An efficient and mild procedure for the preparation of benzoic acids via oxidation of aromatic carbonyl compounds by employing N-bromoimides and mercuric acetate system

Article abstract of DOI:10.1246/cl.2001.900

Aromatic carbonyl compounds are efficiently converted into the corresponding benzoic acids under mild reaction conditions by employing N-bromoimide and mercuric acetate in good to excellent yields. This procedure works efficiently at room temperature for aromatic aldehydes as well as aromatic ketones to give the corresponding benzoic acids.

Full text of DOI:10.1246/cl.2001.900

9
00
Chemistry Letters 2001
An Efficient and Mild Procedure for the Preparation of Benzoic Acids via Oxidation of Aromatic
Carbonyl Compounds by Employing N-Bromoimides and Mercuric Acetate System
Amena Anjum and P. Srinivas*
Department of Chemistry, Nizam College, Osmania University, Hyderabad-1, India
(Received April 23, 2001; CL-010374)
Aromatic carbonyl compounds are efficiently converted
into the corresponding benzoic acids under mild reaction condi-
tions by employing N-bromoimide and mercuric acetate in good
to excellent yields. This procedure works efficiently at room
temperature for aromatic aldehydes as well as aromatic ketones
to give the corresponding benzoic acids.
Oxidation of carbonyl compounds into the corresponding
carboxylic acids is one of the most important reactions in
organic chemistry, as the carboxylic acids are versatile interme-
diates in a variety of synthetic transformations. In recent years
oxidation of organic compounds under non-aqueous and aprotic
conditions is emerging as a useful reaction. For this purpose
1
various oxidants are reported in the literature. Recently, car-
bonyl compounds are efficiently converted into carboxylic
2
3
acids by using H O2 , sodium chlorite , and lithium hypochlo-
2
4
rite–clorax as an oxidative mixture. However, some of the
reagents suffer from disadvantages such as instability, hygro-
scopicity, low selectivity, long reaction time, difficulty of
preparation of the reagent, high cost, and need for a large
excess of the reagent. Thus, a milder, selective and inexpensive
reagent is still in demand.
It is well known that N-haloimides are useful reagents for
5
6
oxidation of benzyl alcohols , α–hydroxy acids , methyl-
7
8
benzenes , and halogenation of alkenes . A recent report by
Rao et al described the oxidative deamination of aliphatic
9
amines to carbonyl compounds by N-bromophthalimide
(
NBP)–Hg(OAc) system. However, oxidation of carbonyl
2
compounds has not been studied.
We wish to report here an efficient and mild oxidation of
aromatic carbonyl compounds to the corresponding carboxylic
To check the generality of oxidative properties of
N-haloimides, the reactions were carried out using N-bromosuc-
cinimide (NBS) in place of NBP. It was observed that the reac-
tions were slower and it took longer time in case of NBS com-
pared to NBP. Thus, it is evident that NBP is a more efficient
oxidising agent than NBS. The reactions failed to proceed in
the absence of N-haloimides, even after a longer period under
refluxing conditions. Thus, N-haloimides are necessary for the
reaction. It is also observed that the reactions were sluggish in
the absence of Hg(OAc) . Thus, it is assumed that Hg(OAc) is
acids using the N-haloimides and Hg(OAc) system.
2
2
2
acting as a co-oxidant.
While optimizing the reaction conditions for the oxidation
of carbonyl compounds, it was noticed that the yields were
We found that the treatment of aromatic carbonyl com-
pounds with NBP–Hg(OAc) in chloroform at room tempera-
maximum with a 1:1:1 (substrate:NBP:Hg(OAc) ) stoichiomet-
2
2
ture afforded the corresponding carboxylic acids (benzoic
acids) in quantitative yields (Table 1). The oxidation of car-
ric ratio. A variety of aprotic solvents such as dichloromethane,
1,2-dichloroethane, and acetonitrile were screened. However,
none of these solvents were superior to chloroform.
1
0
bonyl compounds in the presence of NBP–Hg(OAc) system
2
proceeds rapidly to afford high yields of the corresponding car-
boxylic acids. All the products were characterized by IR, H
NMR, mass spectra, and other physical data or by comparison
of their data with those of authentic samples.
Halo-aromatic aldehydes showed remarkable selectivity in
giving the corresponding carboxylic acids (1c–1d) without any
dehalogenation and other carbonyl compounds with oxidizable
funtional groups (1f–1n) were selectively oxidized into the cor-
1
Copyright © 2001 The Chemical Society of Japan

Chemistry Letters 2001
901
responding carboxylic acids without affecting the substituent.
It is also worth mentioning that benzophenone was also oxi-
dized smoothly into benzoic acid (1q) as the main product with-
out the formation of phenol under the above reaction condi-
tions. It is observed that neither electron donating group nor
electron withdrawing group affects the yield of the product.
This procedure proved satisfactory even with bifunctional
substrates such as phthalaldehyde, diacetylbenzene which were
efficiently oxidized into the corresponding phthalic acids in
good yields. The results demonstrate the synthetic utility of this
method.
Aoki, J. Takagi, K. Zimmermann, and R. Noyori, Bull.
Chem. Soc. Jpn., 72, 2287 (1999) and references cited
therein.
K. Sato, M. Hyodo, J. Takagi, M. Aoki, and R. Noyori,
Tetrahedron Lett., 41, 1439 (2000).
2
3
4
R. B. Babu and K. K. Balasubramanian, Org. Prep.
Proced. Int., 26, 123 (1994).
M. M. Madler, J. Klucik, P. S. Soell, C. W. Brown, S. Liu,
K. D. Berlin, D. M. Benbrook, P. J. Birckbichler, and E. C.
Nelson, Org. Prep. Proced. Int., 30, 230 (1998).
a) S. Hanessian, D. H. C. Wong, and M. Therien,
Synthesis, 1981, 394. b) T. Mukaiyama, M. Tsunoda, and
K. Saigo, Chem. Lett., 1975, 691. c) G. C. Hiegel and M.
Nalbandy, Synth. Commun., 22, 1589 (1992).
V. Thiagarajan and S. Ramakrishnan, Ind. J. Chem., 37B,
443 (1998).
W. Baik, H. J. Lee, J. M. Jang, S. Koo, and B. H. Kim, J.
Org. Chem., 65, 108 (2000).
U. Luning, Douglas S. McBain, and Philip S. Skell, J. Org.
Chem., 51, 2077(1986).
5
In conclusion, the present study demonstrates the novelty
of NBP–Hg(OAc) combination system which shows unique
2
selectivity and constitutes a useful alternative to the commonly
accepted procedure for the synthesis of benzoic acids.
Moreover, this simple, mild and efficient method affords vari-
ous benzoic acids in excellent yields without formation of any
undesirable side products.
One of the authors A. Anjum. thanks Nawab Shah Alam
Khan, Chairman and Nawab Mahboob Alam Khan, Secretary
of Nawab Shah Alam Khan Centre for Post Graduate Studies
and Research, Mallepally, for their constant encouragement.
6
7
8
9
1
S. F. Amatul Jabbar and V. S. Rao, Ind. J. Chem., 33A, 69
(1994).
0 A typical procedure is as follows: To a solution of ben-
3
Reference
zaldehyde (1a) (1 mmol) in chloroform (20 cm ) was added
1
a) H. O. House, “Modern Synthetic Reactions,” 2nd ed.,
Benzamin, Menlopark (1972), p 257. b) G. Gainelli and G.
Cardillo, “Chromium Oxidations in Organic Chemistry,”
Springer-Verlag, Berlin (1984). c) S. V. Ley and A.
Madin, “Comprehensive Organic Synthesis,” ed. by B. M.
Trost, I. Fleming and S. V. Ley, Pergamon, Oxford (1991),
Vol. 7, p 251. d) R. Stewart, “Oxidation in Organic
Chemistry,” ed. by K. B. Wiberg, Academic Press, New
York (1965), Vol. 5A, p 1. e) A. J. Mancuso and D.
Swern, Synthesis, 1981, 165. f) D. B. Dess and J. C.
Margin, J. Org. Chem., 48, 4155 (1983). g) K. Sato, M.
N-bromophthalimide (1 mmol) and Hg(OAc) (1 mmol)
2
and the reaction mixture was stirred for 2–3 h at rt. After
completion of reaction as indicated by TLC, the reaction
3
mixture was washed with water (25 cm × 2). The organic
layer was separated and dried over Na SO . Evaporation
2
4
of the solvent under vacuum and purification by column
chromatography using ethyl acetate:hexane (3:7) as eluent
gave the pure benzoic acid (2a) in 94% yield : mp 120–122
1
°C; H NMR(CDCl ) δ 7.2–8.2 (m, ArH, 5H) 11.4
3
(COOH, 1H), MS m/z 121, 105, 77.