I2/Fe(NO3)3·9H2O-catalyzed oxidative synthesis of aryl carboxylic acids from aryl alkyl ketones and secondary benzylic alcohols

Article abstract of DOI:10.1016/j.tetlet.2018.10.060

An interesting and convenient procedure for the oxidative transformation of aryl alkyl ketones and secondary benzylic alcohols to aryl carboxylic acids has been developed. By using iodine and Fe(NO₃)₃·9H₂O as the catalysts, DMSO and oxygen as the oxidants, the desired aryl carboxylic acids were synthesized in moderate to excellent yields (up to 91%).

Full text of DOI:10.1016/j.tetlet.2018.10.060

Accepted Manuscript
I /Fe(NO ) ·9H O-catalyzed oxidative synthesis of aryl carboxylic acids from
2
3 3
2
aryl alkyl ketones and secondary benzylic alcohols
Liang Xu, Yingying Chen, Zhenlu Shen, Yuru Wang, Meichao Li
PII:
S0040-4039(18)31291-7
https://doi.org/10.1016/j.tetlet.2018.10.060
TETL 50370
DOI:
Reference:
To appear in:
Tetrahedron Letters
Received Date:
Revised Date:
Accepted Date:
14 September 2018
15 October 2018
26 October 2018
Please cite this article as: Xu, L., Chen, Y., Shen, Z., Wang, Y., Li, M., I /Fe(NO ) ·9H O-catalyzed oxidative
2
3 3
2
synthesis of aryl carboxylic acids from aryl alkyl ketones and secondary benzylic alcohols, Tetrahedron Letters
(
2018), doi: https://doi.org/10.1016/j.tetlet.2018.10.060
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I /Fe(NO ) ·9H O-catalyzed oxidative synthesis of aryl carboxylic acids from
2
3 3
2
aryl alkyl ketones and secondary benzylic alcohols
Liang Xu, Yingying Chen, Zhenlu Shen*, Yuru Wang, Meichao Li*
College of Chemical Engineering, Zhejiang University of Technology, Hangzhou 310014, China
E-mail address: zhenlushen@zjut.edu.cn; limc@zjut.edu.cn
Tel.: +86-571-88320305, fax: +86-571-88320305
ABSTRACT:
An interesting and convenient procedure for the oxidative transformation of aryl alkyl ketones
and secondary benzylic alcohols to aryl carboxylic acids has been developed. By using iodine and
Fe(NO ) ·9H O as the catalysts, DMSO and oxygen as the oxidants, the desired aryl carboxylic
3
3
2
acids were synthesized in moderate to excellent yields (up to 91%).
Keywords: Aryl alkyl ketones; Aryl carboxylic acids; Secondary benzylic alcohols; Ferric nitrate;
Iodine.
Aryl carboxylic acid is a key motif in the structure of dyes, functional polymers, natural products,
pharmaceuticals, agricultural chemicals and bioactive molecules. Furthermore, aryl carboxylic acids
can be used as starting materials for the synthesis of esters, acid halides, amides and anhydrides.1
Therefore, the development of efficient and environmentally friendly methods for the preparation of
aryl carboxylic acids has received much attention.

Traditionally, aryl carboxylic acids can be synthesized from methylarenes by direct oxidation.2
Stoichiometric hazardous metal oxidants, particularly KMnO , Na Cr O , and CrO are employed for
4
2
2
7
3,
this oxidative process. Some efficient catalytic oxidation systems containing transition-metal catalysts
have also been successfully employed. In addition, primary benzylic alcohols, aromatic aldehydes,
aromatic nitriles, aryl halides, 2-oxo-2-arylacetaldehyde, arylacetic acid, arylolefins and arylalkynes
3
can be used as raw materials for the preparation of carboxylic acids. The direct transformation of
ketones has been studied intensively, and numerous compounds can be prepared from ketones via C–C,
4
C–H or C–O bond cleavage. Aryl alkyl ketones can also be used for the synthesis of aryl carboxylic
acids via C–C bond cleavage. Various transition-metal catalysts such as Mn, Hg, Cu, W, and Ru have
5
been applied for the transformation of aryl alkyl ketones to aryl acids. The pioneering work reported
by Wang et al revealed that aryl alkyl ketones could be oxidized to aryl carboxylic acids via C–C bond
cleavage with 20 mol% Cu(NO ) ·3H O as the catalyst and 0.6 MPa of O as the oxidant (Scheme 1,
3
2
2
2
Eq. 1).5a A few transition-metal-free reagents such as Oxone/TFA, 1,3-dinitrobenzene/t-BuOH,
KOH/DMF, I /DMSO/NH OH·HCl, (hyroxyl(2,4-dinitrobenzensulfonyloxy)iodo)benzene and
2
2
6
pentafluoroiodobenzene bis(trifluoroacetate) have been used to achieve this transformation. However,
some disadvantages are inevitable in these methods: (1) substrates scope is limited; (2) yields are need
to be improved; (3) expensive or environmentally unfriendly reagents are utilized. As a versatile,
inexpensive, and readily available catalyst, molecular iodine has been widely used for various organic
7
reactions. Very recently, we reported a method for the synthesis of aryl carboxylic acids from aryl
alkyl ketones with iodine as the catalyst, DMSO and TBHP as the oxidants (Scheme 1, Eq. 3).8

9
Secondary benzylic alcohols could also be used for synthesis of aryl carboxylic acids. In 2017, Wang
and co-workers reported C(OH)–C bond cleavage of secondary benzylic alcohols to produce aryl
carboxylic acids, using Cu(OAc) /1,10-phenanthroline as the catalysts and 0.4 MPa of O as the
2
2
9
a
oxidant in the presence of stoichiometric KOH (Scheme 1, Eq. 2). This method is efficient for the
oxidative cleavage of lignin linkages and shows potential in the synthesis of carboxylic acids from
lignin.
It is well-known that iron is a cheap, environmentally friendly metal element and one of the most
abundant elements in the earth. In addition, iron plays an important role in the life reactivity. Therefore,
1
0
the use of iron compounds as catalysts in organic synthesis is quite attractive. It has been reported that
1
1
iron compounds could be applied for selective C–C bond cleavage. On the other hand, molecular
oxygen (O ) is a green oxidant and is often used as a natural oxygen resource for oxygen-containing
2
chemicals.12 As a continuation of our previous work on cleavage of C–C bond and aerobic
oxidation,8,13 we here report an unexpected selective oxidative transformation of alkyl ketones and
secondary benzylic alcohols to the corresponding aryl carboxylic acids using I /Fe(NO ) ·9H O as the
2
3 3
2
catalysts and O as the terminal oxidant (Scheme 1, Eq. 4).
2

Previous works:
O
O
O
Cu(NO ) (20 mol%)
3
2
R
Ar
Ar
OH
OH
ref 5a
ref 9a
(1)
(2)
o
Ar
CH CN, O (0.6 Mpa), 120 C
3 2
Cu(OAc) (8 mol%)
2
OH
Phen (8 mol%)
R
Ar
KOH (2 equiv.)
o
DMSO, O (0.4 Mpa), 120 C
2
O
(
1) I (10 mol%), DMSO (6 equiv.)
R
2
O
Ar
(2) TBHP (2 equiv.)
ref 8
(3)
OH
o
Ar
OH
PhCl, 130 C
R
Ar
This work:
O
R
Ar
O
I (10 mol%), Fe(NO) 9H O (10 mol%)
2
3
2
or
(4)
o
OH
DMSO, O (0.1 Mpa), 130 C
Ar
OH
2
R
Ar
Scheme 1. Methods for the preparation of aryl carboxylic acids via oxidative C–C bond cleavage.
Initially, acetophenone (1a) was selected as the model substrate to optimize the reaction conditions
Table 1). The reaction was performed with 10 mol% of FeCl , 10 mol% of I in the solution of DMSO
(
3
2
under 0.1 MPa of oxygen at 130 °C. The desired product benzoic acid (2a) was only obtained with
0% yield as determined by GC using an internal standard method in 12 h (Table 1, entry 1). It was
3
found that benzaldehyde was the main product with about 60% GC yield. As outlined in Table 1, the
influence of different iron catalysts was tested (Table 1, entries 1-4). To our delight, the yield of 2a was
improved to 91% when Fe(NO ) ·9H O was used as the catalyst (Table 1, entry 3). Then iron catalyst
3
3
2
was removed from the reaction system, as we expected, no desired produt could be obtained, 1a was
8
completely converted into the intermediate phenylglyoxal (Table 1, entry 5). A series of solvents

including PhCl, H O, CH CN, EtOAc, and PhCH were screened, the experimental results showed that
2
3
3
none of them was superior to DMSO (Table 1, entries 6-10).
Table 1 Optimization of Reaction Conditions a
O
I2 (Cat.)
O
Iron salt (Cat.)
OH
o
Solvent, O (0.1 MPa), 130 C
2
1a
2a
o
b
Entry
1
[Fe](mol%)
Solvent
DMSO
DMSO
DMSO
DMSO
DMSO
PhCl
Temp. ( C)
Conv. (%)
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
Yield (%)
FeCl (10)
130
130
130
130
130
130
130
130
130
130
130
130
130
130
130
120
140
30
34
91
39
ND
70
44
84
74
64
89
38
71
27
66
65
90
3
2
FeCl (10)
2
3
Fe(NO ) ·9H O (10)
3
3
2
.
4
FeSO 7H O (10)
4 2
–
5
6 c
7 c
8 c
9 c
Fe(NO ) ·9H O (10)
3 3 2
Fe(NO ) ·9H O (10)
H O
2
3
3
2
Fe(NO ) ·9H O (10)
CH CN
3
3
2
3
Fe(NO ) ·9H O (10)
EtOAc
PhCH3
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
3
3
2
1
1
1
1
1
1
1
0 c
Fe(NO ) ·9H O (10)
3 3 2
1
Fe(NO ) ·9H O (5)
3
3
2
2
Fe(NO ) ·9H O (1)
3 3 2
3 d
4 e
5 f
6
Fe(NO ) ·9H O (10)
3 3 2
Fe(NO ) ·9H O (10)
3
3
2
Fe(NO ) ·9H O (10)
3
3
2
Fe(NO ) ·9H O (10)
3
3
2
1
7
Fe(NO ) ·9H O (10)
3 3 2
a
Reaction conditions: 1a (1 mmol), DMSO (2 mL), I (10 mol%), O (0.1 MPa), 12 h.
2
2
b
c
d
e
f
Determined by GC using an internal standard method with biphenyl as the internal standard substance.
Reaction conditions: 1a (1 mmol), solvent (2 mL), DMSO (6 equiv.), I (10 mol%).
2
I2 (5 mol%).
N .
2
Air.
Then the loadings of Fe(NO ) ·9H O and I were further optimized. When the loading of
3
3
2
2
Fe(NO ) ·9H O was reduced to 5 mol%, the GC yield of 2a was slightly decreased to 89% (Table 1,
3
3
2
entry 11). The loading of Fe(NO ) ·9H O was further reduced to 1 mol%, and only 38% GC yield of 2a
3
3
2

was obtained (Table 1, entry 12). In addition, decreasing the loading of I could also lead to a lower
2
yield of 2a (Table 1, entry 13). When nitrogen was employed, the yield of 2a was dramatically dropped
into 27% along with 65% yield of benzaldehyde (Table 1, entry 14 ). When the reaction was performed
under air atmosphere, the yield of 2a was only 66% (Table 1, entry 15). After that, we attempted to
decrease the reaction temperature. Unfortunately, the yield of 2a was dropped into 65% when the
reaction was carried out at 120 °C (Table 1, entry 16). When the reaction temperature was increased to
1
40 °C, the yield of 2a was not improved (Table 1, entry 17). Thus, the optimal reaction conditions
included I (10 mol%)/Fe(NO ) ·9H O (10 mol%) as the catalysts and DMSO as solvent under 0.1 Mpa
2
3 3
2
of O at 130 °C for 12 h. Subsequently, various aryl methyl ketones were examined under the optimal
2
reaction conditions for the synthesis of substituted benzoic acids to explore the scope and generality of
1
4
this protocol (Scheme 2). In general, this protocol could tolerate different functional groups including
electron-donating groups and electro-withdrawing groups, and moderate to good yields of the desired
aryl carboxylic acids could be obtained from aryl methyl ketones. Acetophenones bearing electron-
i
t
donating substituents such as 4-CH , 4- Pr, 4- Bu and 4-OCH underwent oxidation smoothly to
3
3
provide the corresponding benzoic acids 2a-2e in 85%-93% isolated yields. The reaction of 3-methyl-
and 2-methyl-acetophenones gave corresponding benzoic acids 2f and 2g in 85% and 70% isolated
yields, respectively. Acetophenones with electron-withdrawing groups (4-NO , 4-CN, and 4-COOCH )
2
3
could also afford the desired products 2h, 2i and 2j in good yields. Generally, electron-donating
substituted acetophenones gave higher yields of products than electron-withdrawing substituted
substrates. The halo-substituted acetophenones could be oxidized into the corresponding halo-

substituted benzoic acids in high yields as well (2k-2n). However, substrate containing 2-Cl on phenyl
ring showed lower reactivity, and the isolated yield of 2o was only 61%. A multi-substituted substrate,
3
,4,5-trimethoxyacetophenone, was converted to the corresponding benzoic acids 2p in 81% isolated
yield. When 4-acetylbiphenyl was subjected to this protocol, 81% isolated yield of 4-
biphenylcarboxylic acid (2q) could be obtained. 1-Acetonaphthone and 2-acetonaphthone reacted
smoothly under the optimal conditions and delivered the desired products 2r and 2s in 78% and 81%
isolated yields, respectively. Furthermore, this transformation was expanded to various heteroaryl
methyl ketones. For example, conversion of 2-acetylthiophene and 2-acetylfuran to their corresponding
acids could be achieved although the isolated yields of product 2s and 2t were only moderate. However
the reaction temperature should be lowered to 110 °C because the starting materials or the products
o
would be polymerized at 130 C.
Then several aryl alkyl ketones were submitted to this protocol to further extend the substrate scope
(Scheme 3). Aryl alkyl ketones 3a-3d could be oxidized smoothly to give the desired aryl carboxylic
acids 2a, 2b, 2l and 2a in good yields (77%-85%). Interestingly, in case of the substrate 3e which is an
important fragment of lignin, it could be converted smoothly to the corresponding product 2e. GC-MS
analysis showed that o-methoxyphenol was one of the by-products.

O
O
I2 (10 mol%)
Fe(NO ) 9H O (10 mol%)
OH
3
3
2
R'
R'
o
DMSO, O (0.1 MPa), 130 C, 12 h
2
1
2
COOH
COOH
COOH
COOH
COOH
2
a, 85%
2b, 90%
2c, 91%
COOH
2d, 91%
COOH
COOH
O
O2N
2e, 92%
2f, 85%
2g, 70%
2h, 85%
COOH
COOH
COOH
COOH
COOH
COOH
O
F
NC
Cl
O
2i, 82%
2j, 79%
2k, 82%
2l,85%
COOH
COOH
O
COOH
Cl
O
Br
Cl
O
2p, 81%
2m, 81%
2n, 76%
2o, 61%
COOH
S
COOH
COOH
b
2q, 81%
2s, 81%
2t, 43%
2r, 78%
O
COOH
b
2
u, 58%
.
a
Scheme 2. I /Fe(NO ) 9H O-catalyzed oxidation of aryl methyl ketones to aryl carboxylic acids.
2
3 3
2
a
The reactions were carried out with 1 mmol of 1, 10 mol% of I and 10 mol% of Fe(NO ) ·9H O in 2 mL of DMSO
2
3 3
2
b
under 0.1 Mpa of O at 130 °C for 12 h (isolated yields are given). Reaction temperature: 110 °C.
2

O
O
I2 (10 mol%)
Fe(NO ) 9H O (10 mol%)
R
3
3
2
OH
R1
R1
o
DMSO, O (0.1 MPa), 130 C, 12 h
2
3
2
Substrate
Product
isolated yield)
Substrate
O
Product
(isolated yield)
(
O
COOH
COOH
3
d
2a, 77%
3
a
2a, 82%
2b, 85%
2l, 81%
O
COOH
COOH
O
O
COOH
O
O
O
3
b
3
e
2e, 74%
O
Cl
Cl
3
c
.
a
Scheme 3. I /Fe(NO ) 9H O-catalyzed oxidation of aryl alkyl ketones to aryl carboxylic acids.
2
3 3
2
a
The reactions were carried out with 1 mmol of 3, 10 mol% of I and 10 mol% of Fe(NO ) ·9H O in 2 mL of DMSO
2
3 3
2
under 0.1 Mpa of O at 130 °C for 12 h (isolated yields are given).
2
The selective oxidation of secondary alcohols is an important way for the preparation of ketones.15
Inspired by aforementioned work, we hoped that the substrates of this efficient reaction system could
be further extended to secondary benzylic alcohols. 1-Phenylethanol was selected to examine whether
secondary benzylic alcohols could be oxidized into benzoic acids. To our delight, expected product was
obtained in 71% yield. Then a series of substituted 1-phenylethanols were applied to this
transformation, and they could successfully deliver the corresponding benzoic acids in moderate to
good yields (Scheme 4). The electronic property of the substituents on the benzene ring had little effect
on the reaction results. For example, p-methyl, m-methyl, p-methoxy, p-nitro and p-cyano substituted
1
7
-phenylethanols were oxidized into their corresponding benzoic acids 2b, 2f, 2e, 2h and 2i in 68%-
6% isolated yields. Meta- and para-substituted 1-phenylethanols gave higher product yields than
ortho-substituted substrates (2b and 2f vs 2g). Additionally, 1-phenylethanols with p- and m-chloro
substituents were also tolerated this protocol and provided target benzoic acids 2l and 2n in moderate

yields. When 1-(2-chlorophenyl)ethanol was examined under the standard reaction conditions, 2-
chlorobenzoic acid (2o) was obtained only in 10% isolated yield. 1-(3,4,5-Trimethoxyphenyl)ethanol
could also be converted to the 3,4,5-trimethoxybenzoic acids (2p) in 68% isolated yield. When
heteroaromatic analogues 1s and 1t were submitted to this oxidation protocols, the isolated yields of 2t
2
u were 44% and 52%, respectively. When 1-(p-tolyl)propan-1-ol was chosen as the substrate, 77%
isolated yield of 4-methylbenzoic acid (2b) could be obtained (Scheme 5).
OH
O
I2 (10 mol%)
Fe(NO ) 9H O (10 mol%)
3
3
2
OH
R1
R1
o
DMSO, O (0.1 MPa), 130 C, 12 h
2
4
2
COOH
COOH
COOH
COOH
2
a, 71%
2b, 76%
COOH
2f, 77%
2g, 51%
COOH
COOH
COOH
O N
2
NC
Cl
O
2
e, 73%
COOH
2h, 68%
2i, 76%
COOH
2l, 68%
O
O
COOH
Cl
S
COOH
O
Cl
b
2n, 67%
2o,10%
2p, 68%
2t, 44%
O
COOH
b
2
u, 52%
.
a
Scheme 4. I /Fe(NO ) 9H O-catalyzed oxidation of 1-arylethanols to aryl carboxylic acids.
2
3 3
2
a
The reactions were carried out with 1 mmol of 4, 10 mol% of I and 10 mol% of Fe(NO ) ·9H O in 2 mL of DMSO
2
3 3
2
b
under 0.1 Mpa of O at 130 °C for 12 h (isolated yields are given). Reaction temperature: 110 °C.
2
OH
O
I (10 mol%)
2
.
Fe(NO ) 9H O (10 mol%)
3
3
2
OH
o
DMSO, O (0.1 MPa), 130 C, 12 h
2
5
2b, 77%
.
Scheme 5. I /Fe(NO ) 9H O-catalyzed oxidation of 1-(p-tolyl)propan-1-ol to 4-methylbenzoic acid.
2
3 3
2

Next, to gain insights into the reaction process, we performed several control experiments. Firstly,
with 10 mol% of iodine as the catalyst, acetophenone (1a) could be readily converted into
8
phenylglyoxal (1aa) in 95% yield in DMSO (Scheme 6, Eq. 1). In addition, using 1aa instead of 1a as
the substrate, the reaction smoothly occurred to produce benzoic acid (2a) in 93% GC yield (Scheme 6,
Eq. 2). However, the reaction without oxygen furnished 2a only in 24% GC yield, along with 65% GC
yield of benzaldehyde (1ab) (Scheme 6, Eq. 3). The intermediate 1aa was stable in DMSO under N2
atmosphere at 130 °C (Scheme 6, Eq. 4). When 10 mol% of FeCl was added, 1aa was converted into
3
1
ab in 87% GC yield. These experimental results indicated the reaction of 1aa to 1ab was catalyzed by
Fe(III) (Scheme 6, Eq. 5). Benzaldehyde (1ab) could be transformed to 2a in 10% GC yield in the
presence of iodine and DMSO (Scheme 6, Eq. 6). It is well-known that tert-butyl nitrite (TBN) can
liberate nitric oxide under acidic condition, which can be oxidized into nitrogen dioxide by dioxygen 16
.
Thus 30 mol% of TBN was applied in the oxidation of 1ab as NO equivalent, and 2a could be obtained
in 69% GC yield (Scheme 6, Eq. 7). When 1ab was treated with FeCl /DMSO under an acidic
3
condition, 33% GC yield of 2a could be achieved (Scheme 6, Eq. 8).

O
O
O
I2 (10 mol%)
(1)
o
DMSO, 130 C, 12 h
1aa
1a
GC yield: 95%
O
O
I2 (10 mol%)
Fe(NO ) 9H O (10 mol%)
3
3
2
OH
H
1aa
o
(2)
DMSO, O (0.1 MPa), 130 C, 12 h
2
2a
1ab
GC yield: 93%
5%
I2 (10 mol%)
Fe(NO ) 9H O (10 mol%)
3
3
2
1aa
2a
1ab
65%
(3)
o
DMSO, N (0.1 MPa), 130 C, 12 h
2
GC yield: 24%
1
aa
No reaction
(4)
(5)
o
DMSO, N (0.1 MPa), 130 C, 12 h
2
FeCl (10 mol%)
3
1
aa
1ab
o
DMSO, N (0.1 MPa), 130 C, 12 h
2
GC yield: 87%
I2 (10 mol%)
1ab
2a
o
(6)
(7)
DMSO, N (0.1 MPa), 130 C, 12 h
2
GC yield: 10%
TBN (30 mol%)
HOAc (30 mol%)
1ab
2a
o
DMSO, O (0.1 MPa), 130 C, 12 h
2
GC yield: 69%
FeCl (10 mol%)
3
HOAc (10 mol%)
1ab
2a
(8)
o
DMSO, O (0.1 MPa), 130 C, 12 h
2
GC yield: 33%
Scheme 6. Control experiments for mechanism studies.
Based on the experimental results and previous literatures, we proposed a plausible mechanism
which is depicted in Scheme 7. Initially, α-iodoketone 1ac is formed from substrate 1a and molecular
iodine.17 Then 1ac is oxidized into phenylglyoxal (1aa) by DMSO and releases HI.8,18 HI can be
regenerated to I by DMSO. C–C cleavage of 1aa proceeds through the Fe-promoted attack by H O
2
2

molecule to give benzaldehyde (1ab), along with the release of formic acid. Fe(NO ) ·9H O liberates
3
3
2
o
19
NO under 130 C . Benzaldehyde can be oxidized into benzoic acid via multiple pathway: (1)
2
2
0
3t
3+
21
oxidized by NO /O ; (2) oxidized by I /DMSO; (3) oxidized by Fe /O . However path (1) is the
2
2
2
2
main pathway based on the experimental results. When 1-phenylethanol was used as the substrate, it
will first be oxidized into 1a.
O
O
OH
H O
2
I2
DMS
1a
2a
NO
O2
O
Fe3+/O2
I2/DMSO
HI
I
DMSO
NO2
DMSO
DMS
O
H
1ac
heat
Fe(NO3)3
O
O
1ab
H O
2
Fe3+
heat
1aa
CO2
HCOOH
Scheme 7. Plausible reaction pathways.
In conclusion, a novel and efficient strategy of I /Fe(NO ) ·9H O-catalyzed C–C bond cleavage of
2
3 3
2
aryl alkyl ketones and secondary benzylic alcohols to their corresponding acids has been developed.
DMSO and O were used as the oxidants. This catalytic system is practical, environmentally friendly
2
and accommodates a wide range of alkyl ketones ketones and secondary benzylic alcohols with
moderate to excellent yield. In addition, a plausible reaction mechanism has also been proposed.
Acknowledgement: This work was financially supported by the National Natural Science
Foundation of China (21776260 and 21773211), and the Natural Science Foundation of Zhejiang
Province (LY17B060007).
Supplementary data

Supplementary data (experimental details and copies of H NMR and 13C NMR for the products)
associated with this article can be found, in the online version, at http://.
References and notes
1
1
1
2
3
4
5
6
2
7
8
9
1
1
1
1
1
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4. Typical Procedure for the Synthesis of carboxylic acid (2a) from acetophenone (1a): To a 20-mL tube
equipped with a magnetic stirring bar was added acetophenone 1a (120 mg, 1 mmol), 2 mL of DMSO, iodine (25
mg, 0.1 mmol) and Fe(NO ) ·9H O (40 mg, 0.1 mmol). Then the tube was sealed after being charged with
3
3
2
oxygen to replace the air in it. The tube was placed into a preheated oil bath (130 °C), and the reaction solution
was stirred for 12 h. Then the reaction was quenched with water, and the pH of the aqueous phase was adjusted to
1
1 with 0.1 mol/L NaOH. After being washed with ethyl acetate (3 x 3 mL), the pH of the aqueous phase was
adjusted to 2 with 0.1mol/L HCl and extracted with ether (3 x 6 mL). The combined ether phase was dried over
anhydrous sodium sulfate and concentrated on a rotary evaporator to obtain the crude product. The crude product
was purified by column chromatography on silica gel using ethyl acetate/petroleum ether as eluent to afford 2a as
1
a white solid (104 mg, 85% yield). H NMR(600 MHz, DMSO-d ) δ 12.88 (s, 1H), 7.95 (d, J = 7.9 Hz, 2H), 7.62-
6
1
3
7
.59 (m, 1H), 7.50-7.48 (m, 2H); C NMR (125MHz, DMSO-d ) δ 167.3, 132.7, 130.8, 129.2, 128.5.
6
1
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O
R
R
Ar
Ar
I2 (10 mol%)
Fe(NO) 9H O (10 mol%)
O
3
2
or
o
Ar
OH
DMSO, O (0.1 MPa) , 130 C
2
OH
Ar: aryl, heteroaryl
R: H, alkyl, phenoxy
40 examples
up to 91% isolated yields
Highlights
1
2
3
. Oxidation of aryl alkyl ketones and secondary benzylic alcohols into aryl carboxylic acids.
. Iodine and Fe(NO ) ·9H O as the catalysts, DMSO and oxygen as the oxidants.
3
3
2
. Moderate to excellent yields can be obtained (up to 91%).