solution from pale yellow solution decides the completion of the
oxidation reactions. The product, acetone being the main product is easily separated by
fractional distillation from the product mixture and is precipitated to yellow coloured 2,4-DNP
derivative in H
2
SO medium. Thereafter the derivative was recrystallized in ethanol and the
4
melting point of this recrystallized one was found to be 126ºC, very close to the melting point of
1
hydrazine derivative of acetone (128ºC). For product confirmation IR-Spectra and H-NMR of
acetone derivative was recorded.
As each oxidation reaction follows pseudo-first order reaction condition here so, in
presence of excess substrate molecule Cr(VI) is expected to be entirely reduced to Cr(III)
leaving minimum chances of producing Cr(VI) with industrial discharge. Producing of Cr(III) in
the reaction mixture was confirmed by the λmax of the product mixture at 582.25 nm
characteristic of Cr(III) [33]. To measure the stoichiometry of the reaction varying amount of 2-
propanol solutions are treated with known concentration of Cr(VI) solution at constant H+
concentration 0.5 (M) and the mixtures were kept over a period of 5 days for completion. Then
the absorbances at 582.25 nm were taken with calculated absorption coefficient of Cr(III) 3250
-1
-1
L mol cm which exhibited the stoichiometry of the reaction as follows --
H C
3
H C
3
-
H+
3
CH
OH + 2HCrO +
8
3
=
C
O
+ 2Cr(III) + 8H O
4
2
H C
H C
3
3
2
.3.1. IR-Spectral analysis
From the IR spectra of the 2,4-dinitrophenylhydrazone of the product (Fig. S1a) and 2,4-
dinitrophenylhydrazine (Fig. S1b) we can make a comparative study from which we can see a
-1
stretching frequency in first one (Fig. S1a) at about 3312 cm for N-H (symmetric stretching)

ACCEPTED MANUSCRIPT
-1
and 1615 cm for C=N which conforms to 2,4-dnp derivative of acetone in the following
reaction.
O N
2
H C
3
H N
O N
2
H C
2
3
H+
C
O +
HN
NO2
C
N
H
H C
N
NO2
3
H C
3
Acetone
2,4-DNP
2,4-DNP derivative of acetone
1
2
.3.2. H-NMR spectral analysis
1
The H-NMR spectrum of the product was recorded with reference to TMS in CDCl
3
solvent at
4
00MHz (Fig. S2). The chemical shift (δ) at 2.2 ppm is due to –CH
3
and the highest intensity in
the spectrum mostly correspond to acetone (ignoring the additional peaks for some impurities).
3
. Results and discussion
3
.1. UV-Vis spectral analysis
The absorbances of Cr(VI) shows a reduction at 5 minutes time interval at λmax = 440nm with the
progress of the reaction (Fig. 1). Using the plot of –ln(A440) vs time (in minute) we can calculate
the pseudo-first order rate constants (k ) (Fig. 4). The half-life for all those reactions can also
obs
be calculated by using the equation, t1/2 = 0.693/k . We have mentioned here the calculated
obs
kobs and t1/2 of the reactions in each case (Table 1). It is seen from the experimental data that the
presence of Ru(III) enhances rate of the reaction greater amount than that of surfactants only.
When both Ru(III) and surfactants are present the reaction rate gets more than the previous. In
the scanned UV spectrum a successive decay of Cr (VI) and formation of Cr(III) is indicated
with an isosbestic point at 535.52 nm (Fig. 1) though the isosbestic point gets shifted in
presence of Ru(III) to 545.17 nm (Fig. 2) and 542.15 nm (Fig. 3). Actually after the reaction is
over the Cr(III) but not Cr(II) is confirmed from the peak values of the scanned UV-vis spectra
of the pale blue ultimate solution. After completion of reaction under the experimental
conditions, in absence and presence of Ru(III), reaction solution appears to be pale blue (λmax
=
4
4
4
5
82.25 nm and 407.12 nm ) corresponding to the transitions A (F)
→
T (F) and A (F)
2g 2g
2
g
4
→
T (F) of Cr(III) species (Fig. S3) [34-35].
1g

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Fig. 1 Scanned absorption spectra of the reaction in absence of any catalysts at a regular time
-3
-4
interval (5min): [2-Propanol]
Temperature = 30ºC.
T
= 4×10 (M), [Cr(VI)]
T
= 2×10 (M), [H
2 4
SO ]
T
= 0.5(M),

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Fig. 2 Scanned absorption spectra or the reaction in presence of Ru(III) catalyst at a regular time
-3
-4
interval (5 mins): [2-Propanol]
T
= 4×10 (M), [Cr(VI)]
T
= 2×10 (M), [H
2
SO
4
] = 0.5(M),
T
-6
[
Ru(III)]
T
= 2×10 (M), Temperature = 30ºC.
Fig. 3 Scanned absorption spectra of the reaction in presence of Ru(III) and SDS solutions at a
-3
-4
regular time interval (5min): [2-Propanol]
T
= 4×10 (M), [Cr(VI)]
T
= 2×10 (M), [H
2
SO
4
T
] =
-6
0
.5(M), [Ru(III)]
T
= 2×10 (M), [SDS]
T
= 0.04(M), Temperature = 30ºC.

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6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0
20
40
60
80
100
120
Time (minutes)
Fig. 4 Representative plot for Ru(III) + SDS catalysed oxidation path at 30°C for calculation of
-3
pseudo first order rate constant: A440 is the absorbance at 440 nm. [2-Propanol] = 4×10 (M),
T
-4
[
Cr(VI)]
T
= 2×10 (M), [H
2
SO
4
] = 0.5(M), Temperature = 30ºC.
T
Table 1 kobs and half life (t ) of the reaction in presence and absence of metal and micellar
1/2
catalysts.
-
1
Metal catalyst(M)
Micellar catalyst (M)
k
obs (s ) X
Half life
[t1/2](h)
X 106
105
None
None
None
1.05±0.05
1.72±0.09
2.52±0.09
3.33±0.10
4.73±0.14
2.75±0.09
3.05±0.10
3.78±0.10
5.88±0.20
7.95±0.10
18.2
11.21
7.64
5.78
4.06
7.00
6.31
5.10
3.27
2.42
Ru(III)
1.0
1
1
2
.2
.6
.0
---
SDS
SDS
0.04
0.04
1
1
1
2
.0
.2
.6
.0

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2
.0
CPC
0.04
0.02
0.68±0.07
1.48±0.09
1.66±0.09
2.03±0.10
2.52±0.10
2.30±0.10
1.96±0.10
1.74±0.10
27.92
13.00
11.60
9.46
----
TX-100
0
.04
0.02
.04
2
.0
0
7.64
1
1
1
.6
.2
.0
8.37
9.81
11.06
-3
-4
[
2-Propanol]
T
= 4×10 (M), [Cr(VI)]
T
= 2×10 (M), [H
2
SO
4
T
] = 0.5(M), Temperature = 30ºC
3
.2. Mechanism of the reaction
The mechanistic approach of forming the product, acetone, in the oxidation reaction is divided
into i) uncatalysed path and ii) catalysed path. The mechanism of uncatalysed path is already
nd
reported [21]. So, this is not mentioned here but we are interested to the 2 one, the Ru(III)
catalysed path where Ru(III) is playing a significant role to enhance the reaction rate.

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K1
2
-
2HCrO4-
Cr O
2
+ H O
2
7
3-
H C
3
Cl
Cl
III
H
C
K2
II
2
-
H C
3
CH  [RuCl (H O)]
+ H O
2
3
5
2
CH
O
Ru Cl
+
+
H
Cl
Cl
OH
H C
3
[
C ]
1
3-
H C
3
Cl
H C
3
Cl
II
VI
HCrO + H
IV
O + H CrO3
-
+
k1
rds
Ru Cl
+
4
C
2
CH
H C
O
III
+ [RuCl (H O)]
Cl
Cl
H C
3
2-
5
2
3
H C
3
H3C
H3C
fast
III
IV
CH OH + H2CrO3
+
+
H CrO + H
2 3
C
OH
H C
3
H C
3
H C
3
VI
OH + HCrO4 + H
V
-
+
C
O + H3CrO4
C
H C
3
H C
3
H C
3
H C
3
V
III
+
H CrO4
C
O + H CrO + H O
CH OH
H C
3
2
3
2
H C
3
3
Scheme 1. Mechanistic pathway of oxidation of 2-propanol by Cr(VI) in presence of Ru(III)
catalyst.
There are few examples where in acidic or alkaline medium the extensive use of Ru(III) as
a catalyst in oxidation reactions has been reported with different oxidants [36-46]. In this
reaction also the catalytic effect of Ru(III) is observed where, the actual reactive species in
2
-
2-
acidic medium is [RuCl
5
(H
2
O)] (Ru(III) chloride in acidic medium gives[RuCl
5
(H O)] ) [47].
2
The metallic species enhances the rate of oxidation reaction many times where Cr(VI) is used to
oxidise 2-popanol to acetone. To sketch a mechanistic approach (scheme 1) of the catalytic
reaction UV-vis spectrum of mixture of 2-propanol and Ru(III) solution was taken (Fig. S4). The
UV-vis spectrum of the mixture is distinctly different from the solution of metal salt solution. In
the comparative study we found a glimpse of light to have an insight into the probable reaction

ACCEPTED MANUSCRIPT
pathway (scheme 1). Possibility of association after one electron transfer and forming an 1:1
2
-
type complex (C
1
) between alcohol and [RuCl
5
(H
2
O)] is considered where Ru(III) is reduced to
Ru(II). Now, with the intervention of C
1
-complex the Ru(II) is oxidised to Ru(III) by Cr(VI) and
the product (here, acetone) is formed with Cr(IV) intermediate and catalytic species as well in
acidic medium following the rds (rate determining step). There after by subsequent fast steps
final oxidation products are obtained. The possibility of free radical involvement in the reaction
was also tested by acetonitrile, which gives white precipitate on keeping the reaction mixture 4h
undisturbed. This proves the presence of free radical in the reaction mixture [48]. Therefore the
previously reported mechanism of 2-propanol oxidation by Cr(VI) is supposed to be quite
different here in presence of Ru(III) species.
From our chemical intuition we can say that Ru(III) might be playing here a role of a
coordinator which facilitates the electron transfer from 2-propanol to Cr(VI). In absence of
Ru(III) there is a kind of inhibition in electron transferring process. The rate enhancement of
Ru(III) can be explained with the help of activation energy required for the progress of rate
determining step (k
1
) of the oxidation process. Perhaps, Ru(III) lowers the activation energy of
≠
electron transferring process and thus lowers the free energy of activation (ΔG ) of the process
enhancing the rate of the reaction. With the increase in Ru(III) concentration in the reaction
mixture the rate of the oxidation reaction becomes faster (Fig. 5).
8
8
7
7
6
6
5
5
4
4
3
3
2
2
1
1
0
.5
.0
.5
.0
.5
.0
.5
.0
.5
.0
.5
.0
.5
.0
.5
.0
.5
Ru(III)
Ru(III)+SDS
Ru(III)+TX-100
1
.0
1.5
2.0
6
[
Metal catalyst] (M)X10
T
Fig. 5 Dependence of kobs of 2-propanol oxidation by Cr(VI) on concentration of Ru(III) metal
-3
catalyst (in presence of surfactant) in aqueous H
2
SO
4
media at 30°C. [2-Propanol] = 4×10 (M),
T

ACCEPTED MANUSCRIPT
-4
[
Cr(VI)]
T
= 2×10 (M), [H
2
4
SO ]
T
= 0.5(M), [SDS]
T
= 0.04(M), [TX-100] = 0.04(M),
T
Temperature = 30ºC.
3
.2.1. Oxidation in presence of the surfactant
In addition to homogenize organic substrates in aqueous medium surfactants can also cause rate
enhancement depending upon their charges (anionic, cationic or neutral) [29-33, 49]. This
enhancement may be attributed to micelle formation of those surfactants above CMC (critical
micelle concentration) and congregation of reactants by dint of ion-dipole, dipole–induced
dipole or induced dipole-induced dipole interaction in a small volume of stern layer around the
micelle [29, 50].
Oxidation of 2-propanol by Cr(VI) has already been studied in micellar media and
reported [21]. In the present paper we have studied the same reaction in presence of Ru(III) as a
metal catalyst. In SDS rate enhancement in presence of Ru(III) is found to be extraordinarily
high whereas in CPC rate is retarded even in presence of Ru(III). In case of TX-100 the
oxidation rate is not as elevated as in SDS and TX-100 cannot enhance the rate jointly even with
Ru(III) may be due to its non-ionic nature. The surplus rate enhancement by Ru(III) in SDS and
TX-100 can be explained considering the nano-sized micelle formation by those surfactants and
pulling all the reacting species closure to happen the reaction smoothly. SDS being an anionic
surfactant construct a micelle with negatively charged peripheral surface. So, one should expect
VI
-
2-
that the anionic species, HCr O
4
and [RuCl
5
(H O)] (R) , in stern layer [29] should be inhibited
2
to reach the miceller surface and the substrate. But, we can say from our chemical intuition that
in acidic medium all the anionic species get protonated and become neutral. Now, in presence of
+
H these neutral species can bind to all kind of surfactants (anionic, cationic and neutral) through
an ion–dipole interaction and hydrogen bonding [50]. In SDS micellar media the positively
+
charged H can smoothly approach the substrate molecule (in the palisade layer) [51-53], the
Ru(III) chloride complex (R) and Cr(VI), bonded to the miceller surface (in the stern layer),
without any electrostatic repulsion due to the intensely negative charged miceller surface. Thus
SDS facilitates and boosts up the rate (k
1
) of the rate determining step of the oxidation reaction
favouring the C -complex formation (Fig. 6a).
1
+
In case of TX-100 also the closure approach of R, Cr(VI) and H to the substrate occurs
easily but, with less affinity due to the non-ionic nature of TX-100 micellar surface (Fig. 6b).
That is why, in presence of Ru(III) catalyst and TX-100 micellar media the rate of the present
oxidation reaction is higher than its normal rate but quite lower than the previous one, in
presence of the Ru(III) and SDS micelle. Whereas, in CPC micelle the whole case is logically

ACCEPTED MANUSCRIPT
different. In that case, CPC forms a micelle of positively charged surface. Therefore after the
inception of the reaction when the reaction approaches the product with the intervention of C1-
+
complex an energy barrier of electrostatic repulsion among cationic surface and H ions is to be
overcome to reach the substrate, R, Cr(VI) and so on (Fig. 6c). Thus, the reaction is slowed
down even in presence of Ru(III) as a catalyst.
Fig. 6 Schematic representation of micellar catalysed reactions. (a) SDS catalysed; (b) TX 100
catalysed; (c) CPC .
3
.3.
Interaction between 2-propanol and surfactants
In the whole discussion of the experiment the formation of micelle and position of the substrate
molecule with respect to the micelle has been predicted several times. Formation of micelle has
been proved before by DLS, 2D NOESY and HRTEM [32, 51-55] but it is truly difficult to
provide any concrete evidence in favour of the position of 2-propanol with respect to any micelle
in solution phase. Yet, we have tried to establish a support to the advantage of interaction
1
between micelle and 2-propanol at the stern layer in terms of H-NMR studies of mixture of each
surfactant and 2-propanol respectively.

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1
Table 2 δ (ppm) value of head group protons of SDS from H-NMR spectrum
α- CH
2
β- CH
2
SDS
3.982
3.687
1.634
3.355
SDS + 2-propanol
1
Table 3 δ (ppm) value of head group protons of TX 100 from H-NMR spectrum
d
e
f
g
h
TX-100
7.184
7.056
6.821
6.818
4.031
3.746
3.638
TX-100 +2-propanol
Up-field shifting and more
splitting
1
Table 4 δ (ppm) value of head group protons of CPC from H-NMR spectrum
α
β
a, a’
b, b’
c
CPC
4.699
1.980
1.916
8.976
8.878
8.114(dd)
8.061
8.585(t)
8.525
CPC +2-propanol

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In case of each and every mixture of surfactants (SDS, TX-100 and CPC) and our
substrate, 2-propanol, a notable change in every chemical shift value has been obtained either
upfield or downfield or more splitting sometimes [(Table 1, 2, 3) and (Fig. S5, S6, S7, S8, S9,
S10)]. Though we are yet to know the reason of these changes with confirmation, the alcoholic –
OH group can be taken into account to alter the position of chemical shift (δ ppm) value for its
electron withdrawing effect and H-bond forming ability with the N or O atom of the surfactants
resulting in upfield or downfield shifting duly of the polar head protons. We can vaguely say that
in most of the cases the upfield shift of polar head protons is due to increase of their electron
density for the closeness of alcoholic –OH to them. And as surfactants form micelle [32, 51-55]
then of course the substrate molecules house at the palisade layer to concord with the altered
chemical shifts.
4
. Conclusion
After evolving water-compatible micellar catalysts the scepticism apropos the water based
organic synthesis has been quenched. Surfactants are exemplary chemical species exerting
unique properties of enhancing many reaction rates [12,15, 21, 29-32, 51]. From many decades
metals are also keeping pace with surfactants to enhance reaction rate of many synthetic organic
reactions [36-46]. In case of 2-propanol oxidation by Cr(VI) in acidic medium also we have
found Ru(III) salt to be considered as a good metal catalyst and the togetherness of SDS and
Ru(III) makes the rate quite faster giving a footprint of better catalysis than Ru(III) only. TX-100
is also shows some rate enhancement but CPC being a cationic surfactant retards the oxidation
of 2-propanol. So, among SDS, TX-100 and CPC, SDS is the best pair with Ru(III) metal salt to
be used as catalyst. This very work is very unique from our side because an oxidation of alcohol
by Cr(VI) in acidic medium has never been reported with metal catalysis in micellar media
before.
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Graphical Abstract

ACCEPTED MANUSCRIPT
Highlights
1
2
3
4
5
. The oxidation carried out in aqueous medium.
. Micellar media is used to accelerate the oxidation.
-6
. Metal catalyst Ru(III) is used in trace concentration [10 (M)].
. Combination of SDS and Ru(III) is the best to accelerate the oxidation.
. SDS and TX-100 accelerate the oxidation but CPC reduces the rate of oxidation.