Mild and convenient synthesis of organic carbamates from amines and carbon dioxide using tetraethylammonium superoxide

Article abstract of DOI:10.1080/00397910701465149

A safe and simple method of preparing organic carbamates has been achieved from amines and carbon dioxide using tetraethylammonium superoxide generated in situ. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910701465149

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Mild and Convenient Synthesis of Organic
Carbamates from Amines and Carbon Dioxide
using Tetraethylammonium Superoxide
Krishna Nand Singh a
a Department of Applied Chemistry , Institute of Technology, Banaras Hindu
University , Varanasi, India
Published online: 14 Aug 2007.
To cite this article: Krishna Nand Singh (2007) Mild and Convenient Synthesis of Organic Carbamates
from Amines and Carbon Dioxide using Tetraethylammonium Superoxide, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 37:16, 2651-2654, DOI:
10.1080/00397910701465149
To link to this article: http://dx.doi.org/10.1080/00397910701465149
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Synthetic Communicationsw, 37: 2651–2654, 2007
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910701465149
Mild and Convenient Synthesis of Organic
Carbamates from Amines and Carbon
Dioxide using Tetraethylammonium
Superoxide
Krishna Nand Singh
Department of Applied Chemistry, Institute of Technology, Banaras
Hindu University, Varanasi, India
Abstract: A safe and simple method of preparing organic carbamates has been
achieved from amines and carbon dioxide using tetraethylammonium superoxide
generated in situ.
Keywords: amines, carbamates, carbon dioxide, tetraethylammonium superoxide
Organic carbamates represent an important class of compounds that have
unique applications in the field of pharmaceutics (drugs), agriculture (pesti-
cides, herbicides, and fungicides), and chemical industries (polyurethane-
based polymers and novel protecting groups).[1–3] Recently, because of
rapid development of combinatorial techniques in the field of drug
discovery and owing to their medicinal and biological properties, carbamates
have gained immense importance in the preparation of small molecule
libraries.[4] The common methodologies for carbamate synthesis are based
on specialized reagents and operational complexity due to the use of highly
corrosive and toxic reagents such as phosgene and its derivatives or isocya-
nates or chloroformates.[3,5–7] Nevertheless, none of these methods are
environmentally benign. To avoid the use of such toxic and harmful
Received in India January 8, 2007
Address correspondence to K. N. Singh, Department of Applied Chemistry,
Institute of Technology, Banaras Hindu University, Varanasi, India. E-mail:
knsinghbhu@yahoo.co.in
2651

2652
K. N. Singh
Scheme 1. R ¼ Alkyl, aryl, heteroaryl; R1 ¼ alkyl, H.
reagents, several efforts have been made to develop environmentally benign,
phosgene-free routes.[8–13]
As part of our research on the superoxide ion,[14–16] we report herein a
milder and convenient method to achieve organic carbamates from amines
in the presence of gaseous carbon dioxide using tetraethylammonium super-
oxide (Et4NO2) generated in situ, obtained by the phase-transfer reaction of
KO2 and Et4NBr in dry DMF (Scheme 1).
The reactions were accomplished using a 2.0-fold molar excess of KO2
and the same molar ratio of Et4NBr with respect to substrate 1 in dry DMF.
Table 1. Synthesis of carbamates from amines and carbon dioxide activated by
tetraethylammonium superoxide
1/2
Substrate (1)
Product (2)
Yield (%)
a
b
c
CH3(CH2)3NH2
CH3(CH2)5NH2
CH3(CH2)3NHCOOCH3
CH3(CH2)5NHCOOCH3
80
82
85
d
90
e
f
C6H5NH2
C6H5NHCOOMe
p-ClC6H4NHCOOMe
p-NO2C6H4NHCOOMe
p-CH3OC6H4NHCOOMe
79
66
54
76
67
p-ClC6H4NH2
p-NO2C6H4NH2
p-CH3OC6H4NH2
g
h
i
j
61
k
l
Ph2NH
Ph2NCOOCH3
38
55
86
81
p-MeC6H4(Et)NH
C6H5(Me)CHNH2
C6H5CH2NH2
p-MeC6H4(Et)NCOOMe
C6H5(Me)CHNHCOOMe
C6H5CH2NHCOOCH3
m
n

Synthesis of Organic Carbamates
2653
Generally, the reaction continued for 2–7 h at room temperature until the
completion of the reaction was indicated by TLC. The reaction was then
quenched with cold brine solution and worked up to afford the product 2 in
reasonably good yields (Table 1). All the products 2 exhibited physical and
spectral data consistent with their structures.
EXPERIMENTAL
General Experimental Procedure
Potassium superoxide (0.5688 g, 8 mmol) and tetraethylammonium bromide
(0.8406 g, 4 mmol) were weighted under a nitrogen atmosphere using an
atmosbag and were transferred to a two-necked, round-bottom flask contain-
ing dry dimethylformamide (15 ml) and fitted with an N2/CO2 inlet and a
Leibig condenser protected by a drying tube. The mixture was agitated mag-
netically for 15 min while purging CO2 and N2 and then the amine 1 (4 mmol)
was admitted. The stirring continued for 2–7 h at room temperature. A three-
fold molar excess of methyl iodide was added, and the mixture was maintained
under stirring. The mixture was then treated with brine solution (10 ml) and
extracted with diethyl ether/dichloromethane (3 Â 20 ml). The combined
organic extract was washed with water, dried over anhydrous Na2SO4,
filtered, and evaporated to give the product 2.
ACKNOWLEDGMENT
The authors are thankful to the Council of Scientific and Industrial Research
(CSIR), New Delhi, India, for financial support (Ref. No. 01(1875)/03/
EMR-II).
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