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European	Journal	of	Chemistry	3	(4)	(2012)	433‐436	

European	Journal	of	Chemistry	
ISSN	2153‐2249	(Print)	/	ISSN	2153‐2257	(Online)		2012	EURJCHEM	

DOI:10.5155/eurjchem.3.4.433‐436.673	

	
	

	

	

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

	 	 	

Application	of	SBA‐Pr‐SO3H	in	the	synthesis	of	benzoxazole	derivatives	

Ghodsi	Mohammadi	Ziarani	a,*,	Alireza	Badiei	b,	Monireh	Shakiba	Nahad	a	and	Malihe	Hassanzadeh	a	

a	Department	of	Chemistry,	Alzahra	University,	Vanak	Square,	Tehran,	199389‐1176,	Iran	
b	School	of	Chemistry,	College	of	Science,	University	of	Tehran,	Tehran,	14155‐6455,	Iran	

*Corresponding	author	at:	Department	of	Chemistry,	Alzahra	University,	Vanak	Square,	Tehran,	199389‐1176,	Iran.	
Tel.:	+98.21.88041344;	Fax:	+98.21.88041344.	E‐mail	address:	gmziarani@hotmail.com	(G.M.	Ziarani).	

	
	

	 	

	 	 	
ARTICLE	INFORMATION	 	 ABSTRACT
Received:	19	August	2012		
Received	in	revised	form:	23	September	2012	
Accepted:	23	September	2012	
Online:	31	December	2012	

KEYWORDS	

	 Propylsulfonic	 acid	 functionalized	 SBA‐15	 (SBA‐Pr‐SO3H)	 catalyzed	 the	 synthesis	 of	 2‐aryl
benzoxazoles	 from	 2‐aminophenol	 and	 benzoyl	 chloride	 derivatives	 in	 good	 yields	 under
reflux	condition	in	acetic	acid.	In	solvent	free	condition,	hydroxybenzanilide	derivatives	were
obtained.	

Benzoxazole	
Nanoreactor	
SBA‐Pr‐SO3H	
2‐Aminophenol	
Benzoyl	chlorides	
Hydroxy	benzanilide	

	
1.	Introduction	
	

Benzoxazoles	 and	 other	 heterocycles	 are	 found	 in	 very	
important	 classes	 of	 bioactive	 compounds	 such	 as	 antibiotic,	
antibacterial,	 antiinflammatory,	 antistress,	 antiulcer,	 and	
anticancer	 agents	 [1‐7].	 They	 have	 recently	 received	
considerable	 attention	 for	 their	 pharmaceutical	 activities.	
Flunoxaprofen,	 benoxaprofen	 and	 boxazomycine	 B	 are	 three	
example	of	this	class	of	compounds	(Figure	1).	
	

 
	

Figure	1.	Structure	of	some	benzoxazole	drugs.	
	

General	methods	for	the	synthesis	of	benzoxazoles	involve	
two	 approaches.	 The	 first	 approach	 is	 the	 copper‐catalyzed	
intramolecular	 ortho‐arylation	 of	 o‐haloanilides	 or	 the	
intermolecular	 annulations	 of	 o‐arylhalides	 with	 acylamides.	
The	 second	 approach	 is	 the	 condensation	 of	 2‐aminophenol	
with	 carboxylic	 acid	 derivatives	 in	 the	 presence	 of	 strong	

acid/high	 temperature	 conditions,	 or	 aldehydes	 with	
subsequent	oxidation	using	strong	oxidants	such	as	PhI(OAc)2,	
pyridiniumchlorochromate	(PCC)	[8].	In	this	reaction,	different	
catalysts	 such	 as	 ThClO4	 [9],	 2,3‐dichloro‐5,6‐dicyano‐l,4‐
benzoquinone	 (DDQ)	 and	 BaMnO4	 [10],	 In(OTf)3	 [11],	 I2	 [12],	
N,N'‐dibenzyl‐1,1'	 binaphthyl‐2,2'‐diamine‐copper(II)	 complex	
[13],	 p‐TsOH.H2O	 [14],	 4‐methoxy‐2,2,6,6‐tetra	 methyl‐1‐
piperidinyloxy(4‐methoxy‐TEMPO)	[10],	CuI/1,10‐phenanthro‐
line	 [15],	 Cu(OTf)3	 [16,17],	 FeCl3/2,2,6,6‐tetra‐methyl‐3,5	
heptanedione	 (TMHD)	 [18],	 Zn(OAc)2.2H2O	 [19],	 SiO2/FeCl3	
[20]	 and	 CuO	 nano	 particles	 [21]	 were	 also	 used.	 However	
many	of	 these	methodologies	have	difficulties	 in	recovery	and	
reusability	of	the	catalysts.		

Therefore,	 in	 this	 article	 we	 used	 SBA‐Pr‐SO3H	 as	
heterogeneous	 nanocatalyst	 in	 the	 one	 pot	 synthesis	 of	
benzoxazoles.	The	heterogeneous	catalysts	can	conveniently	be	
removed	 from	 the	 reaction	mixture,	making	 the	 experimental	
procedure	 simple	 and	 eco‐friendly	 [22].	 SBA‐Pr‐SO3H	 has	
mesoporous	silica	structure	with	pore	size	of	6	nm	which	can	
act	as	reactive	nano‐reactor	in	organic	synthesis	[23]. 
	
2.	Experimental	
	
2.1.	Instrumentation	

	
Electronic	 ionization	 GC‐MS	 spectra	 were	 recorded	 on	 a	

5973	 network	 mass	 selective	 detector,	 GC	 6890	 Agilent	
spectrometer.	 IR	 spectra	 were	 obtained	 with	 a	 FT‐IR	 Bruker	
500	scientific	spectrometer	as	KBr	pellets.	The	1H	NMR	was	run	
on	 a	 Bruker	 DPX,	 250	 MHz,	 in	 CDCl3.	 Chemical	 shifts	 are	
reported	in	δ	from	TMS.	Melting	points	were	measured	by	the	
capillary	 tube	method	with	 a	 9200‐Barnstead	 electro	 thermal	
apparatus.	 SEM	 analysis	 was	 performed	 on	 a	 Philips	 XL‐30	
field‐emission	scanning	electron	microscope	operated	at	16	kV	
while	TEM	was	carried	out	on	a	Tecnai	G2	F30	at	300	kV.	
	



434	 Ziarani	et	al.	/	European	Journal	of	Chemistry	3	(4)	(2012)	433‐436	
	
2.2.	Synthesis	
	
2.2.1	Preparation	of	catalyst	
	

The	 nanoporous	 compound	 SBA‐15	 was	 synthesized	 and	
functionalizaed	 according	 to	 our	 previous	 report	 and	 the	
modified	 SBA‐15‐Pr‐SO3H	was	 used	 as	 nanoporous	 solid	 acid	
catalyst	 in	 the	 following	 reaction	 [24‐26].	For	 the	preparation	
of	the	catalyst,	calcinated	SBA‐15	(2	g)	and	(3‐mercaptopropyl)	
trimethoxysilane	(10	mL)	in	dry	toluene	(20	mL)	were	refluxed	
for	 24	 h.	 The	 product	 was	 filtered	 and	 extracted	 for	 6	 h	 in	
CH2Cl2	 using	 a	 soxhlet	 apparatus,	 then	 dried	 under	 vacuum.	
After	 this,	 the	 solid	 product	 was	 oxidized	with	 H2O2	 (excess)	
and	one	drop	of	H2SO4	 in	methanol	 (20	mL)	 for	24	h	at	 room	
temperature.	 Then	 the	mixture	was	 filtered	 and	washed	with	
H2O,	and	acetone.	The	modified	SBA‐15‐Pr‐SO3H	was	dried	and	
used	as	nanoporous	solid	acid	catalyst	in	the	following	reaction.	
	
2.2.2.	General	procedure	for	the	synthesis	of	
hydroxybenzanilide	derivatives	(3)	

	
SBA‐Pr‐SO3H	(0.02	g)	was	placed	in	a	flask	and	activated	at	

100	 °C	under	vacuum	condition	 for	20	min.	Then	 the	 catalyst	
was	allowed	to	cool	to	room	temperature.	The	reaction	mixture	
of	 substituted	 benzoyl	 chloride	 (2a‐i)	 (3	 mmol)	 and	 2‐
aminophenol	(1)	(3	mmol,	0.33	g)	was	stirred	at	70	°C	(Scheme	
1,	Table	1).	The	solid	benzoyl	 chlorides	 (3‐nitro‐,	4‐nitro‐	and	
3,5‐dinitro‐benzoyl	 chloride)	 were	 kept	 in	 90	 °C.	 After	
completion	 of	 the	 reaction	 which	 was	 monitored	 by	 TLC	 (n‐
hexane:EtOAC,	 1:1),	 convenient	 crystallization	 solvent	 was	
added	 to	 the	 reaction	 mixture	 for	 recrystallization	 of	 crude	
product	and	catalyst	was	separated	by	simple	filtration.	
 
2.2.3.	General	procedure	for	the	synthesis	of	benzoxazoles	
(4)	
	

Substituted	 benzoyl	 chloride	 (2a‐i)	 (3	 mmol),	 2‐amino‐
phenol	(1)	(3	mmol,	0.33	g)	and	acetic	acid	(3	mL)	was	added	
to	activate	catalyst	(SBA‐Pr‐SO3H	(0.02	g))	(Scheme	2,	Table	2).	
The	mixture	was	stirred	 for	8	h	under	reflux	conditions.	After	
completion	 of	 the	 reaction	 which	 was	 monitored	 by	 TLC	 (n‐
hexane:EtOAC,	 3:1),	 the	 crude	 product	 was	 dissolved	 in	
acetone,	 and	 catalyst	 was	 removed	 by	 simple	 filtration	 of	
reaction	mixture.	The	gradual	evaporation	of	acetone,	gave	the	
pure	crystals	of	product. 

2‐Phenyl	benzoxazole	 (4a):	FT‐IR	 (KBr,	 cm‐1):	3043	(C‐H)	
(aromatic),	 1693	 (C=N)	 (imine),	 1579	 (C=C)	 (aromatic),	
1247	 (C‐O)	 (ether).	 1H	 NMR	 (250	 MHz,	 DMSO‐d6,	 δ,	 ppm):	
7.28‐7.37	(m,	2H,	Ar‐H),	7.47‐7.58	(m,	4H,	Ar‐H),	8.22‐8.25	(m,	
2H,	Ar‐H).	MS	(m/z,	(%)):	195	(100),	63	(53).	

2‐(2,4‐Dichlorophenyl)benzoxazole	 (4e):	 FT‐IR	 (KBr,	 cm‐1):	
3073	 (C‐H)	 (aromatic),	 1700	 (C=N)	 (imine),	 1647	 (C=C)	
(aromatic),	1282	(C‐O)	 (ether).	 1H	NMR	(250	MHz,	DMSO‐d6,	
δ,	ppm):	7.26	(m,	4H,	Ar‐H),	7.34	(s,	1H,	Ar‐H),	7.36	(d,	2H,	Ar‐
H)  . MS	(m/z,	(%)):	263	(100),	63	(60).	

2‐(3‐Nitrophenyl)benzoxazole	(4f):	FT‐IR	(KBr,	 cm‐1):	2979	
(C‐H)	 (aromatic),	 1611	 (C=C),	 1613	 (C=N)	 (imine),	 1527	
(NO2),	1360	(NO2).	1H	NMR	(250	MHz,	DMSO‐d6,	δ,	ppm):	9.1	
(d,	1H,	Ar‐H),	8.37‐8.61	(m,	3H,	Ar‐H),	7.26‐7.85	(m,	4H,	Ar‐H).	
MS	(m/z,	(%)):	240	(100),	194	(44),	139	(16),	63	(13).	

2‐(4‐Nitrophenyl)benzoxazole	(4g):	FT‐IR	(KBr,	cm‐1):	3052	
(C‐H)	 (aromatic),	 1608	 (C=N)	 (imine),	 1508	 (NO2),	 1246	
(C‐O)	(ether).	1H	NMR	(250	MHz,	DMSO‐d6,	δ,	ppm):	6.86‐7.06	
(m,	4H,	Ar‐H),	7.7	(d,	1H,	Ar‐H),	8.1	(d,	1H,	Ar‐H),	8.2	(d,	1H,	Ar‐
H),	 8.5	 (d,	 1H,	Ar‐H).	MS	 (m/z,	 (%)):	 240	 (100),	 195	 (45),	 63	
(14).	

2‐(3,5‐Dinitrophenyl)benzoxazole	 (4h):	 FT‐IR	 (KBr,	 cm‐1):	
3181	 (C‐H)	 (aromatic),	 1657	 (C=N)	 (imine),	 1535	 (NO2),	
1282	 (C‐O)	 (ether).	 1H	 NMR	 (250	 MHz,	 DMSO‐d6,	 δ,	 ppm):	

6.88‐7.15	(m,	4H,	Ar‐H),	7.73	(s,	1H,	Ar‐H),	9.15	(s,	1H,	Ar‐H),	
9.31	(s,	1H,	Ar‐H).	
 
3.	Results	and	discussion		

	
In	this	investigation	the	synthesis	of	2‐hydroxy‐benzanilide	

derivatives	 (3)	 (Scheme	 1)	 and	 2‐aryl	 benzoxazoles	 (4)	
(Scheme	 2)	 from	 the	 condensation	 of	 2‐aminophenol	 (1)	 and	
benzoyl	 chlorides	 (2a‐i)	 in	 the	 presence	 of	 SBA‐Pr‐SO3H	 as	
heterogeneous	and	reusable	nanocatalyst	were	studied.		
	

	
Scheme	1	

	
	
	

Scheme	2	
	

At	first,	for	optimization	of	reaction	conditions,	the	catalyst	
free	 reaction	 in	 acetic	 acid	 solvent	 was	 examined.	 In	 this	
condition,	 the	 reaction	 did	 not	 proceed	 satisfactory	 and	 the	
product	was	2‐hydroxy‐benzanilide	derivatives	 (3a‐i).	Then	 it	
was	 practiced	 in	 the	 presence	 of	 SBA‐Pr‐SO3H	 in	 solvent	 free	
condition	at	70	°C.	In	this	time,	only	the	acylation	product	(3a‐
i)	 was	 obtained	 too.	 The	 reaction	 was	 developed	 with	
derivatives	 of	 benzoyl	 chlorides,	 and	 the	 results	 were	
demonstrated	 in	 Table	 1.	 The	 demonstrated	 results	 were	
monitored	that	the	more	electron	withdrawing	groups	gave	the	
products	 in	shorter	 reaction	 time	and	higher	yield	 (Entry	5‐6,	
Table	1).		

When	 this	 reaction	 was	 refluxed,	 the	 product	 (3a‐i)	 was	
converted	 to	 benzoxazole	 derivatives	 in	 good	 to	 high	 yields.	
The	 reaction	 was	 developed	 with	 different	 benzoyl	
chloridesthat	 their	 results	 were	 listed	 in	 Table	 2.	 After	
completion	 of	 the	 reaction	 (monitored	 by	 TLC),	 the	 crude	
product	was	dissolved	in	hot	convenient	crystallization	solvent,	
the	insolubility	of	SBA‐Pr‐SO3H	in	different	organic	solvents	led	
to	very	easy	work	up	of	 catalyst	by	simple	 filtration	and	after	
cooling	 of	 the	 filtrate,	 the	 pure	 crystals	 of	 products	 were	
obtained.	
	
	
	
	



Ziarani	et	al.	/	European	Journal	of	Chemistry	3	(4)	(2012)	433‐436	 435	
 

	 	
Table	1.	Synthesis	of	hydroxyl‐benzanilide	derivatives	(3a‐i)	catalyzed	by	SBA‐Pr‐SO3H	in	solvent	free	conditions.	
Entry	 Product	 X	 Temp.	(°C)	 Time Yield	(%) M.p.	(°C) M.p.	(Lit.) Crystallization	solvent
1	 3a	 2‐Cl	 70	 1	h 71 190‐191 192‐193	[27]	 EtOH	
2	 3b	 3‐Cl	 70	 1.30	h	 52	 173‐174	 171‐172	[28]		 Acetone	
3	 3c	 2,4‐di‐Cl	 70	 1.30	h	 46	 173‐175	 173‐174	[29]		 Acetone	
4	 3d	 3‐NO2	 90	 2	h 93	 205‐207	 206	[30]	 EtOH	
5	 3e	 4‐NO2	 90	 50	min	 72	 209‐210	 206‐207	[28]	 Acetone	
6	 3f	 3,5‐di‐NO2	 90	 40	min 98 259‐260 ‐ EtOH	
	
Table	2.	Synthesis	of	benzoxazole	derivatives	(4a‐i)	catalyzed	by	SBA‐Pr‐SO3H. 
Entry	 Product	 R	 Time	(h) Yield	(%) M.p.	(°C) M.p.	(Lit.)	
1	 4a	 H	 8	 91 102‐103	 102‐104	[31]	
2	 4b	 2‐Cl	 8 83 72‐74 70‐72	[11] 
3	 4c	 3‐Cl	 8	 85	 123‐125 124‐125	[32]	
4	 4d	 4‐Cl	 8	 78	 140‐142	 140‐142	[13] 
5	 4e	 2,4‐di‐Cl	 8	 82	 119‐120 118‐119	[13] 
6	 4f	 3‐NO2	 8 81 205‐207 207	[33] 
7	 4g	 4‐NO2	 8 75 258‐260 257‐263	[34]	
8	 4h	 3,5‐di‐NO2	 8 87 205‐207 205‐207	[35]	
9	 4i	 2‐Me	 8 85 66‐70 68‐69	[10]	
	

	
	
A	 plausible	 mechanism	 was	 shown	 in	 Scheme	 3.	 At	 first,	

SBA‐Pr‐SO3H	 as	 a	 Bronsted	 nano‐catalyst	 protonates	 the	
carbonyl	 group	 of	 benzoyl	 chloride.	 Then,	 the	 reaction	 was	
followed	 by	 nucleophilic	 attack	 of	 amino	 group	 of	 2‐
aminophenol	 to	 carbonyl	 group	 of	 benzoyl	 chloride.	 The	
nucleophilic	 attack	of	OH	 to	 carbonyl	group	of	compound	 (3),	
gave	 the	 cyclization	 product	 (5)	 which	 converted	 to	
benzoxazole	derivatives	by	dehydration.	
	

	
Scheme	3	

	
The	 acid	 catalyst	 can	 be	 reactivated	 by	 simple	 washing	

subsequently	with	diluted	acid	solution,	water	and	acetone,	and	
then	 reused	 without	 noticeable	 loss	 of	 reactivity.	 The	 new	
products	were	characterized	by	IR	and	NMR	spectroscopy	data.	
Melting	 points	 are	 compared	 with	 reported	 values	 in	 the	
literature	as	shown	in	Table	2. 

For	 the	 preparation	 of	 the	 catalyst,	 at	 first,	 the	 surface	 of	
SBA‐15	 was	 functionalized	 and	 grafted	 with	 (3‐
mercaptopropyl)	 trimethoxysilane	 (MPTS),	 the	 thiol	 groups	
have	 been	 incorporated	 to	 surface	 of	 SBA‐15	 under	 reflux	
condition	 in	dry	 toluene.	Then	 the	 thiol	groups	were	oxidized	
into	 sulfonic	 acid	 groups	 by	 hydrogen	 peroxide	 (Figure	 2)	
[36,37].	
	

SH

SHSH

SO3H

SO3HSO3H

	
Figure	2.	Preparation	of	SBA‐Pr‐SO3H.	

	
Nanopore	 size	 about	 6	 nm	 of	 SBA‐Pr‐SO3H	 could	 act	 as	

nano‐reactor	 and	 catalyzed	 synthesis	 of	 benzoxazole	
derivatives.	A	schematic	illustration	for	this	activity	was	shown	
in	Figure	3.	

	
	

Figure	3.	SBA‐Pr‐SO3H	acts	as	a	nano‐reactor.	
	

The	 SEM	 and	 TEM	 images	 of	 SBA‐Pr‐SO3H	 illustrated	 in	
Figure	 4.	 Figure	 4a	 shows	 SEM	 image	 of	 SBA‐Pr‐SO3H	 that	
indicates	uniform	particles	about	1	µm.	The	TEM	image	(Figure	
4b)	 represents	 the	 parallel	 channels	 that	 were	 not	 collapsed	
during	two	step	reactions.	In	general,	organic	functionalization	
did	not	alter	the	long‐range	mesoporous	arrangement	[25,26].	
	

	(a)	
	

	(b)	
	

Figure	4.	SEM	(a)	and	TEM	(b)	image	of	SBA‐Pr‐SO3H.
	
	



436	 Ziarani	et	al.	/	European	Journal	of	Chemistry	3	(4)	(2012)	433‐436	
	
4.	Conclusion	

	
In	summary,	we	have	described	the	use	of	nano	acid	solid	

catalyst	 of	 SBA‐Pr‐SO3H	 in	 the	 synthesis	 of	 benzoxazole	
derivatives	 and	 2‐hydroxy‐benzanilide.	 Furthermore,	 opera‐
tional	 and	 experimental	 simplicity,	 readily	 availability,	 easy	
work‐up	procedure	and	good	yields	make	it,	a	facile	method	for	
the	synthesis	of	these	compounds.	
	
Acknowledgements	
	

We	 gratefully	 acknowledge	 for	 financial	 support	 from	 the	
Research	 Council	 of	 Alzahra	 University	 and	 University	 of	
Tehran. 
	
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