Simple, novel synthesis for 1-carbamoyl-lH-benzotriazole and some of its analogs

Article abstract of DOI:10.1080/00397910802136698

1-Carbamoyl-1H-benzotriazole (benzotriazole-1-carboxamide, 2a), an effective carbamoyl chloride substitute, and a range of its analogs can be synthesized in good yields in two very simple steps from 1,2-diaminobenzene. The facile preparation of the interm

Full text of DOI:10.1080/00397910802136698

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Simple, Novel Synthesis for 1-
Carbamoyl-lH-benzotriazole
and Some of Its Analogs
Christopher John Perry a , Keith Holding a &
Elizabeth Tyrrell b
a School of Applied Sciences, University of
Wolverhampton , Wolverhampton, UK
b School of Pharmacy and Chemistry, Kingston
University , Kingston upon Thames, Surrey, UK
Published online: 12 Sep 2008.
To cite this article: Christopher John Perry , Keith Holding & Elizabeth Tyrrell (2008)
Simple, Novel Synthesis for 1-Carbamoyl-lH-benzotriazole and Some of Its Analogs,
Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 38:19, 3354-3365, DOI: 10.1080/00397910802136698
To link to this article: http://dx.doi.org/10.1080/00397910802136698
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Synthetic Communications1, 38: 3354–3365, 2008
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910802136698
Simple, Novel Synthesis for 1-Carbamoyl-lH-
benzotriazole and Some of Its Analogs
Christopher John Perry,1 Keith Holding,1 and Elizabeth Tyrrell2
1School of Applied Sciences, University of Wolverhampton,
Wolverhampton, UK
2School of Pharmacy and Chemistry, Kingston University,
Kingston upon Thames, Surrey, UK
Abstract: 1-Carbamoyl-1H-benzotriazole (benzotriazole-1-carboxamide, 2a), an
effective carbamoyl chloride substitute, and a range of its analogs can be synthe-
sized in good yields in two very simple steps from 1,2-diaminobenzene. The facile
preparation of the intermediate o-aminophenylurea is key to this process. A
preliminary study of the reactivity of 2a has shown that once in solution in tetra-
hydrofuran (THF), the 1-carbamoyl isomer equilibrates to give a mixture of both
1- and 2-isomers. If the solvent is ethanol or water, equilibration occurs rapidly
compared to the ultimate formation of solvolysis products.
Keywords: Aminophenylthioureas, aminophenylureas, benzotriazole-1-carboxa-
mide, thioureas, ureas
INTRODUCTION
The synthesis of substituted urea has recently become an area of con-
siderable activity because of the significance of the urea functionality in
several important groups of compounds (including enzyme inhibitors,
peptidomimetics, intermediates for carbamate synthesis, dyestuffs, and
antioxidants).[1,2] Katritzky et al. have highlighted the significance of a
new reagent, 1-carbamoyl-1H-benzotriazole (2a), in the synthesis of
mono- and di-substituted ureas and shown how it may be prepared from
benzotriazole, via 1-cyano-1H-benzotriazole.[2,3]
Received February 24, 2008.
Address correspondence to Christopher John Perry, School of Applied
Sciences, University of Wolverhampton, Wulfruna Street, Wolverhampton,
WV1 1SB, UK. Email: c.j.perry@wlv.ac.uk
3354

Synthesis of 1-Carbamoyl-1H-benzotriazole
3355
We report an inexpensive procedure that gives 2a very readily
compared to the previously published method, avoiding the use of cya-
nogen bromide[2] (or phosgene[4]) and lending itself, through appropriate
adaptation, to the preparation of relatively large-scale batches of 2a and
its analogs in good yields (Schemes 1 and 2).
RESULTS AND DISCUSSION
The diazotization of N-substituted 1,2-diaminobenzenes in acidic
aqueous solution to provide N-substituted benzotriazoles has been long
established and was described by Fieser for the preparation of N-acetyl-
benzotriazole as far back as 1935.[5] More recently, it has been demon-
strated[6] that N-(2-aminophenyl)-N0-alkylureas of the type 1a with
R ¼ alkyl (prepared by reduction of N-(2-nitrophenyl)ureas to the
corresponding amino compound) form benzotriazoles, chemoselectively,
upon diazotization. This observation contrasts with the formation of a
seven-membered benzotetrazepinone formed when using N,N0-dialkyl
examples.[6] We have extended this observation to the unsubstituted
parent urea itself (1a) and found that the -CO-NH2 group survives the
diazotization reaction to give the corresponding benzotriazole 2a.
Key to the reported preparation is the ease with which 1,2-diamino-
benzene reacts with cyanate ions in aqueous solution to furnish urea 1a
in good yield. This extension of a standard preparation for phenylurea[7]
Scheme 1. Simple routes from 1,2-diaminobenzene to some substituted
ortho-aminophenylureas and substituted benzotriazoles. Cyanate ions give the
N-substituted urea 1a and subsequent benzotriazole 2a (a). Isocyanates and iso-
thiocyanates produce the N,N0-substituted ureas 1c–e and their corresponding
benzotriazoles 2c–e on diazotization (b). See Scheme 2 for details of substituents.

3356
C. J. Perry, K. Holding, and E. Tyrrell
Scheme 2. A key to the substituted areas and benzotriazoles prepared or
attempted.
proceeds smoothly with none of the problems that might be expected from
side reactions at the second amino function. We have also demonstrated
that analagous substituted arylureas and arylthioureas (1c–e) are easily
obtained directly from the corresponding isocyanates or isothiocyanates
by reaction with 1,2-diaminobenzene. In contrast, our attempt to produce
the analogous compound 1b with thiocyanate ions has not been success-
ful. All of the subsituted ureas 1a and 1c–e may be readily cyclized to their
corresponding benzotriazoles by diazotization in aqueous hydrochloric
acid, with acetic acid added to assist solvation where necessary (Schemes
1 and 2). Our survey of the literature has highlighted only one other simi-
lar, direct methodology that uses 4-nitro-1,2-diaminobenzene to facilitate
regioselectivity in the N-acylation step prior to benzotriazole ring
formation.[8,9] In the examples of N-carbamoylation and thiocarbamoyla-
tion reported here, such induced regioselectivity has proven unnecessary.
If 2a is prepared as described here, the 1-carbamoyl isomer is isolated
(which is also true for 2c–e, based on IR and NMR evidence) but in keep-
ing with some other examples of N-substituted benzotriazoles,[10–12] there
is equilibration with the 2-carbamoyl isomer (3a) upon solvation. The
rate of equilibration is clearly solvent dependent and is relatively fast in
ethanol (keqm ꢀ 1 ꢁ 10ꢂ3sꢂ1 at 333 K) but slower in THF. When 2a is
refluxed in either solvent for periods in the range 1–20 h, there is a shift
over time in nC O from ꢃ 1740 cmꢂ1 to ꢃ 1652 cmꢂ1 in the solid material
=
recovered (Fig. 1).
During equilibration in ethanol, the rate of ethanolysis of 2a is suffi-
ciently slow to allow equilibration to occur before the significant buildup

Synthesis of 1-Carbamoyl-1H-benzotriazole
3357
Figure 1. Details of reflectance FTIR spectra in the 1400 cmꢂ1 to 2000 cmꢂ1
region: (a) pure 2a, (b) a mixture of 2a and 3a (prepared by boiling 2a in absolute
ethanol for 50 min and cooling the solution), and (c) a mixture of 2a and 3a (pre-
pared by boiling 2a in THF for 18 h and removing the solvent).
of solvolysis products. This is supported by both IR evidence (Fig. 1) and
NMR evidence (Fig. 2). The residual isomeric mixtures obtained from
solvent evaporation become increasingly contaminated with benzotria-
zole and ethylurethane over time. This is entirely consistent with the
use of 2a as a carbamoylating agent as described earlier.[2] These observa-
tions are interesting, because N-acylbenzotriazoles are reported as
existing exclusively as the 1-isomers.[13] Furthermore, a cross-over
intermolecular mechanism has been confirmed for the observed isomeri-
zation of N-(aminoalkyl)benzotriazoles in aprotic solvents.[10,11]
Monitoring the equlibration of dilute solutions of 2a by change in
ultraviolet (UV) absorbance in ethanol and water gives observed first-
order kinetics, suggestive of a mechanism where ionization and recombi-
nation is occuring rapidly compared to the reaction with protic solvent. It
can be postulated that resonance effects facilitate separation into
þ
=
=
H2 N C O and benzotriazole anion, with or without solvent assistance,
allowing isomerization to occur much more readily in 2a than in N-acyl
examples (Scheme 3). It is therefore conceivable that the mechanism of
isomerization could be either intramolecular or intermolecular depending
þ
=
=
on the degree of solvent separation of H2 N C O and benzotriazole
anion. The relatively slow rates observed for solvolysis in protic solvents
(ethanol and water) would indicate that the rate constants for

3358
C. J. Perry, K. Holding, and E. Tyrrell
Figure 2. Details of 13C NMR spectra for the mixture of 2a and 3a (prepared by
boiling 2a in absolute ethanol for 50 min and cooling the solution): (a) the DEPT-
135 spectrum, confirming the 6 CH environments in the mixture, (b) all 11 of the
carbon environments expected, with signals from the 2-isomer (3a) labeled 2.
equilibration in steps 1,þ2, and 3 of Scheme 3 are large compared to those
=
=
for the reaction of H2 N C O with water or ethanol under neutral
conditions. Preliminary experiments indicate that the observed pseudo-
first-order rate constant for isomeric equilibration in water is very similar
to that in ethanol. This would suggest no solvent involvement in the rate-
determining step for isomerization, and this is therefore evidence of rapid
pre-equilibration, with step 3 of Scheme 3 being the rate-determining
step. Alternatively in an aprotic solvent such as THF, our data suggest
a mechanism without solvent assistance, where the rate-determining step
þ
=
is likely to be the slow formation of the H2 N C O=benzotriazole anion
=
pair. We have yet to study this system in further detail, but we have

Synthesis of 1-Carbamoyl-1H-benzotriazole
3359
Scheme 3. Suggested scheme for the equilibration of 2a and 3a via a solvent-
assisted mechanism.
already established that while being very easy to synthesise, 1-carbamoyl-
1H-benzotriazole has a more complex chemistry than hitherto reported
and warrants further investigation, by itself and through the behavior
of analogs such as 2c–e.
EXPERIMENTAL
NMR spectra were recorded in D6-DMSO at 270 MHz or 400 MHz
(1H NMR) and at 67.5 MHz or 100 MHz (13C NMR) using tetramethyl-
silane (TMS) as the internal standard. Mass spectra were obtained using
an HPP7 direct insertion probe attached to an HP 5973=5975 MSD
instrument. Infrared spectra were recorded as Nujol mulls on a Nicolet

3360
C. J. Perry, K. Holding, and E. Tyrrell
Impact 404 FT-IR, or neat on a Mattson Genesis II Reflectance FT-IR
instrument. Melting-points were recorded using a capillary melting-point
apparatus with mercury thermometer and are uncorrected. All CHN
analysis was undertaken by Warwick Analytical Service, University of
Warwick Science Park, UK.
N(2-Aminophenyl)urea (1a)
1,2-Diaminobenzene (0.1 mol, 10.8 g) was dissolved in glacial acetic acid
(10 mL) and diluted to 100 mL with distilled water. Separately, potassium
cyanate (0.1 mol, 8.1 g) was dissolved in 100 mL of distilled water and
then added to the first solution, with stirring, at room temperature. After
1 h, the mixture was cooled in an ice bath for 30 min or left overnight in a
refrigerator. The product was isolated by vacuum filtration, washed with
ice-cold distilled water, dried at 100 ꢄC, and recrystallized from ꢄmethanol
1
or ethanol if required. Off-white needles (78%); mp 166–168 C[14]; H
NMR: d 7.76 (s, 1H), 7.25 (m, 1H), 6.78 (m, 1H), 6.68 (m, 1H), 6.52 (m,
1H), 5.88 (s, 2H), 4.75 (br s, 2H); 13C NMR d 156.59, 140.64, 125.46,
123.89, 123.49, 116.64, 115.72: DEPT-135 confirms the three 4ry C environ-
ments expected. MS m=z 151 (Mþ), 134, 108 (100%). Anal. calcd. for
C7H9N3O: C, 55.62; H, 6.00; N, 27.88%. Found: C, 54.76; H, 5.90; N,
27.77%. IR (neat) 3417, 3333, 3288, 1646, 1620, 1525, 1355, 747 cmꢂ1.
N-(2-Aminophenyl)-N0-phenylurea (1c)
1,2-Diaminobenzene (0.1 mol, 10.8 g) was dissolved in sodium-dried Et2O
(300 mL) with stirring. Phenylisocyanate (0.1 mol, 11.9 g) was added
dropwise, and the solution was stirred for a further 1 h, then cooled in
an ice bath, whereupon 1c precipitated. It was recrystallized from ethanol
ꢄ
1
if required. White solid (90%); mp 189–191 C, H NMR: d 8.77 (s, 1H),
7.73 (s, 1H), 7.45 (m, 2H), 7.35 (m, 1H), 7.25 (m, 2H), 6.94 (m, 1H), 6.84
(m, 1H), 6.74 (m, 1H), 6.58 (m, 1H), 4.80 (br s, 2H); 13C NMR d 153.1,
140.9, 140.1, 128.8, 124.7, 124.4, 123.8, 121.5, 117.9, 116.8, 115.9: DEPT-
135 confirms the four 4ry C environments expected. MS m=z 227 (Mþ),
134 (100%), 119, 108, 93. Anal. calcd. for C13H13N3O: C, 68.71; H,
5.77; N, 18.49%. Found: C, 68.54; H, 5.71; N, 18.34%. IR (neat) 3424,
3278, 1646 (shoulder), 1610, 1593, 1549, 743 cmꢂ1.
N-(2-Aminophenyl)-N0-phenylthiourea (1d)
1,2-Diaminobenzene (0.1 mol, 10.8 g) was dissolved in boiling CHCl3
(200 mL) with stirring. Phenyl isothiocyanate (0.1 mol, 13.5 g) was added

Synthesis of 1-Carbamoyl-1H-benzotriazole
3361
dropwise. About 100 mL of CHCl3 was removed by distillation, and the
solution was cooled to room temperature, whereupon 1d precipitated.
ꢄ
1
recrystallized from ethanol. Off-white solid (75%); mp 147–148 C, H
NMR: d 9.59 (s, 1H), 9.07 (s, 1H), 7.52 (m, 2H), 7.31 (m, 2H), 7.10
(m, 2H), 6.97 (m, 1H), 6.75 (m, 1H), 6.56 (m, 1H), 4.90 (br s, 2H); 13C
NMR d 180.1, 144.0, 139.6, 128.3, 128.1, 127.1, 124.2, 124.0, 123.6,
116.3, 115.9: DEPT-135 confirms the four 4ry C environments expected.
MS m=z 243 (Mþ), 210, 150 (100%), 135, 108, 93. Anal. calcd. for
C13H13N3S: C, 64.17; H, 5.38; N, 17.27%. Found: C, 64.12; H, 5.37;
N, 17.01%. IR (nujol mull) 3329, 3210, 1612, 1457, 1336, 761 cmꢂ1.
N-(2-Aminophenyl)-N0-(1-naphthyl)thiourea (1e)
Compound 1e was forme as for 1d, but using 1,2-diaminobenzene
(0.05 mol, 5.4 g, dissolved in 100 mL CHCl3) and 1-naphthyl isothio-
cyante (0.05 mol, 9.25 g, dissolved in the minimum volume of CHCl3)
in place of phenyl isothiocyanate. White solid (80%); mp 165–167 ꢄC;
1H NMR: d 9.62 (br s, 1H), 9.08 (br s, 1H), 8.00 (m, 2H), 7.83 (m,
1H), 7.63–7.45 (m, 4H), 7.12 (m, 1H), 6.98 (m, 1H), 6.76 (m, 1H), 6.58
(m, 1H), 4.93 (br s, 2H); 13C NMR d 181.7, 144.2, 135.3, 133.9, 130.1,
128.4, 128.1, 127.2, 126.6, 126.0 (2 C), 125.6, 125.5, 124.2, 123.2, 116.4,
115.9: DEPT-135 confirms the six 4ry C environments expected. MS
m=z 293 (Mþ), 258, 243, 185, 143 (100%), 108. Anal. calcd. for
C17H15N3S: C, 69.60; H, 5.15; N, 14.32%. Found: C, 69.35; H, 5.08;
N, 14.12%. IR (nujol mull) 3313, 3132, 1612, 1456, 1371, 778 cmꢂ1.
Preparation of Benzotriazoles
The ureas and thioureas 1a and 1c–e were converted to the corresponding
benzotriazoles by diazotization using either method 1 or method 2.
Method 1 is applicable when the urea is readily soluble in aqueous
HCl, and method 2 is employed when low solubility is observed.
Method 1
The substituted urea (0.05 mol) was mixed with 75 mL of water and
18 mL of conc. HCl. The mixture was cooled to 0–5 ꢄC, stirring con-
stantly. A separate solution of NaNO2 (0.05 mol) in 18 mL of distilled
water was then prepared and cooled to 0–5 ꢄC. This solution was then
added dropwise to the solution of urea, maintaining the temperature
colder than 10 ꢄC throughout. Efficient stirring was essential because

3362
C. J. Perry, K. Holding, and E. Tyrrell
the mixture thickened considerably toward the end of the addition. The
product was vacuum filtered immediately, washed with cold distilled
water, and dried to constant weight in an oven at 60–70 ꢄC.
Method 2
The substituted urea or thiourea (0.05 mol) was dissolved in 250 mL of
glacial acetic acid with gentle heating, and then 18 mL of conc. HCl and
150 mL of distilled water were added. The mixture was cooled to 0–5 ꢄC,
stirring constantly. A separate solution of NaNO2 (0.05 mol, 3.45 g) in
40 mL of distilled water was then prepared and cooled to 0–5 ꢄC. With
efficient stirring, this solution was then added in small aliquots to the sol-
ution of urea or thiourea, maintaining the temperature at less than 10 ꢄC
throughout. After 5 min of further stirring at or less than 5 ꢄC, the product
was vacuum filtered, washed with cold distilled water, and dried to con-
stant weight in an oven at 60–70 ꢄC or at room temperature in air, then over
potassium hydrochloride (KOH) pellets in a dessicator in the case of 2e.
Where less than 0.05 mol of urea or thiourea was available (in particular
for 2e), the method was followed at a reduced scale throughout.
1-Carbamoyl-1H-benzotriazole (2a)
This was prepared from 1a using method 1. White solid (77%); mp
164–166 ꢄC (decomposes), (lit.[2] 160–161 ꢄC, but also reported as having
no definite mp,[16] which we also observed, depending on heating rate).
1H NMR: d 8.62 (br s, 1H), 8.29 (br s, 1H), 8.22 (m, 1H), 8.18 (m,
1H), 7.72 (m, 1H), 7.55 (m, 1H); 13C NMR d 149.96, 145.62, 131.38,
129.84, 125.44, 119.75, 113.76: MS m=z 162 (Mþ), 134, 119, 91 (100%),
64. Anal. calcd. for C7H6N4O: C, 51.85; H, 3.73; N, 34.55%. Found:
C, 51.63; H, 3.72; N, 34.25%. IR (neat) 3331, 3242, 3163, 1741, 1605,
1403, 1299, 1053, 729 cmꢂ1. This material can be recrystallized from meth-
anol if required but prolonged boiling causes significant isomeric equili-
bration and solvolysis.
1-(N-Phenyl)carbamoyl-1H-benzotriazole (2c)
This was prepared from 1c using method 2. White solid (68%); mp
138–140 ꢄC; 1H NMR: d 11.15 (s, 1H), 8.25 (m, 2H), 7.90–7.70 (m,
3H), 7.60 (m, 1H), 7.44 (m, 2H), 7.22 (m, 1H); 13C NMR d 147.0,
145.5, 137.2, 131.5, 130.1, 128.8, 125.8, 124.7, 121.2, 119.9, 113.7: DEPT
confirms the four 4ry C environments expected. MS m=z 238(Mþ), 146,

Synthesis of 1-Carbamoyl-1H-benzotriazole
3363
119 (100%), 91, 64. Anal. calcd. for C13H10N4O: C, 65.54; H, 4.23; N,
23.52%. Found: C, 65.46; H, 4.23; N, 23.47%. IR (neat) 3234, 1731,
1598, 1057, 743 cmꢂ1.
1-(N-Phenyl)thiocarbamoyl-1H-benzotriazole (2d)
This was prepared from 1d using method 2. White solid (66%); mp
ꢄ
ꢄ
1
96–97 C (lit.[15] 98–99 C); H NMR: d 10.71 (br s, 1H), 8.92 (m, 1H),
8.12 (m, 1H), 7.76–7.55 (m, 3H), 7.54–7.36 (m, 3H), 7.33 (m, 1H); 13C
NMR d 172.4, 147.2, 136.6, 132.3, 130.4, 129.1, 127.3, 125.8, 124.3,
120.3, 116.2: DEPT-135 confirms the four 4ry C environments expected.
MS m=z (254, Mþ not seen), 135 (100%), 119 (summing to 254), 91, 77,
64; IR (nujol mull) 3218, 1603, 1534, 1285, 752 cmꢂ1.
1-(N-(1-Naphthyl))thiocarbamoyl-1H-benzotriazole (2e)
This was prepared from 1e (0.025 mol) using method 2. Yellow solid
ꢄ
1
(75%); mp 76–79 C (decomposes); H NMR: d 10.88 (br s, 1H), 8.95
(m, 1H), 8.18 (m, 1H), 8.06–7.87 (m, 4H), 7.76–7.48 (m, 5H); 13C
NMR d 174.4, 147.3, 134.3, 132.5, 132.4, 130.6, 129.1, 128.8, 128.7,
127.1, 126.6, 126.0, 125.3, 125.1, 121.7, 120.5, 116.3: DEPT confirms
the six 4ry C environments expected. MS m=z (304, Mþ not seen), 185
(100%), 119 (summing to 304), 91, 64. Anal. calcd. for C17H12N4S: C,
67.09; H, 3.97; N, 18.41%. Found: C, 66.94; H, 3.95; N, 18.24%. IR
(nujol mull) 3175, 1594, 1156, 727 cmꢂ1.
Mixtures of 1-Carbamoyl-1H-benzotriazole (2a) and 2-Carbamoyl-1H-
benzotriazole (3a)
Compound 2a (2.0 g) was refluxed in absolute ethanol (50.0 mL) for
50 min and cooled in a freezer (ꢂ20 ꢄC) for 2 h. A white solid (1.2 g,
60%) crystallized. This was identified as a roughly equimolar mixture
of 2a and 3a only. IR C ¼ O stretches are observed at 1740 cmꢂ1 and
1651 cmꢂ1 in the neat sample (Fig. 1B). 13C NMR (signals due to 3a
are shown in bold type): 156.73, 149.96, 145.62, 131.68, 131.38, 129.84,
125.44, 123.70, 123.24, 119.75, 113.76: DEPT-135 confirms the five 4ry
C environments expected in the mixture (Fig. 2). A sample of 2a (2.0 g)
was also refluxed in analytical-grade THF (50.0 mL) for 18 h, and the sol-
vent was removed by rotary evaporation. A white solid (2.0 g) was recov-
ered. The IR spectrum of the neat sample suggests a mixture of 2a and 2b,
with 2a as the major component (Fig. 1C).

3364
C. J. Perry, K. Holding, and E. Tyrrell
ACKNOWLEDGMENT
The authors acknowledge the contributions of Perdip Singh Bahia and
Jon Northall who, while students at the University of Wolverhampton,
carried out and recorded significant experiments related to the current
submission. This work was conducted as part of their MSc and BSc
programs, respectively.
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