An improved method for the preparation of alkyl/arylurea derivatives using chlorocarbonylsulfenyl chloride as carbonylating agent

Article abstract of DOI:10.1007/s11164-012-0563-4

A convenient procedure has been developed for preparation of aminesubstituted or monomethylamine-substituted alkyl/arylurea derivatives. The method comprises two steps-reaction of an alkyl/aryl amine with chlorocarbonylsulfenyl chloride in a non-polar solvent to produce an alkyl/arylcarbonylsulfenyl chloride, then reaction of this alkyl/ arylcarbonylsulfenyl chloride with ammonia or monomethylamine in a two-phase reaction with a phase-transfer catalyst, to produce the corresponding alkyl/aryl-substituted urea. Springer Science+Business Media B.V. 2012.

Full text of DOI:10.1007/s11164-012-0563-4

Res Chem Intermed (2012) 38:2479–2489
DOI 10.1007/s11164-012-0563-4
An improved method for the preparation of alkyl/
arylurea derivatives using chlorocarbonylsulfenyl
chloride as carbonylating agent
D. M. Manidhar
C. Suresh Reddy
Krishna Misra
•
K. Uma Maheswara Rao
Ch. Syamasunder K. Adeppa
•
•
•
•
Received: 11 January 2012 / Accepted: 18 April 2012 / Published online: 8 May 2012
Ó Springer Science+Business Media B.V. 2012
Abstract A convenient procedure has been developed for preparation of amine-
substituted or monomethylamine-substituted alkyl/arylurea derivatives. The method
comprises two steps—reaction of an alkyl/aryl amine with chlorocarbonylsulfenyl
chloride in a non-polar solvent to produce an alkyl/arylcarbonylsulfenyl chloride, then
reaction of this alkyl/arylcarbonylsulfenyl chloride with ammonia or monomethylamine
in a two-phase reaction with a phase-transfer catalyst, to produce the corresponding
alkyl/aryl-substituted urea.
Keywords Aryl ureas ꢀ Cyclohexylamine ꢀ Chlorocarbonylsulfenyl chloride ꢀ
Carbonylation
Introduction
Alkyl/aryl ureas (3) are well known commercial intermediates used for preparation
of drugs and fine chemicals. Some of these ureas, shown in Fig. 1 (3a–h), have been
produced industrially on a large scale.
D. M. Manidhar ꢀ K. Uma Maheswara Rao ꢀ C. Suresh Reddy ꢀ Ch. Syamasunder
Sri Venkateswara University, Tirupathi, Andhra Pradesh, India
e-mail: markmanidar@gmail.com
K. Adeppa
Gautam Buddh Technical University, Lucknow 226021, Uttar Pradesh, India
K. Adeppa (&)
R&D Centre, India Pesticides Limited, Lucknow 226004, India
e-mail: adeppa_33@rediffmail.com
K. Misra
Indian Institute of Information Technology, Jhalwa Campus, Allahabad 211002,
Uttar Pradesh, India
123

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D. M. Manidhar et al.
O
O
O
H N
2
N
H
N
H
NH2
N
H
NH2
Methyl urea (3a)
Ethyl urea (3b)
Propyl urea (3c)
H
N
O
H N
2
O
O
HN
N
NH
HN
Butyl urea (3d)
N-ethyl-N'-methyl urea (3e) N,N-dibutyl-N'-methyl urea (3f)
O
O
NH
H N
2
H N
2
N
H
Benzyl urea (3g)
Fig. 1 Some commercially available alky/arylurea derivatives
Cyclohexyl urea (3h)
Alkyl/aryl ureas are a family of well-known compounds. They are important
intermediates [1] in the production of isocyanate drugs, phytomedicines, and
herbicides, and are used in coloring agents. Several methods for synthesis of mono
alkyl/aryl ureas have been reported in the literature. Much literature is available,
dealing with a wide variety of procedures for the preparation of alkyl/arylurea
derivatives; most of the procedures entail:
1
reaction of ammonia with a suitable carbamoyl chloride obtained by phosgen-
ation of the corresponding amine [2, 3];
2
3
4
reaction of salts of suitable amines with the cyanate of an alkaline metal [4–8];
reaction of suitable isocyanates with ammonia [9–12];
reaction of a suitable amine with nitrourea then transamidation of the resulting
products with dimethylamine [13, 14];
5
6
transamidation of diaryl ureas with dimethylamine [15–18]; and
oxidative–reductive carbonylation of nitroarenes and dimethylamine with
carbon monoxide as catalyst [11, 19, 20].
The starting materials used in the first four procedures are fairly expensive, highly
toxic, and difficult to obtain. The fifth process does not have the same disadvantages
as the first four processes. For example, in methods 1 and 2 the raw materials
are toxic, difficult to obtain, and very expensive. Phosgene is a potentially toxic
chemical, an environmental hazard, a source of accidents, and is difficult to handle,
thus posing a risk not only to workers but also to the health of nearby inhabitants as a
result of environmental pollution. In method 5, the urea used in transamidation is an
innocuous non-toxic, and inexpensive compound, but yields of the reaction products
are fairly low, and purity, as indicated by melting point, is very low.
1
23

Improved method for the preparation of alkyl/arylurea derivatives
2481
The objective of this study was to elaborate a economical, commercially viable
process for preparation of alkyl/arylurea derivatives of general formula 3. In
this communication, the corresponding amines are first reacted with chloro-
carbonylsulfenyl chloride (CCSC) in dichloromethane under a nitrogen atmosphere.
The resulting alkyl/arylcarbonylsulfenyl chlorides are then further reacted with
ammonia or monomethylamine in a two phase reaction using a phase-transfer
catalyst (PTC) to produce the corresponding alkyl/aryl ureas.
Results and discussion
In this work, carbonylation of the corresponding amine with the carbonylating agent
CCSC under an N atmosphere was followed by condensation with ammonia or
2
monomethylamine in aqueous solution in a two-phase reaction using different
non-polar solvents and different PTCs.
Because carbonylation of the corresponding amine with CCSC is a very fast
reaction initiated by nucleophilic substitution of the loan pair of electrons present on
the nitrogen of the amine with a positively charged carbonyl carbon to form N-alkyl/
arylcarbonylsulfenyl chloride, a further loan pair of electrons present on the
nitrogen of ammonia or methylamine can undergo nucleophilic substitution with the
positively charged carbonyl carbon of the alkyl/arylcarbonylsulfenyl chloride to
form the corresponding alkyl/arylurea derivatives. The detailed reaction mechanism
is shown in Scheme 1.
_
O
Cl
R1
R1
O
N
2
Atm., 2h
- HCl
N
C
S
Cl
Cl
N
0
R2
DCM, 40 C
R2
S
N
R3
0
C
_
O
0
4
,
C
5h.
T
P
.
r
p
Cl
p
R1
A
R2
- HSCl
N
C
N
S
N
R2
R1
H
Cl
Scheme 1 General method for the preparation of monomethylamine/amine substituted alkyl/arylurea
derivatives (3a–h): 3a: Methylurea; 3b: Ethylurea; 3c: Propylurea; 3d: Butylurea; 3e: N-ethyl-N’-
methylurea; 3f: N,N-dibutyl-N’-methylurea; 3g: Benzylurea; 3h: Cyclohexylurea
123

2482
D. M. Manidhar et al.
The factors that affect completion of the second stage of the reaction include the
two-phase system, the catalyst, the sequence of addition of the starting materials,
and the quantity of solvent used.
Alkyl/arylcarbonylsulfenyl chloride in solvent was added dropwise to a solution
of the PTC, sodium chloride, sodium hydroxide, boric acid, and monomethylamine
or ammonia in water and triethylamine in organic solvent (dichloromethane).
The total amount of water and organic solvent used were optimized. Use of smaller
amounts of water and organic solvent increased the viscosity of the mixture at the
beginning of the reaction and affected the rate of stirring and the separation of the
organic phase.
The purity and yield of the synthesized urea derivatives depend on different
factors, for example the PTC, triethylamine, their respective concentrations,
reaction temperature and time, and stirring rate. Considering these factors, the types
of catalyst and their concentrations were first optimized.
To follow the reaction, GC with flame-ionization detection (FID) was chosen
as the most appropriate technique for analysis of the composition of the alkyl/
arylcarbonylsulfenyl chloride present in the organic phase.
In the first five experiments (Table 1, entries 1–5) the reaction was performed in
H O–DCM at 40 °C in the presence of the PTC. In the absence of TEBA (Table 1,
2
entry 5), most of starting alkyl/arylcarbonylsulfenyl chloride was found to be
unreacted with organic phase after 3 h whereas on addition of TEBA the rate of
conversion was increased (Table 1, entries 1–4).
Among the trialkylamines used in the literature, 4-dimethylaminopyridine
4-DMAP), a more sterically hindered amine, was successfully applied in our next
(
experiments (Table 1 entry 6). Replacement of triethylenediamine (TEDA) by
Table 1 Effect of PTC and solvents in the synthesis of alkyl/aryl ureas 3a–h
Entry
1
Tertiary amine
PTC
Solvent
Yield (%)
95
TEDA (0.11 mM)
Triethylbenzylammonium
chloride (0.22 mM)
Dichloromethane–water
2
3
4
TEA (0.11 mM)
TEDA (0.11 mM)
TEDA (0.11 mM)
Triethylbenzylammonium
chloride (0.15 mM)
Dichloromethane–water
Dichloromethane–water
Dichloromethane–water
72
55
88
Triethylbenzylammonium
chloride (0.05 mM)
Triethylbenzylammonium
chloride (0.10 mM)
5
6
TEDA (0.22 mM)
–
Dichloromethane–water
Dichloromethane–water
45
85
4-DMAP (0.11 mM)
Triethylbenzylammonium
chloride (0.22 mM)
7
8
9
TEDA (0.11 mM)
TEDA (0.11 mM)
TEDA (0.11 mM)
Triethylbenzylammonium
chloride (0.22 mM)
Ethylene dichloride
Tetrahydrofuran
75
52
28
Triethylbenzylammonium
chloride (0.22 mM)
Triethylbenzylammonium
chloride (0.22 mM)
Dimethyl sulfoxide
Reaction using alkyl/arylamine:CCSC 1.0 M:1.20 M
1
23

Improved method for the preparation of alkyl/arylurea derivatives
2483
4
-dimethylaminopyridine (4-DMAP) caused urea yield to decrease by 6–12 %.
To eliminate byproduct formation by alky/arylcarbonylsulfenyl chloride hydrolysis,
the concentration of unreacted alky/arylcarbonylsulfenyl chloride was kept as low
as possible.
As indicated in Table 1, 0.22 mM TEBA, 0.11 mM TEDA, and a 5 h reaction time
enabled maximum conversion of alky/arylcarbonylsulfenyl chloride with minimum
hydrolysis at 40 °C using H O–DCM as solvent system (Table 1, entry 1).
2
In summary, both yield and purity of alkyl/arylurea derivatives produced by
reaction of alky/arylcarbonylsulfenyl chloride with aqueous ammonia/monometh-
ylamine using the PTC system are affected by different factors, for example the
catalyst, temperature, and stirring of the reaction mixture.
The tertiary amine catalyst should act as a protecting agent to prevent hydrolysis
of the alky/arylcarbonylsulfenyl chloride and, at the same time, act as a suitable
leaving group to enhance the reaction of alky/arylcarbonylsulfenyl chloride with
ammonia/monomethylamine. TEDA was a good protecting agent, alky/arylcarbo-
nylsulfenyl chloride was not hydrolyzed. Both DMAP and triethylamine (TEA)
were suitable as temporary protecting agents and better leaving groups facing
ammonia/monomethylamine. Therefore, in the presence of DMAP or TEDA. The
reaction time must be minimized to prevent hydrolysis of alky/arylcarbonylsulfenyl
chloride.
Use of 0.22 mM TEBA and 0.11 mM TEDA resulted in a reasonable rate of
reaction with minimum hydrolysis of alky/arylcarbonylsulfenyl chloride. Perform-
ing the reaction under the optimized conditions resulted in conversion of the alky/
arylcarbonylsulfenyl chloride to the urea derivative at 40 °C (using CH Cl /H O
2
2
2
as solvent system) after 2 h with 90–95 % purity. The final optimized reaction
conditions used for preparation of the alkyl/arylurea derivatives starting from the
amine are listed in Table 2. Yields of the alkyl/arylurea derivatives formed by
conducting the reaction under different conditions are compared in Table 3.
Conclusion
The method described is a simple efficient one-pot process for synthesis of
commercially important urea derivatives by reaction of amines with CCSC followed
by reaction with ammonia/monomethylamine. A notable feature of the method of
preparation is that the process is economically viable, i.e. high rate of reaction,
negligible byproducts, and cleaner reaction profiles, which makes it a useful and
attractive process, especially for commercial synthesis. The general nature of the
procedure is another important benefit, and producing a method requiring no
phosgene is a major achievement. Simple experimental and product-isolation
procedures are certainly important in the development of greener and more efficient
procedures for synthesis of the urea derivatives used as commercially important
intermediates in the synthesis of different products, specifically drugs and
herbicides. This is an important improvement over phosgenation and other costlier
methods currently being used.
123

2484
D. M. Manidhar et al.
1
23

Improved method for the preparation of alkyl/arylurea derivatives
2485
Table 3 Comparison of the yields of alkyl/arylurea derivatives obtained by conducting the reaction
under different conditions
No. Product
Yield (%), this method Yield (%) of methods reported in the
literature
A [24]
91.20
B [25]
–
C [26]
79.00
D [27]
–
1
92.00
93.50
92.00
91.00
O
H N
2
N
H
2
3
4
89.93
–
83.00
81.00
–
–
–
–
O
N
NH2
H
–
78.43
03.50
O
N
NH2
H
95.13
H N
2
O
NH
5
6
88.00
85.00
97.70
90.25
–
–
–
–
–
–
O
HN
HN
H
N
O
N
7
8
88.00
86.00
93.10
94.57
40.66
–
–
–
O
NH
H N
2
–
90.95
O
N
H
H N
2
123

2486
D. M. Manidhar et al.
Experimental
All chemicals (ammonia, monomethylamine, benzylamine, ethylamine, propylamine,
butylamine, dibutylamine, cyclohexylamine, DCM, TEBA, TEDA, 4-DMAP,
and TEA) were purchased from Merck, India. Perchloromethyl mercaptan was
donated by India Pesticides Limited, India. Melting points were determined on a
Paramount digital melting point instrument. Gas chromatographic (GC) analysis was
1
performed on a Thermo Fisher GC model, GC-1000. H NMR spectra were obtained
on a AVAN DMX 400 (Brukerspectrometer). Mass and exact-mass spectra were
recorded on a Perkin–Elmer mass spectrometer.
General procedure for synthesis of the urea derivatives
A 2,000 ml four-necked double-glass-walled reactor (with water at the desired
temperature circulating between the walls) was equipped with a mechanical stirrer
(
made up of one four-blade turbine), a condenser, a dropping funnel, and a
thermometer. Anhydrous amine (0.5 mol) in 600 ml dichloromethane was placed in
the reactor, then CCSC solution (1.05–1.25 M) was added dropwise over a period of
6
0–90 min under vigorous reflux in a nitrogen atmosphere. The reaction was mildly
exothermic. The progress of the reaction was monitored by GC. After the addition, the
reaction was further maintained at reflux temperature for an additional 2 h, by which
time evolution of HCl had ceased. Partial distillation of dichloromethane (*250 ml)
was conducted to remove any dissolved HCl. The alkyl/arylcarbonylsulfenyl chloride
was removed from the flask and placed in a pressure-equalizing addition funnel. Then,
1
2
0.55 g (0.17 mol) boric acid, 58.5 g (1.0 mol) NaCl, 5.73 g (0.145 mol) NaOH, and
50 mg (4.55 mM) TEBA were dissolved in 600 ml water. The pH of the solution was
maintained between 10.0 and 10.5 at 25 °C. This solution and 62 mg (0.11 mM)
TEDA in 300 ml dichloromethane were then placed in the stirred reaction flask. The
temperature of the reaction mixture was stabilized at 30 °C, by use of water
circulation, while stirring at 1,600 rpm, and the solution of alky/arylcarbonylsulfenyl
chloride in dichloromethane was added dropwise during 25 min while the reaction
mixture temperature was maintained at 40 °C, and vigorous stirring was continued.
The reaction mixture, especially the organic layer, became a milky viscous suspension
within 30 min. Stirring was continued for a further 2 h until the mixture became
completely clear. The aqueous layer pH was maintained above 9.0 throughout the
reaction. The lower organic layer was removed after settling for 15 min and the reflux
condenser was replaced by a distillation head connected to a condenser and collector.
The water and volatile impurities were removed by vacuum distillation. The residue
obtained was extracted with 200 ml dimethylformamide followed by crystallization
to obtain the urea as a 98.5 % pure product (GC area %).
Methylurea (3a)
Yield: 34.10 g (92 %); 97.0 % purity (GC), colorless needles from chloroform, mp:
2
4
1
02–102.5 °C (Lit ).
1
23

Improved method for the preparation of alkyl/arylurea derivatives
1
2487
H NMR (400 MHz): d ppm = 2.46 (d, J = 5.0 Hz, 3 H, CH ), 5.49 (s, 2H,
3
NH ), 5.85 (s, H, NH).
MS (E1, 70 eV): m/z (%) = 75.8.
2
Ethylurea (3b)
Yield: 41.10 g (93.5 %); 95.80 % purity (GC), colorless needles from ethyl acetate,
4
2
mp: 92.0–92.5 °C (Lit ).
1
NMR (400 MHz): d ppm = 1.16 (t, J = 7.00, 2H, –CH ),3.20 (d, J = 7.0 Hz, 2
3
H, N–CH ), 5.01 (br s, 2H, NH ).
MS (E1, 70 eV): m/z (%) = 89.1.
2
2
Propylurea (3c)
Yield: 45.65 g (92 %) 95.4 % purity (GC), colorless needles, mp: 173–174 °C
2
5
Lit ).
(
1
NMR (400 MHz): d ppm = 1.06 (t, J = 7.00, 3H, –CH ), 1.68(m, 2H,
3
J = 7.00, –CH ), 3.40 (t, J = 7.0 Hz, 2H, N–CH ), 5.51 (br s, 2H, NH ).
MS (E1, 70 eV): m/z (%) = 103.1.
2
2
2
Butylurea (3d)
Yield: 52.80 g, (91 %), 94.5 % purity (GC), colorless needles, mp: 95–96.5 °C
2
Lit ).
4
(
1
NMR (400 MHz): d ppm = 1.1 (t, 3H, CH –CH ), 1.32 (m, 2H, CH –(CH )–
2
3
2
2
CH ), 1.5 (m, 2H, –CH ), 2.9 (t, 2H, –N–CH –), 5.50 (br s, 2H, NH ), 5.89 (br s, 1
H, NH).
3
2
2
2
MS (E1, 70 eV): m/z (%) = 117.2.
0
N-ethyl-N -methylurea (3e)
Yield: 38.70 g, (88 %), 94 % purity (GC), colorless needles, mp: 50–51.5 °C
2
Lit ).
4
(
1
NMR (400 MHz): d ppm = 1.12 (t, J = 7.00, 3H, CH –CH ), 2.75 (d,
2
3
J = 5.00, 3H, NH–CH ), 3.17 (dq, J = 7.00, 2H, CH ), 5.53 (br s, 2H, NH ).
MS (E1, 70 eV): m/z (%) = 103.2.
3
2
2
N,N-dibutylurea (3f)
2
4
Yield: 67 g, (85 %), 92 % purity (GC), colorless needles, mp: 45.5–46.0 °C (Lit ).
1
NMR (400 MHz): d ppm = 1.12–1.75 (m, 8H, CH –(CH ) –CH ), 2.84 (d,
2
2 2
3
J = 5.00, 3H, NH–CH ), 3.20 (t, J = 7.20, 4H, N[CH –(CH ) –CH ], 4.35 (br s, 1
H, NH).
MS (E1, 70 eV): m/z (%) = 173.2.
3
2
2 2
3
123

2488
D. M. Manidhar et al.
Benzylurea (3g)
Yield: 66 g, (88 %), 93.5 % purity (GC), organic layer was washed with water
followed by concentration under vacuum the crude product was further recrystal-
2
1
lized in diethyl ether. mp: 148–149 °C (Lit ).
1
NMR (400 MHz): d ppm = 4.15(d, J = 6.00, 2H, CH ), 5.42 (br s, 2H, NH ),
2
2
6
.35 (br s, 1H, NH), 7.05–7.25 (m, 5H, phenyl).
MS (E1, 70 eV): m/z (%) = 151.2
Cyclohexylurea (3h)
2
4
Yield: 61 g, (86 %), 95 % purity (GC), colorless needles, mp: 193–194.5 °C (Lit ).
1
NMR (400 MHz): d ppm = 0.51–1.30 (5 m, 10H, 5 9 CH ), 2.75–2.89 (m, 1H,
2
CH), 4.88 (br s, 2H, NH ), 5.39 (d, 1H, NH).
MS (E1, 70 eV): m/z (%) = 143.2.
2
Chlorocarbonylsulfenyl chloride (CCSC) [21–23]
Trichloromethanesulfenyl chloride (PCMM) (294 ml, 500 g, 2.7 mol) was placed in
a 2-l reaction flask equipped with reflux condenser, thermometer, and stirrer.
A mixture of water (54 ml, 3.0 M) in concentrated sulfuric acid (620 ml) was added
dropwise over 3 h. The heterogenous mixture was vigorously stirred for 6 h at
45–50 °C as HCl evolved and was then stirred overnight at 25 °C to ensure
complete conversion of PCMM to CCSC. The progress of the reaction was
monitored by GC. The upper phase (280 g, 80 %) was separated and distilled
2
1
through a column, b.p. 98–101 °C (Lit , b.p. 98 °C) to provide, typically, 230 g
65 %) CCSC as a clear light yellow liquid.
(
Acknowledgments The authors gratefully acknowledge the Center for Biomedical Magnetic
Resonance (CBMR; SGPGIMS), Lucknow, for NMR spectra, and the Central Drug Research Institute
(CDRI), Lucknow, for mass spectra. One of the authors (K. Adeppa) wishes to convey his grateful
feelings of gratitude to India Pesticides Ltd, Lucknow, India, for providing all laboratory facilities and
financial support, which made it possible to complete this work successfully.
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