Combustion-derived CdO nanopowder as a heterogeneous basic catalyst for efficient synthesis of sulfonamides from aromatic amines using p-toluenesulfonyl chloride

Article abstract of DOI:10.2478/s11696-012-0253-0

A simple and rapid synthesis of CdO nanopowder via the solution combustion route employing l-(+)-tartaric acid as a fuel is reported for the first time. The catalyst was characterized by PXRD, SEM, TEM, BET surface area measurement, basic site measurement from back titration and FTIR. Combustion derived CdO nanopowder acts as a catalyst in the sulfonylation of amines with p-toluenesulfonyl chloride to obtain sulfonamides in excellent yield (85-95 %) and high purity under mild reaction conditions. CdO nanopowder has been found to be an efficient catalyst requiring a shorter reaction time (10-30 min) to obtain sulfonamide when compared with the commercial CdO powder requiring 2 h under similar conditions. The catalyst can be recovered and reused four times without any significant loss of catalytic activity. Potential role of CdO nanopowder in the synthesis of sulfonamides and its mechanism is proposed.

Full text of DOI:10.2478/s11696-012-0253-0

Chemical Papers 67 (2) 135–144 (2013)
DOI: 10.2478/s11696-012-0253-0
ORIGINAL PAPER
Combustion-derived CdO nanopowder as a heterogeneous basic
catalyst for efficient synthesis of sulfonamides from aromatic amines
using -toluenesulfonyl chloride
a
aBelladamadu Siddappa Anandakumar, Muthukur Bhojegowd Madhusudana
b
a
Reddy, Kumarappa Veerappa Thipperudraiah, Mohamed Afzal Pasha,
aGujjarahalli Thimmanna Chandrappa*
aDepartment of Chemistry, Bangalore University, Bangalore-560001, India
bDepartment of Physics, National Degree College, Jayanagar, Bangalore-560070, India
Received 1 December 2011; Revised 1 May 2012; Accepted 14 May 2012
A simple and rapid synthesis of CdO nanopowder via the solution combustion route employ-
ing L-(+)-tartaric acid as a fuel is reported for the first time. The catalyst was characterized by
PXRD, SEM, TEM, BET surface area measurement, basic site measurement from back titration
and FTIR. Combustion derived CdO nanopowder acts as a catalyst in the sulfonylation of amines
with p-toluenesulfonyl chloride to obtain sulfonamides in excellent yield (85–95 %) and high purity
under mild reaction conditions. CdO nanopowder has been found to be an efficient catalyst requir-
ing a shorter reaction time (10–30 min) to obtain sulfonamide when compared with the commercial
CdO powder requiring 2 h under similar conditions. The catalyst can be recovered and reused four
times without any significant loss of catalytic activity. Potential role of CdO nanopowder in the
synthesis of sulfonamides and its mechanism is proposed.
c
ꢀ 2012 Institute of Chemistry, Slovak Academy of Sciences
Keywords: nanopowder, solution combustion, amines, p-toluenesulfonyl chloride, tartaric acid,
sulfonamide
Introduction
also widely used for gas sensors, solar cells, and op-
tics as well as in catalysis. Over the past two decades,
several methods such as sol–gel (Santos-Cruz et al.,
2007; Ashoka et al., 2010), sonochemical, and co-
precipitation methods (Askarinejad & Morsali, 2008;
Waghulade, et al., 2007) have been developed for the
synthesis of CdO nanopowder. Solution combustion
synthesis (Patil et al., 2008; Nagappa & Chandrappa,
2007) is one of the most fruitful methods for the syn-
thesis of metal oxide nanoparticles in general and CdO
nanopowder in particular because of its shorter reac-
tion time at ambient conditions and its low cost with a
potential to scale up. In addition, this method is useful
for the production of homogeneous, porous, and fine
crystalline powders. To the best of our knowledge, the
synthesis of CdO nanopowder via the solution com-
Transition metal oxides of nanometric size have at-
tracted considerable attention because of their unique
properties and potential for extensive applications in
catalysis, electronics, and environment. Recently, sev-
eral transition metal oxides (Thakuria et al., 2007;
Glin´ski et al., 1995) including CdO (Mazaheritehrani
et al, 2010; Alves et al., 2010; Abd El-Salaam & Has-
san, 1982; Okuhara & Tanaka, 1980; Balandin et al.,
1960) have been used as catalysts in organic synthesis
because of their beneficial physicochemical properties
such as particle size, large surface area and tunable
pore structure. In addition to the large surface area,
their strong basic active sites make CdO nanopow-
der a promising catalyst in organic synthesis. It is
*Corresponding author, e-mail: gtchandrappa@yahoo.co.in

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B. S. Anandakumar et al./Chemical Papers 67 (2) 135–144 (2013)
tion method was investigated. Catalytic activity of the
CdO nanopowder was evaluated for the sulfonylation
reaction of amines with p-toluenesulfonyl chloride (p-
TsCl) using acetonitrile solvent under reflux condi-
tions. Catalytic activity of commercial CdO powder
in comparison with the combustion derived CdO was
also examined.
bustion method has not been reported so far.
In the present investigation, tartaric acid was used
as the fuel in the synthesis of CdO nanopowder via a
solution combustion route. Combustion derived CdO
nanopowder possesses a large surface area with large
porosity. The large surface area can provide a greater
number of active sites than the low coordinated ox-
ide sites (edges, corners) (Sterrer et al., 2003) and
lattice defects (cation and anion vacancies) (Sousa
et al., 1999). The pore diameter of CdO nanopow-
der is another key factor affecting the contact perfor-
mance between the reactant and the catalyst (Znahg
et al., 2009). Higher surface area of the nano powder
can provide more active sites, whereas a porous struc-
ture facilitates the adsorption and diffusion of reactant
molecules. Both factors enhance the catalytic perfor-
mance in the present system (Davis, 2002). In addi-
tion, the CdO nanopowder possesses a greater number
of basic sites as compared to commercial CdO. There-
fore, CdO nanopowder can act as a strong Lewis base
in catalytic reactions. It has been found that hetero-
geneous basic catalysts have more advantages over the
homogeneous organic basic catalysts, e.g. easy recov-
ery of the catalyst, simple isolation, recyclability, and
minimization of metal oxide impurities in the product.
Thus, heterogeneous basic catalysts have been recog-
nized as a potential alternative to the homogeneous
organic basic catalysts.
Sulfonylation of amines is an important step in syn-
thetic organic chemistry. The sulfonyl group is one
of the most versatile amino- or hydroxyl-protecting
groups in organic synthesis (Nishida et al., 1988;
Yuan et al., 1989; O’Connell & Rapoport, 1992;
Chandrasekhar & Mahapatra, 1998). Sulfonyl deriva-
tives are useful as drugs and they exhibit a wide-
range of biological activities such as anti-cancer, anti-
inflammatory, and anti-viral functions (Supuran et
al., 2003; Scozzafava et al., 2003; Harter et al., 2004;
Reddy et al., 2004; Stranix et al., 2006). Many of
the methods (Anderson, 1979; Russell et al., 2001)
reported for the synthesis of sulfonamides have lim-
itations such as harsh reaction conditions (Poisson-
net et al., 1996), long reaction time (Yasuhara et al.,
1999), the use of toxic reagents such as pyridine, and
difficult catalyst recovery (Chan & Berthelette, 2002).
To overcome all these drawbacks, a general, mild, and
novel method to synthesize sulfonamides has been de-
veloped.
Experimental
Cadmium nitrate tetrahydrate of the purity of
99 %, L-(+)-tartaric acid crystals of the purity of
99.7 %, and commercial CdO powder of the purity
of 99 % were purchased from Merck Chemicals, In-
dia. Commercial CdO powder had the particle size
of 0.5–1.5 µm and the BET specific surface area of 3–
4 m2 g−1. All organic chemicals used were commercial
grade and all solid amines were used without further
purification, liquid amines were distilled before use.
An aqueous solution containing cadmium nitrate
as the oxidizer (O) and tartaric acid as the fuel (F)
(corresponding F : O ratio Ø = 1 as shown in (Eq. (1))
was put in a pyrex dish (Nagappa & Chandrappa,
2007). Excess water was evaporated by heating on a
hot plate until a viscous gel was formed. The pyrex
dish was then placed in a muffle furnace maintained
at (400 10)◦C. Initially, the reaction mixture under-
went dehydration followed by smoldering (low flame)
combustion. The product, cadmium oxide nanopow-
der, left behind was porous and voluminous.
(400
10) ◦C
Cd(NO)3(aq) + C4H6O6(aq) −−−−−−−−−−−→
CdO(s) + N2(g) + 4CO2(g) + 3H2O(g)
(1)
In the general procedure for sulfonylation of aro-
matic amines, p-toluenesulfonyl chloride (5.5 mmol)
and CdO nanopowder (1 mole %) were added to a
solution of aromatic amines (5 mmol) in acetonitrile
(5 mL). The reaction mixture was stirred at reflux for
10–30 min (Fig. 1.). The progress of the reaction was
monitored by thin-layer chromatography (TLC) and
after its completion, the reaction mixture was cooled
to room temperature (r.t.), the CdO nanopowder sus-
pension was filtered using a cellulose nitrate mem-
brane filter Whatman (Scientific & Surgical Corpora-
tions, India) and extracted with ethylacetate (20 mL).
Organic extract was dried using anhydrous MgSO4
and concentrated under reduced pressure. In all cases,
products obtained from the sulfonamides were pure.
Powder X-ray diffraction patterns were obtained
by a Philips X’pert PRO X-ray diffractometer (PAN-
alytical, B. V. Almelo, Netherlands SPECTRIS PTE,
Our ongoing research program is aimed at the de-
velopment of a heterogeneous catalyst to synthesize
widely used organic compounds (Madhusudana Reddy
et al., 2010, 2011).
Studies on organic reactions catalyzed by CdO
nanopowder are very scarce and no reports on the
synthesis of sulfonamides are available. It is there-
fore desirable to develop a new green and reusable
catalyst for this synthesis; the use of CdO nanopow-
der prepared via a low temperature solution combus-
The Netherland) using CuKα radiation (λ
=
◦
˚
1.54056 A) at the scanning rate of 0.02 per second
for 2θ in the range from 10◦ to 70◦ and operated at
40 kV and 30 mA. Morphologies of the products were
examined by a Quanta-200 scanning electron micro-
scope (JEOL, Japan) equipped with an energy dis-

B. S. Anandakumar et al./Chemical Papers 67 (2) 135–144 (2013)
137
Fig. 1. Scheme of general procedure for sulfonylation of aromatic amines with p-TsCl and CdO nanopowder.
R = CH3, F, Cl, Br, OCH3, NO2.
Fig. 2. PXRD pattern of CdO nanopowder (a) and H+ ion adsorbed on the CdO nanopowder (b).
persive X-ray spectroscope (JEOL, Japan). Samples
were gold-coated prior to the scanning electron mi-
croscopy (SEM) analysis. Nano/microstructure of the
products was observed by transmission electron mi-
croscopy (TEM) and selected-area electron diffraction
(SAED) which was performed with a Hitachi model
H-600 instrument (White Brook Park, UK) operat-
ing at 100 kV. Surface area measurements and pore
size distribution analysis were done after degassing
the sample under high vacuum at 300◦C for 4 h;
and nitrogen adsorption measurements were carried
out at 77 K using a gas sorption analyzer Quanta
chrome corporation NOVA 1000 (Quantachrome In-
struments, USA). All melting points were determined
using a Bu¨chi apparatus. Nuclear magnetic resonance
spectra were obtained on a 400 MHz Bruker AMX
spectrometer (IET, USA) in DMSO-d6 using TMS as
the standard. GC-mass spectra were obtained using a
Shimadzu GC-MS QP 5050A instrument (SpectraLab
Scientific, Canada) equipped with a 30 m long BP-5
column with the diameter of 0.32 mm and the column
temperature of 80–15–250◦C. Infrared spectra were
recorded using a Shimadzu FT-IR-8400s spectrome-
ter (Shimadzu Corporation, Japan) as KBr pellets for
solids and as thin films between NaCl plates for liq-
uids.
CuKα radiation. The PXRD pattern clearly shows
that CdO crystalline powder is in the cubic phase
˚
with lattice constant a = 4.695 A (JCPDS 75-0594)
as shown in Fig. 1a. Broadness of the peaks indicates
the nanocrystalline nature of the CdO nanopowder
and the particle size calculated from the Scherrer’s
formula is in the range of 40–60 nm. The amount of
basic sites present in the CdO nanopowder was deter-
mined by back titration. Eq. (2) presents the proposed
mechanism of the determination of the amount of ba-
sic sites.
CdO + H+ + OH− → Cd O · · · H+ + OH− (2)
—
—
In this reaction, the prepared CdO nanopowder
was allowed to stand in distilled water for 24 h to
let the nanoparticles of CdO submerge into distilled
water. The H+ ion was provided by distilled water,
it was absorbed by the lone pair of oxygen from
the CdO nanopowder and the OH− ion was formed.
This technique helps to estimate the amount of H+
ions absorbed by the prepared CdO nanopowder. Fi-
nally, the H+ ions formed a bond with the CdO
nanopowder resulting in the formation of Cd(OH)2.
The H+ ion adsorbed on the CdO nanopowder is
shown in the PXRD pattern in Fig. 2b. All diffraction
peaks can be indexed to hexagonal crystal structure
of Cd(OH)2 which is in good agreement with the re-
ported data and with the respective JCPDF card no
73-0969.
Results and discussion
Powder X-ray diffraction
The formation of Cd(OH)2 can be caused by the
reaction between the CdO nanopowder with water
(Nondek et al., 1979; Samadi et al., 2010).
Powder X-ray diffraction patterns were obtained
on a Philips X’pert PRO X-ray diffractometer using

138
B. S. Anandakumar et al./Chemical Papers 67 (2) 135–144 (2013)
Fig. 3. SEM image of commercial CdO powder (a) and SEM image of CdO nanopowder (b).
Fig. 4. TEM image of CdO nanopowder (a) and SAED pattern of CdO nanopowder (b).
Scanning electron microscopy (SEM)
bution of porous secondary particles. The observed
mesoporosity can be referred to the voids between the
interconnected primary particles; the macroporosity
results from voids between the secondary particles.
Mesopores provide large surface area and active sites,
and macropores enhance mass diffusion of the reac-
tant molecules during the catalysis (Yuan et al., 2004;
Blin et al., 2003; Khaleel & Al-Mansouri, 2010).
Morphologies of the combustion derived CdO
nanopowder and the commercial CdO powders were
examined using a JEOL-JSM-6490 LV scanning elec-
tron microscope (SEM). The SEM image of commer-
cial CdO powder (Fig. 3a) revealed that the commer-
cial powder has very low porosity compared to that of
the combustion derived CdO nanopowder. The SEM
micrograph of CdO nanopowder (Fig. 3b) shows that
the powder is porous and agglomerated with polycrys-
talline nanoparticles. The pores and voids can be at-
tributed to the large amount of gas escaping during
the combustion. The macroporous framework is com-
posed of accessible mesochannels with a wormhole-
like array. It can be seen that the macropore sizes
are not as homogeneously distributed as the meso-
porous ones. This is due to the non uniform distri-
Transmission electron microscopy (TEM)
The micrograph in Fig. 4a shows a network of
large particles of moderate sizes and irregular shapes
formed by agglomeration of well dispersed nanopar-
ticles with the average size of 40–60 nm. The size
of these nanoparticles is in good agreement with the
values obtained from XRD experiments. In order to
obtain deep insight into the pore morphology of this

B. S. Anandakumar et al./Chemical Papers 67 (2) 135–144 (2013)
139
Fig. 5. Nitrogen adsorption–desorption isotherm of CdO nanopowder (a) and pore size distribution curve determined from the N2
adsorption–desorption isotherm (b): adsorption ( ) and desorption ( ) data.
•
material, the macroporous structure image of the sam-
ple was further investigated by TEM measurements
(Fig. 4a). TEM directly visualized the porous net-
work which appeared to have a higher structural order
relative to macropores in the powders obtained. The
polycrystalline nature of the obtained sample was con-
firmed by selected area electron diffraction (SAED)
performed on a Hitachi model H-600 instrument op-
erating at 100 kV as shown in Fig. 4b.
isotherms by the BJH method, are shown in Fig. 5b.
A narrow pore size distribution with an average pore
diameter of 46 nm and a pore volume of 0.039 cm3 g−1
can be observed. This narrow pore size distribution of
mesopores with diameters between 40 nm and 50 nm
exhibits a peak maximum at 46 nm which indicates
the homogeneity of the mesopores of the prepared ma-
terials. Thus, SEM and TEM observations and N2 ad-
sorption analysis revealed that the materials exhibit a
bimodal pore size distribution and that they are in
fact meso–macroporous systems.
Surface area and pore size distribution
Nitrogen adsorption measurements were carried
out at 77 K using the gas sorption analyzer Quanta
chrome corporation NOVA 1000. Surface area of the
CdO nanopowder was calculated by the BET method.
Basic site measurement
About 0.15 g of CdO nanopowder was inserted into
the centrifuge tube and 10 mL of distilled water were
added. The mixture was shaken vigorously and then
allowed to stand for 24 h at room temperature. The
solution was centrifuged to separate the solid from the
liquid phase. Supernatant liquid was transferred into
a conical flask and 10 mL of 0.1 M hydrochloric acid
were added. Then, 2–3 drops of the phenolphthalein
indicator were dropwise added to the mixture under
vigorous shaking of the flask. The solution was titrated
with NaOH (0.05 M) until the color of the solution
changed from colorless to pink. The change of the color
indicates that the reaction had reached its endpoint
(Nondek et al., 1979; Samadi et al., 2010). The back
titration carried out to estimate the basic sites present
on 0.15 g of the CdO nanopowder was found to be
0.92 mmol. This result was also confirmed by FTIR
and XRD studies.
CdO nanopowder has a large surface area, 34 m2 g−1
,
compared to that of commercial CdO (3–4 m2 g−1).
Surface area of the product mainly depends on the
type of the fuel used. The larger surface area is at-
tributed to the liberation of gaseous products such
as H2O, CO2, and N2 during combustion; the ag-
glomerates disintegrate and most of the heat is car-
ried away from the system thus hindering particle
growth. This larger surface area is important for cat-
alytic/adsorbent applications because small size of the
particles maximizes the surface area exposed to the
reactant, allowing thus more reactions to take place.
Fig. 5a shows a representative adsorption–desorption
isotherm of nitrogen obtained at the temperature of
liquid nitrogen and corresponding pore size distribu-
tion for CdO nanopowder which exhibited a typi-
cal type IV isotherm according to the IUPAC clas-
sification with hysteresis reflecting the mesoporosity
and continuous increase in the nitrogen uptake at
higher relative pressure (p/p0) indicating the presence
of macropores. These macropores are clearly distinct
from the mesopores also observed in SEM and TEM
images (Yuan et al., 2004).
Proposed mechanism of basic site measure-
ment for CdO nanopowder
The amount of basic sites present in CdO nano-
powder was determined by back titration. Eq. (2)
shows the proposed mechanism for the determination
of the amount of basic sites. In this reaction, the pre-
pared CdO nanopowder was allowed to stand in dis-
Pore size distributions (pore diameter, pore vol-
ume), calculated from the corresponding desorption

140
B. S. Anandakumar et al./Chemical Papers 67 (2) 135–144 (2013)
Fig. 6. FTIR spectra of CdO nanopowder (a) and H+ ion adsorbed on the CdO nanopowder (b).
tilled water for 24 h to let the nanoparticles of CdO
submerge into distilled water. The H+ ion was pro-
vided by distilled water and it was absorbed by the
lone pair of oxygen from the CdO nanopowder re-
leasing the OH− ion. This technique estimates the
amount of the H+ ions absorbed by the prepared
CdO nanopowder. Finally, the H+ ions formed a bond
with the CdO nanopowder resulting in the forma-
tion of Cd(OH)2. This mechanism was further sup-
ported by FTIR spectra (Fig. 6b) and XRD diffrac-
togram (Fig. 2b) which confirmed the formation of
Cd(OH)2.
can be assigned to Cd(OH)2 were observed (Maza-
heritehrani et al., 2010).
Role of L-(+)-tartaric acid
The solution combustion reaction mainly depends
on the nature of fuel, temperature, and on the stoi-
chiometric ratio of fuel to oxidizer. In the present in-
vestigation, different organic compounds such as cit-
ric acid, malic acid, succinic acid, lactic acid, and
also tartaric acid were examined as fuels in the syn-
thesis of CdO nanopowder. Among these, tartaric
acid with two OH groups and two COOH groups
seems to be chemically suitable for the preparation of
CdO nanopowder because of its versatile co-ordination
modes and conformational flexibility (Blomqvist &
Ebbe, 1984; Johnston et al., 2010; Zheng et al., 2010,
2004).
FTIR studies
FTIR spectrum of the CdO nanopowder is shown
in Fig. 6a. The spectrum exhibits a common broad
band near 3445 cm−1 due to the OH-stretching vibra-
tions of free and hydrogen-bonded hydroxyl groups,
and a second typical absorption region at 1649 cm−1
which is assigned to the bending vibration of water
molecules, most probably caused by the water adsorp-
tion during the compaction of the powder specimens
with KBr (Angappan et al., 2004). Formation of the
CdO phase is characterized by poorly resolved shoul-
ders at 704 cm−1 (Risti´c et al., 2004). Fig. 6b shows
the FTIR spectrum of the H+ ion adsorbed on CdO
nanopowder. The main characteristic peak is a sharp
and intensive band corresponding to the OH stretch-
ing vibrations at 3601 cm−1 (Angappan et al., 2004).
This indicates that the adsorbed H+ ions are bound
to the surface of the CdO nanopowder, at least par-
tially or covalently, which resulted in the formation of
Cd(OH)2. The shoulder at 1649 cm−1 can be associ-
ated with the bending vibrations of water molecules,
suggesting that the CdO nanopowder contains basic
sites absorbed by water molecules. IR bands in the
region of 1500–1450 cm−1 can be assigned to a resid-
ual organic component. In the region of lower wave
numbers, IR bands at 858 cm−1 and 457 cm−1 which
Tartaric acid plays a dual role in the synthesis of
CdO nanopowder; it functions as a complexing agent,
prevents the precipitation of ions by complexation
with Cd2+ ions (Masoumeh et al., 2011), and as a
fuel in the combustion reaction. During the combus-
tion reaction, a redox reaction takes place resulting
in a very high temperature and the evolution of large
volumes of gases. Even though the furnace tempera-
ture was maintained at (400
10)◦C, the particles
could have attained higher temperature during the ig-
nition. The heat energy released is different for differ-
ent fuels based on their value of heat of combustion
and hence, every system is expected to form different
phases based on the total heat content of the system.
Here, tartaric acid forms a polynuclear complex with
Cd2+ ions. Morphology of the particles is generally
based on the nature of the fuel, polynuclear complex
formation, and on the fuel to oxidizer ratio.
Catalytic activity
Initially, the reaction between aniline and p-TsCl

B. S. Anandakumar et al./Chemical Papers 67 (2) 135–144 (2013)
141
Table 1. Optimization of conditions for the reaction between aniline and p-TsCl
Temperature
◦C
Time
min
Isolated yield
%
Entry
Catalyst
1
2
3
4
5
6
2 mole % Commercial-CdO
3 mole % Commercial-CdO
2 mole % Commercial-CdO
1 mole % Nano-CdO
1 mole % Nano-CdO
–
25
25
Reflux
25
Reflux
25
120
120
120
60
10
120
40
43
62
75
95
Trace
Table 2. CdO catalyzed synthesis of sulfonamides from the reaction of amines with p-TsCl at reflux conditionsa
Yield
Time
min
CdO nanopowder
Common CdO
Entry
Amine
Product
%
a
b
c
Aniline
10
25
15
20
95
90
90
92
56
44
45
54
4-Toluidine
4-Fluoroaniline
4-Chloroaniline
d
e
f
4-Bromoaniline
4-Anisidine
25
15
25
30
86
88
89
87
42
49
59
43
g
h
4-Nitroaniline
3-Nitroaniline
i
j
Diphenylamine
30
20
85
90
42
58
2-Naphthylamine
a) All reactions were performed using substituted aromatic amine (5 mmol), MeCN (5 mL), p-TsCl (5.5 mmol), and CdO nanopow-
der (1 mole %), b) all compounds are known and physical properties agree with the reported values; IR and MS data match with
the reported spectral data.

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B. S. Anandakumar et al./Chemical Papers 67 (2) 135–144 (2013)
Fig. 7. Possible mechanism for catalytic activity of CdO nanopowder in sulfonation of aromatic amines with p-TsCl.
at room temperature was carried out using com-
mercial CdO (2 mole %) as the catalyst in ace-
tonitrile as a solvent and a 40 % yield of the
desired product (Table 1, entry 1) was obtained.
There was no significant increase in the yield of
the product either with the increase of the reaction
time, the temperature or the amount of CdO (Ta-
ble 1, entry 2). When the same reaction was car-
ried out using 1 mole % of CdO nanopowder, 75 %
of the product (Table 1, entry 4) were obtained.
The increased catalytic activity of CdO nanopow-
der over the commercial CdO can be attributed to
the larger surface area of the CdO nanopowder (SA:
Possible mechanism for catalytic activity of
CdO nanopowder in sulfonation of aromatic
amines with p-toluenesulfonyl chloride
To understand the relationship between the struc-
ture and the reactivity of the catalyst in this reaction
it is important to know the structure and nature of the
reactive sites of CdO nanopowder. The catalyst has
a polycrystalline, three dimensional cubic structure
with high surface concentrations of edges, corners,
and various exposed crystal planes (111), (200), (220),
(311), and (222), which leads to inherently high sur-
face reactivity per unit area. Moreover, CdO nanopow-
der has Lewis acid sites Cd2+, Lewis basic sites O2−
and O−, lattice bound, and anionic and cationic va-
cancies (Fahim & Abd El-Salaam, 1967; Chintareddy
& Kantam, 2011). Acid-base and redox properties are
important surface chemical properties of metal oxide
catalysts. Since the CdO nanopowder is found to be
more basic, it is more efficient in the sulfonation reac-
tion of amines than the commercial CdO powder.
Thus, CdO nanopowder displays higher activity
compared to the commercial CdO powder. In the first
step of the reaction, H of the amino group of the aro-
matic amine is expected to be activated by O2− (Lewis
base) and p-toluenesulfonyl group can be activated by
Cd2+ (Lewis acid) of nanocrystalline CdO. The acti-
vated substrates can react with each other to form the
corresponding product I as shown in Fig. 7.
34 m2
g
−1) compared to that of commercial CdO
(SA: 3–4 m2
g
−1). Catalytic activity of the CdO
nanopowder was evident when a negligible amount of
the product was obtained in the absence of the cata-
lyst even after 2 hours of the reaction (Table 1, entry
6).
To reduce the reaction time and to improve the
yield of the product, the reaction was carried out at
reflux condition. Aromatic amines were sulfonylated
using MeCN as the solvent at reflux condition and a
95 % yield was obtained within 10 min of the reaction
(Table 1, entry 5). To determine the general applica-
bility of this process, syntheses of a variety of sulfon-
amides were studied (Table 2). It is noteworthy that
1-naphthylamine can also be used to obtain the corre-
sponding sulfonamide in a good yield (Table 2, entry
j), which is also of interest due to its biological activ-
ity. The use of just 1 mole % of the CdO nanopowder
in MeCN was found to be sufficient for the reaction
to take place. Higher amounts of the CdO nanopow-
der did not provide higher yields. The yields are, in
general, very high regardless of the structural varia-
tions in amines. The products obtained are of high
purity.
Recycling studies
Experiments were conducted to determine the
reusability of the catalyst. The catalyst can be eas-
ily separated by filtration and it can be reused after
its activation at 200◦C for one hour in a muffle fur-
nace. Efficiency of the recovered catalyst was tested
using a model reaction under similar conditions (Ta-
ble 2, entry a). Using the fresh catalyst, the yield of
the product (Table 2, entry a) was 95 % while the
recovered catalyst in the three subsequently repeated
experiments provided yields of 94 %, 90 %, and 91 %,
It is important to note that the synthesis procedure
is very simple. The catalyst was collected by filtration
and the filtrate was evaporated to get the pure prod-
uct.

B. S. Anandakumar et al./Chemical Papers 67 (2) 135–144 (2013)
143
respectively. These results demonstrate that the cata-
lyst can be reused several times without a significant
loss of its activity.
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Conclusions
A simple combustion synthesis using tartaric acid
as a fuel to obtain CdO nanopowder has been de-
veloped. We are the first to develop the process of
CdO nanopowder synthesis and employ it as a catalyst
in the sulfonylation of amines with p-toluenesulfonyl
chloride to rapidly obtain sulfonamides in an excellent
yield (85–95 %) and high purity under mild reaction
conditions. The catalyst can be recovered by simple
filtration and reused in four cycles without any signif-
icant loss of its catalytic activity.
Acknowledgements. Gujjarahalli Thimmanna Chandrappa
gratefully acknowledges financial support of the University
Grants Commission, New Delhi, to carry out this research
work. The authors are thankful to Prof. Sarala Upadhya, De-
partment of Mechanical Engineering, UVCE, Bangalore Uni-
versity, for recording SEM images and to Prof. Jai Prakash,
Bangalore Institute of Technology for surface area measure-
ments.
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