DMSO/NaNO2/49% HBr: A novel and powerful oxidant for the direct conversion of primary benzylamines to benzoic acids

Article abstract of DOI:10.1080/00397910500334165

A mixture of DMSO, NaNO₂, and 49% HBr is found to oxidize primary benzyl amines to benzoic acids at 100°C. Copyright Taylor & Francis LLC.

Full text of DOI:10.1080/00397910500334165

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DMSO/NaNO /49% HBr: A Novel and Powerful
2
Oxidant for the Direct Conversion of Primary
Benzylamines to Benzoic Acids
a
a
Ramesh Naik & M. A. Pasha
a
Department of Studies in Chemistry, Central College Campus , Bangalore
University , Bangalore, India
Published online: 15 Aug 2006.
To cite this article: Ramesh Naik & M. A. Pasha (2006) DMSO/NaNO /49% HBr: A Novel and Powerful
2
Oxidant for the Direct Conversion of Primary Benzylamines to Benzoic Acids, Synthetic Communications:
An International Journal for Rapid Communication of Synthetic Organic Chemistry, 36:2, 165-168, DOI:
10.1080/00397910500334165
To link to this article: http://dx.doi.org/10.1080/00397910500334165
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Synthetic Communications , 36: 165–168, 2006
Copyright # Taylor & Francis LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910500334165
DMSO/NaNO /49% HBr: A Novel and
2
Powerful Oxidant for the Direct Conversion
of Primary Benzylamines to Benzoic Acids
Ramesh Naik and M. A. Pasha
Department of Studies in Chemistry, Bangalore University, Bangalore,
India
Abstract: A mixture of DMSO, NaNO
benzyl amines to benzoic acids at 1008C.
2
, and 49% HBr is found to oxidize primary
Keywords: Benzoic acid, benzyl amine, DMSO, HBr, NaNO2
INTRODUCTION
Recently, we have developed a method to convert primary benzyl amines into
[1]
the corresponding benzyl ester derivatives. The transformations of primary
benzylamines into variety of derivatives include oximes using methyltrioxo-
[
2]
[3]
rhenium (MTO)-catalyzed oxidation,
nitriles using tetrabutylammonium peroxydisulfate catalyzed by nickel,
and halides by pyrolysis of the respective pyrylium, quinolium, or pyridinium
imines using Fremy’s salts,
[4]
[5–10]
salts. In continuation of our ongoing work, we report for the first time an
efficient oxidation of primary benzylamines to benzoic acids using DMSO/
NaNO /49% HBr at 1008C (Scheme 1).
2
A mixture of benzylamine, inorganic acid, and DMSO was heated to
1008C for 32 h to obtain benzylammoniumbromide salt, which gave the
starting material upon neutralization. We then carried out the diazotisation
of benzylamine by using aq. NaNO2 at 0–108C in DMSO and under
Received in India July 14, 2005
Address correspondence to M. A. Pasha, Department of Studies in Chemistry,
Central College Campus, Bangalore University, Bangalore 560 001, India. E-mail:
m_af_pasha@yahoo.co.in
1
65

1
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R. Naik and M. A. Pasha
Scheme 1. Oxidation of benzylamines to benzoic acids.
an acidic medium at room temperature. This produced benzyloxydimethyl-
sulfoxide salt intermediate. However, the reaction mixture was heated to
1
008C for 30 min, we obtained benzoic acid (92%) but not benzaldehyde.
1
This was further characterized by H NMR, IR, and melting points. To
optimize the conditions to select a suitable inorganic acid, conc. HCl, conc.
H SO , and 49% HBr were utilized. Aq. HBr (49%) was the better acid to
2
4
produce benzoic acid in 92% yield.
The mechanism proposed for this transformation is given in Scheme 2.
To substantiate the mechanism, benzaldehyde was subjected to same
oxidation condition to yield benzoic acid as expected (Scheme 3).
A noteworthy feature of the reaction is that electron-accepting groups
(
entries 4–7, Table 1) and electron-releasing groups (entries 2 and 3,
Table 1) on the aromatic ring do not contribute significantly to the rate of
the reaction.
In conclusion, we have developed a novel and efficient oxidizing agent,
DMSO/NaNO /49% HBr, to convert primary benzylamines into benzoic
2
acids.
EXPERIMENTAL
TLC was performed on precoated aluminum plates with Merck silica gel 60
F-254 as the adsorbent. The developed plates were air dried and irradiated
with UV light. GC analysis was performed on a Shimadzu GC-MS
QP 5050A instrument. IR spectra were recorded on a Nicolet 400D FT-IR
1
spectrometer. H NMR spectra were recorded on Bruker 400-MHz
spectrometer as CDCl solutions with TMS as internal standard.
3
Scheme 2. Plausible mechanism for oxidation of primary benzylamine to benzoic acid.

DMSO/NaNO /49% HBr
2
167
Scheme 3. Oxidation of benzaldehyde to benzoic acid.
Table 1. Oxidation of benzylamines into benzoic acids
Time
(h)
Yield
a
(%)
Entry
Substrate
Benzylamine
Product
Benzoic acid
1
2
3
4
5
6
7
1.0
1.5
1.5
2.0
2.5
2.0
2.5
92
78
82
80
82
80
86
4-Methoxybenzylamine
4-Hydroxybenzylamine
4-Chlorobenzylamine
3-Chlorobenzylamine
3-Nitrobenzylamine
4-Nitrobenzylamine
4-Methoxybenzoic acid
4-Hydroxybenzoic acid
4-Chlorobenzoic acid
3-Chlorobenzoic acid
3-Nitrobenzoic acid
4-Nitrobenzoic acid
a
Isolated yields. All products are known and characterized by comparing mp, and IR
spectral analysis with authentic samples.
General Procedure for the Conversion of Benzylamine
into Benzoic Acid
An aqueous solution of NaNO (2.54 g, 37.38 mmol) was added to an ice-cold
2
solution of benzylamine (2.0 g, 18.69 mmol), DMSO (10 mL), and 49% HBr
(3.5 mL, 21 mmol) over a period of 15 min. The reaction mixture was
allowed to attain room temperature and then heated to 1008C for 30 min.
Water (10 mL) and brine (10 mL) were added and extracted into ether
(
4 Â 10 mL). The ethereal solution was washed with brine (3 Â 10 mL) and
made alkaline with 10% NaHCO solution, and the ether layer separated.
3
Upon neutralizing the aqueous layer with 15% HCl, a precipitate of benzoic
acid (2.09 g, 92%, mp 1228C, lit. mp 1238C) was obtained.
ACKNOWLEDGMENT
Ramesh Naik acknowledges the Bangalore University and State Bank
of Mysore, Yidagur branch, for financial assistance and the Department of
Organic Chemistry, Indian Institute of Science, Bangalore, for recording
NMR spectra.

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R. Naik and M. A. Pasha
REFERENCES
1
2
3
4
. Ramesh, N.; Pasha, M. A. Transformation of primary benzyl amines to benzyl
esters. Synth. Commun. (accepted).
. Yamazaki, S. Methyltrioxorhenium-catalyzed oxidation of secondary and primary
amines with hydrogen peroxide. Bull. Chem. Soc. Jpn. 1997, 70, 877–883.
. Castedo, L.; Ricardo, R.; Rodriguez, J. M. Fremy’s salt oxidation of benzylamines:
An oxidative deamination reaction. Tetrahedron 1982, 38, 1569–1570.
. Chen, F. E.; Peng, Z. Z.; Fu, H.; Liu, J. D.; Shao, L. Y. Tetrabutylammonium
peroxydisulfate in organic synthesis—Part 8: An efficient and convenient
nickel-catalyzed oxidation of primary amines to nitriles with tetrabutylammonium
peroxydisulfate. J. Chem. Res. Synop. 1999, 726–727.
5
6
7
8
9
. Katritzky, A. R.; Chermprapai, A.; Patel, R. C. Preparation of alkyl and benzyl
fluorides from the corresponding primary amines. J. Chem. Soc., Perkin Trans 1
1
980, 2901–2903.
. Katritzky, A. R.; Chermprapai, A.; Patel, R. C. Preparation of alkyl and benzyl
fluorides from the corresponding primary amines. J. Chem. Soc., Chem.
Commun. 1979, 238.
. Katritzky, A. R.; Harvath, K.; Plau, B. The conversion of primary aliphatic amines
into chlorides by reaction with 2,4,6-triphenylpyryliumchloride. Synthesis 1979,
437–438.
. Katritzky, A. R.; Al-Omran, F.; Patel, R. C.; Thind, S. S. Improved methods for
conversion of primary amines into bromides. J. Chem. Soc., Perkin Trans. 1
1
. Guziec, F. S., Jr.; Wie, D. Convenient halodeamination and hydrodeamination of
980, 1890–1894.
primary amines. J. Org. Chem. 1992, 57, 3772–3776.
0. Katritzky, A. R.; Eweiss, N. F.; Nie, P. L.; Ramsden, C. A. The conversion of
amines into iodides. Synthesis 1977, 634–635.
1