New effective synthetic method for preparation of N,N-dichlorocarbamates

Article abstract of DOI:10.1080/00397911.2010.488311

A rapid, efficient, economical, and easy-to-scale method for the effective conversion of carbamates to corresponding N,N-dichlorocarbamates by using sodium hypochlorite in acidic medium has been described. N,N-Dichlorocarbamates were obtained in quantitative yield through a simple workup in reduced reaction time.

Full text of DOI:10.1080/00397911.2010.488311

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New Effective Synthetic Method for
Preparation of N,N-Dichlorocarbamates
P. K. Gutch a , Ravindra Singh a , S. Prabha b & M. V. S.
Suryanarayana a
a Synthetic Chemistry Division, Defence Research and Development
Establishment , Gwalior , India
b School of Studies in Chemistry, Jiwaji University , Gwalior , India
Published online: 30 Mar 2011.
To cite this article: P. K. Gutch , Ravindra Singh , S. Prabha & M. V. S. Suryanarayana (2011) New
Effective Synthetic Method for Preparation of N,N-Dichlorocarbamates, Synthetic Communications:
An International Journal for Rapid Communication of Synthetic Organic Chemistry, 41:10, 1554-1557,
DOI: 10.1080/00397911.2010.488311
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Synthetic Communications1, 41: 1554–1557, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.488311
NEW EFFECTIVE SYNTHETIC METHOD FOR
PREPARATION OF N,N-DICHLOROCARBAMATES
P. K. Gutch,1 Ravindra Singh,1 S. Prabha,2 and
M. V. S. Suryanarayana1
1Synthetic Chemistry Division, Defence Research and Development
Establishment, Gwalior, India
2School of Studies in Chemistry, Jiwaji University, Gwalior, India
GRAPHICAL ABSTRACT
Abstract A rapid, efficient, economical, and easy-to-scale method for the effective conversion
of carbamates to corresponding N,N-dichlorocarbamates by using sodium hypochlorite in
acidic medium has been described. N,N-Dichlorocarbamates were obtained in quantitative
yield through a simple workup in reduced reaction time.
Keywords Acidic medium; sodium hypochlorite; substituted N,N-dichlorocarbamates
INTRODUCTION
N-Chloro compounds have been extensively exploited, for both fundamental
research and a wide range of industrial applications, owing to their easy handling,
commercial availability, and high stability. As a result, intensive research and studies
have been carried out over a long period of time on their chlorination, oxidation,
water disinfection, and other applications[1–3] in synthetic organic chemistry.
N-Chloro compounds have also been reported for decontamination of chemical
warfare agents.[4,5] N,N-Dichlorocarbamate was prepared by Dutta and Gupta[6]
and subsequently by Houben[7] and Chabrier,[8] but explicit details concerning yield,
method of isolation, purity, and physical characteristics of products were not
reported. One of the major drawbacks of Foglia and Swern’s method[9] was passing
chlorine gas for long time at room temperature, which creates inhalation toxicity.
White and Kovaic[10] have also reported poor yield and a time-consuming process
for the synthesis of N,N-dichlorocarbamates, and also isolation of pure N,N-
dichlorocarbamate was very difficult.
Received January 29, 2010.
Address correspondence to P. K. Gutch, Synthetic Chemistry Division, Defence Research and
Development Establishment, Jhansi Road, Gwalior 474002, MP, India. E-mail: pkgutch@rediffmail.com
1554

SYNTHESIS OF N,N-DICHLOROCARBAMATES
1555
These limitations prompted us to develop a rapid and efficient synthetic
procedure for N,N-dichlorocarbamates that involves easy workup and quantitative
yields in shorter reaction times by making use of sodium hypochlorite. In this paper,
we report an improved method, which gives greater yield in less time of pure N,N-
dichlorocarbamates in an acidic medium without any volatile solvents for extraction.
RESULTS AND DISCUSSION
Sodium hypochlorite is a commercially available compound that produce
positive chlorine for N-chlorination of carbamate. For chlorination of carbamate,
an acidic medium is required to avoid the formation of sodium salt of monochloro-
carbamates. In this procedure, the carbamate was first suspended in acetic acid, and
the reaction mixture cooled to 5 ꢀC with stirring until the starting material was
completely dissolved. Sodium hypochlorite was added to this slowly within 15 min
with stirring. Acetic acid was added in portions to turn the pH of the mixture acidic.
After 15 min, a translucent yellow organic layer was separated in the aqueous
medium.
The reaction of various substituted carbamates with sodium hypochlorite
afforded corresponding N,N-dichlorocarbamates in 15–20 min with excellent yields.
The reaction scheme and yield of N,N-dichlorocarbamates are depicted in Scheme 1
and Table 1. This method has allowed us to obtain the quantitative yields of the
products in reduced reaction time. The important advantage of this reaction is no
inhalation of chlorine at 5 ꢀC, and completion of the reaction is indicated by separ-
ation of the pure product in the organic phase in the bottom of the flask within
15–20 min.
NaOCl solution is basic, and by adding acetic acid the pH of the reaction
mixture was changed to acidic (from pH 9 to pH 6). It is necessary to avoid the
formation of sodium salt during N-chlorination, so an acidic medium is mandatory
for N-chlorination. The products formed were characterized by Fourier transform–
infrared (FT-IR) and NMR. Yields of all compounds were quantitative. The positive
chlorine content of these compounds was determined by standard iodometric
titration.[11]
EXPERIMENTAL
General Procedure
A mixture of ethyl carbamate (8.9 g, 0.1 mol) and acetic acid (30 mL) were
taken in a two-necked round-bottom flask equipped with condenser and dropping
Scheme 1. Synthesis of N,N-dichlorocarbamates.

1556
P. K. GUTCH ET AL.
Table 1. Synthesis of N,N-dichlorocarabamates
Active chlorineb (%)
Entry
R
Time (min)
Yielda (%)
Bp(ꢀC)=(mm Hg)
Observed
Calculated
1
2
3
4
5
-CH3
-C2H5
15
15
15
16
16
94
95
81
86
82
49–50=7.5
44–45=6.0
46.0=0.3
49.27
44.46
37.79
38.25
29.55
49.31
44.90
38.17
38.17
29.34
-CH2CH2CH2CH3
-C(CH3)3
-CH2(CH2)6CH3
44–45=2.6
51–52=2.5
6
7
8
16
20
20
87
89
88
122=3.0
120=1.0
124=1.5
33.12
34.31
32.11
33.49
34.46
32.27
9
20
78
126=5.0
29.41
30.34
aIsolated yield.
bActive chlorine of products was determined by iodometric titration.
funnel and mounted on a magnetic stirrer. The reaction mixture was cooled to 5 ꢀC
in an ice bath, and sodium hypochlorite (25–30 mL, 12–15%) was added slowly with
the help of dropping funnel within 15 min with stirring. Acetic acid (5–10 mL) was
added in portions to bring down the pH of the mixture to acidic. After 15 min, a
translucent yellow layer of the product was separated from the aqueous layer. The
organic phase was washed with water and dried with anhydrous sodium sulfate.
Yield was 95% as a yellow oil, bp 44–45 ꢀC at 6.0 mm Hg. The positive chlorine of
N,N-dichloro ethyl carbamates were checked by standard iodometric titration, and
results are given in Table 1.
Spectral Data for Selected Compounds
N,N-Dichloro ethyl carbamate (2). 1H NMR (CDCl3=TMS 400 MHz): d
=
1.39 (t, 3H, CH3), 4.37 (q, 2H, CH2). IR (KBr) 1753 (C O), 1230, 1100, 1047,
993, 900, 827, 803, 766, 735 cmꢁ1. Analysis (iodometric titration) calcd. for
C3H5Cl2NO2: Cl, 44.9. Found: Cl, 44.5.
N,N-Dichloro t-butyl carbamate (4). 1H NMR (CDCl3=TMS 400 MHz): d
=
1.53 (s, CH3). IR (KBr) 1765 (C O), 1400, 1373, 1274, 1240, 1143, 1045, 994,
882, 820, 785, 753 cmꢁ1. Analysis (iodometric titration) calcd. for C5H9Cl2NO2:
Cl, 38.25. Found: Cl, 38.17.

SYNTHESIS OF N,N-DICHLOROCARBAMATES
1557
CONCLUSION
In conclusion we have reported an efficient, convenient, and rapid one-pot
conversion of carbamates to N,N-dichlorocarbamates in excellent yield by making
use of sodium hypochlorite in an acidic medium.
ACKNOWLEDGMENT
We thank Dr. R. Vijayaraghavan, director, Defence Research and Develop-
ment Establishment, Gwalior, for his keen interest and encouragement.
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