Ceric ammonium nitrate catalyzed oxidation of aldehydes and alcohols

Article abstract of DOI:10.1002/cjoc.201180406

A variety of aromatic, aliphatic and conjugated aldehydes and alcohols were transformed to the corresponding carboxylic acids and ketones with a quantitative conversion in high yields with 70% t-BuOOH solution in water in the presence of catalytic amounts of ceric ammonium nitrate [Ce(NH ₄)₂(NO₃)₆] (CAN) under room temperature conditions. The scope of our catalytic system is applicable for a wide range of aromatic, conjugated and aliphatic substrates. These aldehydes were converted to the corresponding carboxylic acids in good isolated yields in reasonable times. This method possesses a wide range of capabilities since it can be used with other functional groups which may not tolerate oxidative conditions, involves fairly simple method for work-up, exhibits chemoselectivity and proceeds under ambient conditions. The resulting products are obtained in good yields within reasonable time.

Full text of DOI:10.1002/cjoc.201180406

FULL PAPER
Ceric Ammonium Nitrate Catalyzed Oxidation of Aldehydes
and Alcohols
Gowda, Ravikumar R.
Chakraborty, Debashis*
Department of Chemistry, Indian Institute of Technology Madras, Chennai-600 036, Tamil Nadu, India
A variety of aromatic, aliphatic and conjugated aldehydes and alcohols were transformed to the corresponding
carboxylic acids and ketones with a quantitative conversion in high yields with 70% t-BuOOH solution in water in
the presence of catalytic amounts of ceric ammonium nitrate [Ce(NH ) (NO ) ] (CAN) under room temperature
4
2
3 6
conditions. The scope of our catalytic system is applicable for a wide range of aromatic, conjugated and aliphatic
substrates. These aldehydes were converted to the corresponding carboxylic acids in good isolated yields in reason-
able times. This method possesses a wide range of capabilities since it can be used with other functional groups
which may not tolerate oxidative conditions, involves fairly simple method for work-up, exhibits chemoselectivity
and proceeds under ambient conditions. The resulting products are obtained in good yields within reasonable time.
Keywords oxidation, aldehyde, alcohol, ceric ammonium nitrate (CAN), t-BuOOH
Introduction
hydes to carboxylic acid using 30% H
in the presence of catalytic amounts of AgNO
were successful in employing Bi as a suitable cata-
We were interested in CAN oxi-
dations since it is a table-top reagent familiar to a
chemist from early years of education.
2 2
O as the oxidant
47
3
.
We
The oxidation of alcohols has been of contemporary
interest due to diversified potential in organic chemistry
and industrial manufacturing, and is recognized a fun-
damental reaction. The oxidation of primary alcohols
gives aldehydes that may be further oxidized to carbox-
ylic acids. The most popular and widely used reagent
2
O
3
48,49
lyst for oxidation.
1
-5
6-11
Experimental section
for oxidation is Jones reagent.
However, the reaction
is stoichiometric and is performed under highly acidic
conditions. Substrates having acid sensitive functional-
ities may not tolerate such acidity. In addition, the gen-
eration of Cr-based side products may be viewed as a
General reagents and equipments
All the substrates along with t-BuOOH, used in this
study were purchased from Aldrich and used as received.
The solvents used were purchased from Ranchem, India
and purified using standard methods. H and C spectra
were recorded with a Bruker Avance 400 instrument.
Chemical shifts were referenced to residual solvent
1
2
potential environmental hazard.
Other reagents that have been used successfully in-
1
13
1
3
14
clude Oxone, calcium hypochlorite and 2-hydro-
1
5
peroxyhexafluoro-2-propanol. Catalytic methods with
metals have been developed for oxidation reactions.
Different methodologies for metal mediated transforma-
tion of aldehydes to carboxylic acids have been reported
resonances and are reported relative to SiMe
4
. 0.5 mL
CDCl was used for every NMR spectral measurements.
3
1
H NMR spectra were collected at 400 MHz using a
6000 Hz spectral width, a relaxation delay of 3.5 s, a
1
6-27
recently.
The catalytic oxidations of alcohols em-
3
pulse width of 38°, 30k data points, and CDCl (δ 7.27)
ploying transition metals such as Ru, Co, Mo, Pd, V and
13
2
8-39
as an internal reference. C NMR spectra were col-
lected at 100 MHz using a 25000 Hz spectra width, a
relaxation delay of 1.5 s, 75k data points, a pulse width
W have been reported.
In addition, 2,2,6,6-tetra-
methylpiperidinyl-1-oxyl often referred to as TEMPO
along with NaClO has been an efficient combination for
4
0-46
of 40°, and CDCl
About 8— 10 mg of sample was dissolved in CDCl
3
(δ 77.23) as the internal reference.
and
such oxidations.
The above reagents and methods have one or more
limitations which include the use of superstoichiometric
amounts of expensive reagents and use of highly basic
or acidic reaction conditions. The search for catalytic
processes that use environmentally benign reagents is
always an attractive avenue.
3
used for measurement. HPLC analysis was done with
Waters HPLC instrument fitted with Waters 515 pump
and Waters 2487 dual λ absorbance detector. The col-
umn employed was washed thoroughly until a consis-
tent base line was found. Suitable methods were devel-
oped with different propotions of MeCN and alcohol.
Our recent results highlight the oxidation of alde-
*
E-mail: dchakraborty@iitm.ac.in
Received February 15, 2011; revised June 3, 2011; accepted June 15, 2011.
Chin. J. Chem. 2011, 29, 2379— 2384
© 2011 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
2379

Gowda & Chakraborty
FULL PAPER
Typical procedure for the oxidation of aldehyde to
carboxylic acid
Table 1 Optimization of the reaction conditions for the conver-
sion of benzaldehyde to benzoic acid with different solvents, 1
equiv. 70% t-BuOOH (water) and 1 mol% Ce salts
To a stirred solution of CAN (5 mg, 0.01 mmol or 50
mg, 0.1 mmol) and aldehyde (1 mmol or 10 mmol) in
a
b
Entry Catalyst
Solvent
EtOAc
MeCN
toluene
CH Cl
Time /h
Yield /%
2.5 mL or 25 mL MeCN was added 70% t-BuOOH
1
2
3
4
5
6
7
8
9
1
CAN
CAN
CAN
CAN
CAN
CAN
CAN
CAN
CAN
CeCl3
CeBr3
20
12
40
30
35
32
28
18
32
34
37
85
95
79
84
79
78
87
83
85
45
30
(water) (0.13 mL, 1 mmol or 1.3 mL, 10 mmol). The
progress of the reaction was monitored using TLC until
all aldehyde was found consumed. The crude product
was treated with saturated NaHCO
3
solution. This was
2
2
extracted with ethyl acetate. Finally, the aqueous layer
－
1
DMF
was acidified using 2 mol•L HCl and extracted with
ethyl acetate. The organic layer was concentrated and
subjected to column chromatography. The spectral data
of the various carboxylic acids were found to be satis-
factory in accord with the literature (see supplementary
material for details).
DMSO
THF
MeOH
CH NO
3 2
0
MeCN
MeCN
Typical procedure for the oxidation of primary al-
cohol to carboxylic acid in MeCN
11
a
To a stirred solution of CAN (10 mg, 0.02 mmol or
00 mg, 0.2 mmol) and primary alcohol (1 mmol or 10
Time required for complete conversion with 2% standard devia-
b
1
tion. Isolated yield after column chromatography of the crude
mmol) in 2.5 mL or 25 mL MeCN was added 70%
t-BuOOH (water) (0.26 mL, 2 mmol or 2.6 mL, 20
mmol). The progress of the reaction was monitored
using TLC until all aldehyde was found consumed. The
product with ethyl acetate and hexane with 2% standard devia-
tion.
The conversion of benzaldehyde to benzoic acid is
extremely facile in MeCN at ambient temperature in the
presence of 1 mol% CAN and 1 equiv. 70% t-BuOOH
(water) as the oxidant (Table 1, Entry 2). Oxidation with
t-BuOOH (water) alone in MeCN was found to be neg-
crude product was treated with saturated NaHCO
3
solu-
tion. This was extracted with ethyl acetate. Finally, the
－
1
aqueous layer was acidified using 2 mol•L HCl and
extracted with ethyl acetate. The organic layer was con-
centrated and subjected to column chromatography. The
spectral data of the various carboxylic acids were found
to be satisfactory in accord with the literature (see
supplementary material for details).
－
1
ligible (＜ 5%). With 1 equiv. 5 mol•L
t-BuOOH
(decane), the reaction was complete in 15 h with 90%
isolated yield.
The reaction took longer for completion (18 h) when
2 2
performed with 1 equiv. 30% H O in MeCN. Among
the different solvents used for optimization (Table 1,
Entries 1— 9), MeCN gave the best results. The other
Ce(III) salts (Table 1, Entries 10 and 11) yielded poor
results. In the absence of solvent, the reaction has gone
to completion in 16 h with 85% yield when performed
with 1 equiv. 70% t-BuOOH (water) and 1 mol% CAN.
Since most of the aldehydes in Table 2 are solids at am-
bient temperature, we have chosen MeCN as appropri-
ate solvent.
Typical procedure for the oxidation of secondary
alcohol to ketone in MeCN
To a stirred solution of CAN (10 mg, 0.02 mmol or
1
1
00 mg, 0.2 mmol) and secondary alcohol (1 mmol or
0 mmol) in 2.5 mL or 25 mL MeCN was added 70%
t-BuOOH (water) (0.26 mL, 2 mmol or 2.6 mL, 20
mmol). The progress of the reaction was monitored
using TLC until all aldehyde was found consumed. The
crude product was treated with saturated NaHCO
3
solu-
tion. This was extracted with ethyl acetate. Finally, the
We have performed large scale reaction (10 mmol of
benzaldehyde) in MeCN at ambient temperature in the
presence of 1 mol% CAN and 1 equiv. 70% t-BuOOH
(water) as the oxidant (Table 1, Entry 2), the reaction
has gone to completion in 12 h and yield is found to be
95%.
－
1
aqueous layer was acidified using 2 mol•L HCl and
extracted with ethyl acetate. The organic layer was
concentrated and subjected to column chromatography.
Spectral characterization of the various ketones was
found to match with the literature.
Having realized the correct conditions for oxidation,
we proceeded with a variety of aromatic and aliphatic
substrates (Scheme 1, Table 2).
Results and discussion
Oxidation of aldehydes and alcohols
Initial attempts to optimize the reaction conditions
for the oxidation of aldehydes to the corresponding
carboxylic acids were done using benzaldehyde as the
substrate in the presence of different solvents, oxidants
and 1 mol% of CAN (Table 1).
Scheme 1 CAN catalyzed oxidation of aldehydes to carboxylic
acids
2
380
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© 2011 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2011, 29, 2379— 2384

Ceric Ammonium Nitrate Catalyzed Oxidation of Aldehydes and Alcohols
Table 2 CAN catalyzed oxidation of aldehydes to carboxylic
acids
The scope of our catalytic system is applicable for a
wide range of aromatic, conjugated and aliphatic sub-
strates. These aldehydes were converted to the corre-
sponding carboxylic acids in good isolated yields in
reasonable times (Table 2).
a
b
c
EntryAldehyde
Acid
Time /minYield /%
1
12
10
95
93
It is pertinent to mention here that mild halogenic
1
4,50,51
52,53
oxidants like hypochlorites,
NBS
chlorites
and
5
4,55
2
3
are not suitable for substrates with electron
rich aromatic rings, olefinic bonds and secondary hy-
droxyl groups. Substitutions at different positions on the
phenyl ring do not hinder the reaction, although the re-
action time is affected.
Our catalytic system is mild and shows sufficient
selectivity in carrying out the expected oxidation with-
out affecting other functionalities like phenol and amine
15
94
93
94
90
4
5
6
19.5
10
(Table 2, Entries 6— 9). Oxidation of α, β unsaturated
derivatives (Table 2, Entries 15— 16) resulted in the
formation of the expected acid in very good yield.
Having made success in the transformation of the
aldehyde functionality into carboxylic acid, we decided
to explore the possibility of converting primary alcohols
to carboxylic acids and secondary alcohols to ketones
with CAN. The optimization of reaction conditions for
the oxidation of primary alcohols to the corresponding
carboxylic acids was performed with benzyl alcohol as a
suitable substrate in the presence of different solvents,
oxidants and 2 mol% of CAN (Table 3).
15
7
8
9
15
45
10
88
86
89
Table 3 Optimization of the reaction conditions for the conver-
sion of benzyl alcohol to benzoic acid with different solvents, 2
equiv. 70% t-BuOOH (water) and 2 mol% Ce salts
a
b
Entry Catalyst
Solvent
EtOAc
MeCN
toluene
CH Cl
Time /h
Yield /%
1
2
3
4
5
6
7
8
9
1
CAN
CAN
CAN
CAN
CAN
CAN
CAN
CAN
CAN
23
15
44
35
39
42
37
29
37
45
43
84
96
77
89
75
72
85
79
82
30
18
1
0
27
88
90
91
2
2
11
32.5
35
DMF
DMSO
THF
1
2
MeOH
CH NO
3
2
0
CeCl3
MeCN
MeCN
1
3
4
44
15
92
93
11
CeBr3
a
Time required for complete conversion with 2% standard devia-
1
b
tion. Isolated yield after column chromatography of the crude
product with ethyl acetate and hexane with 2% standard devia-
tion.
15
16
17
13
20
24
94
92
85
The oxidation of benzyl alcohol to benzoic acid
takes place rapidly in the presence of 2 mol% Ce salts
and 2 equiv. 70% t-BuOOH (water) using MeCN as a
suitable solvent (Table 3, Entry 2). With 2 equiv. 5
a
Reactions performed in MeCN with 1 mol% CAN and 1 equiv.
b
t-BuOOH (water) under ambient conditions. Time required for
complete conversion with 2% standard deviation. Isolated yield
c
－
1
mol•L t-BuOOH (decane), the reaction was found
after column chromatography of the crude product with ethyl
acetate and hexane with 2% standard deviation.
complete in 17 h with 90% isolated yield. Various trials
Chin. J. Chem. 2011, 29, 2379— 2384
© 2011 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
2381

Gowda & Chakraborty
Continued
FULL PAPER
were done in the presence of different solvents (Table 3,
Entries 1— 9) and other Ce(III) salts (Table 3, Entries 10
and 11). In the absence of solvent, the reaction has gone
to completion in 19 h with 86% yield when performed
with 2 equiv. 70% t-BuOOH (water) and 2 mol% CAN.
Since most of the alcohols in Table 4 are solids at am-
bient temperature, we have chosen MeCN as appropri-
ate solvent.
a
b
Time / Yield /
Entry
Alcohol
Acid/Ketone
h
%
1
0
39
49
51
85
We have performed large scale reaction (10 mmol of
benzyl alcohol) in MeCN at ambient temperature in the
presence of 2 mol% CAN and 2 equiv. 70% t-BuOOH
11
84
92
(
water) as the oxidant (Table 3, Entry 2), the reaction
has gone to completion in 15 h and yield is found to be
6%.
We proceeded with investigation of the oxidation of
1
2
9
various aromatic and aliphatic substrates (Scheme 2,
Table 4).
13
58
23
88
92
Scheme 2 CAN catalyzed oxidation of alcohols
1
4
15
16
17
21
30
31
88
86
90
1
8
12
28
80
85
Table 4 CAN catalyzed oxidation of primary alcohols to car-
boxylic acids and secondary alcohols to ketones
a
b
Time / Yield /
19
Entry
1
Alcohol
Acid/Ketone
h
%
15
19
96
2
0
9
89
92
2
3
92
95
2
1
32
23
27
18
22
a
Time required for complete conversion with 2% standard devia-
b
tion. Isolated yield after column chromatography of the crude
product with ethyl acetate and hexane with 2% standard deviation.
4
5
6
90
88
86
c
Reactions performed in MeCN with 2 mol% CAN and 2 equiv.
t-BuOOH (water) under ambient conditions.
Again we see that CAN actively catalyzes the trans-
formation of different primary alcohols to the corre-
sponding benzoic acid with variety of different sub-
strates. Our catalyst shows sufficient selectivity in this
oxidation without disturbing functional groups like
phenol and amine (Table 4, Entries 6— 9). Oxidation of
α,β-unsaturated derivatives (Table 4, Entries 15 and 17)
resulted in the formation of the expected acid in good
yield. In addition, the transformation of secondary al-
cohols to ketones is extremely facile as indicated by
Entries 18— 21 of Table 4.
7
8
9
24
58
22
90
89
92
Kinetic studies
The kinetic studies of the oxidation with
3
,4-dimethoxybenzaldehyde, 2-nitrobenzaldehyde, cro-
2
382
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Chin. J. Chem. 2011, 29, 2379— 2384

Ceric Ammonium Nitrate Catalyzed Oxidation of Aldehydes and Alcohols
tonaldehyde, (3-nitrophenyl) methanol and di-p-tolyl-
methanol were explored next. High-pressure liquid
chromatography (HPLC) was used to determine the
various starting materials, products and aldehyde inter-
mediates for alcohol oxidation present as a function of
time. Different trials were done under the same condi-
tions till concordant readings were observed. The con-
centration of reactant, intermediate and product for the
oxidation of (3-nitrophenyl) methanol is shown in Fig-
ure 1.
of the tangent at each point on the curve corresponding
to that of (3-nitrophenyl) methanol. With these data,
lg(rate) versus lg(concentration) is plotted. The order (n)
and rate constant (k) is given by the slope of the line and
its intercept on the lg(rate) axis. From Figure 2, it is
clear that this reaction proceeds with second-order ki-
−
3
netics (n＝ 2.02) and the rate constant k＝ 9.699× 10
－
1
－
1
L•mol •min . For the other substrates namely
3,4-dimethoxybenzaldehyde, 2-nitrobenzaldehyde, cro-
tonaldehyde, and di-p-tolylmethanol, the order of the
reaction n≈ 2 with rate constants (k) 0.1266, 6.653×
−
3
−2
−2
－
1
－
1
1
0 , 5.662× 10 and 9.826× 10 L•mol • min re-
spectively (see supplementary material for details).
Conclusions
In summary, we have developed a simple, efficient,
chemoselective and inexpensive catalytic method for the
oxidation of aldehydes to carboxylic acids, primary al-
cohols to carboxylic acids and secondary alcohols to
ketones using a table top reagent such as CAN. It is
noteworthy that this method does not use ligands and
other additives.
Acknowledgements
Figure 1 Concentration versus time in the oxidation of
(
3-nitrophenyl) methanol with 2 mol% CAN and 2 equiv.
This work was supported by the Department of Sci-
ence and Technology, New Delhi.
t-BuOOH in MeCN under ambient conditions with 2% standard
deviation.
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2383

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FULL PAPER
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