Synthesis of new active o-nitrophenyl carbamates

Article abstract of DOI:10.1081/SCC-200057986

A very high-yielding reaction of bis(o-nitrophenyl) carbonate with aliphatic amines under mild conditions has been developed. The resulting o-nitrophenyl carbamates were characterized by IR, ¹H-NMR, ¹³C-NMR, and elemental analysis. Copyright Taylor & Francis, Inc.

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Synthesis of New Active
o‐Nitrophenyl Carbamates
Monika Simon a , Carol Csunderlik a , Livius Cotarca b
, Miron Teodor Căproiu c , Ion Neda d , Maria Cristina
Turoczi a & Raffaella Volpicelli b
a Industrial Chemistry and Environmental
Engineering Faculty , Politehnica University of
Timişoara , Timisoara, Romania
b Zambon Group SpA , Lonigo (VI), Italy
c C. D. Nenitescu Institute of Organic Chemistry ,
Burcharest, Romania
d InnChemTech GmbH , Braunschweig, Germany
Published online: 17 Dec 2010.
To cite this article: Monika Simon , Carol Csunderlik , Livius Cotarca , Miron Teodor
Căproiu , Ion Neda , Maria Cristina Turoczi & Raffaella Volpicelli (2005) Synthesis of
New Active o‐Nitrophenyl Carbamates, Synthetic Communications: An International
Journal for Rapid Communication of Synthetic Organic Chemistry, 35:11, 1471-1479,
DOI: 10.1081/SCC-200057986
To link to this article: http://dx.doi.org/10.1081/SCC-200057986
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Synthetic Communicationsw, 35: 1471–1479, 2005
Copyright # Taylor & Francis, Inc.
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1081/SCC-200057986
Synthesis of New Active o-Nitrophenyl
Carbamates
Monika Simon and Carol Csunderlik
Industrial Chemistry and Environmental Engineering Faculty, Politehnica
University of Timis¸oara, Timisoara, Romania
Livius Cotarca
Zambon Group SpA, Lonigo (VI), Italy
˘
Miron Teodor Caproiu
C. D. Nenitescu Institute of Organic Chemistry, Burcharest, Romania
Ion Neda
InnChemTech GmbH, Braunschweig, Germany
Maria Cristina Turoczi
Industrial Chemistry and Environmental Engineering Faculty, Politehnica
University of Timis¸oara, Timisoara, Romania
Raffaella Volpicelli
Zambon Group SpA, Lonigo (VI), Italy
Abstract: A very high-yielding reaction of bis(o-nitrophenyl) carbonate with aliphatic
amines under mild conditions has been developed. The resulting o-nitrophenyl carba-
1
mates were characterized by IR, H-NMR, 13C-NMR, and elemental analysis.
Keywords: o-Nitrophenyl carbamates, bis(o-nitrophenyl) carbonate, phosgene-free
carbonylations, triphosgene
Received in the USA January 31, 2005
Address correspondence to Livius Cotarca, Zambon Group SpA, Via Dovaro 2,
36045 Lonigo (VI), Italy. E-mail: livius.cotarca@zambongroup.com
1471

1472
M. Simon et al.
INTRODUCTION
Many carbamates are biologically active or represent key intermediates for the
synthesis of biologically active compounds.[1–3] They are usually prepared by
addition of an amine to a chloroformate[4] or alternately by addition of a
hydroxy compound to an isocyanate[5] or to an N-substituted carbamoyl
chloride.[6] However, the aforementioned methods share a common disadvan-
tage: toxic phosgene is used as the starting material. Recently, there is a
tendency to use nonphosgenation methods to obtain this class of
compounds. Therefore, highly reactive organic carbonates have been
preferred as phosgene substitutes in the synthesis of carbamates.[7–9] In par-
ticular, bis(p-nitrophenyl) carbonate has been extensively used in peptide
synthesis as a coupling reagent for the preparation of various biologically
active esters[10] and in the synthesis of carbonates,[11] carbamates, and
ureas[9] as an efficient alternative to phosgene.
While investigating the reactivity of several active carbonates by theoreti-
cal calculations, we found that bis(o-nitrophenyl) carbonate could be a valid
alternative reagent to phosgene.[12] Literature precedent, describing the
synthesis of various carbonates[11] and polycarbonates[13] by transesterifica-
tion reactions, reported bis(o-nitrophenyl) carbonate among the key
examples. Howevew, no account on its reactivity toward nucleophiles was
mentioned. In the recent studies, showed that bis(o-nitrophenyl) carbonate
displays an enhanced reactivity toward N-nucleophiles with respect to
bis(p-nitrophenyl) carbonate.[14] Our aim consisted in seeking viable
synthetic conditions to obtain o-nitrophenyl carbamates by using stable and
nontoxic bis(o-nitrophenyl) carbonate.[15,16]
RESULTS AND DISCUSSION
In this article, we report the reaction of bis(o-nitrophenyl) carbonate with
various amines as a simple and convenient method for the synthesis of new
biologically active o-nitrophenyl carbamates. Johnston et al. have reported
the synthesis of one o-nitrophenyl carbamate as a key intermediate for
synthesis of antitumor active ingredients N-(2-fluoroethyl)-N-nitrosoureas.[17]
Their strategy consisted of combining o-nitrophenyl chloroformate with the
corresponding amine to furnish the o-nitrophenyl carbamate. However, the
instability of o-nitrophenyl chloroformate, which undergoes uncontrolled
decomposition during purification by vacuum distillation, represents a great
disadvantage of this method.
Our route toward the synthesis of variously substituted o-nitrophenyl car-
bamates consisted of treating stable and nontoxic bis(o-nitrophenyl) carbonate
(DoNFC) with primary and secondary amines. In turn, the starting material
DoNFC was efficiently obtained following a recent literature procedure,

o-Nitrophenyl Carbamates
1473
which consisted of reacting triphosgene with o-nitrophenol in dichloro-
methane in the presence of triethylamine.[16]
Reactions of bis(o-nitrophenyl) carbonate (DoNFC) with primary
amines proceeded smoothly, furnishing the desired carbamates in 85–95%
isolated yield (Scheme 1, Table 1). A typical reaction occurred at ambient
temperature, in dichloromethane, at a molar ratio 1:1.3 of carbonate–
amine, going to completion within 5–10 min. No traces of disubstituted
ureas were observed when the products were examined by thin-layer
chromatography.
Secondary amines required longer reaction times. Reaction with dibenzyl-
amine was completed after 2 days at molar ratio 1:1.3 of carbonate–amine and
in 90 min at molar ratio of 1:2.1. Diisobutylamine completely converted bis(o-
nitrophenyl) carbonate in the corresponding carbamate only after 5 days at a
molar ratio of 1:2.5.
The products were isolated by column chromatography (on silica gel,
eluent: dichloromethane) and characterized by IR, elemental analysis, and
1H- and 13C-NMR. Selected data are reported in Table 1.
Reactivity studies on the reaction of DoNPC and DpNPC toward propyl-
amines (nPrA and isoPrA) in terms of yield and reaction time were executed
(Table 2). It was noticed that bis(p-nitrophenyl) carbonate (DpNFC) reacted at
least six times slower when compared with bis(o-nitrophenyl) carbonate
(DoNPC) (Table 2).
It is also known from literature data that the N,N-dibenzyl-p-nitrophenyl
carbamate has been obtained only after 2 days from bis(p-nitrophenyl)
carbonate,[9] using the same molar ratio of 1:2.1 (carbonate–amine) we used
in the reaction between bis(o-nitrophenyl) carbonate and N,N-dibenzylamine.
Once again, this fact confirms that bis(o-nitrophenyl) carbonate is much more
effective than its p-isomer.
As can be seen from Table 1, the N-alkyl-o-nitrophenyl carbamates
present two carbonyl-stretching bands in solid state. The similar N-
alkyl-p-nitrophenyl carbamates have only one carbonyl stretching band.
N,N0-dicyclohexylurea has been obtained when bis(o-nitrophenyl) carbonate
was allowed to react with an excess of amine (1:2.1 ratio) (Scheme 2). The
product was separated from the reaction medium by precipitation and
had the carbonyl stretching band at 1626 cm21. This fact also confirms that
both of the two carbonyl stretching bands belong to the carbamate group.
Scheme 1.

Table 1. Synthesis of o-nitrophenyl carbamates
Yielda
(%)
Molecular
formula
Calculated/found
%C; %H; %N
nC¼O
Entry
1
R(R0)
Mp (8C)
(cm21
)
iso-Propyl(H)
90
89
85
91
88
90
95
93
70
85
141–143
C10H12N2O4
224.2
53.57; 5.36; 12.5
53.72; 5.51; 11.90
53.57; 5.36; 12.5
54.18; 5.69; 11.85
55.46; 5.88; 11.76
54.92; 6.20; 11.23
55.46; 5.88; 11.76
55.38; 5.95; 11.53
55.46; 5.88; 11.76
55.08; 6.33; 10.95
57.14; 6.35; 11.11
56.70; 6.52; 10.48
59.10; 6.00; 10.61
59.37; 5.92; 10.10
61.76; 4.41; 10.29
61.88; 4.33; 10.03
61.22; 7.48; 9.52
60.60; 7.18; 9.33
69.61; 4.97; 7.74
69.43; 5.06; 7.72
1748
1707
1750
1715
1744
1716
1750
1716
1747
1711
1752
1716
1748
1714
1728
1709
1731
2
3
n-Propyl(H)
49–51
39–41
56–58
55–57
54–56
144–146
81–83
Oil
C10H12N2O4
224.2
n-Butyl(H)
C11H14N2O4
238
4
iso-Butyl(H)
C11H14N2O4
238
5
sec-Butyl(H)
iso-Pentyl(H)
c-C6H11(H)
C11H14N2O4
238
6
C12H16N2O4
252.3
7
C13H16N2O4
264.3
8
CH2C6H5(H)
iso-Butyl(iso-Butyl)
CH2C6H5(CH2C6H5)
C14H12N2O4
272
9
C15H22N2O4
294
10
67–70
C21H18N2O4
362.4
1707
aAfter column chromatography separation and trituration with petroleum ether.

o-Nitrophenyl Carbamates
1475
Table 2. Comparative study for the synthesis of N-propyl-nitrophenyl carbamates
using DoNPC and DpNPC
Entry
Carbonate
Amine
Time (min)
Yield (%)
1
2
3
4
DoNFC
DoNFC
DpNFC
DpNFC
n-PrA
iso-PrA
n-PrA
ꢀ5
ꢀ10
60
89
90
92
89
iso-PrA
90
In summary, o-nitrophenyl carbamates could be easily obtained in mild
conditions and high yields. The attained results demonstrate on the one
hand the high reactivity of bis(o-nitrophenyl) carbonate and on the other
hand the possibility of efficiently synthesizing new and known active carba-
mates using a novel and mild procedure.
EXPERIMENTAL
Melting points were determined on Boetius apparatus (Carl Zeiss Jena). The
IR spectra were recorded in KBr pellet for the solid compounds with a
Jasco FT/IR-430 instrument. TLC analyses were carried out on precoated
plates of silica gel 60 F254 (Merck). To visualize spots, the plates were
1
exposed under a UV 254 lamp. The H-NMR and 13C-NMR spectra were
recorded on a Bruker DPX at 200 MHz. Elemental analysis was carried out
on a Vario EL instrument.
Preparation of Carbamates
The following procedure for preparation of N-iso-propyl-o-nitrophenyl
carbamate is representative of the general method used for synthesis of the
carbamates.
N-iso-Propyl-o-nitrophenyl carbamate. A solution of bis(o-nitrophenyl)
carbonate (0.506 g, 1.665 mmol) in CH2Cl2 (10 mL) was mixed in a 50-mL
flask at room temperature with iso-propylamine (0.2 mL, 2.164 mmol). After
the consumption of carbonate (TLC analysis, silica; eluent: dichloromethane),
Scheme 2.

1476
M. Simon et al.
the reaction mixture was transferred to a separating funnel and washed with 1 M
of HCl solution (5 mL). The organic layer was separated, dried with anhydrous
MgSO4, filtered, and the solvent removed by evaporation in vacuo to 1–2 mL
volume. The solution was separated by column chromatography on silica gel
using dichloromethane as eluent. More polar o-nitrophenol was first isolated
(Rf ¼ 0.82), followed by the carbamate (Rf ¼ 0.43). The title compound was
isolated as a white solid, which was further triturated with petroleum ether to
yield 0.336 g of product (90%). Mp 80–828C; nmax(KBr)/cm21 ¼ 1748;
1707 (C ¼ 0); dH (200 MHz; CDCl3) 1.13 (d, 6H), 3.8 (m, 1H), 5 (NH), 7.25
(m, 2H), 7.55 (t, 1H), 7.95 (d, 1H); dC (200 MHz; CDCl3) 23 (2CH3),
44 (CH), 125.46 (CH), 125.54 (CH), 126 (CH), 134 (CH), 142 (C), 144 (C),
152 (C).
N-n-Propyl-o-nitrophenyl carbamate. Obtained in 89% yield as a white solid.
Mp 49–518C; nmax(KBr)/cm21 ¼ 1750; 1715 (C ¼ O); dH (200 MHz;
CDCl3) 0.9 (t, 3H), 1.5 (m, 2H), 3.2 (c, 2H), 5.2 (NH), 7.25 (m, 2H), 7.55
(t, 1H), 7.95 (d, 1H); dC (200 MHz; CDCl3) 11 (CH3), 22.5 (CH2), 44 (CH2),
125.5 (CH), 125.53 (CH), 126 (CH), 134 (CH), 142 (C), 144 (C), 153 (C).
N-n-Butyl-o-nitrophenyl carbamate. Obtained in 85% yield as a white solid.
Mp 53–558C; nmax(KBr)/cm21 ¼ 1744; 1716 (C ¼ O); dH (200 MHz;
CDCl3) 0.87 (t, 3H), 1.35 (s, 2H), 1.5 (p, 2H), 3.21 (c, 2H), 5.2 (NH), 7.25
(m, 2H), 7.55 (t, 1H), 7.95 (d, 1H); dC (200 MHz; CDCl3) 14 (CH3), 19.5
(CH2), 31.7 (CH2), 41 (CH2), 125.5 (CH), 125.53 (CH), 126 (CH), 134
(CH), 142 (C), 144 (C), 153 (C).
N-iso-Butyl-o-nitrophenyl carbamate. Obtained in 91% yield as a white solid.
Mp 56–588C; nmax(KBr)/cm21 ¼ 1750; 1716 (C ¼ O); dH (200 MHz; CDCl3)
0.96 (d, 6H), 1.85 (m, 1H), 3.1 (t, 2H), 5.3 (NH), 7.25 (m, 2H), 7.55 (t, 1H), 7.95
(d, 1H); dC (200 MHz; CDCl3) 20 (CH3), 28.6 (CH), 48.8 (CH2), 125.48 (CH),
125.53 (CH), 126 (CH), 134 (CH), 142 (CH), 144 (C), 153 (C).
N-sec-Butyl-o-nitrophenyl carbamate. Obtained in 88% yield as white solid.
Mp 55–578C; nmax(KBr)/cm21 ¼ 1747; 1711 (C ¼ O); dH (200 MHz;
CDCl3) 0.9 (t, 3H), 1.15 (d, 3H), 1.5 (p, 2H), 3.61 (s, 1H), 5 (NH), 7.25
(m, 2H), 7.55 (t, 1H), 7.95 (d, 1H); dC (200 MHz; CDCl3) 10 (CH3), 20.5
(CH3), 29.5 (CH2), 49 (CH), 125.48 (CH), 125.53 (CH), 126 (CH), 134
(CH), 142 (C), 144 (C), 152.5 (C).
N-iso Penthyl-o-nitrophenyl carbamate. Obtained in 90% yield as white solid.
Mp 54–568C; nmax(KBr)/cm21 ¼ 1752; 1716 (C ¼ O); dH (200 MHz;
CDCl3) 0.9 (d, 6H), 1.4 (c, 2H), 1.6 (m, 1H), 3.2 (c, 2H), 5.1 (NH), 7.2
(m, 2H), 7.55 (t, 1H), 7.95 (d, 1H); dC (200 MHz; CDCl3) 22 (2CH3), 25.5
(CH), 38.5 (CH2), 40 (CH2), 125.48 (CH), 125.53 (CH), 126 (CH), 134
(CH), 142 (C), 144 (C), 153 (C).

o-Nitrophenyl Carbamates
1477
N-Ciclohexyl-o-nitrophenyl carbamate. Obtained in 95% yield as a white
solid. Mp 144–1468C;
n
max(KBr)/cm21 ¼ 1748; 1714 (C ¼ O); dH
(200 MHz; CDCl3) 1.2 (m, 6H), 2 (m, 4H), 3.5 (p, 1H), 5 (NH), 7.25
(m, 2H), 7.55 (t, 1H), 7.95 (d, 1H); dC (200 MHz; CDCl3) 24.6 (CH2), 25.4
(CH2), 30 (CH2), 33 (CH2), 50 (CH), 125.48 (CH), 125.53 (CH), 126 (CH),
134 (CH), 142 (C), 144 (C), 153 (C).
N-Benzyl-o-nitrophenyl carbamate. Obtained in 93% yield as a white solid.
Mp 81–838C; nmax(KBr)/cm21 ¼ 1728; 1709 (C ¼ O); dH (200 MHz;
CDCl3) 4.35 (d, 2H), 5.5 (NH), 7.25 (m, 2H), 7.52 (t, 1H), 7.93 (d, 1H); dC
(200 MHz; CDCl3) 45.5 (CH2), 125.52 (CH), 125.6 (CH), 126.15 (CH),
127.59 (CH), 127.74 (CH), 128.77 (CH), 134.5 (CH), 137.5 (C), 142 (C),
144.3 (C), 153.3 (C).
N,N-Diisobutyl-o-nitrophenyl carbamate. Obtained in 70% yield as a pale
yellow oil. nmax(KBr)/cm21 ¼ 1731 (C ¼ O); dH (200 MHz; CDCl3) 0.96
(dd, 12H), 2.1 (m, 2H), 3.25 (dd, 4H), 7.3 (m, 2H), 7.6 (t, 1H); 8.05
(d, 1H); dC (200 MHz; CDCl3) 19.94 (CH3), 20.05 (CH3), 26.7 (CH), 27.39
(CH), 55.25 (CH2), 55.72 (CH2), 125.35 (CH), 125.40 (CH), 125.71 (CH),
134.21 (CH), 142.3 (CH), 144.86 (C), 153.5 (C).
N,N-dibenzyl-o-nitrophenyl carbamate. A solution of bis(o-nitrophenyl)
carbonate (0.506 g, 1.665 mmol) in CH2Cl2 (10 mL) was mixed in a 50-mL
flask at room temperature with dibenzylamine (0.67 mL, 3.498 mmol). When
TLC analysis (silica; eluent: dichloromethane) indicated the carbonate
consumption, the reaction mixture was treated with 1 M of HCl solution
(5 mL). The dibenzylamine chlorohydrate precipitated and was filtered off.
The organic layer was separated, dried with anhydrous MgSO4, filtered, and
the solvent removed by evaporation in vacuo until 1–2 mL solution
remained. This solution passed down a silica column using dichloromethane
as eluent. The solvent was removed from the fractions that contain
carbamate and the residue was triturated with petroleum ether yielding
0.512 g of white solid (h ¼ 85%). Mp 67–708C; nmax(KBr)/cm21 ¼ 1707
(C ¼ O); dH (200 MHz; CDCl3) 4.56 (s, 2H), 4.6 (s, 2H), 7.35 (m, 2H),
7.65 (t, 1H), 8.12 (d, 1H); dC (200 MHz; CDCl3) 49.52 (CH2), 49.85 (CH2),
125.46 (CH), 125.7 (CH), 126.14 (CH), 127.6 (CH2), 127.7 (CH), 128.16
(CH), 128.7 (CH), 134.5 (CH), 136.2 (C), 136.34 (C), 142 (C), 144.8 (C),
153.7 (C).
N-iso-Propyl-p-nitrophenyl carbamate. The procedure is similar to that for
o-nitrophenyl carbamates. At column chromatography separation, the p-nitro-
phenyl carbamate came out first (Rf ¼ 0.42), followed by p-nitrophenole
(Rf ¼ 0.19). Obtained in 89% yield as white solid. Mp 141–1438C; (lit.
144–147)[9]). nmax(KBr)/cm21 ¼ 1713 (C ¼ O); dH (200 MHz; CDCl3)
1.25 (d, 6H), 3.95 (m, 1H), 4.95 (NH), 7.33 (d, 2H), 8.25 (d, 2H); dC

1478
M. Simon et al.
(200 MHz; CDCl3) 23 (2CH3), 44 (CH), 123 (2CH), 125 (2CH), 143 (C), 155
(C), 156 (C). Anal. calcd. for C10H12N2O4: C, 53.57; H, 5.36; N, 12.5. Found:
C, 53.73; H, 5.52; N, 12.12.
N-n-Propyl-p-nitrophenyl carbamate. Obtained in 92% yield as white solid.
Mp 104–1068C; (lit. 106–108[9]). nmax(KBr)/cm21 ¼ 1709 (C ¼ O); dH
(200 MHz; CDCl3) 0.95 (t, 3H), 1.6 (m, 2H), 3 (c, 2H), 4.9 (NH), 7.33
(d, 2H), 8.25 (d, 2H); dC (200 MHz; CDCl3) 11 (CH3), 23 (CH2), 44 (CH2),
123 (2CH), 125 (2CH), 143 (C), 155 (C), 156 (C). Anal. calcd. for
C10H12N2O4: C, 53.57; H, 5.36; N, 12.5. Found: C, 53.96; H, 5.21; N, 12.03.
N,N0-Dicyclohexylurea. A solution of bis(o-nitrophenyl) carbonate (0.506 g,
1.665 mmol) in CH2Cl2 (10 mL) was mixed in a 50–mL flask at room temp-
erature with cyclohexylamine (0.4 mL, 3.4965 mmol). After TLC analysis
(silica; eluent: dichloromethane) indicated that no carbamate remained, the
precipitate formed was filtered and washed with dichloromethane. The crys-
talline product yielded 0.28 g (75%). Mp 227–2278C; (lit. 228,[9] 229–
230[18]) nmax(KBr)/cm21 ¼ 1626 (C ¼ O) (lit. nC¼O (KBr)/cm21 ¼ 1635).[9]
ACKNOWLEDGMENTS
M.S., C.C., M.T.C., and M.C.T. thank CNCSIS for financial support (Grant A,
Cod CNCSIS 475/18/2000).
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