Gas-phase thermolysis of benzotriazole derivatives. Part 4. Pyrolysis of 1-acylbenzotriazole phenylhydrazones. Interesting direct routes towards N-aminobenzimidazoles

Article abstract of DOI:10.1002/jhet.5570450314

(Chemical Equation Presented) Flash vacuum pyrolysis (FVP) of 1-acylbenzotriazole phenylhydrazones gave benzonitriles, aniline and 2-arylbenzimidazole derivatives. Static pyrolysis of the same substrates at 180°C gave exclusively the corresponding N-anili

Full text of DOI:10.1002/jhet.5570450314

May-Jun 2008
723
Gas-phase Thermolysis of Benzotriazole Derivatives. Part 4.
Pyrolysis of 1-Acylbenzotriazole phenylhydrazones. Interesting
Direct Routes Towards N-Aminobenzimidazoles
Hanan Al-Awadi, Maher R. Ibrahim, Nouria A. Al-Awadi and Yehia A. Ibrahim*
Author's address and e-mail address : Chemistry Department, Faculty of Science, Kuwait University, P.O. Box
5969, Safat 13060, Kuwait.
E-mail: yehiaai@kuc01.kuniv.edu.kw, Fax: +965-4816482
Received May 20, 2007
N
N
N
H
N
N
Ph
R
Pyrolysis
R
CN
R
NH2
NHPh
N
N
+
+
+
NH
N
R
Flash vacuum pyrolysis (FVP) of 1-acylbenzotriazole phenylhydrazones gave benzonitriles, aniline and
2-arylbenzimidazole derivatives. Static pyrolysis of the same substrates at 180 °C gave exclusively the
corresponding N-anilino-2-arylbenzimidazole derivatives. Pyrolysis of the isomeric 2-acylbenzotriazole
phenylhydrazones gave similar products.
J. Heterocyclic Chem., 45, 723 (2008).
required starting materials 1a-d as the main products
(45-66%) along with their isomeric products 3a-d as
minor by-product (15-20%) by reacting benzotriazole
INTRODUCTION
We have recently studied kinetically and mechan-
istically the pyrolytic behavior of a number of substituted
benzotriazole derivatives [1]. We also reported the
products obtained under different pyrolytic techniques
including mainly static and flash vacuum conditions.
These reactions offer some advantageous synthetic
approach to many interesting heterocyclic systems, which
have been reviewed in our previous publications [1d].
These pyrolytic reactions have been extensively used for
the preparation of many interesting heterocyclic systems
[1,2-11]. The primary step in the pyrolysis of these
compounds involves mainly N2 elimination, yielding the
corresponding diradical intermediates followed by
intramolecular cyclization.
with the
appropriate N-phenylbenzohydrazonoyl
chloride derivatives. The reaction was performed either
at room temperature for 24 hrs in dichlromethane
(DCM) in the presence of triethyl amine (TEA) or by
reflux for 3 hrs in benzene in the presence of TEA
(Scheme 1). The symmetry of the benztriazole ring of
3a-d confirmed their structures over 2a-d as found
mainly from 13C NMR spectra which displayed two less
carbon signals than is expected for 2a-d.
FVP of each of 1a-d at 700 °C and 0.01 Torr gave
the corresponding 2-arylbenzimidazoles 5a-d, aniline
6 and benzonitrile derivatives 7a-d. On the other hand,
gas phase pyrolysis of 1a-d at 250 °C and 0.045 Torr
gave aniline and compounds 5a-d. Since these
pyrolytic conditions did not give the anticipated
products 4a-d but a secondary thermolysis product we
tried other conditions. Finally compounds 4a-d have
been obtained as the sole reaction products in good
yields (70-78%) by heating the corresponding starting
materials 1a-d in an oil bath at 180-190 °C for 10
minutes. The pyrolyzates were qualitatively and
quantitatively determined by HPLC (Table 1) and by
1H NMR spectroscopy. Scheme 2 and Table 1
summarize the pyrolysis products under different
pyrolytic conditions.
The present work describes the pyrolytic behavior of
1-acylbenzotriazole phenylhydrazone derivatives 1a-d
together with suggested mechanism for this pyrolytic
reaction in comparison with the analogous benzotriazole
derivatives.
RESULTS AND DISCUSSION
Literature shows that compounds 1a,c have been
obtained with another isomeric products assigned as 2a,c
[12]. The latter structures have been corrected by Elguero
etal. as 2-benzoylbenzotriazole phenylhydrazones 3a,c
[13]. In the present investigation we prepared the

724
H. Al-Awadi, M. R. Ibrahim, N. A. Al-Awadi, Y. A. Ibrahim
Vol 45
Scheme 1
for Bt derivatives containing RCO instead of the Ar
moieties in the present study). The formation of the
nitriles 7 results from fragmentation of the starting
compounds 1a-d into BtH and ArCNNPh. The latter
under FVP gave 7 and aniline. Under static conditions
(250 °C, 0.045 Torr) compounds 5a-d and aniline were
the only observed products which indicate that the
fragmentation to ArCN required the more drastic
conditions of FVP. By lowering the pyrolytic temperature
to 180-190 °C we have been able to obtain exclusively the
primary expected pyrolysis products 4a-d in excellent
yields. The formation of 5a-d from 4a-d was confirmed
by subjecting compounds 4a-d to the same static pyrolytic
conditions (250 °C, 0.045 Torr) where this led to the
formation of 5a-d and aniline (Table 1).
Ar
N
N
N
N
N
N
N
Ph
Cl
H
H
N
H
N
N
Ph
2a-d
R
TEA/DCM or Benzene
Ph
HN
N
N
N
N
N
N
N
H
N
N
Ph
R
R
R
1a-d
3a-d
a H
b Cl
c CH3
d OCH3
45-66%
15-20%
Similar attempts to pyrolyze the isomeric derivatives
3a-d was only successful under the static conditions at
Table 1
Pyrolysis products of 1a-d, 3a-d, 4a-d under different pyrolytic conditions.
% yield of pyrolysis products
substrate
Condition
Compound
4a-d
Compound
Compound
6
Compound
7a-d
29
5a-d
18
34
-
5
45
-
7
28
-
3
40
-
20
31
22
21
34
46
43
56
i
ii
iii
i
ii
iii
i
ii
iii
i
ii
iii
ii
ii
ii
ii
ii
ii
ii
ii
-
-
78
-
-
75
-
-
76
-
-
70
-
-
-
-
-
-
-
-
54
58
-
43
55
-
61
49
-
58
47
-
41
42
33
35
28
43
39
39
1a
1b
1c
1d
-
-
26 (5)iv
-
-
27 (4)iv
-
-
10 (8)iv
-
-
-
-
-
-
-
-
3a
3b
3c
3d
4a
4b
4c
4d
(i) FVP, 700°C (0.02 Torr); (ii) Static pyrrolysis 250°C (0.045 Torr)/15 min; (iii) static pyrrolysis (oil bath) 180-190°C/10
min; (iv) benzonitrile formed in FVP from substituted benzonitrile by pyrolysis of the initial formed substituted
benzonitriles.14
Scheme 3 illustrates possible mechanistic routes
explaining the formation of the products 4a-d and 5a-d
obtained in the present pyrolytic study. The reaction starts
by extrusion of N2 to give the diradicals 8a-d which then
undergo intramolecular cyclization to give the
corresponding 1-anilinobenzimidazoles 4a-d. The latter
undergo further fragmentation under FVP conditions to
give the corresponding benzimidazole derivatives 5a-d
and aniline (similar mechanism [1a] has been suggested
250 °C, 0.045 Torr for 15 min. This was found to give
also the corresponding benzimidazoles 5a-d (20-31%) and
aniline 6 (33-42%) (Table 1). The reaction presumably
proceeds via first 1,5-sigmatropic shift (most probably via
the azo tautomers 3') to give the corresponding isomeric
1-substituted Bt derivatives 1a-d followed by the same
mechanistic pyrolysis proposed in Scheme 3. Such 1,5-
sigmatropic shifts have also been reported for other 2-
substituted Bt derivatives [1b].

May-Jun 2008
Gas-phase Thermolysis of Benzotriazole Derivatives. Part 4
725
Scheme 2
derivatives [15] by stirring at room temperature with CCl4 and
Ph3P in acetonitrile at room temperature overnight following
reported procedure [17].
N
N
N
Preparation of starting compounds 1a-d and 3a-d.
General procedure
R
H
N
N
Ph
a H
b Cl
c CH3
d OCH3
i) FVP/700 oC, 0.01 Torr
R
Method A. To a mixture of benzotriazole (1.19 gm, 10 mmol)
in DCM (40 mL) and TEA (3 mL) was added dropwise with
stirring at room temp. the appropriate N-phenylbenzo-
hydrazonoyl chloride derivatives (10 mmol). The mixture was
then stirred overnight. The solvent was then removed in vacuo
and the residue was washed with water and recrystallized from
the proper solvent to give yellow crystals of 1a-d and 3a-d.
Method B. To a mixture of benzotriazole (1.19 gm, 10 mmol)
in benzene (40 mL) and TEA (3 mL) was added dropwise with
string at room temp. the appropriate N-phenylbenzohydrazonoyl
chloride derivatives (10 mmol). The reaction mixture was then
heated under reflux for 3 hrs. The solvent was then removed in
vacuo and the residue was washed with water and recrystallized
from the proper solvent to give yellow crystals of 1a-d and 3a-d.
1-Benzoylbenzotriazole phenylhydrazone (1a). Yellow
crystals from ethanol, yield 45% (A), 45% (B), mp 193-94 °C
(lit.12 mp 194 °C). MS; m/z: 313 (M+, 10 %), 285 (100%), 194
ii) or Static/250 oC, 0.045 Torr (15 min)
iii) or 180-190 oC (10 min)
1a-d
R
CN
NH2
NHPh
N
N
+
+
+
NH
N
R
R
7
4
5
6
i)
ii)
iii)
0%
0%
7-18%
28-40%
0%
54-61%
47-58%
0%
18-30%
0%
0%
70-78%
In conclusion different pyrolytic studies on 1-acyl-
benzotriazole phenylhydrazones gave direct easy efficient
synthesis of N-anilino-2-arylbenzimidazole derivatives,
which are otherwise difficult to synthesize. Combined
with interesting diverse biological activity of benzimi-
dazole derivatives, [16] this synthetic route can be used in
strategic synthesis of biologically active compounds
containing this ring system.
1
(60%). H NMR (CDCl3): δ 8.68 (br, 1H, NH), 8.22 (m, 1H),
7.49 (m, 2H), 7.45-7.39 (m, 5H), 7.32 (t, J 7.4 Hz, 2H), 7.20 (d,
J 7.7 Hz, 2H), 7.14 (m, 1H), 6.97 (t, J 7.4 Hz, 1H).
1-p-Chlorobenzoylbenzotriazole phenylhydrazone (1b).
Yellow crystals from ethanol, yield 48% (A), 66% (B), mp 185-87
°C. MS; m/z: 349 (M + 2, 5%), 347 (M + 1, 15%), 319 (100%),
284 (70%), 228 (42%). IR (KBr) 3440, 3289, 3237, 3057, 1594,
1517, 1493, 1255, 1171, 1091, 1070, 951, 832, 747, 692. 1H
NMR (CDCl3): δ 8.61(br, 1H, NH), 8.23 (m, 1H), 7.54-7.49 (m,
2H), 7.37-7.28 (m, 6H), 7.19 (d, J 8.2 Hz, 2H), 7.14 (m, 1H), 6.98
(t, J 7.7 Hz, 1H). 13C NMR (CDCl3): δ 145.2 (C), 143.0 (C), 135.2
(C), 132.1 (C), 131.4 (C), 129.4 (2CH), 129.1 (CH), 129.0 (2CH),
127.2 (2CH), 127.0 (C), 125.2 (CH), 121.8 (CH), 120.4 (CH),
113.7 (2CH), 111.1 (CH). Anal. Calcd for C19H14ClN5 (347.8): C
65.61; H 4.06; N 20.14. Found: C 65.49; H 4.31; N 20.17.
Scheme 3
NHPh
NHPh
Ar
N
N
N
N
!
N
C•
Ar
-N2
NHPh
N
N•
N
Ar
1
8
4
NH2
N
H
N
1-p-Toluoylbenzotriazole phenylhydrazone (1c). Yellow
crystals from DMF / EtOH, yield 63% (A), 55% (B), mp 182-83
°C (lit. [12] mp 180 °C). MS; m/z: 327 (M+, 10%), 299 (90%),
284 (100%), 208 (55%), 194 (45%). IR (KBr): 3443, 3284,
3055, 3031, 3004, 2918, 1602, 1583, 1497, 1447, 1269, 1252,
Ar
+
N
5
6
N
N
N
1,5-sigmatropic
rearrangement
1
1171, 1069, 821, 783, 747, 693. H NMR (CDCl3): δ 8.60 (br,
H
Ar
N
Ar
N
N
N
N
N
N
H
N
1H, NH), 8.23 (m, 1H), 7.47 (m, 2H), 7.34-7.28 (m, 4H), 7.20
(m, 4H), 7.13 (m, 1H), 6.95 (t, J 7.4 Hz, 1H), 2.41 (s, 3H, CH3).
13C NMR (CDCl3): δ 145.2 (C), 143.5 (C), 139.6 (C), 132.3 (C),
130.1 (C), 129.5 (2CH), 129.3 (2CH), 128.8 (CH), 128.3 (C),
126.2 (2CH), 125.0 (CH), 121.3 (CH), 120.3 (CH), 113.5 (2CH),
111.4 (CH), 21.4 (CH3). Anal. Calcd for C20H17N5 (327.4): C
73.37; H 5.23; N 21.39. Found: C 73.03; H 5.40; N 21.47.
1-p-Methoxybenzoylbenzotriazole phenylhydrazone (1d).
Yellow crystals from ethanol yield 50% (A), 54% (B), mp 166-
168 °C. MS; m/z: 343 (M+, 10%), 315 (100%), 224 (60%). IR
(KBr): 3443, 3287, 3060, 3006, 2919, 2834, 1603, 1503, 1446,
1305, 1247, 1169, 1069, 1030, 831, 750. 1H NMR (CDCl3): δ
8.51 (br, 1H, NH), 8.24 (m, 1H), 7.50 (m, 2H), 7.37 (d, J 8.0 Hz,
2H), 7.29 (t, J 8.0 Hz, 2H), 7.17 (d, J 8.0 Hz, 2H), 7.14 (m, 1H),
6.94 (t, J 7.6 Hz, 1H), 6.91 (d, J 8.2 Hz, 2H), 3.86 (s, 3H,
OCH3). 13C NMR (CDCl3): δ 160.6 (C), 145.2 (C), 143.6 (C),
132.3 (C), 129.3 (2CH), 128.8 (CH), 128.2 (C), 127.8 (2CH),
Ar
PhN
N
PhN
PhNH
1'
3'
3a-d
EXPERIMENTAL
All melting points are uncorrected. IR spectra were recorded
in KBr disks using Perkin Elmer System 2000 FT-IR
spectrophotometer. H and 13C NMR spectra were recorded on a
Bruker DPX 400, 400 MHz super-conducting NMR
spectrometer. LCMS were measured using Agilent 1100 series
LC/MSD with an API-ES/APCI ionization mode. Microanalyses
were performed on LECO CHNS-932 Elemental Analyzer. The
starting N-phenylbenzohydrazonoyl chloride derivatives were
prepared from the corresponding N-aroyl-N'-phenylhydrazine
1

726
H. Al-Awadi, M. R. Ibrahim, N. A. Al-Awadi, Y. A. Ibrahim
Vol 45
1
Relative and percent yields were determined from H NMR.
described in our recent.
125.5 (C), 125.0 (CH), 121.2 (CH), 120.3 (CH), 114.2 (2CH),
113.5 (2CH), 111.4 (CH), 55.4 (OCH3). Anal. Calcd for
C20H17N5O (343.4): C 69.96; H 4.99; N 20.39. Found: C 69.73;
H 4.90; N 20.32.
(B) Static Pyrolysis. Each substrate (0.2 g) was introduced in
the reaction tube (1.5 x 12 cm Pyrex), cooled in liquid nitrogen,
sealed under vacuum of 0.045 Torr and placed in the pyrolyser
for 15 min at 250 °C. The products were analyzed by H, 13C
NMR, IR and GC-MS. Relative and percent yields were
determined from 1H NMR.
(C) Pyrolysis in an oil bath of 1a-d. Each substrate (0.2 g)
was introduced in a test tube which was placed in an oil bath for
10 min at 180-190 °C. The product was crystallized from
benzene/petroleum ether (60-80) to give compounds 4a-d.
2-Benzoylbenzotriazole phenylhydrazone (3a). Yellow
crystals from dilute ethanol, m.p. 173-175 °C (lit. [12] mp
175 °C), yield 18% (A), 20% (B). IR (KBr): 3450, 3310,
3056, 3032, 1598, 1579, 1497, 1487, 1266, 1253, 1151, 1093,
1
1
1071, 831, 746, 692. H NMR (CDCl3): δ 11.10 (br, s, 1H,
NH), 8.01 (m, 2H), 7.94 (dd, J 8.0, 1.3 Hz, 2H), 7.75 (m, 2H),
7.48-7.41 (m, 2H), 7.35-7.19 (m, 3H), 7.20 (d, J 8.0 Hz, 2H),
6.97 (t, J 7.8 Hz, 1H).
2-p-Chlorobenzoylbenzotriazole phenylhydrazone (3b).
Yellow crystals from petroleum ether 60-80, yield 18% (A),
15% (B), mp 188-89 °C. IR (KBr): 3436, 3241, 3063,
Reaction products from complete gas-phase pyrolysis of
substrates 1a-d, 3a-d and 4a-d.
1
1588,1514, 1494, 1262, 1146, 1087, 951, 830, 747, 692. H
1-Anilino-2-phenylbenzimidazole (4a). Colorless crystals
from aq. ethanol, yield (Table 1), mp 210-12 °C (lit. [18] mp
211-13). MS; m/z: 285 (M+, 100 %), 193 (45%). 1H NMR
(CDCl3): δ 8.07 (m, 2H), 7.87 (d, J 8.0 Hz, 1H), 7.45 (m, 3H),
7.34 (t, J 7.8 Hz, 1H), 7.31-7.25 (m, 3H), 7.21 (t, J 8.4 Hz, 1H),
7.01 (t, J 7.4 Hz, 1H), 6.80 (br, 1H, NH), 6.72 (d, J 7.8Hz, 2H).
13C NMR (CDCl3): δ 152.6 (C), 145.6 (C), 141.1 (C), 134.7 (C),
130.1 (CH), 129.7 (2CH), 129.0 (2CH), 128.9 (C), 128.5 (2CH),
123.4 (CH), 123.3 (CH), 122.0 (CH), 120.4 (CH), 113.0 (2CH),
109.8 (CH). Anal. Calcd for C19H15N3 (285.4): C 79.98; H 5.30;
N 14.73. Found: C 79.96; H 5.21; N 14.75.
NMR (CDCl3): δ 11.24 (br, 1H, NH), 8.02 (m, 2H), 7.73 (d, J
8.5 Hz, 2H), 7.56 (m, 2H), 7.45 (d, J 8.5 Hz, 2H), 7.38 (t, J 7.2
Hz, 2H), 7.31 (d, J 7.5 Hz, 2H), 7.00 (t, J 7.12 Hz, 1H). 13C
NMR (CDCl3): δ 143.3 (C), 143.2 (C), 134.9 (C), 131.8 (C),
129.5 (2CH), 129.3 (2CH), 128.4 (2CH), 128.3 (2CH), 128.1
(C), 121.6 (CH), 118.3 (2CH), 113.7 (2CH). Anal. Calcd for
C19H14ClN5 (347.8): C 65.61; H 4.06; N 20.14. Found: C 65.58;
H 4.19; N 19.95.
2-p-Toluoylbenzotriazole phenylhydrazone (3c). Yellow
crystals from hexane, yield 15% (A), 18% (B), mp 141-143 °C
(lit. [12] 145 °C), IR (KBr): 3440, 2919, 1630, 1593, 1504,
1383, 1262, 1147, 952, 819, 748. 1H NMR (CDCl3): δ 11.09 (br,
1H, NH), 8.01 (m, 2H), 7.64 (d, J 8.1 Hz, 2H), 7.55 (m, 2H),
1-Anilino-2-p-chlorophenylbenzimidazole (4b). Colorless
crystals from benzene/petroleum ether 60-80, yield (Table 1),
mp 232-34 °C. MS; m/z: 321 (M + 2, 27%) 319 (M+, 85%), 227
(100 %). IR (KBr): 3437, 3165, 3108, 3022, 10602, 1492, 1326,
7.37-7.28 (m, 6H), 6.98 (t, J 7.0 Hz, 1H), 2.45 (s, 3H, CH3). 13
C
NMR (CDCl3): δ 143.8 (C), 143.4 (C), 139.3 (C), 130.6 (C),
129.5 (C) 129.4 (2CH), 129.1 (2CH), 128.3 (2CH), 128.1
(2CH), 121.3 (CH), 118.5 (2CH), 113.7 (2CH), 21.5 (CH3).
2-p-Methoxybenzoylbenzotriazole phenylhydrzone (3d).
Yellow crystals from petroleum ether, yield 16% (A), 20% (B),
mp 146-48 °C. MS; m/z: 343 (M+, 10%), 315 (100%), 300
1
1093, 1013, 829, 745, 696. H NMR (CDCl3): δ 8.05 (d, J 8.6
Hz, 2H), 7.85 (d, J 8.4 Hz, 1H), 7.41 (d, J 8.4 Hz, 2H), 7.38-
7.22 (m, 4H), 7.16 (d, J 8.4 Hz, 1H), 7.02 (t, J 8.0 Hz, 1H), 6.89
(br, 1H, NH), 6.69 (d, J 7.9 Hz, 2H). 13C NMR (CDCl3): δ 151.4
(C), 145.3 (C), 140.9 (C), 136.4 (C), 134.7 (C), 130.2 (2CH),
129.8 (2CH), 128.8 (2CH), 127.2 (C), 123.7 (CH), 123.5 (CH),
122.2 (CH), 120.4 (CH), 113.1 (2CH), 109.9 (CH). Anal. Calcd
for C19H14N3Cl (319.8): C 71.36; H 4.41; N 13.14. Found: C
71.30; H 4.30; N 13.01.
1
(15%), 284 (30%), 224 (55%). H NMR (CDCl3): δ 11.03 (br,
1H, NH), 8.01 (m, 2H), 7.70 (d, J 8.8 Hz, 2H), 7.54 (m, 2H),
7.38-7.28 (m, 4H), 7.00 (d, J 8.8 Hz, 2H), 6.95 (t, J 8.4 Hz, 1H),
3.89 (s, 3H, OCH3). 13C NMR (CDCl3): δ 160.4 (C), 143.8 (C),
143.3 (C), 129.7 (2CH), 129.3 (2CH), 128.8 (C), 128.1 (2CH),
125.9 (C), 121.1 (CH), 118.4 (2CH), 113.7 (2CH), 113.6 (2CH),
55.4 (OCH3). Anal. Calcd for C20H17N5O (343.4): C 69.96; H
4.99; N 20.39. Found: C 69.68; H 4.98; N 20.33.
1-Anilino-2-p-tolylbenzimidazole (4c). Colorless crystals
from benzene/petroleum ether, yield (Table 1), mp 234-36 °C.
MS; m/z: 299 (M+, 100 %), 207 (70%). IR (KBr): 3434, 3168,
3108, 3060, 3022, 2997, 2917, 1602, 1495, 1451, 1392, 1324,
1
1255, 1180, 820, 743. H NMR (CDCl3): δ 7.96 (d, J 7.9 Hz,
2H), 7.85 (d, J 8.0 Hz, 1H), 7.35-7.28 (m, 6H), 7.18 (t, J 7.9 Hz,
1H), 7.0 (t, J 7.8 Hz, 1H), 6.83 (br, 1H, NH), 6.70 (d, 2H, J =
8.0 Hz), 2.41 (s, 3H, CH3). 13C NMR (CDCl3): δ 152.8 (C), 145.7
(C), 141.0 (C), 140.4 (C), 134.8 (C), 129.7 (2CH), 129.3 (2CH),
128.9 (2CH), 126.0 (C), 123.5 (CH), 123.2 (CH), 121.9 (CH),
120.2 (CH), 113.0 (2CH), 109.8 (CH), 21.5 (CH3). Anal. Calcd
for C20H17N3 (299.4): C 80.24; H 5.72; N 14.04. Found: C 80.20;
H 5.65; N 14.01.
1-Anilino-2-p-methoxyphenylbenzimidazole (4d). Color-
less crystals from benzene/petroleum ether 60-80, yield (Table
1), mp 228-30 °C. MS; m/z: 315 (M+, 40 %), 224 (100 %). IR
(KBr): 3435, 3172, 3110, 3001, 2932, 1605, 1496, 1478, 1323,
1256, 1179, 1027, 832, 746. 1H NMR (CDCl3): δ 8.04 (d, J 8.8
Hz, 2H), 7.82 (d, J 8.0 Hz, 1H), 7.33-7.24 (m, 3H), 7.21 (t, J 7.8
Hz, 1H), 7.15 (t, J 8.0 Hz, 1H), 7.00 (t, J 7.8 Hz, 1H), 6.95 (d, J
8.8 Hz, 2H), 6.86 (br, 1H, NH), 6.71 (d, J 8.0 Hz, 2H), 3.85 (s,
3H, OCH3). 13C NMR (CDCl3): δ 161.3 (C), 152.5 (C), 145.6
(C), 141.1 (C), 134.7 (C), 130.5 (2CH), 129.8 (2CH), 123.2 (2
Pyrolysis of 1a-d, 3a-d, 4a-d.
General Procedures.
A) Flash Vacuum Pyrolysis. The apparatus used was similar
to the one that has been publications [1]. The sample was
volatilized from a tube in a Büchi Kugelrohr oven through a
30x2.5 cm horizontal fused quartz tube. This was heated
externally by a Carbolite Eurotherm tube furnace MTF-12/38A
to a temperature of 500 °C, the temperature being monitored by
a Pt/Pt-13%Rh thermocouple situated at the center of the
furnace. The products were collected in a U-shaped trap cooled
in liquid nitrogen. The whole system was maintained at a
pressure of 10-2 Torr by an Edwards Model E2M5 high capacity
rotary oil pump, the pressure being measured by a Pirani gauge
situated between the cold trap and the pump. Under these
conditions the contact time in the hot zone was estimated to be ≅
10 ms. The different zones of the products collected in the U-
shaped trap were analyzed by H, 13C NMR, IR and GC-MS.
1

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Gas-phase Thermolysis of Benzotriazole Derivatives. Part 4
727
[3] (a) Lawrence, R.; Waight, E. S. Org. Mass. Spectrom. 1970,
3, 367-377. (b) Barker, S. J.; Storr, R. C. J. Chem. Soc., Perkin Trans. 1
1990, 485-488. (c) Maquestiau, A.; Beugnies, D.; Flammang, R.;
Katritzky, A. R.; Soleiman, M.; Davis, T.; Lam, J. N. J. Chem. Soc.,
Perkin Trans. 2 1988,1071-1075. (d) Cox, M; Heidarizadeh, F.; Prager,
R. H. Aust. J. Chem. 2000, 53, 665-671.
[4] Graebe, C.; Ullmann, F. Justus Liebigs Ann. Chem. 1896,
291, 16-17. (b) Kulagowski, J. J.; Moody, C. J.; Rees, C. W. J. Chem.
Soc., Perkin Trans. 1 1985, 2725-2732. (c) Kulagowski, J. J.; Moody, C.
J.; Rees, C. W. J. Chem. Soc., Perkin Trans. 1 1985, 2733-2739. (d)
Maquestiau, A.; Flammang-Barbieux, M.; Flammang, R.; Chen, L.-Z.
Bull. Soc. Chim. Belg. 1988, 94, 245-254.
overlapped CH), 121.9 (CH), 121.3 (C), 120.0 (CH), 114.0
(2CH), 113.0 (2CH), 109.7 (CH), 55.3 (OCH3). Anal. Calcd for
C20H17N3O (315.1): C 76.19; H 5.39; N 13.33. Found: C 76.10;
H 5.22; N 13.26.
2-Phenyl-1H-benzimidazole (5a). White crystals, mp 289-
1
290°C (lit. [19,20] 286-289 °C). LCMS; m/z: 266 (M + 1). H
NMR (CDCl3): δ 7.29 (m, 3H), 7.45 (m, 3H), 7.68 (m, 2H), 8.12
(m, 2H).
2-p-Chlorophenyl-1H-benzimidazole (5b). White crystals,
mp 289-290 °C (lit. [21] 290-292 °C). LCMS; m/z: 231 (M + 3),
1
229 (M + 1). H NMR (DMSO-d6): δ 7.19 (m, 2H), 7.57 (m,
[5] Nantka-Nemirski, P.; Kalinowski, J. Uniw. Adama
Mickiewicza Poznaniu, Wydz. Mat., Fiz. Chem., Ser. Chem. 1975, 18,
259-271. (b) Hubert, A. J. Chem. Commun. 1969, 328. (c) Nantka-
Nemirski, P.; Kalinowski, J. Acta Polon. Pharm. 1974, 2, 137-145.
[6] Hurbert, A.; Reimlinger, H. Chem. Ber. 1970, 103, 2828-
2835.
2H), 7.58 (d, J 8.4 Hz, 2H), 8.18 (d, J 8.4Hz, 2H), 12.98 (br, 1H,
NH).
2-p-Tolyl-1H-benzimidazole (5c). Colorless crystals, mp
269-270 °C (lit. [21] 270-272 °C). LCMS; m/z: 209 (M + 1). 1H
NMR (DMSO-d6): δ 2.33 (s, 3H, CH3), 7.16 (m, 2H), 7.32 (d, J
8.0 Hz, 2H), 7.56 (m, 2H), 8.05 (d, J 8.0 Hz, 2H), 12.80 (br, 1H,
NH).
[7] Prager, R. H.; Baradarani, M. M.; Khalafy, J. J. Heterocycl.
Chem. 2000, 37, 631-637.
[8] Lin, D. C. K.; DeJongh, D. C. J. Org. Chem. 1974, 39, 1780-
1781.
2-p-Methoxyphenyl-1H-benzimidazole (5d). White crystals,
mp 223-224 °C (lit. [21] 222-225 °C). LCMS; m/z: 225 (M + 1).
1H NMR (CDCl3): δ 3.84 (s, 3H, OCH3), 7.24 (d, J 8.8 Hz, 2H),
7.48 (m, 2H), 7.74 (m, 2H), 8.08 (d, J 8.8 Hz, 2H), 12.80 (br,
1H, NH).
[9] Khalafy, J.; Prager, R. H. Aust. J. Chem. 1998, 51, 925-929.
[10] (a) Maquestiau, A.; Beugnies, D.; Flammang, R.; Freiermuth, B.;
Wentrup, C. Org. Mass Spectrom. 1990, 25, 197-203. (b) Drulliner, J. D. J.
Am. Chem. Soc. 1968, 90, 6879-6880. (c) Baradarani, M. M.; Khalafy, J.;
Prager, R. H. Aust. J. Chem. 1999, 52, 773-780. (d) Ohashi, M.; Tsujimoto,
K.; Yoshino, A.; Yonezawa, T. Org. Mass Spectrom. 1970, 4, 203-210.
[11] Barker, S. J.; Jones, G. B.; Randles, K. R.; Storr, R. C.
Tetrahedron Lett. 1988, 29, 953-954.
[12] Sayanna, E; Venkataratnam; R.V; Thyagarajan, G.
Heterocycles 1984, 22, 1561-1564.
[13] Venkataratnam, R.V; Elguero, J; Heterocycles 1985, 23,
2779-2782.
[14] The partial conversion of substituted benzonitriles to
benzonitrile in FVP was proved by FVP of pure samples of these
substituted benzonitriles at 700 °C and 0.01 Torr.
[15] Fitton, A. O.; Smally, R. K.; “Practical Heterocyclic
Chemistry” Academic Press 1968, 26.
Aniline (6). 1H NMR spectroscopic data identical to that
reported in the literature [22a].
Benzonitrile 7a. LCMS: m/z = 104 (M + 1). 1H NMR
spectroscopic data identical to that reported in the literature
[22b].
p-Chlorobenzonitrile 7b. 1H NMR spectroscopic data
identical to that reported in the literature [22c].
p-Tolunitrile 7b. LCMS; m/z: 118 (M + 1). 1H NMR
spectroscopic data identical to that reported in the literature [23].
1
p-Methoxybenzonitrile 7d. LCMS; m/z: 134 (M + 1). H
NMR spectroscopic data identical to that reported in the
literature [22d].
[16] a) Grimmett, M. R. in Imidazoles “Comprehensive
Heterocyclic Chemistry II” Katritzky, A. R.; Rees, C. W.; Scriven, E. F.
V. eds; Elsevier, Amstrdam, 1995, 3, page 220 and references cited
therein; b) Huang, S.; Lin, R.; Yu, Y.; Lu, Y. Connolly, P. J.; Chiu, G.;
Li, S.; Emanuel, S. L.; Middleton, S. A. Bioorg. Med. Chem. Lett. 2007,
17, 1243-1245 and references cited therein.
Acknowledgment. The support of the University of Kuwait
received through research grant no. SC04/05 and the facilities of
ANALAB and SAF (grants no. GS01/01, GS03/01) are
gratefully acknowledged.
[17] Welkff, P. Cand. J. Chem. 1975, 53, 1333.
REFERENCES
[18] a) Witt, F. H. Ber. 1913, 46, 2557-2559; b) Fischer, O. J.
Prakt. Chem. 1924, 107, 16-49.
[19] FT- NMR Aldrich Catalogue; III, 180A.
[20] Jacques, J.; Eynde, V.; Deffosse, F.; Lor, P.; Haverbeke, Y.
V. Tetrahedron, 1995, 51, 5813-5818.
[21] Perry, R. J.; Wilson, B. D. J. Org. Chem., 1993, 58(25),
7016-7021.
[22] FT-NMR Aldrich Catalog (a) II, 451A; (b) II, 1509A; (c) II,
1518C; (d) II, 1519C.
[1] a) Dib, H. H.; Al-Awadi, N. A.; Ibrahim, Y. A.; El-Dusouqui,
O. M. E. Tetrahedron 2003, 59, 9455-9464; b) Dib, H. H.; Al-Awadi,
N. A.; Ibrahim, Y. A.; El-Dusouqui, O. M. E. J. Phys. Org. Chem. 2004,
17, 267-272; c) Al-Awadi, N. A.; George, B. J.; Dib, H. H.; Ibrahim, M.
R.; Ibrahim, Y. A.; El-Dusouqui, O. M. E. Tetrahedron 2005, 61, 8257-
8263; d) Al-Awadi, H.; Ibrahim, M. R.; Dib, H. H.; Al-Awadi, N. A.;
Ibrahim, Y. A. Tetrahedron 2005, 61, 10507-10513; 9455-9464.
[2] Katritzky, A. R.; Lan, X.; Yang, J. Z.; Denisko, O. V. Chem.
Rev. 1998, 98, 409-548.
[23] Yamamoto, O. Hayamizu, K.; Sekine, K.; Funahira, S. Anal.
Chem. 1972, 44, 1794-1803.