Novel synthesis and antimicrobial activity of 3-substituted 5-bromo-7-methyl-1,2,4-triazolo-[3,4-b]-benzothiazoles

Article abstract of DOI:10.1002/jhet.885

4-Methyl acetanilide (1) on treatment with bromine in acetic acid, followed by hydrolysis with dilute HCl/NaOH solution, yielded 2-bromo-4-methyl aniline (2), which on treatment with sodium thiocyanate in acetic acid afforded 2-amino-4-bromo-6-methyl benzothiazole (3). Compound 3 in ethylene glycol was heated at 150°C with 80% hydrazine hydrate to get 4-bromo-2-hydrazino-6- methyl benzothiazole (4). This hydrazino compound 4 on heating with formic acid for 3 h yielded 4-bromo-2-hydrazinoformyl-6-methyl benzothiazole (5). Same compound 4 when heated independently with formic acid for 6 h/urea for 3 h/carbon disulfide in alkali afforded 5-bromo-7-methyl (6)/5-bromo-3-hydroxy-7- methyl (7)/5-bromo-3-mercapto-7-methyl (8)-1,2,4-triazolo-[3,4-b]- benzothiazoles, respectively. Compound 4 on heating with acetic acid/acetic anhydride gave acetyl benzothiazolyl derivative 9, which on cyclization with orthophosphoric acid yielded 5-bromo-3,7-dimethyl-1,2,4-triazolo-[3,4-b]- benzothiazole (10). All these newly synthesized compounds were screened for antimicrobial activity against Escherichia coli (Gram -ve), Bacillus subtilis (Gram +ve), Erwinia carotovora, and Xanthomonas citri using ampicillin, streptomycin, and penicillin as a standard for comparison.

Full text of DOI:10.1002/jhet.885

July 2012
Novel Synthesis and Antimicrobial Activity of 3-Substituted 5-bromo-7-
873
methyl-1,2,4-triazolo-[3,4-b]-benzothiazoles
a
b
c
*
T. M. Bhagat, S. K. Deshmukh, and S. V. Kuberkar
aPG Department of Chemistry, G. S. Gawande College, Umarkhed 445206, Maharashtra, India
bPG Department of Chemistry, N. E. S. Science College, Nanded 431602, Maharashtra, India
cPG Chemistry Research Center, Department of Chemistry, Yeshwant College, Nanded 431602,
Maharashtra, India
*
E-mail: bhagat_tm@rediffmail.com
Received November 22, 2010
DOI 10.1002/jhet.885
View this article online at wileyonlinelibrary.com.
4-Methyl acetanilide (1) on treatment with bromine in acetic acid, followed by hydrolysis with dilute HCl/
NaOH solution, yielded 2-bromo-4-methyl aniline (2), which on treatment with sodium thiocyanate in acetic
acid afforded 2-amino-4-bromo-6-methyl benzothiazole (3). Compound 3 in ethylene glycol was heated at
150ꢀC with 80% hydrazine hydrate to get 4-bromo-2-hydrazino-6-methyl benzothiazole (4). This hydrazino
compound 4 on heating with formic acid for 3 h yielded 4-bromo-2-hydrazinoformyl-6-methyl benzothia-
zole (5). Same compound 4 when heated independently with formic acid for 6 h/urea for 3 h/carbon disulfide
in alkali afforded 5-bromo-7-methyl (6)/5-bromo-3-hydroxy-7-methyl (7)/5-bromo-3-mercapto-7-methyl
(8)-1,2,4-triazolo-[3,4-b]-benzothiazoles, respectively. Compound 4 on heating with acetic acid/acetic anhy-
dride gave acetyl benzothiazolyl derivative 9, which on cyclization with orthophosphoric acid yielded 5-
bromo-3,7-dimethyl-1,2,4-triazolo-[3,4-b]-benzothiazole (10). All these newly synthesized compounds were
screened for antimicrobial activity against Escherichia coli (Gram ꢁve), Bacillus subtilis (Gram +ve), Erwi-
nia carotovora, and Xanthomonas citri using ampicillin, streptomycin, and penicillin as a standard for
comparison.
J. Heterocyclic Chem., 49, 873 (2012).
© 2012 HeteroCorporation

874
T. M. Bhagat, S. K. Deshmukh, and S. V. Kuberkar
Vol 49
INTRODUCTION
assigned. The IR spectrum of the compound 5 in KBr
showed absorption bands at 3246 cmꢁ1 and 3184 cmꢁ1
due to N—H stretching and absorption band of medium in-
tensity at 2856 cmꢁ1 accompanied by a strong carbonyl
(—C¼O) stretching absorption band at 1683 cmꢁ1 indicat-
ing the presence of an aldehyde group. The 1H NMR spec-
trum in CDCl3 showed peak at d 2.5 due to Ar-CH3, d 2.7
due to —NH proton, d 7.4–7.7 due to Ar-H, and d 9.5 due
to aldehydic proton.
1,2,4-Triazole and their derivatives are important class
of organic compounds with diverse agriculture, industrial
and biological activities [1–3], including antimicrobial
[4,5] anticonvulsant [6,7], and anti-inflammatory [8].
Similarly, benzothiazoles are known to possess different
activities such as anticancer [9], anthelmintic activity
[10], and antitubercular activity [11].
A survey of literature reveals such fused substituted tri-
cyclic triazoles are prepared by different methods [12,13]
but little work is carried out on bromo derivative of such
fused tricyclic triazoles. Hence, it was thought worthwhile
to synthesize 5-bromo-7-methyl as a substituent on ben-
zene moiety in the 1,2,4-triazolo-[3,4-b]-benzothiazole
system by following series of reactions and study the
chemistry and biological activity of these compounds.
As the first step, 2-bromo-4-methyl aniline (2) was
prepared by treating 4-methyl acetanilide (1) with bromine
in acetic acid, followed by hydrolysis with dilute HCl/
NaOH solution.
To the solution of sodium thiocyanate in glacial acetic
acid, 2-bromo-4-methyl aniline (2) was added. The mixture
was stirred well and bromine in glacial acetic acid was
added dropwise maintaining the temperature below 5ꢀC.
The residue is filtered, dissolved in hot water, and neutral-
ized by alkali. The obtained product 2-amino-4-bromo-6-
methyl benzothiazole (3) was recrystallized by ethanol.
On the basis of elemental analysis and spectral data, the
resulting product 3 has assigned the structure 2-amino-4-
bromo-6-methyl benzothiazole. The IR spectrum showed
absorption bands at 3440 cmꢁ1 and 3340 cmꢁ1 due to
asymmetric and symmetric stretching of —NH2 group, re-
spectively. The PMR spectrum exhibited singlet at d 2.4
due to Ar-CH3, broad peak of d 6.0 due to —NH2 protons,
and two singlets in the region d 7.0–7.5 due to two Ar-H
protons. The mass spectrum reveals molecular ion peaks
at 244 (M + 2, 98%) and 242 (M+, 100%). It also con-
firmed the presence of one bromine atom.
The mass spectrum of the compound exhibits peaks of
equal intensity at 287 (M + 2, 48%) and 285 (M+, 50%)
which corresponds to the molecular weight and also con-
firms the presence of one bromine atom.
When same reaction mixture was refluxed for 6 h, the
expected tricyclic triazolo benzothiazole, 5-bromo-7-
methyl-1,2,4-trizolo-[3,4-b]-benzothiazole
(6)
was
obtained. The IR spectrum showed the absence of absorp-
tion band at 3246 cmꢁ1, 3184 cmꢁ1, 2856 cmꢁ1, and 1683
cmꢁ1 indicating the absence of —NH and —CHO groups,
respectively. It supports the formation of cyclized product.
1H NMR spectrum exhibits singlets at d 2.5 due to Ar-CH3
peaks, d 7.4–7.7 due to Ar-H and singlet at d 8.3 due to aryl
—CH proton. Moreover, the mass spectrum exhibits molecu-
lar ion peak of equal intensity at 269 (M + 2, 88%) and 267
(M+, 90%) which corresponds to its molecular weight and
confirms the presence of one bromine atom.
Compound 4 on heating with urea at 200ꢀC for 3 h
afforded the product to which, on the basis of elemen-
tal analysis and spectral data, was assigned the struc-
ture 4-bromo-3-hydroxy-6-methyl-1,2,4-triazolo-[3,4-b]-
benzothiazole (7).
The IR spectrum showed characteristics absorption bands
at 3493 cmꢁ1 and C—O stretching band at 1250 cmꢁ1
which indicates the presence of —O—H group. Moreover,
it also exhibits strong absorption band at 1717 cmꢁ1 due
to C¼O group. It indicates that compound 7 exists in its tau-
tomeric form.
1H NMR spectrum of compound 7 in dimethyl sulfoxide
(DMSO) showed two singlets at d 7.4 and 7.6 due to two
Ar-H protons. The singlets at d 2.3 and 2.6 can be assigned
to Ar-CH3 and O—H proton, respectively. The mass spec-
trum shows molecular ion peaks of equal intensity at 286
(M+ + 2) and 284 (M+).
Another 3-substituted tricyclic triazolo benzothiazole,
3-mercapto-5-bromo-7-methyl-1,2,4-triazolo-[3,4-b]-
benzothiazole (8) was obtained by refluxing 4-bromo-2-
hydrazino-6-methyl benzothiazole (4) with carbon disulfide
in the presence of alkali for 3 h, followed by neutralization
with hydrochloric acid solution.
2-Amino-4-bromo-6-methyl benzothiazole (3) in ethyl-
ene glycol, as solvent, was heated with 80% hydrazine
hydrate hydrochloride over an oil bath for 3 h at 150ꢀC
to get the product, 4-bromo-2-hydrazino-6-methyl ben-
zothiazole (4). The IR spectrum of 4 showed absorption
bands at 3452 cmꢁ1 and 3353 cmꢁ1 due to —NH2 asym-
metric and symmetric stretching, respectively. The mass
spectrum exhibits molecular ion peaks of equal intensity
at 259 (M + 2) and 257 (M+) confirming the formation
of compound 4 with one bromine atom.
Compound 4 was heated with formic acid for 3 h to get
expected tricyclic triazolo benzothiazole (6), but it resulted
in the formation of 4-bromo-2-hydrazinoformyl-6-methyl
benzothiazole (5). On the basis of elemental analysis and
spectral data, the structure of the resulting product has been
The compound dissolves in sodium hydroxide solution
and gets reprecipitated with hydrochloric acid solution in-
dicating the presence of mercapto (—SH) group.
The IR spectrum shows the absorption band at 2750
cmꢁ1 due to mercapto group. 1H NMR spectrum of
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

July 2012
Novel Synthesis and Antimicrobial Activity of 3-Substituted
875
5-Bromo-7-methyl-1,2,4-triazolo-[3,4-b]-benzothiazoles
Table 1
compound 8 in DMSO showed singlets at d 2.5, 3.6, 7.6,
and 7.9 due to Ar-CH3, —S—H, and two Ar-H protons, re-
spectively. The mass spectrum exhibits molecular ion peaks
of equal intensity at 301 (M + 2) and 299 (M+) which corre-
sponds to its molecular weight.
Evaluation of antimicrobial activity of 3-substituted 5-bromo-7-methyl-
1,2,4-triazolo-[3,4,-b]-benzothiazole.
The preparation of trisubstituted triazolo benzothiazole
was undertaken with 3-methyl substituent on triazolo ring
and 5-bromo-7-methyl substituent on benzene ring. 4-
Bromo-2-hydrazino-6-methyl benzothiazole (4) on heat-
ing with acetic acid/acetic anhydride gave acetyl thiazolyl
derivative 9. The acetyl derivative shows the IR absorp-
tion bands at 3274 cmꢁ1, 3188 cmꢁ1, and 1710 cmꢁ1
Antimicrobial activity
(zone of inhibition in mm)
1
Sr.
no.
E.
E.
B.
X.
citri
due to NH and C¼O stretching, respectively. H NMR
Comp.
R
coli carotovora subtilis
spectrum exhibits peaks at d 2.3, 2.6, 7.3–7.5, 10.1, and
10.5 due to Ar-CH3, —COCH3, Ar-H, and N—H protons,
respectively. The mass spectrum exhibits molecular
ion peaks of equal intensity at 301 (M + 2, 98%) and
299 (M+, 100%) which corresponds to its molecular
weight.
1
2
3
4
5
6
7
8
6
7
8
–H
–OH
–SH
1.5
00
03
04
03
03
21
22
24
00
03
02
01
03
17
22
18
00
01
03
02
02
18
18
20
00
03
02
16
20
15
00
10 –CH3
Ampicillin
Streptomycin
Penicillin
The acetyl thiazolyl derivative 9 on cyclization with
orthophosphoric acid afforded the product to which, on
the basis of elemental analysis and spectral data, was
assigned the structure, 5-bromo-3,7-dimethyl-1,2,4-tria-
zolo-[3,4-b]-benzothiazole (10).
The IR spectrum of 10 showed the absence of strong ab-
sorption band in the region 1650–1750 cmꢁ1 indicating the
absence of —COCH3 group. The 1H NMR spectrum
exhibited two singlets at d 2.3 and 2.5 due to Ar-CH3
and —CH3 attached to triazole ring, respectively, and
two singlets at d 7.4 and 7.6 due to Ar-H protons.
Control
and mass spectra on FT VG-7070H mass spectrometer using
the GI technique at 70 eV. Elemental analysis was carried out
on Heraeus CHN-O Rapid analyzer. Purity of the compound
was checked by thin layer chromatography (TLC).
Synthesis of 2-amino-4-bromo-6-methyl benzothiazole
(3).
2-Bromo-4-methyl aniline (18.6 g, 0.2M) and sodium
thiocyanate (16 g, 0.2M) were dissolved in glacial acetic acid
(150 mL). The solution was cooled in freezing mixture. Bromine
(32 g, 10 mL, 0.2M) in glacial acetic acid (25 mL) was added
with stirring and maintaining temperature below 5ꢀC. The mixture
was allowed to stand for 1 h at room temperature. The resulting
hydrobromide was dissolved in hot water and neutralized
with 10% NaOH to obtain base. The amine thus obtained was
filtered, washed with water, and recrystallized in aqueous ethanol
(50 mL ethanol + 50 mL water) to ꢁg1et the product 11 g (45%),
mp 208–210ꢀC. IR (KBr): 3440 cm (asymmetric stretching of
—NH2), 3340 cmꢁ1 (N—H symmetrical stretching of —NH2),
2922 cmꢁ1 (Ar-C—H stretching), 3052 cmꢁ1 (Ar-H stretching),
ANTIMICROBIAL SCREENING: RESULTS AND
DISCUSSION
The compounds 6–8 and 10 were tested for their antimi-
crobial activity by cup plate agar diffusion method against
Escherichia coli (Gram -ve), Bacillus subtilis (Gram +ve),
Erwinia carotovora, and Xanthomonas citri using ampicil-
lin, streptomycin, and penicillin as a standard for compari-
son. The antibacterial screening data of the compounds are
presented in Table 1. DMSO was used as a control solvent.
Compounds 6 and 10 are more active than compounds 7
and 8 against B. subtilis, whereas compound 8 is active
against E. coli. Compared with other compounds, com-
pound 7 is active against X. citri and E. carotovora, and in-
active against E. coli.
1630 cmꢁ1 (—C¼N stretching), 650 cmꢁ1 (C—S stretching); H
1
NMR (CDCl3): d 2.4 (s, 3H, Ar-CH3), 6.0 (br, 2H, —NH2), 7.0–
7.5 (two singlets, 2H, Ar-H); MS: m/z 244 (M + 2, 98%), 242
(M+, 100%), 163, 136; Anal. Calcd for C8H7BrN2S (243): C,
39.5; H, 2.88; N, 11.52; Br, 32.92; S, 13.16. Found: C, 39.2; H,
2.62; N, 11.38; Br, 32.8; S, 13.0.
4-Bromo-2-hydrazino-6-methyl benzothiazole (4). Hydrazine
hydrate (80%, 17 mL) was taken in a flask cooled to 5ꢀC and
concentrated HCl (11 mL) was added with stirring. The flask was
kept at room temperature for few minutes and then 2-amino-4-
bromo-6-methyl benzothiazole (11 g) was added in portions.
Ethylene glycol (44 mL) was added into the flask. The contents of
the flask were heated at 150ꢀC on an oil bath for 3 h. On
cooling, the product 4-bromo-2-hydrazino-6-methyl benzothiazole
crystallized out. It was filtered at pump, washed with cold water,
and recrystallized from ethyl alcohol to give 10.5 g (90%), mp
246–248ꢀC. IR (KBr): 3452 cmꢁ1 (asymmetric N—H stretching in
EXPERIMENTAL
Melting points were determined in open capillaries and are
uncorrected. Infrared spectra were recorded in Nujol/potassium
bromide pellets on Bomen MB 104FT infrared spectrophotom-
eter. 1H NMR spectra were obtained on a Gemini 200 MHz
spectrometer with trimehylsilane (TMS) as an internal standard
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

876
T. M. Bhagat, S. K. Deshmukh, and S. V. Kuberkar
Vol 49
—NH2), 3353 cmꢁ1 (symmetric N—H stretching in —NH2); MS: m/z
259 (M + 2), 257 (M+); Anal. Calcd for C8H8BrN3S (258): C, 37.2; H,
3.1; N, 16.2; Br, 31.0; S, 12.40. Found: C, 36.9; H, 2.9; N, 16.0; Br,
30.8; S, 12.2.
C9H6BrN3S2 (300): C, 36; H, 2.00; N, 14.00; Br, 26.66; S,
21.33. Found: C, 35.90; H, 1.96; N, 13.94; Br, 26.42; S,
21.14.
2-Acetyl-4-bromo-6-methyl benzothiazole (9). 4-Bromo-2-
hyrdazino-6-methyl benzothiazole (1.29 g, 0.005M) was
refluxed with acetic anhydride (2 mL) and glacial acetic acid (4
mL) on an oil bath at 150ꢀC for 1.5 h. The reaction mixture
was cooled and poured with stirring over crushed ice. The
acetyl derivative thus obtained was filtered, washed with cold
water, and recrystallized from hot ethanol to give 1.2 g (80%),
mp 208–210ꢀC. IR (KBr): 3274 cmꢁ1, 3188 cmꢁ1 (N—H
4-Bromo-2-hydrazinoformyl-6-methyl benzothiazole (5).
A mixture of 4-bromo-2-hydrazino-6-methyl benzothiazole
(0.516 g, 0.002M) and formic acid (5 mL) in 50-mL round-
bottom flask was refluxed on an oil bath at 150ꢀC for 3 h.
The contents of the flask were cooled and poured on crushed
ice with stirring. The white precipitate obtained was
recrystallized from ethanol to give 0.37 g (64.68%), mp 238–
240ꢀC. IR (KBr): 3246 cmꢁ1, 3184 cmꢁ1 (N—H stretching),
2856 cmꢁ1 (C—H stretching of CHO group), 1683 cmꢁ1
(C¼O stretching of CHO); 1H NMR (CDCl3): d 2.5 (s, 3H,
Ar-CH3), 2.7 (s, 2H, —NH2), 7.4–7.7 (2s, 2H, Ar-H), 9.5 (s,
1H, CHO); MS: m/z 287 (M + 2, 48%), 285 (M+, 50%);
Anal. Calcd for C9H8BrN3OS (286): C, 37.76; H, 2.79; N,
14.68; Br, 27.97; S, 11.18. Found: C, 37.68; H, 2.74; N,
14.53; Br, 27.72; S, 11.02.
5-Bromo-7-methyl-1,2,4-triazolo-[3,4-b]-benzothiazole (6).
Reaction mixture of 4-bromo-2-hydrazino-6-methyl benzothiazole
(0.516 g, 0.002M) and formic acid (5 mL) was refluxed on an oil
bath at 150ꢀC for 6 h. The contents of the flask were cooled and
poured on crushed ice with stirring. The white precipitate obtained
was filtered at pump, washed with cold water, and recrystallized
from 1,4-dioxane to get 0.32 g (62%), mp 276–278ꢀC. IR (KBr):
absence of absorption band in the region 3400–3100 cmꢁ1 due to
NH and at 2856 cmꢁ1 and 1683 cmꢁ1 due to —CHO; 1H NMR: d
2.5 (s, 3H, Ar-CH3), 7.4–7.7 (2s, 2H, Ar-H), 8.3 (s, 1H, CH); MS:
m/z 269 (M + 2, 98%), 267 (M+, 100%); Anal. Calcd for
C9H6BrN3S (268): C, 40.29; H, 2.23; N, 15.67; Br, 29.85; S, 11.94.
Found: C, 40.14; H, 2.12; N, 15.48; Br, 29.62; S, 11.8.
1
stretching), 1710 cmꢁ1 (C—O stretching in C¼O); H NMR: d
2.3 (s, 3H, Ar-CH3), 2.6 (s, 3H, COCH3), 7.3–7.5 (s, 2H, Ar-
H), 10.5 (s, 1H, N—H); MS: m/z 301 (M + 2, 98%), 299 (M+,
100%); Anal. Calcd for C10H10BrN3OS (300): C, 40.0; H, 3.33;
N, 14.0; Br, 26.66; S, 10.66. Found: C, 39.92; H, 3.12; N,
13.94; Br, 26.52; S, 10.44.
5-Bromo-3,7-dimethyl-1,2,4-triazolo-[3,4-b]-benzothiazole
(10). The acetyl derivative (1 g, 0.0035M) was refluxed on an oil
bath with acetic anhydride (5 mL) and syrupy phosphoric acid
(0.75 mL) for 1.5 h at 150ꢀC. The reaction mixture was cooled,
poured in 150 mL ice cold water with stirring, then rendered
alkaline with ammonia solution. The solid product was filtered,
washed with water, and recrystallized from hot ethanol to obtain
0.38 g (40.4%), mp 260–262ꢀC; 1H NMR: d 2.3 (s, 3H, Ar-
CH3), 2.5 (s, 3H, COCH3), 7.3–7.6 (s, 2H, Ar-H); Anal. Calcd
for C10H8BrN3S (282): C, 42.55; H, 2.32; N, 14.89; Br, 28.36;
S, 11.32. Found: C, 42.42; H, 2.12; N, 14.76; Br, 28.22; S, 11.18.
Acknowledgments. The authors are grateful to Principal, Science
College, Nanded, for providing laboratory facilities, Director,
Indian Institute of Chemical Technology, Hyderabad, for
providing spectra, and Dr. V. N. Kadam, Principal, G. S.
Gawande College, Umarkhed, for encouragement.
5-Bromo-3-hydroxy-7-methyl-1,2,4-triazolo-[3,4-b]-
benzothiazole (7). A mixture of 4-bromo-2-hydrazino-6-
methyl benzothiazole (1.29 g, 0.005M) and urea (3 g,
0.05M) was crushed together in a mortar. Then the
powdered mixture transferred into 50-mL round-bottom
flask and heated on an oil bath at 190ꢀC for 3 h. The
contents of the flask were cooled. The solid obtained was
then dissolved in 10% NaOH and filtered. The clear
filtrate cooled and acidified with HCl to obtain white
precipitate. It was filtered, washed with cold water, and
REFERENCES AND NOTES
[1] Bala, S.; Gupta, R. B.; Sachdeva, M. L.; Singh, A.; Pujari,
H. K. Indian J Chem 1978, 16B, 481.
[2] Mohan, J. Indian J Chem 1983, 22B, 270.
[3] Prasad, A.; Ramalingam, R. J.; Rao, A. B.; Diwan, P. V.;
Sattur, P. B. Eur J Med Chem 1989, 24, 199.
[4] El-Masry, A. H.; Ali Abdelwahed, S. H. Molecules 2000, 5,
1429.
[5] Orabi, A. S.; Moneim, M. A.; El-Din Salem, E.; El-Din Abd
El-Fattah, M. Polish J Chem 2000, 74, 1675.
[6] Martin, G. Ger. Pat. 2,240,043 (Cl. 07 d), March 1873; Martin,
G. Chem Abstr 1973, 78, 136302t.
[7] Parmar, S. S.; Rastogi, V. K.; Agrawal, V. K.; Sinha, J. N.;
Chaudhari, A. Can J Pharm Soc 1974, 9, 107.
[8] George, T.; Mehata, D. V.; Tahilramani, R.; Davvid, J.;
Talwalker, P. K. J Med Chem 1971, 14, 335.
[9] Stvens, M. F. G.; McCall, C. J.; Lelieveld, P.; Alexander, P.;
Richter, A.; Davies, D. E. J Med Chem 1994, 37, 1689.
[10] Nadkarni, A. B.; Vijayalaxmi Kamath, R.; Khadse, G. B.
Indian J Heterocycl Chem 2000, 9, 09.
[11] Bhusari, K. P.; Khedkar, P. B.; Umathe, S. N.; Bhhakar, R. H.;
Akkinpalli Raghu Ram Rao, A. J Heterocycl Chem 2000, 9, 13.
[12] Brooker, G. S.; Vanlare, E. J. Chem Abstr 1975, IS9385.
[13] Bower, J. D.; Doyle, F. P. J Chem Soc 1957, 727.
recrystallized from 1,4-dioxane to obtained 0.66
g
(46.4%), mp 278–280ꢀC. IR (KBr): 3493 cmꢁ1 (O—H),
1717 cmꢁ1 (C¼O stretching), 1203 cmꢁ1 (C—O in —C—OH); 1H
NMR: d 2.3 (s, 3H, Ar-CH3), 2.6 (s, 1H, O—H), 7.8–7.5 (2s, 2H,
Ar-H); Anal. Calcd for C9H6BrN3OS (284): C, 38.02; H, 2.11; N,
14.78; Br, 28.16; S, 11.26. Found: C, 37.98; H, 2.02; N, 14.66; Br,
28.0; S, 11.12.
5-Bromo-3-mertcapto-7-methyl-1,2,4-triazolo-[3,4-b]-
benzothiazole (8). 4-Bromo-2-hydrazino-6-methyl benzothiazole
(1.29 g, 0.005M) in 40 mL of ethanol was mixed with sodium
hydroxide (0.4 g in 5 mL water) and then carbon disulfide (0.5 mL)
was added. The mixture was refluxed on water bath for 3 h at
60ꢀC. The solid left behind dissolved in 10% NaOH, filtered, and
the clear filtrate acidified in cold condition with concentrated
hydrochloric acid afforded product. It was washed with water and
recrystallized from hot nitrobenzene to give 0.68 g (45.7%), mp
263–265ꢀC. IR (KBr): 2750 cmꢁ1 (S—H stretching); 1H NMR:
d 2.5 (s, 3H, Ar-CH3), 3.6 (s, 1H, S—H), 7.6–7.9 (2s, 2H,
Ar-H); MS: m/z 301 (M + 2), 299 (M+); Anal. Calcd for
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet