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European	Journal	of	Chemistry	8	(2)	(2017)	149‐154	

	

European	Journal	of	Chemistry	
ISSN	2153‐2249	(Print)	/	ISSN	2153‐2257	(Online)		2017	Atlanta	Publishing	House	LLC	‐	All	rights	reserved	‐	Printed	in	the	USA	

http://dx.doi.org/10.5155/eurjchem.8.2.149-154.1563 

	
	

	

	

European	Journal	of	Chemistry	
Journal	webpage:	www.eurjchem.com	 	

	 	 	

Synthesis	and	antimicrobial	activity	of	some	novel	N‐substituted	
benzimidazoles	

Dnyandev	Radhu	Gund	1,	Alok	Pramod	Tripathi	2	and	Sanjay	Dashrath	Vaidya	1,*	

1	Department	of	Chemistry,	Jagdishprasad	Jhabarmal	Tibrewala	University,	Jhunjhunu,	Rajasthan,	333001,	India	
2	Department	of	Chemistry,	Rajasthan	University,	Jaipur	302004,	India	

*	Corresponding	author	at:	Department	of	Chemistry,	Jagdishprasad	Jhabarmal	Tibrewala	University,	Jhunjhunu,	Rajasthan,	333001,	India.		
Tel.:	+91.09821282877.	Fax:	+91.01595.265114.	E‐mail	address:	sanjayjjtu@gmail.com	(S.D.	Vaidya).	

	
	

	 	

	 	 	

ARTICLE	INFORMATION	 	 ABSTRACT	

	
DOI: 10.5155/eurjchem.8.2.149-154.1563	

Received:	08	March	2017	
Received	in	revised	form:	08	April	2017	
Accepted:	09	April	2017	
Published	online:	30	June	2017	
Printed:	30	June	2017

 

	 Synthesis	 of	 a	 series	 of	 new	 substituted	 benzimidazole	 derivatives	 by	 the	 condensation	 of
o‐phenylenediamine	with	 urea	 to	 give	1,3‐dihydro‐benzimidazol‐2‐one	which	 reacted	with
phosphoryl	 chloride	 to	 give	 2‐chloro‐1H‐benzimidazole	 is	 reported.	 The	 product	was	 then
alkylated	 at	 the	 benzimidazole	 NH	 with	 different	 electrophilic	 reagents	 leading	 to
functionalized	derivatives.	Structures	of	the	newly	synthesized	products	have	been	deduced
on	the	basis	of	spectral	and	analytical	data.	The	synthesized	compounds	were	screened	for
their	antimicrobial	activity.	This	exhibited	some	promising	results	towards	testing	organism
in‐vitro.	

KEYWORDS	
Alkylation	
Benzoylation	
Benzimidazole	
Antifungal	activity	
Antibacterial	activity	
Condensation	reaction	

Cite	this: Eur.	J.	Chem.	2017,	8(2),	149‐154

	
1.	Introduction	
	

Benzimidazoles	 and	 their	 analogs	 are	 well	 known	
biologically	 active	N‐containing	heterocycles	 [1],	widely	used	
as	drugs	such	as	proton	pump	inhibitor	omeprazole	[2,3],	anti‐
helmentic	 albendazole	 [4,5],	 anti‐dopaminergic	 domperidone	
[6,7],	anti‐psychotic	pimozide	[8,9],	etc.	Some	of	their	analogs	
are	 the	 constitutional	 parts	 of	 the	 marine	 alkaloids,	 such	 as	
kealiiquinone	 and	 antitumor	 agents	 such	 as	 pyrrolo[1,2‐a]	
benzimidazole	quninone	 (APBI‐A)	 [10,11].	 Specifically,	 the	2‐
substituted	 analogues	 of	 benzimidazoles	 are	 known	 to	 be	
potent	 biologically	 active	 compounds	 [12‐14].	 Some	 of	 the	
important	 benzimidazole	 derivatives	 have	 been	 reported	 as	
thyroid	 receptor	 agonists	 [15],	 gonadotropin	 releasing	
hormone	 receptor	 antagonists	 [16],	 non‐nucleoside	 HIV‐1	
reverse	transcriptase	inhibitors	[17]	and	interestingly	alkynyl	
benzimidazoles	 as	 modulators	 of	 metabotropic	 glutamate	
receptors	 [18]	 etc.	 We	 have	 also	 published	 some	 series	 of	
biologically	 active	 benzimidazoles	 [19‐21].	 Owing	 to	 the	
immense	 biological	 importance	 of	 benzimidazole	 derivatives,	
we	 now	 synthesized	 some	 novel	 class	 of	 benzimidazole	
derivatives	and	their	biological	activity	screening	studies.	
	
	

2.	Experimental	
	
2.1.	Chemicals	
	

o‐Phenylenediamine	 acid,	 urea,	 phosphoryl	 chloride	
obtained	 from	 Aldrich.	 Hydrochloric	 acid,	 sodium	 hydroxide,	
potassium	carbonate,	alkylating	agent	and	solvents	used	were	
of	commercial	grade	only.	
	
2.2.	Instrumentations	
	

Melting	 points	 recorded	 on	 a	 MRVIS	 Series,	 Lab.	 India	
Instrument.	TLC	analysis	was	done	using	pre‐coated	silica	gel	
plates	 and	 visualization	 was	 done	 using	 iodine/UV	 lamp.	
Infrared	spectra	were	recorded	on	Perkin	Elmer	model	FT‐IR	
using	 the	 KBr	 disc.	 1H	 NMR	 spectra	 of	 the	 compounds	were	
recorded	 on	BRUKER	Avance	 II	 400	MHz	NMR	 spectrometer	
with	CDCl3	as	solvent	unless	otherwise	mentioned.	Elemental	
analysis	was	carried	out	on	a	Perkin	Elmer	Series	II	Elemental	
Analyzer	2400.	
	
2.3.	Synthesis	
	
	



150	 Vaidya	et	al.	/	European	Journal	of	Chemistry	8	(2)	(2017)	149‐154	
	
	

	
	

Scheme	1
	
	

	
	

Scheme	2	
	
	
2.3.1.	Synthesis	of	1,3‐dihydro‐benzimidazol‐2‐one	(2)	
		

To	a	solution	of	o‐phenylene	diamine	(1)	(5	g,	0.046	mol)	
in	DMF	was	added	urea	(5.52	g,	0.092	mol)	and	mixture	heated	
to	135‐140	°C	for	12	h.	When	the	reaction	was	complete,	DMF	
was	 removed	 in	 vacuum;	 separated	 solid	 was	 washed	 with	
water	 and	 then	 dissolved	 in	 aq.	 10%	 NaOH	 solution.	 The	
aqueous	alkaline	solution	was	filtered	and	neutralised	with	aq.	
HCl	 (35%).	 The	 separated	 product	was	 filtered,	 washed	 and	
dried	 to	obtain	pure	compound	2	 (1,3‐dihydro‐benzimidazol‐
2‐one)	(Scheme	1).	Yield:	5.8	g,	94%.	M.p.:	99‐101	°C	(Lit.	[22]:	
100‐102	°C).	
	
2.3.2.	Synthesis	of	2‐chloro‐1H‐benzimidazole	(3)	
	

A	 mixture	 of	 1,3‐dihydro‐benzimidazol‐2‐one	 (2)	 (10	 g,	
0.07	 mol),	 phosphoryl	 chloride	 (22.88	 g,	 0.14	 mol)	 and	
catalytic	 amount	 of	 phenol	was	 heated	 103‐107	 °C	 for	 12	 h.	
After	 completion	of	 the	 reaction,	 the	mixture	was	cooled	and	
sodium	 hydroxide	 (40%,	 25	 mL)	 solution	 was	 added.	 The	
reaction	 mixture	 was	 stirred	 until	 it	 solidify.	 The	 crude	
material	was	recrystallized	to	obtain	pure	product	3	(2‐chloro‐
1H‐benzimidazole)	 (Scheme	 1).	 Yield:	 11	 g,	 97	%.	M.p.:	 208‐
209	°C	(Lit.	[22]:	207‐211	°C).		
	 	
2.3.3.	General	procedure	for	the	synthesis	of	N‐alkylated	
derivatives	of	2‐chloro‐1H‐benzimidazole	(5a‐e)		
		

To	 a	 solution	 of	 2‐chloro‐1H‐benzimidazole	 (3)	 (13.10	
mmol)	 and	 potassium	 carbonate	 (19.65	mmol)	 in	 water	 (10	
mL)	 was	 added	 compound	 4a‐e	 (15.75	 mmol)	 at	 room	
temperature.	The	 reaction	mixture	was	 then	heated	 to	70‐75	
°C	 for	3‐4	h	by	TLC	monitoring.	After	 completion	of	 reaction,	
added	 20	 mL	 ethyl	 acetate,	 stirred	 for	 15	 min	 layers	 were	
separated.	Ethyl	acetate	 layer	was	washed	with	20	mL	water,	
dried	 over	 sodium	 sulfate.	 After	 concentration	 of	 solvent	
under	 vacuum	 and	 recrystalization	 with	 aq.	 ethanol	 yielded	
corresponding	N‐substituted	derivative	(5a‐e)	as	a	white	solid	
(Scheme	2)	[23].	
	

2.3.4.	General	procedure	for	the	synthesis	of	N‐alkylated	
derivatives	of	2‐chloro‐1H‐benzimidazole	(5f‐j)	
		

To	 a	 solution	 of	 2‐chloro‐1H‐benzimidazole	 (3)	 (13.10	
mmol)	and	potassium	carbonate	(19.65	mmol)	in	acetone	(12	
mL)	 was	 added	 compound	 4f‐j	 (15.75	 mmol)	 at	 room	
temperature.	The	 reaction	mixture	was	 then	heated	 to	50‐55	
°C	 for	4‐6	h	by	TLC	monitoring.	After	completion	of	 reaction,	
solvent	was	 evaporated	 and	 added	 20	mL	water	 and	 25	mL	
ethyl	acetate,	 stirred	 for	15	min	 layers	were	separated.	Ethyl	
acetate	 layer	 was	 washed	 with	 20	 mL	 water,	 dried	 over	
sodium	 sulfate.	 After	 concentration	 of	 solvent	 under	 vacuum	
and	recrystalization	with	aq.	ethanol	yielded	corresponding	N‐
substituted	derivative	(5f‐j)	as	a	white	solid.	(Scheme	3)	[23].	
	
2.3.5.	General	procedure	for	the	synthesis	of	N‐alkylated	
derivatives	of	2‐chloro‐1H‐benzimidazole	(5k‐n)	
	

To	 a	 solution	 of	 2‐chloro‐1H‐benzimidazole	 (3)	 (13.10	
mmol)	 and	 potassium	 carbonate	 (19.65	 mmol)	 in	 DMF	 (12	
mL)	was	added	compound	4k‐n	(15.75	mmol)	at	75‐80	°C.	The	
reaction	mixture	was	then	heated	for	4‐5	h	and	monitored	by	
TLC.	 After	 the	 completion	 of	 reaction,	 it	 was	 quenched	with	
water	 (25	mL)	added	25	mL	ethyl	acetate,	stirred	 for	15	min	
layers	were	separated.	Ethyl	acetate	layer	was	washed	with	25	
mL	 water,	 dried	 over	 sodium	 sulfate.	 After	 concentration	 of	
solvent	 under	 vacuum	 and	 recrystallization	 with	 aq.	 ethanol	
yielded	 corresponding	 N‐substituted	 derivative	 (5k‐n)	 as	 a	
white	solid.	(Scheme	4)	[23].	

3‐[2‐(2‐Chloro‐benzimidazole‐1‐yl)	 ‐ethyl]‐2‐methyl‐pyrido	
[1,2‐a]pyrimidine‐4‐one	 (5a):	 Color:	 White.	 Yield:	 80%.	 M.p.:	
175‐178	 °C.	 FT‐IR	 (KBr,	 ,	 cm‐1):	 1730	 (C=O),	 1664	 (C=N),	
1097	 (C‐N).	 1H	 NMR	 (400	MHz,	 CDCl3,	 δ,	 ppm):	 2.25	 (s,	 3H,	
CH3‐Ph),	3.22	(t,	2H,	J	=	7.2	Hz,	‐CH2‐CH2‐N),	4.49	(t,	2H,	J	=	7.2	
Hz,	 ‐CH2‐CH2‐N),	7.15	(t,	1H,	 J	=	6.72	Hz,	Ar‐H),	7.22‐7.26	(m,	
3H,	 Ar‐H),	 7.43‐7.45	 (m,	 1H,	 Ar‐H),	 7.57‐7.59	 (m,	 1H,	 Ar‐H),	
7.65‐7.73	 (m,	2H,	Ar‐H).	MS	 (EI,	m/z	 (%):	339.1	 (M+1).	Anal.	
calcd.	 for	 C18H15ClN4O:	 C,	 63.81;	 H,	 4.46;	 N,	 16.54.	 Found:	 C,	
63.90;	H,	4.41;	N,	16.61%.	

	



Vaidya	et	al.	/	European	Journal	of	Chemistry	8	(2)	(2017)	149‐154	 151	
 

	

	
	

Scheme	3
	
	

N
H

N

ClH R-X
K2CO3

N

N

Cl

R
(5k-5n)

R-X=

4k 4l 4m

Where,

(3) (4k-4n)

Cl
N

Br
N

Br O

O

DMF, 75-80 oC

Cl
O

O
4n 	

	
Scheme	4	

	
	
3‐[2‐(2‐Chloro‐benzimidazole‐1‐yl)‐ethyl]‐2‐methyl‐6,	 7,8,9‐

tetrahydro‐pyrido[1,2‐a]pyrimidine‐4‐one	 (5b):	 Color:	 White.	
Yield:	74%.	M.p.:	168‐171	°C.	FT‐IR	(KBr,	,	cm‐1):	1722	(C=O),	
1650	 (C=N),	1104	 (C‐N).	 	 1H	NMR	 (400	MHz,	CDCl3,	 δ,	ppm):	
1.84‐1.90	 (m,	4H,	 CH2‐CH2‐CH2),	 2.00	 (s,	 3H,	CH3‐Ph),	 2.84	 (t,	
2H,	J	=	6.64	Hz,	Aliphatic	ring),	3.01	(t,	2H,	J	=	7.2	Hz,	CH2‐CH2‐
N),	3.95	(t,	2H,	J	=	6.2	Hz,	Aliphatic	ring),	4.40	(t,	2H,	J	=	7.2	Hz,	
CH2‐CH2‐Ph),	7.22‐7.28	(m,	2H,	Ar‐H),	7.42	(dd,	1H,	J	=	6.64	Hz,	
Ar‐H),	7.65‐7.67	(m,	1H,	Ar‐H).	MS	(EI,	m/z	(%):	343.2	(M+1).	
Anal.	calcd.	for	C18H19ClN4O:	C,	63.09;	H,	5.59;	N,	16.34.	Found:	
C,	63.15;	H,	5.60;	N,	16.28	%.	

4‐(2‐Chloro‐benzimidazole‐1‐yl)‐2,	 2‐diphenyl‐butyronitrile	
(5c):	Color:	White.	Yield:	76%.	M.p.:	140‐143	°C.	FT‐IR	(KBr,	,	
cm‐1):	2329	(C≡N),	1650	(C=N),	1137(C‐N).	1H	NMR	(400	MHz,	
CDCl3,	δ,	ppm):	2.78	(t,	2H,	J	=	8.0	Hz,	CH2),	4.20	(t,	2H,	J	=	8.0	
Hz,	 CH2‐N),	7.05‐7.08	 (m,	 1H,	Ar‐H),	7.17‐7.22	 (m,	 2H,	Ar‐H),	
7.26‐7.30	(m,	2H,	Ar‐H),	7.32‐7.38	(m,	8H,	Ar‐H),	7.59‐7.61	(m,	
1H,	 Ar‐H).	 MS	 (EI,	 m/z	 (%):	 372.2	 (M+1).	 Anal.	 calcd.	 for	
C23H18ClN3:	C,	74.29;	H,	4.88;	N,	9.53.	Found:	C,	74.35;	H,	4.81;	
N,	9.60.	

4‐(2‐Chloro‐benzimidazole‐1‐yl)‐1‐(4‐fluoro‐phenyl)	‐butan‐
1‐one	 (5d):	Color:	White.	Yield:	 68%.	M.p.:	111‐114	 °C.	FT‐IR	
(KBr,	,	 cm‐1):	1701	 (C=O),	1658	 (C=N),	1135	(C‐F),	1097	(C‐
N).	1H	NMR	(400	MHz,	CDCl3,	δ,	ppm):	2.18‐2.25	(m,	2H,	CH2‐
N),	3.15	(t,	2H,	J	=	8	Hz,	CH2‐N),	3.67	(t,	2H,	J	=	8	Hz,	CH2‐C=O),	
7.11‐7.15	(m,	4H,	Ar‐H),	7.98‐8.02	(m,	4H,	Ar‐H).	MS	(EI,	m/z	
(%):	 317.2	 (M+1).	 Anal.	 calcd.	 for	 C17H14ClFN2O:	 C,	 64.46;	 H,	
4.45;	N,	8.84.	Found:	C,	64.50;	H,	4.41;	N,	8.91	%.	

2‐Chloro‐1‐(3,4‐dimethoxy‐pyridine‐2‐ylmethyl)‐1H‐benzimi	
dazole	(5e):	Color:	White.	Yield:	81%.	M.p.:	172‐174	°C.	FT‐IR	
(KBr,	,	cm‐1):	2940	(OCH3),	1652	(C=N),	1137	(C‐N).	1H	NMR	
(400	 MHz,	 CDCl3,	 δ,	 ppm):	 4.14	 (s,	 3H,	 OCH3),	 4.32	 (s,	 3H,	
OCH3),	5.92	(s,	2H,	CH2‐N),	7.34‐7.41	(m,	2H,	Ar‐H),	7.75‐7.79	
(m,	2H,	Ar‐H),	8.04	(d,	1H,	J	=	6.68	Hz,	Ar‐H),	9.55	(d,	1H,	J	=	8	
Hz,	 Ar‐H).	 MS	 (EI,	 m/z	 (%):	 304.2	 (M+1).	 Anal.	 calcd.	 for	
C15H14ClN3O2:	 C,	 59.31;	H,	 4.65;	N,	 13.83.	 Found:	 C,	 59.42;	H,	
4.55;	N,	13.91%.	

2‐Chloro‐benzimidazole‐1‐carboxylic	acid	phenyl	ester	(5f):	
Color:	White.	Yield:	62%.	M.p.:	138‐141	°C.	FT‐IR	(KBr,	,	cm‐

1):	 1752	 (C=O),	 1592	 (C=N),	 1068	 (C‐N).	 1H	NMR	 (400	MHz,	
CDCl3,	δ,	ppm):	7.05‐7.09	(m,	1H,	Ar‐H),	7.10‐7.15	(m,	1H,	Ar‐
H),	7.16‐7.18	(m,	1H,	Ar‐H),	7.32‐7.36	(m,	3H,	Ar‐H),	7.44‐7.48	
(m,	2H,	Ar‐H),	7.75	(d,	1H,	J	=	7.92	Hz,	Ar‐H).	MS	(EI,	m/z	(%):	
273.2	(M+1).	Anal.	calcd.	for	C14H9ClN2O2:	C,	61.66;	H,	3.33;	N,	
10.27.	Found:	C,	61.60;	H,	3.39;	N,	10.34%.		

(2‐Chloro‐benzimidazole‐1‐yl)‐o‐tolyl‐methanone	 (5g):	
Color:	White.	Yield:	65%.	M.p.:	115‐118	°C.	FT‐IR	(KBr,	,	cm‐

1):	 1722	 (C=O),	 1607	 (C=N),	 1102	 (C‐N).	 1H	NMR	 (400	MHz,	
CDCl3,	δ,	ppm):	2.61	(s,	3H,	CH3),	7.15	(t,	1H,	J	=	6.73	Hz,	Ar‐H),	
7.23‐7.26	(m,	3H,	Ar‐H),	7.43‐7.45	(m,	1H,	Ar‐H),	7.57‐7.59	(m,	
1H,	 Ar‐H),	 7.66‐7.73	 (m,	 2H,	 Ar‐H).	 MS	 (EI,	m/z	 (%):	 271.2	
(M+1).	Anal.	calcd.	for	C15H11ClN2O:	C,	66.55;	H,	4.10;	N,	10.35.	
Found:	C,	66.51;	H,	4.16;	N,	10.29	%.	

1‐(4‐Bromo‐benzyl)‐2‐chloro‐1H‐benzimidazole	 (5h):	
Color:	White.	Yield:	88%.	M.p.:	119‐121	°C.	FT‐IR	(KBr,	,	cm‐

1):	 1650	 (C=N),	 1137	 (C‐N),	 1021	 (C‐Br).	 1H	NMR	 (400	MHz,	
CDCl3,	 δ,	 ppm):	 5.26	 (s,	 2H,	 CH2‐Ph),	 6.97	 (d,	 2H,	 Ar‐H),	 7.12	
(dd,	1H,	J	=	8	Hz,	Ar‐H),	7.14‐7.23	(m,	2H,	Ar‐H),	7.36‐7.41	(m,	
2H,	 Ar‐H),	 7.63‐7.65	 (m,	 1H,	 Ar‐H).	 MS	 (EI,	m/z	 (%):	 322.2	
(M+1).	Anal.	calcd.	for	C14H10BrClN2:	C,	52.29;	H,	3.13;	N,	8.71.	
Found:	C,	52.36;	H,	3.18;	N,	8.65%.	

(2‐Chloro‐benzimidazole‐1‐yl)‐(4‐nitro‐phenyl)	 ‐methanone	
(5i):	Color:	White.	Yield:	85%.	M.p.:	155‐158	°C.	FT‐IR	(KBr,	,	
cm‐1):	1722	(C=O),	1475	(NO2),	1095	(C‐N).	1H	NMR	(400	MHz,	
CDCl3,	δ,	ppm):	7.32‐7.34	(m,	1H,	Ar‐H),	7.36‐7.42	(m,	1H,	Ar‐
H),	7.45	(m,	1H,	Ar‐H),	7.74	(dd,	2H,	J	=	8	Hz,	Ar‐H),	7.95‐7.98	
(m,	1H,	Ar‐H),	8.32‐8.41	(m,	2H,	Ar‐H).	MS	(EI,	m/z	(%):	302.2	
(M+1).	Anal.	calcd.	for	C14H8ClN3O3:	C,	55.74;	H,	2.67;	N,	13.93.	
Found:	C,	55.88;	H,	2.61;	N,	13.87%.	

2‐Chloro‐benzimidazole‐1‐carboxylic	 acid	 hexyl	 ester	 (5j):	
Color:	 White.	 Yield:	 87%.	 M.p.:	 111‐113	 °C.	 FT‐IR	 (KBr,	 ,						
cm‐1):	1752	(C=O),	1592	(C=N),	1068	(C‐N).	

	



152	 Vaidya	et	al.	/	European	Journal	of	Chemistry	8	(2)	(2017)	149‐154	
	

	 	
Table	1.	Antibacterial	activity	(minimal	inhibition	concentration;	MIC)	of	compound	5a‐n.		
Compound	 Antibacterial	activity	(MIC,	µg/mL)	

	E.	coli	
(Gram	negative)	

P.	aeruginosa
(Gram	negative)

S.	aureus
(Gram	positive)

	S.	pyogenus	
(Gram	positive)

5a	 100	 62.5 125 62.5	
5b	 100	 100 150 100	
5c	 62.5	 100 125 125	
5d	 62.5	 125 100 62.5	
5e	 50	 125 62.5 100	
5f	 125	 250 200 125	
5g	 100	 100	 200	 250	
5h	 50	 62.5	 125	 100	
5i	 50	 100	 62.5	 150	
5j	 62.5	 125	 100	 250	
5k	 125	 100 100 500	
5l	 250	 250 200 100	
5m	 200	 250 200 125	
5n	 125	 200 125 150	
Gentamycin	 0.05	 1	 0.25	 0.5	
Ampicillin	 100	 ‐ 250 100	
Chloramphenicol	 50	 50 50 50	
Ciprofloxacin	 25	 25 50 50	
Norfloxacin	 10	 10 10 10	
	

	
	1H	NMR	(400	MHz,	CDCl3,	δ,	ppm):	0.84	(t,	3H,	J	=	6.88	Hz,	

CH3),	1.27‐1.33	 (m,	4H,	2×CH2),	1.38‐1.45	 (m,	2H,	CH2),	 1.75‐
1.82	 (m,	2H,	CH2),	 4.40	 (t,	 2H,	 J	=	6.8	Hz,	CH2),	7.03‐7.13	 (m,	
3H,	Ar‐H),	7.72‐7.74	(d,	1H,	J	=	7.76	Hz,	Ar‐H).	MS	(EI,	m/z	(%):	
281.2	(M+1).	Anal.	calcd.	for	C14H17ClN2O2:	C,	59.89;	H,	6.10;	N,	
9.98.	Found:	C,	9.95;	H,	6.05;	N,	10.04%.		

[2‐(2‐Chloro‐benzimidazole‐1‐yl)‐ethyl]	 ‐diisopropyl‐amine	
(5k):	Color:	White.	Yield:	74%.	M.p.:	123‐126	°C.	FT‐IR	(KBr,	,	
cm‐1):	1582	(C=N),	1213	(C‐N	aliphatic),	1136	(C‐N	aromatic).	
1H	NMR	 (400	MHz,	CDCl3,	 δ,	ppm):	0.97	 (d,	 12H,	 J	=	6.56	Hz,	
4×CH3),	2.77	(t,	2H,	J	=	7.36	Hz,	CH2‐N),	3.00‐3.05	(m,	2H,	CH‐
N),	 4.12	 (t,	 2H,	 J	 =	 7.2	 Hz,	 CH2‐N),	 7.23‐7.32	 (m,	 3H,	 Ar‐H),	
7.66‐7.69	 (m,	1H,	Ar‐H).	MS	 (EI,	m/z	 (%):	280.2	 (M+1).	Anal.	
calcd.	 for	 C15H22ClN3:	 C,	 64.39;	 H,	 7.92;	 N,	 15.02.	 Found:	 C,	
64.32;	H,	7.99;	N,	15.11%.		

4‐(2‐Chloro‐benzimidazole‐1yl)‐butyronitrile	 (5l):	 Color:	
White.	Yield:	88%.	M.p.:	134‐137	°C.	FT‐IR	(KBr,	,	cm‐1):	2329	
(C≡N),	1650	 (C=N),	1137	 (C‐N).	 1H	NMR	 (400	MHz,	CDCl3,	 δ,	
ppm):	2.18‐2.24	(m,	2H,	CH2‐CH2),	2.39	(t,	2H,	J	=	7.12	Hz,	CH2‐
CN),	4.35	(t,	2H,	 J	=	6.84	Hz,	CH2‐N),	7.21‐7.37	(m,	3H,	Ar‐H),	
7.68‐7.71	 (m,	1H,	Ar‐H).	MS	 (EI,	m/z	 (%):	220.2	 (M+1).	Anal.	
calcd.	 for	 C11H10ClN3:	 C,	 60.14;	 H,	 4.59;	 N,	 19.13.	 Found:	 C,	
60.19;	H,	4.52;	N,	19.09%.	

5‐(2‐Chloro‐benzimidazole‐1yl)‐pentanoic	acid	 ethyl	 ester	
(5m):	Color:	White.	Yield:	78%.	M.p.:	118‐121	°C.	FT‐IR	(KBr,	
,	 cm‐1):	1752	(C=O),	1592	(C=N),	1174	(ester).	1H	NMR	(400	
MHz,	CDCl3,	δ,	ppm):	1.23‐1.33	(m,	5H,	CH2	&	CH3),	2.11‐2.16	
(m,	2H,	CH2),	2.37	(t,	2H,	 J	=	7.04	Hz,	CH2),	4.11‐4.17	(m,	2H,	
CH2),	4.28	(t,	2H,	J	=	7.2	Hz,	CH2),	7.26‐7.32	(m,	2H,	Ar‐H),	7.35‐
7.38	(m,	1H,	Ar‐H),	7.68‐7.71	(m,	1H,	Ar‐H).	MS	(EI,	m/z	(%):	
281.2	(M+1).	Anal.	calcd.	for	C14H17ClN2O2:	C,	59.89;	H,	6.10;	N,	
9.98.	Found:	C,	59.95;	H,	6.06;	N,	9.92%.	

(2‐Chloro‐benzimidazole‐1yl)‐acetic	acid	methyl	ester	(5n):	
Color:	White.	Yield:	69%.	M.p.:	131‐134	°C.	FT‐IR	(KBr,	,	 cm‐

1):	 1752	 (C=O),	 1592	 (C=N),	 1068	 (C‐N).	 1H	NMR	 (400	MHz,	
CDCl3,	δ,	ppm):	3.67	 (s,	3H,	CH3‐O),	4.69	 (s,	2H,	CH2‐N),	7.25‐
7.30	 (m,	2H,	Ar‐H),	7.43‐7.47	 (m,	1H,	Ar‐H),	8.07	 (dd,	1H,	 J	=	
8.36	Hz,	Ar‐H).	MS	(EI,	m/z	(%):	225.2	(M+1).	Anal.	calcd.	 for	
C10H9ClN2O3:	 C,	 53.47;	 H,	 4.04;	 N,	 12.47.	 Found:	 C,	 53.39;	 H,	
4.11;	N,	12.51%.	
	
2.4.	Antimicrobial	studies	
	
2.4.1.	Tested	organisms	
	

The	newly	synthesized	compounds	were	screened	for	their	
antibacterial	 activity	 [24,25]	 against	 Gram‐positive	 bacteria	
Staphylococcus	 aureus	 (MTCC	 96),	 Streptococcus	 pyogenes	
(MTCC	443)	 and	Gram	negative	Escherichia	 coli	 (MTCC‐442),	

Pseudomonas	 aeruginosa	 (MTCC	 441).	 The	 same	 compounds	
were	 screened	 for	 their	 antifungal	 activity	 [26]	 against	
Candida	 albicans	 (MTCC	 227),	 Aspergillus	 niger	 (MTCC	 282)	
and	 Aspergillus	 clavatus	 (MTCC	 1323).	 Antibacterial	 activity	
was	 measured	 as	 per	 National	 Committee	 for	 Clinical	
Laboratory	 Standards	 (NCCLS)	 protocol	 by	 Mueller‐Hinton	
Broth	 [27]	 (Becton‐Dickinson,	 USA)	 Standard	 strains	 were	
procured	 by	 The	 Institute	 of	 Microbial	 Technology,	
Chandigarh.	 Compounds	 were	 primarily	 screened	 for	 their	
antibacterial	 activity	 in	 six	 sets	 against	 E.	 coli,	 S.	 aureus,	 P.	
aeruginosa	and	S.	pyogenes	at	different	concentrations	of	1000,	
500	and	250	μg/mL	as	shown	in	Table	1.	
	
2.4.2.	Antibacterial	assay		
	

The	 drugs	 found	 to	 be	 active	 in	 primary	 screening	were	
similarly	diluted	to	obtain	200,	125,	100,	62.5,	50,	25,	and	12.5	
μg/mL	 concentrations	 for	 secondary	 screening	 to	 test	 in	 a	
second	 set	 of	 dilution	 against	 all	microorganisms.	 Inoculums	
size	 for	 test	 strain	 was	 adjusted	 to	 1×106	 CFU/mL	 (colony	
forming	unit	per	milliliter)	by	comparing	the	turbidity	(turbid	
metric	method).	Synthesized	compounds	were	diluted	to	2000	
μg/mL	 concentration,	 as	 a	 stock	 solution.	 A	 control	 tube	
containing	no	antibiotic	was	immediately	sub	cultured	(before	
inoculation)	 by	 spreading	 a	 loopful	 evenly	 over	 a	 quarter	 of	
plate	of	medium	suitable	for	the	growth	of	test	organisms.		

The	 tubes	 were	 then	 incubated	 at	 37.8	 °C	 for	 24	 h	 for	
bacteria.	 Ten	 μg/mL	 suspensions	were	 further	 inoculated	 on	
appropriate	media	 and	 growth	was	noted	 after	 24	 and	 48	h.	
The	lowest	concentration,	which	showed	no	growth	after	spot	
subculture	was	considered	as	MIC	 for	each	drug.	The	highest	
dilution	 (lowest	 concentration)	 preventing	 appearance	 of	
turbidity	was	taken	as	MIC	i.e.,	the	amount	of	growth	from	the	
control	tube	before	 incubation	(which	represents	 the	original	
inoculums)	 was	 compared.	 The	 test	 mixture	 should	 contain	
1×106	 CFU/mL	 organisms.	 2%	 DMSO	 and	 sterilized	 distilled	
water	was	used	as	negative	control,	while	ampicillin	antibiotic	
(1	 U	 strength)	 was	 used	 as	 positive	 control.	 A	 set	 of	 tubes	
containing	 only	 seeded	 broth	 and	 solvent	 controls	 were	
maintained	under	identical	conditions	so	as	to	make	sure	that	
the	 solvent	 had	 no	 influence	 on	 strain	 growth.	 The	 result	 of	
this	 was	 significantly	 affected	 by	 the	 size	 of	 inoculums.	 The	
standard	 drug	 used	 in	 the	 present	 study	 was	 ampicillin	 for	
evaluating	 antibacterial	 activity	which	 showed	100,	100,	 250	
and	100	μg/mL	MIC	against	E.	coli,	P.	aeruginosa,	S.	aureus,	and	
S.	pyogenes,	 respectively.	For	bacterial	growth,	 in	 the	present	
protocol,	 we	 have	 used	 Muller	 Hinton	 broth	 at	 37.8	 °C	 in	
aerobic	 condition	 for	 24‐48	 h.	 Results	 of	 antimicrobial	
evaluation	of	derivatives	5a‐n	are	shown	in	Table	1.	



Vaidya	et	al.	/	European	Journal	of	Chemistry	8	(2)	(2017)	149‐154	 153	
 

	
Table	2.	Antifungal	activity	(minimal	inhibition	concentration;	MIC)	of	compound	5a‐n.		
Compound	 Antifungal	activity	(MIC,	µg/mL)	

C.	albicans	 A.	niger A.	clavatus	
5a	 500	 1000	 	>1000	
5b	 250	 	500	 1000	
5c	 	1000	 500 500	
5d	 	250	 250 500	
5e	 	500	 250 >1000	
5f	 	>1000	 1000 >1000	
5g	 	1000	 500 500	
5h	 	500	 500 1000	
5i	 	500	 	>1000	 250	
5j	 	1000	 	250	 1000	
5k	 	500	 	250	 500	
5l	 	>1000	 500 500	
5m	 	1000	 	1000	 250	
5n	 	500	 >1000 1000	
Nystatin	 	100	 	100	 100	
Griseofulvin	 	500	 	100	 100	
	
	
2.4.3.	Antifungal	assay		
	

The	same	compounds	were	tested	for	antifungal	activity	as	
primary	screening	 in	six	sets	against	Candida	albicans,	Asper‐	
gillus	niger	 and	Aspergillus	clavatus	at	various	concentrations	
of	1000,	500,	200	and	100	μg/mL	as	shown	in	Table	2.	Results	
were	 recorded	 in	 the	 form	 of	 primary	 and	 secondary	
screening.	 Synthesized	 compounds	 were	 diluted	 to	 1000	
μg/mL	 concentration,	 as	 a	 stock	 solution.	 The	 synthesized	
compounds	 which	 were	 found	 to	 be	 active	 in	 this	 primary	
screening	 were	 further	 tested	 in	 a	 second	 set	 of	 dilution	
against	 all	 microorganisms.	 Griseofulvin	 was	 used	 as	 a	
standard	drug	for	antifungal	activity,	which	showed	500,	100	
and	 100	 μg/mL	 MIC	 against	 C.	 albicans,	 A.	 Niger	 and	 A.	
clavatus,	respectively.	2%	DMSO	and	sterilized	distilled	water	
was	used	as	negative	control,	while	Griseofulvin	(1	U	strength)	
was	used	as	positive	control.	For	fungal	growth,	in	the	present	
protocol,	we	have	used	Sabourauds	dextrose	broth	at	28.8	°C	
in	aerobic	condition	for	48	h.	Results	of	antifungal	evaluation	
of	derivatives	5a‐n	are	shown	in	Table	2.	
	
3.	Results	and	discussion		
	

We	 have	 synthesized	 a	 series	 of	N‐substituted	 2‐chloro‐
1H‐benzimidazole	 derivatives	 using	 a	 known	 procedure	 and	
obtained	products	with	good	yield	 (5a‐n).	1,3‐Dihydro‐benzi‐
midazol‐2‐one	 (2)	 was	 synthesized	 from	 the	 reaction	 of	 o‐
phenylenediamine	with	urea	in	dimethyl	form	amide	(Scheme	
1).	 Compound	 2	 was	 reacted	 with	 phosphoryl	 chloride	 in	
absent	 solvent	 to	 give	 2‐chloro‐1H‐benzimidazole	3	 (Scheme	
1).	 Compound	 3	 was	 combined	 with	 3‐(2‐chloroethyl)‐2‐
methyl‐4H‐pyrido[1,2‐a]pyrimidin‐4‐one	 (4a)	 in	 presence	 of	
potassium	carbonate	 in	water	to	yield	3‐[2‐(2‐chloro‐benzimi	
dazole‐1‐yl)‐ethyl]‐2‐methyl‐pyrido[1,	 2‐a]pyrimidine‐4‐one	
(5a)	 (Scheme	 2).	 Its	 IR	 spectra	 showed	 the	 appearance	 of	
carbonyl	 absorption	 band	 at	 1730	 cm‐1.	 Its	 mass	 spectrum	
showed	 a	 peak	 corresponding	 to	 its	 molecular	 ion	 at	 m/z	
339.1	 (M+1).	 Compound	 3	 was	 combined	 with	 3‐(2‐chloro	
ethyl)‐2‐methyl‐6,7,8,9‐tetrahydropyrido[1,2‐a]pyrimidin‐4‐
one	(4b)	in	presence	of	potassium	carbonate	in	water	to	yield	
3‐[2‐(2‐chloro‐benzimidazole‐1‐yl)‐ethyl]‐2‐methyl‐6,	 7,	 8,	 9‐
tetrahydro‐pyrido[1,2‐a]pyrimidine‐4‐one	 (5b)	 (Scheme	 2).	
Its	 IR	 spectra	 showed	 the	appearance	of	carbonyl	absorption	
band	at	1722	cm‐1.	 Its	mass	spectrum	showed	a	peak	corres‐
ponding	to	its	molecular	ion	at	m/z	343.2	(M+1).	Compound	3	
was	combined	with	4‐chloro‐2,2‐diphenylbutane	nitrile	(4c)	in	
presence	of	potassium	carbonate	in	water	to	yield	4‐(2‐chloro‐
benzimidazole‐1‐yl)‐2,2‐diphenyl‐butyro	 nitrile	 (5c).	 Its	 IR	
spectra	 showed	 the	 appearance	 of	 nitrile	 absorption	 band	 at	
2329	cm‐1.	Its	mass	spectrum	showed	a	peak	corresponding	to	
its	 molecular	 ion	 at	 m/z	 372.2	 (M+1).	 Compound	 3	 was	
combined	with	4‐chloro‐1‐(4‐fluorophenyl)	 butan‐1‐one	 (4d)	

in	 presence	 of	 potassium	 carbonate	 in	 water	 to	 yield	 4‐(2‐
chloro‐benzimidazole‐1‐yl)‐1‐(4‐fluoro‐phenyl)	 ‐butan‐1‐one	
(5d).	 Its	 IR	 spectra	 showed	 the	 appearance	 of	 carbonyl	
absorption	 band	 at	 1701	 cm‐1.	 Its	 mass	 spectrum	 showed	 a	
peak	 corresponding	 to	 its	molecular	 ion	at	m/z	317.2	 (M+1).	
Compound	3	was	combined	with	2‐(chloromethyl)‐4‐methoxy	
pyridin‐3‐ol	(4e)	in	presence	of	potassium	carbonate	in	water	
to	 yield	 2‐chloro‐1‐(3,4‐dimethoxy‐pyridine‐2‐ylmethyl)‐1H‐
benzimidazole	 (5e).	 Its	 IR	 spectra	 showed	 the	 appearance	of	
methoxy	 absorption	 weak	 band	 at	 2696	 cm‐1.	 Its	 mass	
spectrum	showed	a	peak	corresponding	to	its	molecular	ion	at	
m/z	304.2	(M+1).	

The	 reaction	 of	 compound	 3	 with	 phenylchloroformate	
(4f)	in	presence	of	potassium	carbonate	in	acetone	to	yield	2‐
chloro‐benzimidazole‐1‐carboxylic	 acid	 phenyl	 ester	 (5f)	
(Scheme	3).	Its	IR	spectra	showed	the	appearance	of	carbonyl	
absorption	 band	 at	 1752	 cm‐1.	 Its	 mass	 spectrum	 showed	 a	
peak	 corresponding	 to	 its	molecular	 ion	at	m/z	273.2	 (M+1).	
Compound	3	was	reacted	with	2‐methylbenzoyl	chloride	(4g)	
in	 presence	 of	 potassium	 carbonate	 in	 acetone	 to	 yield	 (2‐
chloro‐benzimidazole‐1‐yl)‐o‐tolyl‐methanone	 (5g).	 Its	 IR	
spectra	showed	the	appearance	of	carbonyl	absorption	band	at	
1722	cm‐1.	Its	mass	spectrum	showed	a	peak	corresponding	to	
its	 molecular	 ion	 at	 m/z	 271.2	 (M+1).	 Compound	 3	 was	
reacted	 with	 1‐bromo‐4‐(bromomethyl)benzene	 (4h)	 in	
presence	 of	 potassium	 carbonate	 in	 acetone	 to	 yield	 1‐(4‐
bromo‐benzyl)‐2‐Chloro‐1H‐benzimidazole	(5h).	Its	IR	spectra	
showed	the	appearance	of	C‐Br	absorption	band	at	1021	cm‐1.	
Its	 mass	 spectrum	 showed	 a	 peak	 corresponding	 to	 its	
molecular	 ion	 at	m/z	322.2	 (M+1).	 Compound	3	was	 reacted	
with	 4‐nitrobenzoyl	 chloride	 (4i)	 in	 presence	 of	 potassium	
carbonate	 in	 acetone	 to	 yield	 (2‐Chloro‐benzimidazole‐1‐yl)‐
(4‐nitro‐phenyl)‐methanone	 (5i).	 Its	 IR	 spectra	 showed	 the	
appearance	of	carbonyl	absorption	band	at	1722	cm‐1.	Its	mass	
spectrum	showed	a	peak	corresponding	to	its	molecular	ion	at	
m/z	302.2	 (M+1).	Compound	3	was	reacted	with	hexylchloro	
formate	(4j)	in	presence	of	potassium	carbonate	in	acetone	to	
yield	 2‐chloro‐benzimidazole‐1‐carboxylic	 acid	 hexyl	 ester	
(5j).	 Its	 IR	 spectra	 showed	 the	 appearance	 of	 carbonyl	
absorption	 band	 at	 1752	 cm‐1.	 Its	 mass	 spectrum	 showed	 a	
peak	corresponding	to	its	molecular	ion	at	m/z	281.2	(M+1).	

The	 reaction	 of	 compound	 3	 with	 N‐(2‐chloroethyl)‐N‐
isopropylpropan‐2‐amine	 (4k)	 in	 presence	 of	 potassium	
carbonate	 in	 DMF	 to	 yield	 [2‐(2‐chloro‐benzimidazole‐1‐yl)‐
ethyl]‐diisopropyl‐amine	 (5k)	 (Scheme	 4).	 Its	 IR	 spectra	
showed	the	appearance	of	C‐N	Stretch	alkyl	absorption	band	at	
1136	cm‐1.	Its	mass	spectrum	showed	a	peak	corresponding	to	
its	 molecular	 ion	 at	 m/z	 280.2	 (M+1).	 Compound	 3	 was	
reacted	 with	 4‐bromobutanenitrile	 (4l)	 in	 presence	 of	
potassium	 carbonate	 in	 DMF	 to	 yield	 4‐(2‐chloro‐benzimi‐
dazole‐1yl)‐butyronitrile	 (5l).	 Its	 IR	 spectra	 showed	 the	
appearance	 of	 nitrile	 absorption	 band	 at	 2329	 cm‐1.	 Its	mass	



154	 Vaidya	et	al.	/	European	Journal	of	Chemistry	8	(2)	(2017)	149‐154	
	
spectrum	showed	a	peak	corresponding	to	its	molecular	ion	at	
m/z	 220.2	 (M+1).	 Compound	 3	 was	 reacted	 with	 ethyl	 5‐
bromopentanoate	(4m)	in	presence	of	potassium	carbonate	in	
DMF	 to	 yield	 5‐(2‐chloro‐benzimidazole‐1yl)‐pentanoic	 acid	
ethyl	 ester	 (5m).	 Its	 IR	 spectra	 showed	 the	 appearance	 of	
carbonyl	 absorption	 band	 at	 1752	 cm‐1.	 Its	 mass	 spectrum	
showed	 a	 peak	 corresponding	 to	 its	 molecular	 ion	 at	 m/z	
281.2	 (M+1).	 Compound	 3	 was	 reacted	 with	 methyl	 2‐
chloroacetate	(4n)	in	presence	of	potassium	carbonate	in	DMF	
to	yield	(2‐chloro‐benzimidazole‐1yl)‐acetic	acid	methyl	ester	
(5n).	 Its	 IR	 spectra	 showed	 the	 appearance	 of	 carbonyl	
absorption	 band	 at	 1752	 cm‐1.	 Its	 mass	 spectrum	 showed	 a	
peak	corresponding	to	its	molecular	ion	at	m/z	225.2	(M+1).	

All	 the	 compounds	 prepared	 herein	 were	 screened	 for	
their	antimicrobial	activities.	The	structures	of	all	the	synthe‐
sized	 compounds	 were	 characterized	 by	 spectroscopic	 data,	
and	 allowed	 these	 molecules	 for	 study	 of	 antibacterial	 and	
antifungal	activities	(Table	1	and	2).	
	
4.	Conclusion	
	

Newly	 synthesized	 N‐substituted	 2‐chloro‐1H‐benzimi‐
dazole	derivatives	were	thoroughly	characterized	and	some	of	
them	 (5c,	5d,	5e,	5h,	5i	and	5j)	were	 found	 to	 possess	 high	
activity	 against	 Escherichia	 coli	 whereas	 compounds	 5a‐n	
were	 highly	 active	 against	 Staphylococcus	 aureus	 and	
compound	 5a	 and	 5d	 have	 also	 exerted	 very	 good	 activity	
against	Streptococcus	pyogenes	 employed	 for	 screening	when	
compared	to	 the	standard	ampicillin.	The	compounds	5b	and	
5d	 exhibited	 antifungal	 activity.	 However,	 antifungal	 activity	
of	the	other	synthesized	compounds	was	unsatisfactory.	
	
Acknowledgement	
	

The	 authors	 express	 their	 thanks	 to	 Sophisticated	
Analytical	Instrumentation	Facility	Chandigarh,	India	for	NMR	
and	 Mass	 spectra	 and	 Micro‐care	 laboratory,	 Surat,	 Gujarat,	
India	for	biological	activity.	
	
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