Ni(NO3)2·6H2O/I2/water: A new, mild and efficient system for the selective oxidation of alcohols into aldehydes and ketones under sonic condition

Article abstract of DOI:10.1016/j.ultsonch.2012.10.014

A new, simple, efficient and rapid method for the oxidation of alcohols into respective aldehydes and ketones by Ni(NO₃)₂· 6H₂O/I₂/water system under ultrasonic irradiation is reported. The process is mild and i

Full text of DOI:10.1016/j.ultsonch.2012.10.014

Ultrasonics Sonochemistry 20 (2013) 810–814
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Ultrasonics Sonochemistry
journal homepage: www.elsevier.com/locate/ultson
Short Communication
Ni(NO ) Á6H O/I /water: A new, mild and efficient system for the selective
3
2
2
2
oxidation of alcohols into aldehydes and ketones under sonic condition
⇑
Mohamed Afzal Pasha , Shrivatsa Nagashree
Department of Studies in Chemistry, Central College Campus, Bangalore University, Palace Road, Bangalore 560 001, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 5 January 2010
Received in revised form 9 October 2012
Accepted 16 October 2012
Available online 7 November 2012
A new, simple, efficient and rapid method for the oxidation of alcohols into respective aldehydes and
ketones by Ni(NO
and inexpensive; the yields are high and the reactions go to completion within 2–7 min.
Ó 2012 Elsevier B.V. All rights reserved.
3 2 2 2
) Á6H O/I /water system under ultrasonic irradiation is reported. The process is mild
Keywords:
Alcohols
Aldehydes
Ketones
Ni(NO
Iodine
Water
3 2
)
1
. Introduction
of primary alcohols to aldehydes and secondary alcohols into
ketones by a Ni(NO O/iodine/water system under ultrasonic
condition. The process is mild and inexpensive; the yields are high
and the reactions go to completion within 2–7 min as shown in
Schemes 1–3.
3
2
) Á6H
2
First report on the use of ultrasound in organic syntheses was
presented by Richards and Loomis in the year 1927 [1]. Compared
to traditional methods, sonic reactions are more convenient and
high yielding and hence, a large number of organic reactions have
been reported in the literature [2–7]. Organic reactions not only get
accelerated, the number of steps involved can also be reduced, and
cruder reagents can be used under sonic conditions. These effects
of ultrasound are achieved due to the phenomenon of acoustic
cavitation [8] and the primary chemical reactions are due to the
transient state of high temperatures and pressures [9].
Oxidation of alcohols into corresponding carbonyl compounds
is an important transformation in organic synthesis [10–13]. In
particular, the controlled oxidation of primary alcohols to alde-
hydes, without forming over-oxidized product is really a challeng-
ing task. Traditionally, this reaction is carried out by using various
inorganic oxidants. In recent years, efforts have also been made to
develop more valuable catalytic oxidizing processes including
homogenous catalysts as well as heterogeneous catalysts [14,15]
such as transition metal salts [16], oxygen-containing oxidants
2
. Experimental section
2.1. Materials and instruments
Anisyl alcohol, 3-nitrobenzyl alcohol, 2-chlorobenzyl alcohol
and furfuryl alcohol were prepared by the reduction of respective
aldehydes. All the other reagents used were commercially avail-
able. The products were characterized by IR and GC–mass spectral
analysis. All the reactions were studied using SIDILU Indian make
sonic bath working at 35 kHz (constant frequency) at 25 °C; and
followed by SHIMADZU GC–MS QP 5050A instrument equipped
with a 30 m long and 0.32 mm dia BP-5 column with the column
temperature programme 80–15–250 °C.
2.2. Oxidation of alcohols under ultrasonic condition: a general
[
17] including oxygenated organic solvents [18–20]. Recently, we
have oxidized a series of benzyl alcohols into respective benzalde-
hydes by FeCl /HNO under sonic condition in high yields [21]. We,
in this paper, present another simple, efficient and rapid oxidation
procedure
3
3
A
mixture of alcohol (10 mmol), Ni(NO
3
)
2
Á6H
2
O (2.908 g,
1
0 mmol), I
2
(1.3 g, 10 mmol) and water (2 mL) were sonicated in
a sonic bath working at 35 kHz (constant frequency) maintained
at 25 °C by circulating water. After completion of the reaction
(Table 5, monitored on TLC), the product was taken into diethyl
⇑
Corresponding author.
E-mail address: m_af_pasha@ymail.com (M.A. Pasha).
1
350-4177/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ultsonch.2012.10.014

M.A. Pasha, S. Nagashree / Ultrasonics Sonochemistry 20 (2013) 810–814
811
properties were compared with the properties of authentic
samples.
CH OH
CHO
2
Ni(NO ) .6H O / I / Water
3
2
2
2
)
)))
R
R
2
-5 mins
R = H, 4-OCH , 3-NO , 2-Cl
3. Results and discussion
3
2
Scheme 1.
Metal nitrates are known to oxidize alcohols [22]. Laura et al.
[
23] used various metal nitrates and bromides for the selective
sulfoxidation reaction and showed that Fe(NO O–FeBr was
3
)
3
Á9H
2
3
the most effective system. On the same lines we used various me-
tal nitrates in order to develop a new catalytic system for the oxi-
dation of alcohols into respective aldehydes and ketones. Benzyl
alcohol was selected as a standard and the oxidation of benzyl
OH Ni(NO3)2.6H2O / I2 / Water
O
n
)
)))
n
7
mins
n = 0, 1, 2
alcohol, we found that, Ni(NO
amount of benzaldehyde after several hours at 25 °C, without
any solvent. Among the two, Ni(NO gave some promising results
as can be seen from the data presented in Table 1. Reaction of ben-
zyl alcohol was then studied with Ni(NO in different solvents,
3 2
) or ferric nitrate give only a trace
Scheme 2.
3 2
)
Ni(NO ) .6H 0 / I / Water
3 2
)
3
2
2
2
OH
CHO
n
n
)
)))
the results of this study are presented in Table 2. It can be seen
from Table 2 that, in water the yield of benzaldehyde is only 30%
which is again not appreciable. Since, iodine is a good oxidizing
agent, which is non-hazardous and readily available, we used io-
7
mins
n = 0, 1, 6
Scheme 3.
3 2
dine along with Ni(NO ) to get the desired product in 95% yield
in water as a solvent. In order to standardize the conditions, the
reactions were carried out under various conditions and the results
of all these studies are presented in Tables 3–5. From Tables 1–5 it
Table 1
A comparative study on the oxidation of benzyl alcohol (10 mmol) to benzaldehyde
by different metal nitrates (10 mmol) without solvent.
3 2 2
is clear that, oxidation of benzyl alcohol using Ni(NO ) /I /water
system under the influence of ultrasound at 35 kHz is efficient
and gives high yield of the product in short duration (Table 3, entry
5).
Entry
Metal nitrates
Time (min)
Yield (%)a
At 25 °C
))))
Benzaldehydeb
1
2
3
4
5
Fe(NO
Ni(NO
3
)
)
3
Á9H
Á6H
2
O
O
240–300
240–300
240–300
240–300
240–300
180–240
180–240
180–240
180–240
180–240
10
20
ND
ND
ND
From Tables 1 and 2 it is clear that, Ni(NO
in solvent do not have much effect on the oxidation. Table 3 indi-
cates that, equimolar amounts of Ni(NO /I are essential for the
reaction to give high yields of the desired products in water with-
out any side products (entry 5). The data given in Table 4 indicates
that, for 10 mmol of the reactants and reagents, a minimum of
2 mL of water is required for the reaction (entry 10). It is also clear
3 2 3 2
) alone and Ni(NO )
3
2
2
Cu(NO
Ba(NO
NaNO
3
)
2
Á5H
2
O
3 2 2
)
3 2
)
3
ND: not detected.
a
Isolated yields.
b
Characterized by IR and by comparison with authentic sample on TLC.
from Table 5 that, only Ni(NO
3
)/water or only I
2
/water does not
3 2 2
give the expected products; Ni(NO ) /I /water system is essential
to convert primary alcohols into aldehydes and secondary alcohols
into respective ketones and under sonic condition the reactions
goes to completion within 7 min (entry 3).
ether (10 mL), the organic matter was washed with sat. NaHCO
3
(
2 4
2.5 mL), water (5 mL) and then dried over anhydrous Na SO .
The organic layer was evaporated in a fume hood to get almost
pure aldehyde. The crude was then subjected to silica gel column
chromatography to get the pure product. All the products were
characterized by IR, GC–mass spectral analysis; and the physical
3 2 2
In order to find the generality of the use of Ni(NO ) /I /water
system for the oxidation of alcohols, different substituted aromatic
alcohols, primary and secondary aliphatic alcohols were selected
and the oxidation was carried out under sonic condition. The re-
sults of this study are presented in Table 6. It can be seen that, alco-
hols give respective aldehydes and ketones in very high yields
without any side products.
Table 2
A comparative study on the oxidation of benzyl alcohol (10 mmol) into benzaldehyde
by Ni(NO
3 2
) (10 mmol) in different solvents under normal and sonic condition.
Entry
Solventa
Time (min)
Yield (%)b
4
. Mechanism
At 25 °C
))))
Benzaldehydec
1
2
3
4
5
6
7
8
9
No solvent
Water
Water (distilled)
Deionized water
Ether
Ethanol
Acetone
Acetonitrile
Xylene
Hexane
120–180
60–80
60–80
60–80
60–80
60–80
60–80
60–80
60–80
60–80
60–80
60–80
20–40
20–40
20–40
20–40
20–40
20–40
20–40
20–40
20–40
20–40
5d
30
30
30
20
ND
ND
A plausible mechanism for the oxidation of alcohols into alde-
hydes and ketones which is on par with the mechanism proposed
by Mohammad [24] is envisaged in Scheme. 4. Iodine present in
the organic layer of the above mentioned biphasic system may
activate the alcohol in the first step; subsequent loss of HI may give
d
intermediate A. Ni(NO
3
)
2
present in the aqueous layer may react
may then react
d
10
d
with HI to give HNO , the in situ generated HNO
3
3
5
1
1
0
1
25
20
with A to give the intermediate B. Under the influence of ultra-
sound a molecule of nitrous acid may get eliminated from B in
the subsequent step to give the desired carbonyl compound C. As
THF
a
b
c
5
mL.
2
a molecule of HI, HOI and a molecule of HNO have to be removed
Isolated yields.
Characterized by IR and by comparison with authentic sample on TLC.
GC. ND: not detected.
from the intermediates A and B in the steps 2, 3 and 4, we feel, the
steps 2, 3 and 4 are influenced by ultrasound (Scheme 4).
d

8
12
M.A. Pasha, S. Nagashree / Ultrasonics Sonochemistry 20 (2013) 810–814
Table 3
A comparative study on the oxidation of benzyl alcohol to benzaldehyde with different amounts of Ni(NO
3
)
2
and iodine in water (2 mL) under sonic condition.
Entry
Ratio (eq)
Time
Yield (%)a,b
Benzyl alcohol
Ni(NO
)
3 2
I
2
(min)
Benzaldehyde
Benzoic acid
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
1
1
1
0.2
0.4
0.6
0.8
1
1
1
1
1
17
17
10
5
2
8
8
10
10
25
35
60
75
95
30
35
50
75
ND
ND
ND
ND
ND
70
70
45
20
1
0.2
0.4
0.6
0.8
a
Isolated yields; after silica gel column chromatography.
Characterized by IR and by comparison with authentic samples on TLC. ND: not detected.
b
Table 4
Table 6
A comparative study on the oxidation of benzyl alcohol (10 mmol) to benzaldehyde
3 2 2
Oxidation of alcohols to corresponding aldehydes and ketones by Ni(NO ) /I /water
with Ni(NO
3
)
2
(10 mmol) and iodine (10 mmol) in different volumes of water.
under sonic condition (35 kHz constant frequency at 25 °C).
Entry
Water (mL)
Time (min)
)))
Yield (%)a,b
Entry Substrate
Time (min) Producta
Yield (%)b
)
Benzaldehyde
Benzoic acid
1
2
3
4
5
6
7
8
9
1
1
Benzyl alcohol
Anisyl alcohol
3-Nitrobenzyl alcohol
2-Cholorobenzyl alcohol 5
Furfuryl alcohol
Cyclohexanol
Cyclopentanol
Cycloheptanol
n-Butanol
2
2
3
Benzaldehyde
Anisaldehyde
3-Nitrobenzaldehyde 85
2-Chlorobenzaldehyde 83
95
90
1
2
3
4
5
6
7
8
9
0.5
1
1.5
2
2
2
2
2
2
2
15
15
15
15
12.5
10
7.5
5
2.5
2
2
4
2
15
25
70
95
95
95
95
95
95
95
95
95
95
90
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
2
2
2
2
7
7
7
Furfuraldehyde
Cyclohexanone
Cyclopantanone
Cycloheptanone
n-Butanal
90
93
92
90
75
85
85
0
1
n-Pentanol
n-Decanol
n-Pentanal
n-Decanal
1
1
1
1
1
0
1
2
3
4
2.5
2.5
5
a
Characterized by IR and GC–mass spectral analysis and by comparison of
physical constants of authentic samples.
b
Isolated yields after silica gel column chromatography.
10
2
a
Isolated yields; after silica gel column chromatography.
Characterized by IR and by comparison with authentic samples on TLC. ND: not
b
respective aldehydes and ketones than HNO
under sonic condition.
3 2
/I /water system
detected.
4.1. Effect of ultrasound on the reaction
Table 5
A comparative study on the oxidation of benzyl alcohol (10 mmol) to benzaldehyde in
the presence of different reagent systems at 25 °C and under sonic condition (35 KHz).
Ultrasound enhances the chemical reactions through the gener-
ation and subsequent destruction of cavitation bubbles in liquid
media. Ultrasound provides an unusual mechanism for generating
high-energy chemistry due to the immense temperature, pressure
and the extraordinary heating rates generated by the cavitation
bubble collapse. In some cases, it can increase the chemical rate
by nearly million-folds [25]. The present reaction involves a two
phase system: the liquid phase (reagents in solvents viz., iodine
Producta
Yield (%)b
Entry Reagent system
Time (min)
5 °C ))))
60–80 20–40 Benzaldehyde 30c
20–40 3–10 Benzoic Acid 95
2
/water 80 2–7 Benzaldehyde 95
2
1
2
3
Ni(NO
/water
Ni(NO
3
)
2
Á6H
Á6H
2
O/water
O/I
I
2
)
3 2
2
a
Characterized by IR and GC–mass spectral analysis and by comparison with
3 2
in organic layer and Ni(NO ) in water), and the gas phase (dis-
authentic samples on TLC.
b
solved gases in the liquids and gases on the inner-surface of the
vessel). When ultrasonic waves propagate through such a medium
by a series of compression and rarefaction cycles, the rarefaction
cycle exceeds the attractive forces of the molecules of the liquids
and ‘cavitation bubbles’ will form. These cavitation bubbles grow
by a process called ‘rectified diffusion’ which means small amounts
of gas from the medium goes into the cavity (cavitation bubble)
during its expansion phase, and the gas is not fully expelled during
compression. The creation of the so-called hot spots in the reaction
mixture produces intense local temperatures and high pressures
inside the cavitation bubble and at the interfaces. The collapse
can be symmetrical or can occur near the surface of the vessel
resulting in an inrush of liquid predominantly from the side of
the cavitation bubble remote from the surface because the surface
provides resistance from one side leading to generation of power-
ful liquid jets, setting the molecules into rapid motion due to the
energy imparted to them, hence effective collisions take place,
Isolated yields.
After silica gel column chromatography.
c
3
According to the proposed mechanism, HNO which may form
during the course of the reaction participates in the oxidation. To
examine this, the reaction of alcohols with different amounts of
the reagent/s viz., con. HNO (with and without iodine), in water
3
and in acetone as solvents was studied and the results of this study
are presented in Table 7.
3 2
It can be seen from Table 7 that, benzyl alcohol with HNO /I /
water system gives benzaldehyde in 75% yield along with benzoic
acid 25% (entry 3); and cyclohexanol gives cyclohexanone in 90%
yield (entry 4). As benzaldehyde was formed along with an appre-
ciable amount of benzoic acid, we feel that, use of Ni(NO
water system is more useful for the conversion of alcohols into
3 2 2
) /I /

M.A. Pasha, S. Nagashree / Ultrasonics Sonochemistry 20 (2013) 810–814
813
+
))))
O
O-
HO N
.
. I
+ O
N
OH
H R1
H
I2
I
I
))))
:
))))
-HNO2
O
O
O
O +
O-
R
R1
H R1
R1
H R1
-HI
R
R
H
A
-HOI
R
R
C
B
)
)))
[
2HI + Ni(ONO2)2
NiI + 2HNO ]
2 3
Scheme 4.
Table 7
Sonochemical oxidation of alcohols (10 mmol) by con. HNO
(2.5 mmol)a under different conditions.bc
3
Entry
1
Reagent system
Substrate (10 mmol)
Benzyl alcohol
Time (min)
5
Productd,e
Yield (%)f
HNO
3
/water
Benzaldehyde
Benzoic acid
Cyclohexanone
Benzaldehyde
Benzoic acid
Cyclohexanone
Benzaldehyde
Benzoic acid
Cyclohexanone
Benzaldehyde
Benzoic acid
5g
80
85
75
25
90
ND
95
50
ND
ND
70
2
3
HNO
HNO
3
3
/water
Cyclohexanol
Benzyl alcohol
5
5
/I
2
2
/water
/water
4
5
HNO
HNO
3
3
/I
Cyclohexanol
Benzyl alcohol
5
5
/acetone
6
7
HNO
HNO
3
3
/acetone
Cyclohexanol
Benzyl alcohol
5
5
/I
/I
2
2
/acetone
/acetone
8
HNO
3
Cyclohexanol
5
Cyclohexanone
a
b
c
With 10 mmol HNO
Iodine-10 mmol.
Solvent-2 mL.
3
benzoic acid is formed instantaneously.
d,e
Characterized by IR and GC–mass spectral analysis and by comparison with authentic samples.
Isolated yields after silica gel column chromatography.
By GC; ND: not detected.
f
g
thereby enhances the reaction rate of the reaction [21,26–28]. Fur-
through the formation and collapse (both symmetrical as well as
unsymmetrical) of ‘cavitation bubbles’ in the form of micro jets
and the shockwaves in the organic as well as aqueous layers.
ther, in heterogeneous liquid-liquid systems, the cavitation is pos-
sible in both the phases and the tiny droplets of these layers get
distributed into each other forming an emulsion. As the tiny drop-
lets of the substrate molecules get equally distributed in the aque-
ous layer and vice-versa, the rate of the oxidation reaction gets
enhanced because of the maximum exposure due to the large sur-
face area [27].
5
. Conclusion
In conclusion, a mild, simple and an easy approach to the oxida-
tion of alcohols into respective aldehydes and ketones using
Ni(NO O/I /water system under sonic condition is devel-
There are four important steps in the mechanism of formation
3
)
2
Á6H
2
2
of aldehydes and ketones from respective alcohols by Ni(NO
3 2
) /
oped. The reaction is facile, involves simple workup, uses readily
available and inexpensive chemicals and gives high yield of the
products in short duration. As the over oxidation products viz.,
benzoic acids are not formed from primary alcohols, this procedure
could be a useful alternative to the currently available methods.
2
I /water. In the first step of the reaction, the alcohol gets activated
by iodine in the organic layer. In the next step a molecule of HI gets
eliminated from the activated alcohol to give intermediate A under
sonication. In a parallel reaction the water soluble HI reacts with
Ni(NO
3
)
2
in the aqueous layer to give HNO
3
. The intermediate A
to give the nitrate B,
then reacts with the in situ generated HNO
3
and a molecule of HOI may get released during this conversion.
In the final step, B loses a molecule of HNO to give the respective
carbonyl compound as shown in Scheme 4. As the release of HI,
HOI, HNO and HNO from the respective species is an important
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