untitled


European	Journal	of	Chemistry	5	(3)	(2014)	536‐540	

	

European	Journal	of	Chemistry	
ISSN	2153‐2249	(Print)	/	ISSN	2153‐2257	(Online)		2014	Eurjchem	Publishing	‐	Printed	in	the	USA	

http://dx.doi.org/10.5155/eurjchem.5.3.536‐540.1028	

	
	

	

	

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

	 	 	

Glycerol‐based	SO3H‐Carbon	Catalyst:	A	green	recyclable	catalyst	for			
the	chemoselective	synthesis	of	pentaerythritol	diacetals	

Chandrakala	Ummadisetti,	Badari	Narayana	Prasad	Rachapudi	and	
Lakshmi	Anu	Prabhavathi	Devi	Bethala	*	

Centre	for	Lipid	Research,	CSIR‐Indian	Institute	of	Chemical	Technology,	Hyderabad,	500007,	India	

*Corresponding	author	at:	Centre	for	Lipid	Research,	CSIR‐Indian	Institute	of	Chemical	Technology,	Hyderabad,	500007,	India.		
Tel.:	+91.40.27191845.	Fax:	+91.40.27193370.	E‐mail	address:	prabhavathi@iict.res.in	(L.A.P.D.	Bethala).	

	
	

	 	

	 	 	
COMMUNICATION	INFORMATION	 	 ABSTRACT

	
DOI:	10.5155/eurjchem.5.3.536‐540.1028	

Received:	03	February	2014	
Received	in	revised	form:	20	March	2014	
Accepted:	20	March	2014	
Online:	30	September	2014	

KEYWORDS	

	 Glycerol‐based	 SO3H‐functionalized	 carbon	 catalyst	 was	 demonstrated	 as	 an	 efficient	 and
recyclable	 green	 catalyst	 for	 the	 chemoselective	 synthesis	 of	 pentaerythritol	 diacetals	 with
aromatic	 aldehydes	 in	 the	 presence	 of	 ketones	 in	 excellent	 yields	 in	 toluene	 at	 80	 C.	 In
addition,	the	catalyst	also	has	the	capability	for	the	deprotection	of	pentaerythritol	diacetals
in	 methanol	 at	 reflux	 temperature.	 The	 recovered	 catalyst	 without	 any	 pre‐treatment	 was
reused	 for	 5	 cycles	without	 any	 deactivation	 and	 leaching	 into	 the	 reaction	medium	 under
optimum	conditions.	

Reusability	
Chemoselectivity	
Aromatic	aldehydes		
Pentaerythritol	diacetals		
Glycerol‐based	SO3H‐carbon	catalyst	
Protection	and	deprotection	of	diacetals	

	
1.	Introduction	
	

The	 protection	 of	 aldehydes	 and	 ketones	 as	 acetals	 or	
ketals	plays	an	 important	 role	 for	 the	preparation	of	different	
molecules	 in	 the	 presence	 of	 variety	 of	 different	 functional	
groups	 in	 drug	 design	 chemistry,	 medicinal	 chemistry	 and	 in	
multi‐step	organic	synthesis	[1,2].	Acetals	as	a	functional	group,	
which	is	stable	under	neutral	and	basic	conditions	are	not	only	
the	most	widely	used	protective	groups	but	also	efficient	chiral	
auxiliary	groups	 for	enantioselective	synthesis	 [3].	Acetals	are	
used	 in	 the	 pharmaceutical	 and	 fragrance	 industries	 [4]	 as	
intermediates	 or	 as	 end	products.	 Pentaerythritol	 diacetals	 in	
general	 are	 used	 as	 plasticisers	 and	 vulcanisers	 of	 several	
polymeric	 materials,	 as	 raw	 materials	 for	 the	 production	 of	
valuable	resins,	as	physiologically	active	substances	[5],	and	as	
defoamers	 in	washing	solutions	containing	anionic	surfactants	
[6,7].		

Several	 publications	 have	 described	 the	 preparation	 of	
pentaerythritol	(PE)	diacetals	by	using	different	acidic	catalyst	
like	Montmorillonite	clay	[6,7],	ZrO2/S2O8‐2	solid	superacid	[8],	
heteropoly	 acid	 H3PW12O40	 [9],	 InCl3·4H2O	 [10],	 expansive	
graphite	 [11],	 anhydrous	 FeSO4	 [12],	 NH2SO3H	 [13],	 SO3H‐
functionalized	 ionic	 liquids	 [14],	 Al‐MCM‐41	 [15],	 cellulose	
sulfuric	acid	[16],	and	P2O5/SiO2	[17].	However,	many	of	these	
methods	suffer	 from	several	drawbacks	 in	 terms	of	 corrosion,	

long	 reaction	 times,	 tedious	 workup,	 unsatisfactory	 yields,	
large	 excess	 of	 aldehyde,	 non	 reusability	 and	 environmental	
polluting	 of	 catalysts	 and	 no	 selectivity	 towards	 particular	
carbonyl	compound	(aldehyde/ketone).	Hence,	there	is	a	lot	of	
scope	 and	 need	 to	 develop	 a	 mild	 and	 environmentally	 eco‐
friendly,	 most	 suitable	 catalyst	 for	 the	 preparation	 of	 penta‐
erythritol	diacetals	under	mild	conditions	by	the	protection	of	
carbonyl	groups	in	multistep	organic	synthesis	with	selectivity	
towards	particular	carbonyl	compounds.	

In	 recent	 years,	 carbon‐based	 solid	 acid	 catalysts	 have	
gained	 significant	 attraction	 over	 homogeneous	 catalysts	 as	
they	are	highly	efficient,	sustainable,	and	eco‐friendly	[18‐21].	
We	have	reported	a	sustainable	method	for	the	preparation	of		
‐SO3H	 functionalized	 carbon‐based	 solid	 acid	 catalyst	 having	
1.6	mmol/g	 acid	 density	with	 surface	 area	 of	 0.21	m2/g	 from	
bioglycerol	 (biodiesel	 by‐product)	 and	 also	 from	 the	 glycerol‐
pitch	 (waste	 from	 fat	 splitting	 industry)	 by	 the	 in	 situ	partial	
carbonization	 in	 a	 single	 step	 [22,23].	 This	 catalyst	 exhibited	
excellent	catalytic	properties	by	demonstrating	its	effectiveness	
for	 various	 transformations	 [24‐30]	 due	 to	 its	 high	 thermal	
stability,	 reusability	 and	 strong	 acid	 sites	 of	 sulfonic	 acid	
functional	groups.		

In	continuation	of	our	ongoing	research	on	the	applications	
of	 the	 glycerol‐based	 catalyst,	we	 herein	 report	 a	 simple	 and	
highly	efficient	chemoselective	method	for	the	preparation	of	



Ummadisetti	et	al.	/	European	Journal	of	Chemistry	5	(3)	(2014)	536‐540	 537	
 

	 	

	

Scheme	1
	
	

pentaerythritol	 diacetals	 by	 condensation	 of	 pentaerythritol	
with	 aromatic	 aldehydes	 (1:2	 mmol)	 in	 toluene	 at	 80	 C	 in	
quantitative	 yields.	 Deprotection	 of	 the	 prepared	 penta‐
erythritol	diacetals	was	also	obtained	by	changing	 the	solvent	
medium	 to	 MeOH	 in	 the	 presence	 of	 the	 same	 catalyst	 at	
moderate	temperature	(Scheme	1).		

	
2.	Experimental	
	
2.1.	Materials	and	methods	
	

All	 chemicals	 were	 purchased	 from	 Sd.	 Fine	 or	 Merck	
Chemical	 companies	 and	 were	 used	 without	 further	
purification.	 All	 other	 reagents	 and	 solvents	 used	 were	 of	
analytical	 grade.	 All	 yields	 refer	 to	 isolated	 products	 after	
purification.	 Products	 were	 characterized	 by	 comparison	 by	
physical	 data	 with	 authentic	 samples	 and	 spectroscopic	 data	
(IR,	 NMR	 and	 EI‐MS).	 IR	 Spectra	 were	 recorded	 on	 a	 Perkin	
Elmer	(Model:	Spectrum	BX)	FT‐IR	spectrophotometer	by	KBr	
pellet	 method.	 The	 NMR	 spectra	 were	 recorded	 on	 a	 Varian	
300,	Palo	Alto,	USA	spectrometer	at	300	MHz	in	CDCl3	at	25	°C;	
using	 Me4Si	 (TMS)	 as	 an	 internal	 standard.	 EI‐Mass	 spectra	
were	 recorded	on	 a	Waters	 (Micromass‐Quatromicro	 electron	
spray	 ionization)	 LC‐MS	 system.	 Melting	 points	 were	
uncorrected.	
	
2.2.	Glycerol‐based	sulfonic	acid	functionalized	carbon	
catalyst	[22,30]	
	

A	 mixture	 of	 glycerol	 (10	 g)	 and	 concentrated	 sulphuric	
acid	(30	g)	was	heated	from	ambient	temperature	to	220	°C	for	
20	 min,	 to	 facilitate	 in	 situ	 partial	 carbonization	 and	
sulfonation.	The	reaction	mixture	was	allowed	to	remain	at	that	
temperature	for	about	20	min	(until	foaming	ceased)	to	obtain	
solid	carbon	material	and	was	cooled	 to	ambient	 temperature	
and	 washed	 with	 hot	 water	 until	 the	 wash	 water	 becomes	
neutral	to	pH.	The	partially	crystalline	product	was	filtered	and	
dried	in	an	oven	at	120	°C	for	2	h	until	it	was	moisture	free	to	
obtain	the	carbon	acid	catalyst	in	~56%	yield	(5.40	g).	

	
2.3.	General	procedure	for	the	synthesis	of	penterythritol	
diacetal	derivatives	
	

A	 mixture	 of	 aldehyde	 (2	 eq),	 2,2‐bis	 (hydroxymethyl)	
propane‐1,3‐diol	(PE,	1	eq.)	and	carbon	acid	catalyst	(5	wt%	of	
PE)	in	toluene	(10	mL)	was	stirred	at	80	°C.	The	progress	of	the	
reaction	was	monitored	by	TLC	(hexane:ethyl	acetate,	7:3,	v:v).	
After	 completion	of	 the	 reaction,	 the	 catalyst	was	 filtered	and	
crude	product	was	 isolated	 by	distillation	 of	 toluene	 and	was	
purified	by	recrystallization	with	EtOH.	The	recovered	catalyst	
was	washed	with	MeOH	 and	 acetone	 and	 dried	 for	 reuse.	 All	
the	products	were	characterized	by	FT‐IR,	1H	NMR,	EI‐MS	and	
comparison	 of	 their	 melting	 point	 with	 literature	 values	
[6,9,11,14].		

3,9‐Diphenyl‐2,4,8,10‐tetraoxaspiro[5.5]undecane	 (Table	 1,	
entry	 1):	 FT‐IR	 (KBr,	 ν,	 cm‐1):	 2940,	 2853,	 1451,	 1384,	 1334,	
1203,	 1160,	 1075,	 1016,	 970,	 928,	 745.	 1H	 NMR	 (300	 MHz,	
CDCl3,	δ,	ppm):	3.66	(d,	2H,	J	=	11.5	Hz,	OCH2‐Hax),	3.82‐3.87	(m,	
4H,	OCH2‐	Hax,	Heq),	4.87	(d,	2H,	J	=	11.5	Hz,	OCH2‐Heq),	5.46	(s,	
2H,	ArCH),	7.34‐7.40	(m,	6H,	ArH),	7.47‐7.50	(m,	4H,	ArH).	EI‐
MS:	m/z	312.	

3,9‐Bis(2‐methoxyphenyl)‐2,4,8,10‐tetraoxaspiro[5.5]unde	
cane	(Table	1,	entry	2):	FT‐IR	(KBr,	ν,	cm‐1):	2948,	2851,	1610,	
1514,	 1452,	1382,	1248,	1155,	1035,	817.	 1H	NMR	 (300	MHz,	
CDCl3,	δ,	ppm):	3.63	(d,	2H,	J	=	11.5	Hz,	OCH2‐Hax),	3.80‐3.85	(m,	
4H,	 OCH2‐	 Heq),	 3.81	 (s,	 6H,	 OCH3),	 4.84	 (d,	 2H,	 J	 =	 11.5	 Hz,	
OCH2‐Hax),	5.42	(s,	2H,	ArCH),	6.80‐6.96	(m,	4H,	ArH),	7.40‐7.60	
(m,	4H,	ArH).	MS	(EI,	m/z):	372.	

3,9‐Bis(4‐methoxyphenyl)‐2,4,8,10‐tetraoxaspiro[5.5]unde	
cane	(Table	1,	entry	3):	FT‐IR	(KBr,	v,	cm‐1):	2959,	2850,	1611,	
1514,	1459,	1393,	1383,	1312,	1301,	1253,	1157,	1064,	1033,	
823.	1H	NMR	(300	MHz,	CDCl3,	δ,	ppm):	3.63	(d,	2H,J	=	11.5	Hz,	
OCH2‐Hax),	3.80‐3.85	(m,	4H,	OCH2‐Heq),	3.81	(s,	6H,	OCH3),	4.84	
(d,	2H,	J	=	11.5	Hz,	OCH2‐Hax),	5.42	(s,	2H,	ArCH),	6.90	(d,	4H,	J	=	
8.5	Hz,	ArH),	7.41	(d,	4H,J	=	8.5	Hz,	ArH).	MS	(EI,	m/z):	372.	

4,4'‐(2,4,8,10‐Tetraoxaspiro[5.5]undecane‐3,9‐diyl)bis(2‐
methoxyphenol)	 (Table	 1,	 entry	4):	 FT‐IR	 (KBr,	ν,	 cm‐1):	 2950,	
2851,	1603,	1521,	1455,	1427,	1383,	1273,	1176,	1163,	1119,	
1072,	1027,	963,	863,	816.	1H	NMR	(300	MHz,	CDCl3,	δ,	ppm):	
3.64	(d,	2H,	J	=	11.5	Hz,	OCH2‐Hax),	3.80‐3.85	(m,	4H,	OCH2‐Heq),	
3.91	(s,	6H,	OCH3),	4.86	(d,	2H,	 J	=	11.5	Hz,	OCH2‐Hax),	5.40	(s,	
2H,	ArCH),	5.70	(s,	2H,	OH),	6.89‐6.98	(m,	4H,	ArH),	7.03	(s,	2H,	
ArH).	MS	(EI,	m/z):	404.	

3,9‐Bis(2‐chlorophenyl)‐2,4,8,10‐tetraoxaspiro[5.5]undecane	
(Table	1,	entry	5):	FT‐IR	(KBr,	ν,	cm‐1):	2989,	2900,	2848,	1599,	
1576,	 1442,	 1397,	 1286,	 1243,	 1202,	 1160,	 1073,	 1049,	 946,	
754.	1H	NMR	(300	MHz,	CDCl3,	δ,	ppm):	3.7	(d,	2H,	J	=	11.5	Hz,	
OCH2‐Hax),	3.81‐3.88	(m,	4H,	OCH2‐Heq),	4.92	(d,	2H,	J	=	11.5	Hz,	
OCH2‐Hax),	5.79	 (s,	2H,	ArCH),	7.28‐7.71	 (m,	8H,	ArH).	MS	 (EI,	
m/z):	380.	

3,9‐Bis(4‐chlorophenyl)‐2,4,8,10‐tetraoxaspiro[5.5]undecane	
(Table	1,	entry	6):	FT‐IR	(KBr,	ν,	cm‐1):	2952,	2864,	1492,	1382,	
1334,	 1204,	 1163,	 1075,	 1014,	 819,	 715,	 683.	 1H	 NMR	 (300	
MHz,	CDCl3,	δ,	ppm):	3.64	(d,	2H,	 J	=	11.5	Hz,	OCH2‐Hax),	3.80‐
3.85	(m,	4H,	OCH2‐Heq),	4.81	(d,	2H,	J	=	11.5	Hz,	OCH2‐Hax),	5.43	
(s,	2H,	ArCH),	7.34‐7.43	(dd,	8H,	J	=	8.5	Hz,	ArH).	MS	(EI,	m/z):	
380.	

3,9‐Bis(2,6‐dichlorophenyl)‐2,4,8,10‐tetraoxaspiro[5.5]unde	
cane	(Table	1,	entry	7):	FT‐IR	(KBr,	ν,	cm‐1):	2908,	2832,	2849,	
1565,	1584,	1438,	1402,	1272,	1247,	1203,	1163,	1099,	1067,	
769,	 728.	 1H	NMR	 (300	MHz,	 CDCl3,	 δ,	 ppm):	 3.63	 (d,	 2H,	 J	=	
11.5	Hz,	OCH2‐Hax),	3.80‐3.85	(m,	4H,	OCH2‐	Heq),	4.83	(d,	2H,	J	=	
11.5	Hz,	OCH2‐Hax),	5.42	(s,	2H,	ArCH),	6.90‐7.50	(m,	6H,	ArH).	
MS	(EI,	m/z):	449.	

4,4'‐(2,4,8,10‐Tetraoxaspiro[5.5]undecane‐3,9‐diyl)diphenol	
(Table	1,	entry	8):	FT‐IR	(KBr,	ν,	cm‐1):	3395,	2948,	2851,	1610,	
1515,	1452,	1382,	1311,	1248,	1155,	1035,	817.	1H	NMR	(300		

	
	



538	 Ummadisetti	et	al.	/	European	Journal	of	Chemistry	5	(3)	(2014)	536‐540	
	

	
Table	1.	Preparation	of	pentaerythritol	diacetals	with	aromatic	aldehydes	employing	SO3H‐carbon	catalyst	at	80	°C	
Entry	 Aldehyde	 Product	a	 Time	

(h)
Yield	
(%)	b		

M.p.		
[Lit.	M.	p.]	(°C)

1	

	

3.0	 98	
156‐157	
[158‐159,		14]	

2	

	

6.0	 95	 154‐155		
[155,		9]	

3	

	

4.0	 96	
180‐182	
[182‐183,	9]	

4	

	

4.0	 95	
170‐172	
[170‐171,		6]	

5	

	

5.0	 94	
140‐142	
[141‐142,		14]	

6	

	 	

1.5	 95	
198‐200	
[198‐199,		9]	

7	

	

4.5	 94	 176‐179	

8	

	 	

4.5	 95	 169‐170	
[170‐171,		11]	

9	

	
O

O

O

O
O2N

NO2

2.5	 94	 162‐164	
[164‐165,		14]	

10	

	

2.0	 96	 185‐186	
[185,		9,14]	

11	

	

8.5	 95	 189‐190	
[188‐189,	6]	

a	All	the	compounds	were	characterized	by	their	melting	points,	IR	and	1H	NMR	spectra	by	comparing	their	data	reported	in	the	literature.		
b	Isolated	yield.	

	
	

MHz,	CDCl3,	δ,	ppm):	3.61	(d,	2H,	 J	=	11.5	Hz,	OCH2‐Hax),	3.81‐
3.85	(m,	4H,	OCH2‐Heq),	4.83	(d,	2H,	J	=	11.5	Hz,	OCH2‐Hax),	5.42	
(s,	2H,	ArCH),	6.90‐7.60	(m,	8H,	ArH).	MS	(EI,	m/z):	344.	

3,9‐Bis(2‐nitrophenyl)‐2,4,8,10‐tetraoxaspiro[5.5]undecane	
(Table	1,	entry	9):	FT‐IR	(KBr,	ν,	cm‐1):	2955,	2887,	1580,	1456,	
1396,	 1256,	 1208,	 1166,	 1080,	 1016,	 837,	 783.	 1H	NMR	 (300	
MHz,	CDCl3,	δ,	ppm):	3.62	(d,	2H,	 J	=	11.5	Hz,	OCH2‐Hax),	3.79‐
3.84	(m,	4H,	OCH2‐Heq),	4.80	(d,	2H,	J	=	11.5	Hz,	OCH2‐Hax),	5.41	
(s,	2H,	ArCH),	7.10‐7.80	(m,	8H,	ArH).	MS	(EI,	m/z):	402.	

3,9‐Bis(3‐nitrophenyl)‐2,4,8,10‐tetraoxaspiro[5.5]undecane	
(Table	 1,	 entry	 10):	 FT‐IR	 (KBr,	 ν,	 cm‐1):	 2955,	 2887,	 1609,	
1581,	 1456,	 1396,	 1208,	 1080,	 1016,	 913,	 783,	 670.	 1H	 NMR	
(300	MHz,	CDCl3,	δ,	ppm):	3.62	(d,	2H,	 J	=	11.5	Hz,	OCH2‐Hax),	
3.79‐3.84	(m,	4H,	OCH2‐	Heq),	4.80	(d,	2H,	J	=	11.5	Hz,	OCH2‐Hax),	
5.41	(s,	2H,	ArCH),	7.03‐7.80	(m,	8H,	ArH).	MS	(EI,	m/z):	402.	

3,9‐Distyryl‐2,4,8,10‐tetraoxaspiro[5.5]undecane	 (Table	 1,	
entry	11):	FT‐IR	(KBr,	ν,	 cm‐1):	3013,	2936,	2961,	2860,	1614,	
1587,	1518,	1460,	1382,	1251,	1172,	1039,	991,	970,	831,	732,	
690.	1H	NMR	(300	MHz,	CDCl3,	δ,	ppm):	3.63	(d,	2H,	J	=	11.5	Hz,	
OCH2‐Hax),	3.80‐3.84	(m,	4H,	OCH2‐Heq),	4.82	(d,	2H,	J	=	11.5	Hz,	

OCH2‐Hax),	 5.48	 (s,	 2H,	 ArCH),	 6.34	 (m,	 2H,	 C‐CH=),	 7.30‐7.80	
(m,	12H,	ArH	and	ArCH=).	MS	(EI,	m/z):	364.	

7,11,18,21‐Tetraoxatrispiro[5.2.2.5.2.2]heneicosane	(Table	2,	
entry	 4):	 FT‐IR	 (KBr,	 ν,	 cm‐1):	 2911,	 2852,	 1452,	 1380,	 1332,	
1247,	 1201,	 1161,	 1066,	 1012,	 931,	 740,	 718.	 1H	 NMR	 (300	
MHz,	CDCl3,	δ,	ppm):	1.39‐1.75	(m,	20H,	CH2),	3.20‐3.73	(s,	8H,	
OCH2).	MS	(EI,	m/z):	296.	
	
3.	Results	and	discussion		
	

Acetalization	 of	 pentaerythritol	 (1	 mmol)	 with	 benzal‐
dehyde	 (2	mmol)	was	 selected	 as	model	 reaction	 to	 optimize	
the	 reaction	 parameters	 namely,	 reaction	 tempera‐tures	 (60,	
80,	90	and	100	C)	and	the	amount	of	catalyst	(1,	2,	3,	4	and	5	
wt%	of	PE).	The	best	 result	was	obtained	by	carrying	out	 the	
reaction	 with	 2:1	 molar	 ratios	 of	 benzaldehyde	 and	
pentaerythritol,	 in	 the	 presence	 of	 5	 wt%	 g	 of	 SO3H‐carbon	
catalyst	 in	 toluene	 at	 80	 C	 for	 3	 h.	 After	 the	 reaction,	 the	
mixture	was	cooled	and	the	catalyst	was	separated	by	filtration.		

	



Ummadisetti	et	al.	/	European	Journal	of	Chemistry	5	(3)	(2014)	536‐540	 539	
 

	
Table	2.	Chemoselective	diacetalization	of	pentaerythritol	with	aromatic	aldehydes	in	presence	of	aliphatic	aldehydes	and	ketones	using	SO3H‐carbon	catalyst	at	
80	°C.	
Entry	 R	=	Carbonyl	(Aldehyde/Ketone)	 Product	a	 M.p.		

[Lit.	M.p.]	(°C)	
1	 CH3	CHO	 No	reaction ‐	
2	 C7H15	CHO	 No	reaction ‐	
3	 C9H19	CHO	 No	reaction	 ‐	

4	
	 	(	98%)	b		

115‐116			
[114‐115,	14]	

5	 C2H5	CO	CH3	 No	reaction ‐	
6	 C6H5	CO	CH3	 No	reaction ‐	
7	 C6H5	CO	C6H5	 No	reaction	 ‐	
8	 CH3	CO	C6H4(OCH3)	 No	reaction ‐	
9	 (CH3)2CH	CO	CH3	 No	reaction	 ‐	
10	 (CH3)2CH	CO	CH(CH3)2	 No	reaction	 ‐	

11	

	
	

	

156‐157	
[158‐159,	14]	

12	

	 	

156‐157	
[158‐159,	14]	

13	 CH3COC6H5

CHO

	 	
	

156‐157	
[158‐159,	14]	

a	Compound	was	characterized	by	their	melting	point,	IR	and	1H	NMR	spectra	by	comparing	their	data	reported	in	the	literature.		
b	Isolated	yield.	
	
	

The	 crude	 product	 obtained	was	 further	 recrystallized	 in	
hot	EtOH	 to	obtain	pure	product	 in	98%	yield	 (Table	1,	 entry	
1).	

Using	these	optimized	reaction	conditions,	the	scope	of	the	
SO3H‐carbon	 catalyzed	methodology	was	 extended	 for	 a	wide	
variety	 of	 substituted	 aromatic	 aldehydes	 (Table	1).	Aromatic	
aldehydes	 with	 stronger	 electron‐donor	 groups	 such	 as	 MeO	
and	 OH	 (Table	 1,	 entries	 2,	 3,	 4	 and	 8)	 showed	 to	 be	 less	
reactive	 and	 required	 longer	 reaction	 period	 to	 obtain	 the	
product	 in	 95‐96%	 yield.	 Electron‐withdrawing	 substituents	
such	as	mono	NO2	and	Cl	derivatives	of	benzaldehyde	(Table	1,	
entries	6,	9	and	10)	enhanced	the	rate	of	acetal	formation	and	
gave	 the	 corresponding	 PE	 diacetals	 in	 94‐96%	 yields	 in	 1.5,	
2.5	 and	 2	 h,	 respectively.	 In	 case	 of	 cinnamaldehyde,	 corres‐
pondding	 PE	 diacetal	 was	 obtained	 in	 95%	 yield	 after	 8.5	 h	
(Table	1,	entry	11).	All	these	PE	diacetal	compounds	have	sharp	
melting	points,	since	they	are	crystalline.		

Aliphatic	 aldehydes	 did	 not	 show	 any	 reactivity	 for	 this	
reaction	(Table	2,	entries	1,	2	and	3)	and	among	aliphatic	and	
aromatic	 ketones	 (Table	 2,	 entries	 4‐10)	 only	 cyclohexanone	
(Table	 2,	 entry	 4)	 was	 found	 to	 be	 reactive	 to	 obtain	
corresponding	PE‐diketal	 in	96%	yield	 in	6	h.	To	demonstrate	
the	 chemoselectivity	 of	 the	 SO3H‐carbon	 catalyst	 towards	
aromatic	 aldehydes,	 the	 PE	 condensation	 reaction	 was	
conducted	 with	 benzaldehyde	 in	 the	 presence	 of	 aliphatic	
aldehydes	 or	 alphatic	 and	 aromatic	 ketones	 (Table	 2,	 entries	
11,	 12	 and	 13).	 In	 all	 these	 cases,	 only	 the	 PE	 diacetal	 of	
benzaldehyde	 was	 obtained	 even	 after	 48	 h	 of	 reaction	 in	
toluene	 at	 80	 C,	 thus	 demonstrating	 the	 catalyst	 selectivity	
towards	aromatic	aldehydes.	This	methodology	here	 in	pays	a	
greener	 alternative	 route	 for	 the	 direct	 transformation	 of	
aromatic	aldehydes	into	their	respective	PE	diacetals	in	shorter	
reaction	 time	 with	 high	 selectivity	 and	 yield	 in	 contrast	 to	
conventional	method.		

The	 SO3H‐carbon	 catalyst	 was	 also	 found	 to	 be	 active	 for	
the	 deprotection	 of	 all	 the	 prepared	 PE	 diacetals	 in	MeOH	 at	
reflux	temperature	(65	C)	with	in	30	min.	The	catalyst	is	easily	
recoverable	 and	 recyclable.	 The	 recyclability	 experiments	 of	
the	SO3H‐carbon	catalyst	were	conducted	by	the	acetalyzation	
of	 pentaerythritol	 (1	 mmol)	 with	 benzaldehyde	 (2	 mmol)	 in	
toluene	 at	 80	 C	 as	 a	 test	 reaction.	 After	 completion	 of	 the	
reaction,	 the	 reaction	 mixture	 was	 allowed	 to	 cool	 and	 the	

catalyst	 was	 recovered	 by	 simple	 filtration.	 The	 recovered	
catalyst	was	washed	with	MeOH	 and	 acetone,	 then	 dried	 and	
reused	for	the	next	cycle	of	reaction.	The	catalyst	was	used	for	
five	runs	without	significant	loss	of	catalytic	activity	(Figure	1).		
	

	
	

Figure	1.	Recyclability	of	SO3H‐carbon	catalyst.	
	
4.	Conclusion	

	
In	 conclusion	 a	 simple	 and	 efficient	 chemoselective	

methodology	 was	 developed	 for	 the	 preparation	 of	 penta	
erythritol	diacetals	with	aromatic	aldehydes	in	excellent	yields	
by	 employing	 glycerol‐based	 SO3H‐carbon	 solid	 acid	 catalyst.	
These	reactions	can	be	conveniently	performed	in	atmospheric	
conditions	 in	 excellent	 yields.	 The	 salient	 features	 of	 the	
present	methodology	are:	catalyst	ability	for	deprotection	of	PE	
diacetals	in	methanol	at	moderate	temperatures	apart	from	its	
recyclability	 and	 easy	 recovery	 of	 product.	 Further	 investiga‐
tions	 to	 expand	 the	 usage	 of	 this	 catalyst	 to	 more	 catalytic	
reactions	are	underway	in	our	lab.	
	
Acknowledgements	
	

We	 gratefully	 acknowledge	 Department	 of	 Science	 and	
Technology	(DST),	Government	of	India,	New	Delhi	for	financial	
assistance.	
	



540	 Ummadisetti	et	al.	/	European	Journal	of	Chemistry	5	(3)	(2014)	536‐540	
	
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