International Journal of Organic Chemistry, 2011, 1, 41-46
doi:10.4236/ijoc.2011.12008 Published Online June 2011 (http://www.SciRP.org/journal/ijoc)
La2O3 Catalyzed Oxidation of Alcohols
Ravikumar R. Gowda, Debashis Chakraborty*
Department of Chemistry, Indian Institute of Technology Madras, Chennai, India
Received April 8, 2011; revised April 28, 2011; accepted May 12, 2011
Abstract
A variety of aromatic, aliphatic and conjugated alcohols were transformed to the corresponding carboxylic
acids and ketones with a quantitative conversion in high yields with 70% t-BuOOH solution is water in the
presence of catalytic amounts of La2O3. 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, Alcohol, Carboxylic Acid, La2O3, t-BuOOH
1. Introduction
The oxidation of alcohols has been of contemporary in-
terest due to diversified potentials in organic chemistry
and industrial manufacturing, and is recognized a fun-
damental reaction [1-5]. The oxidation of primary alco-
hols yields aldehydes which may be further oxidized to
give carboxylic acids. The most popular and widely used
reagent for oxidation is Jones reagent [6-11]. However,
the reaction is stoichiometric and is performed under
highly acidic conditions. Substrates having acid sensitive
functionalities may not tolerate such acidity. In addition,
the generation of Cr-based side products may be viewed
as a potential environmental hazard [12]. Other reagents
that have been used successfully include Oxone [13],
calcium hypochlorite [14] and 2-hydroperoxyhexafluoro-
2-propanol [15]. Excellent catalytic methods using met-
als have been developed using oxidation reactions. In-
teresting methodologies for metal mediated transforma-
tion of aldehydes to carboxylic acids have been reported
recently [16-27]. The catalytic oxidation of alcohols em-
ploying transition metals such as Ru, Co, Mo, Pd, V and
W have been reported [28-39]. In addition, 2,2,6,6-
tetramethylpiperidinyl-1-oxyl often referred to as TEMPO
along with NaClO has been an efficient combination for
such oxidations [40-46]. The above reagents and meth-
ods 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. Our re-
cent results highlight the oxidation of aldehydes to car-
boxylic acid using 30% H2O2 as the oxidant in the pres-
ence of catalytic amounts of AgNO3 [47]. However, we
were unable to convert alcohols to ketones and carbox-
ylic acids under similar conditions. We were inspired to
venture into the area of La(III) catalyzed oxidation and
explore the possibility of using such compounds as cata-
lysts for oxidation reaction.
2. Results and Discussion
We decided to explore the possibility of converting pri-
mary alcohols to carboxylic acids and secondary alcohols
to ketones with the various La(III) salts. The optimiza-
tion of reaction conditions for the oxidation of primary
alcohols to the corresponding carboxylic acids was per-
formed with (4-nitrophenyl)methanol as a suitable sub-
strate in the presence of different solvents, oxidants and
5 mol% of La(III) salts (Table 1).
The oxidation of (4-nitrophenyl)methanol to 4-nitro-
benzoic acid takes place rapidly in the presence of 5
mol% La2O3 and 5 equiv. 70% t-BuOOH (water) using
MeCN as a suitable solvent (Table 1, Entry 1). In the
presence of 2 equiv. 70% t-BuOOH (water), only 30%
product could be isolated. With 5 equiv. 5M t-BuOOH
(decane), the reaction was found complete in 26 h with
90% isolated yield. Various trials were done in the pres-
ence of different solvents (Table 1, Entries 1-9) and dif-
ferent La(III) salts (Table 1, Entries 10 and 11). Best
results were obtained with 70% t-BuOOH (water) as the
oxidant and 5 mol% of La2O3 as the catalyst in MeCN.

R. R. GOWDA ET AL. 42
Table 1. Optimization of the reaction conditions for the
conversion of (4-nitrophenyl)methanol to 4-nitrobenzoic
acid with different solvents, 5 equiv. 70% t-BuOOH (water)
and 5 mol% La(III) salts.
Entry Catalyst Solvent Time (min)a Yield (%)b
1 La2O3 MeCN 18 98
2 La2O3 EtOAc 24 75
3 La2O3 toluene 24 27
4 La2O3 CH2Cl2 24 71
5 La2O3 DMF 24 42
6 La2O3 DMSO 24 82
7 La2O3 THF 24 25
8 La2O3 EtOH 24 5
9 La2O3 MeNO2 24 88
10 LaCl3 MeCN 24 65
11 LaBr3 MeCN 24 52
aTime required for complete conversion; bIsolated yield after column
chromatography of the crude product with ethyl acetate and hexane.
We proceeded with investigation the oxidation of vari-
ous aromatic and aliphatic substrates (Scheme 1, Table 2).
Again we see that La2O3 actively catalyzes the trans-
formation of different primary alcohols to the corre-
sponding benzoic acid with variety of different sub-
strates. Substitutions at different positions on the phenyl
ring do not hinder the reaction, although the reaction
time is affected. Our catalyst shows sufficient selectivity
in this oxidation without disturbing functional groups
like phenol and amine (Table 2, Entries 7 and 8). Oxi-
dation of
 ,  unsaturated derivatives (Table 2, Entry 15)
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 17-20 of Table 2.
It is pertinent to mention here that mild halogenic
oxidants like hypochlorites [14,48,49], chlorites [50,51]
and NBS [52,53] are not suitable for substrates with
electron rich aromatic rings, olefinic bonds and secon-
dary hydroxyl groups.
The kinetic studies of the oxidation with (4-methoxy-
phenyl)methanol and (3-nitrophenyl)methanol were ex-
plored next. High-pressure liquid chromatography (HPLC)
was used to determine the various starting materials,
products and aldehyde intermediates for alcohol oxidation
present as a function of time. The concentration of reactant,
intermediate and product for the oxidation of (4-meth-
oxyphenyl)methanol is shown in Figure 1.
The concentration of the alcohol decreases steadily
while that of the carboxylic acid increases. The concentra-
tion of the intermediate aldehyde increases, achieves a
steady state and then progressively converts itself to the
acid. The curve showing (4-methoxyphenyl)methanol is
zero-order in substrate. We have calculated the rate of
such reactions. As an example let us consider the conver-
sion of (4-methoxyphenyl)methanol to 4-Methoxy-
benzoic acid. The Van’t Hoff differential method was used
to determine the order (n) and rate constant (k) (Figure 2).
Scheme 1. La2O3 catalyzed oxidation of alcohols.
0510 15 20 25
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
Concentration(mol/L)
T
4-OMeC
ime(h)
6H4COOH
4-OMeC6H4COH
4-OMeC6H4CH2OH
r details).
Figure 1. Van’t Hoff differential plot for the oxidation of
(4-methoxyphenyl)methanol with 5 mol% La2O3 and 5
equiv. 70% t-BuOOH in MeCN under ambient condition.
From Figure 1, the rate of the reaction at different
concentrations can be estimated by evaluating the slope
of the tangent at each point on the curve corresponding
to that of 4-Methoxybenzylalcohol. With these data,
log10(rate) versus log10(concentration) is plotted. The
order (n) and rate constant (k) is given by the slope of the
line and its intercept on the log10 (rate) axis. From Figure
2 it is clear that this reaction proceeds with second-order
kinetics (n = 2.01) and the rate constant k = 9.29 × 10–1
L·mol1·h1. For the other substrate namely
(3-nitrophenyl)methanol, the order of the reaction n =
2.02 with rate constants (k) 1.61 × 10–4 L·mol1·h1 re-
spectively (see supporting information fo
3. Conclusions
In summary, we have developed a simple, efficient,
chemoselective and inexpensive catalytic method for the
oxidation of primary alcohols to carboxylic acids and
secondary alcohols to ketones using a table top reagent
such as La2O3. It is noteworthy that this method does not
use ligands and other additives.
4. Experimental Section
4.1. General Reagents and Equipments
All the substrates along with t-BuOOH, used in this

R. R. GOWDA ET AL.43
Table 2. La2O3 catalyzed oxidation of alcoholsa.
Entry Alcohol Product Time (h)bYield (%)c
1
CH
2
OH COOH
10 88
2
CH2OHMeO
COOHMeO
23 90
3
CH
2
OH
OMe
COOH
OMe
12 96
4
CH
2
OH
MeO
COOH
MeO
15 87
5
CH
2
OHMeO
MeO
COOHMeO
MeO
17 89
6
CH
2
OHMeO
OMe
MeO
COOHMeO
OMe
MeO
25 90
7
CH
2
OHHO COOHHO
27 87
8
CH
2
OHN COOHN
33 85
9
CH
2
OHCl COOHCl
25 88
10
CH
2
OHCl
Cl
COOHCl
Cl
28 86
11
CH
2
OH
NO
2
COOH
NO
2
40 82
12
CH
2
OH
O
2
N
COOH
O
2
N
48 85
13
CH
2
OHO
2
N
COOHO
2
N
18 98
14
OCH
2
OH
OCOOH
25 89
15
Ph CH
2
OH
Ph COOH
25 87
16
CH
2
OH COOH
55 83
17
Ph Ph
OH
Ph Ph
O
6 93
18
Ph Me
OH
Ph Me
O
17 90
19
OH O
4 92
20
OH
O
2
N
O
O
2
N
22 89

R. R. GOWDA ET AL. 44
--1 -1-1 -0 -01.6 .4.2 .0.8.6-0.4
-3.9
-3.6
-3.3
.0
.7
.4
.1
.8
.5
.2
.9
.6
.3-0
-3
-2
-2
-2
-1
-1
-1
-0
-0 Y = -0.03198 + 2.0112 X
log10 (rate)
log10 C
Figure 2. Van’t Hoff differential plot for the oxidation of
(4-methoxyphenyl)methanol with 5 mol% La2O3 and 5
equiv. 70% t-BuOOH in MeCN under ambient condition.
study were purchased from Aldrich and used as received.
The solvents used were purchased from Ranchem, India
and purified using standard methods. 1H and 13C spectra
were recorded with a Bruker Avance 400 instrument.
Chemical shifts were referenced to residual solvent
resonances and are reported as parts per million relative
to SiMe4. CDCl3 was used for NMR spectral measure-
ments. HPLC analysis was done with Waters HPLC in-
strument fitted with Waters 515 pump and Waters 2487
dual λ absorbance detector.
4.2. Typical Procedure for the Oxidation of
Primary Alcohol to Carboxylic Acid in MeCN
Under a nitrogen atmosphere, to a stirred solution of
La2O3 (16.29 mg, 0.05 mmol) and primary alcohol (1
mmol) in 2.5 mL MeCN was added 70% t-BuOOH (wa-
ter) (0.64 mL, 5 mmol). The progress of the reaction was
monitored using TLC until all the alcohol was consumed.
All the volatiles were removed using a rotary evaporator.
The crude product was treated with saturated NaHCO3
solution. This was extracted with ethyl acetate. Finally,
the aqueous layer was acidified using 2N HCl and ex-
tracted with ethyl acetate. The organic layer was concen-
trated in vacuum and subjected to column chromatogra-
phy with ethyl acetate and hexane. The spectral data of
the various carboxylic acids were found to match satis-
factory in accord with the literature.
4.3. Typical Procedure for the Oxidation of
Secondary Alcohol to Ketone in MeCN
Under a nitrogen atmosphere, to a stirred solution of
La2O3 (16.29 mg, 0.05 mmol) and secondary alcohol (1
mmol) in 2.5 mL MeCN was added 70% t-BuOOH (wa-
ter) (0.64 mL, 5 mmol). The progress of the reaction was
monitored using TLC until all the ketone was found
consumed. All the volatiles were removed using a rotary
evaporator. The residue was quenched with 2 mL water
and extracted with ethyl acetate. The organic layer was
concentrated in vacuum and subjected to column chro-
matography with ethyl acetate and hexane. Spectral
characterization of the various ketones was found to
match with the literature.
–
0.3
–
0.6 Y = –0.03198 + 2.0112X
–
0.9
–
1.2
–
1.5
–
1.8
–
2.1
–
2.4
–
2.7
–
3.0
–
3.3 5. Acknowledgements
–
3.6
–
3.9
This work was supported by the Department of Science
and Technology, New Delhi.
–
1.6 –1.4 –1.2 –1.0 –0.8 –0.6 –0.4
6. Electronic Supplementary Material
The online version of this article contains supplementary
material
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