A Green and Efficient Route for Knoevenagel Condensation Over Rice Husk Based MCM-41
M. R. Deshpande1, C.V.Rode2, U.D.Joshi1
1Netaji SubhashChandra Bose College, Nanded
2National Chemical Laboratory Punee-mail: joshiud@yahoo.com, +919850826030,Fax: +912462244486

Abstract
In the recent years, there has been a growing interest to find creative ways not only to reduce natural waste and industrial
hazard to overcome environmental pollution but also its effective utilization. We report eco-friendly synthesis of mesoporous
molecular sieve MCM-41as a member of M41S family using rice husk plentily available as an agro-waste. This contributes
ro the green synthesis of MCM-41 at a cheaper production cost. Synthesised material (denoted as RH-MCM-41) wascharecterised by powder XRD, FT-IR,N2 physisorption, TGA-DTA and SEM to understand the effect of silica source on
physico-chemical propoerties. RH-MCM-41 having basic characteristics was efficiently used to catalyze Knoevenagel
condensation reaction between aldehyde and malonitrile.

Keywords: Rice Husk, MCM-41, Knoevengel condensation, silica, aromatic aldehyde,

1. Introduction
Rise husk is a residue produced during milling of paddy(Oryza sativa). Approximately 22% weight of paddy is
obtained as husk which after burning produces about 25% rice husk ash (RHA). India is a major rice producing
country and annul production of rice husk ash is
approximately 20 million tons [1].Due to low content
moisture, 8-10 % rice husk is commonly used as abiomass fuel [2-4].Even though rice husk is an agriculturalresidue, it is not recommended as cattle feed since itscellulose and other sugar contents are low. Due its highsilica (>90%) content, it can be a renewable resource formaking high value, versatile mesoporous material like
MCM-41[5,6]. This paper reports the synthesis strategy of
MCM-41 from rice husk ash, its characterization andevaluation as base catalyst for Knoevenagel condensation
reaction.

2. Materials and Methods
Cetyl-tri-methyl-ammonium bromide (CTAB), sodiumhydroxide and conc. hydrochloric acid were purchasedfrom SD fine chemicals, India.
The acid pretreated (2.0 M HCl at 100˚C) rice huskwas washed with water to remove the excess acid on thesurface and dried in oven overnight at 100˚C. This wasthen calcined at 750˚C in air for 4h to obtain the extracted
silica from RHA. Silica extracted from RHA was first fusedwith 3M NaOH solution and was stirred for 2h to extract
the silicate from the ash. A clear solution of CTAB
prepared in water was then slowly transferred into silicate
supernatant solution and kept under stirring for 2h. The
reaction gel mixture had the molar composition of
1.0 SiO2:3.0NaOH:0.25CTAB:180 H2O. The pH value ofthe gel was then adjusted to 8.5 by adding 3.0M HClsolution. This homogeneous gel was heated under
autogenous pressure at 80˚C for 2h in a teflon coatedautoclave. After cooling, the solid product was filtered andwashed repeatedly by de-ionized water. The solid thus
obtained was then dried in a muffle furnace at 100˚C andcalcined at 550˚C for 4.5h. This sample was named as

RH-MCM-41 which was evaluated for Knoevenagel
condensation reaction.
Knoevenagel condensation reaction was performed using
1g (0.00943 moles) of benzaldehyde, 1g (0.00885 moles)of ethyl cyanoacetate and 30 ml of DMSO (solvent) in aglass reactor equipped with a magnetic stirrer at thedesired reaction temperatures. After attaining the desired
temperature, 2 g of the catalyst was added and thereaction was started. The liquid samples were periodicallywithdrawn (every 2 h.) and analyzed on GC using 2025
Shimadzu model equipped with RTX-5 capillary column.
The other conditions of analysis were:Injector (split)
temperature: 250 OC; FID temperature: 250 OC Column
final temperature: 220 OC, (N2) carrier gas flow rate: 30
ml/min Inlet Pressure (N2) :30 psig, Split ratio: 1: 100. IRwasrecordedusingBrucker-ATRZnSe
spectrophotometer in transmission mode. Powder X-ray
diffraction patterns of the materials were recorded on
Rigaku MiniFlex2 model with a monochromated Cu Kα
radiation in the angular range from 1.8° to 10° (2θ) with ascanning speed of 0.03° s−1. FT-IR spectra of the RHA
and synthesized materials RH-MCM-41 were recorded on
a FT-IR spectrometer (ATR eco ZnSe) using dry KBr pallet
as a standard reference in the range of 500-4000cm-1.
BET surface area was measured using Surface area
Analyzer Model SAA-2000. Chemical composition of ricehusk ash was estimated on a dry basis by gravimetry inconjunction with atomic adsorption spectrometer(Shimadzu AA 6200). TGA-DTA characteristics of thesynthesized sample were taken on DTG-60H detector.

3. Results and Discussion
3.1. Characterization
Chemical analysis of the rice husk ash confirmed its major
constituent as SiO2 (90 – 95 %) necessary for thesynthesis of mesoporous materials. The crystallinity ofMCM-41 synthesized from rice husk ash was from thecorresponding XRD patterns of RHA and RH-MCM-41 asshown in Fig.s 1 (a) and (b). A broad peak at 2θ = 20°
clearly indicated that silica obtained after fusion andburning of rice husk ash was in the amorphous while the7th International Symposium on Feedstock Recycling of Polymeric Materials (7th ISFR 2013)
New Delhi, India, 23-26 October 2013

peaks at 2θ = 2.40, 4.00, 4.40 and 6.00 indexed as (100),(110), (200) and (210) reflections, respectively, were thecharacteristics of long range ordered hexagonal MCM-41
mesophase of which the corresponding lattice parameter
3000

35000

100

30000
25000

INTENSITY

INTENSITY

2000

20000
15000
10000

110

1000
5000

200
210

0

10RHA,

2030

2θ405060

70
24Fig.1. XRD of(b) RH-MCM-41

68102θ

(a)ao = 47.31Ǻfor peak at 2θ = 2.4o. The specific BET surface
area of as-synthesized sample was 677.162 m2/g whichsignificantly increased to 901.361 m2/g after calcination.
FTIR spectra of RH-MCM-41 before and after calcination
showed the peak at 552.7cm-1 which was characteristic of
Si-O-Si bending while, that observed at 789cm-1 was dueto the symmetric Si-O-Si stretching. The bands observed
at 1240.8 cm-1 and 1083.4 cm-1 were the characteristics ofasymmetric Si-O-Si stretching and the broad band around3604cm-1 was due to surface silanols and adsorbed watermolecules which indicate that the silica framework ishydrophillic. The disappearance of peaks at 2930.4cm-1
and 2858.1cm-1 after calcination confirmed the complete
removal of the organic template at 5500C [7].
Scanning Electron Microscope (SEM) micrograph of thesilicon extracted from the Rice Husk Ash (RHA) in Fig. 2,
shows agglomerated particles varying in sizes confirming
their tendency to cluster together. Fig. 2 (b) exhibited theagglomerated particles with the uniform size in a range of
0.3-0.5 µm and shapes of the particales are like a silik
cocoonwithrandomarrangment.
Fig. 2. SEM of a) Silica from RHA b)Calcined RH-MCM - 41

bearing negative charge of the lattice and consequently
the density of negative charge on a given oxygen(Lewisbasicity). Being a solid catalyst, not only protonabstracting capacity of RH-MCM-41 but its specific (BET)
surface area, pore diameter and type of cationicsurfactant also substantially influence its activity. We havealso studied the effect of other reaction parameters likecatalyst loading, the reaction time and temperature fromprocess optimization point of view. The loading of RHMCM-41 catalyst in the reaction blend was varied from 0.5
g to 3.0 g in the steps of 0.5 g.The effect of duration onreaction was examined for various timings of 8 h,10 h and12 h. Reaction was carried out at different temperaturesi.e.750C,850C and 950C.
The gas chromatographic analysis of reaction
product obtained from Knoevengeal condensation
between benzaldehyde and ethyl cyano acetate gave thehighest conversion of 96.9% for 2g loading of RH-MCM41 at 950C after 8 h of the reaction. However for theKnoevengeal condensation between salicylaldehyde andethyl cyano acetate, we have achieved almost complete
conversion for the same experimental parametersindicating the effect of substituent on the aromaticaldehyde.
FT-IR spectra of the reaction products showeddiagnostic bands in the 2206-2225 cm-1 range attributable
to the stretching vibration of the C≡N group. The spectra
also showed the bands in the 1440-1665 and 2933-3021
cm-1 ranges which are assigned to C=C and C-H group
stretching frequencies, respectively.

4. Conclusion
This study concludes that rice husk extracted silica is an
inexpensive, active and renewable raw material ascompared to the conventional expensive resource for thesynthesis of MCM-41. The synthesised RH-MCM-41 was
thoroughly characterized possessing the basic sites due towhhich it exhibited high activity and selectivity for
Knoevenagel condensation of aromatic aledehydes andcyano esters to give the corresponding α,β unsaturated
nitriles.

TG and DTG thermograms were scanned in a temperature
range of 300 to 1273 K which showed a smooth weightloss due to desorption of water, starting from 310 K to 450
K. The total weight loss was 22 % up to 1273 K. There
was almost no weight loss after 823K indicating that
surfactant had been removed completely after calcination.
This also indicates that the sample was thermally stable
up to 1273 K.
3.2. Activity testing
The above prepared RH-MCM 41 catalyst was tested
for the Knoevenagel condensation rection of aromatic
aldehydes such as benzaldehyde and salicylaldehyde andmolecules containing activated methylene group e.g. ethyl
cyano acetate to give the corresponding α,β unsaturated
nitrile in presence of RH-MCM-41, as shown below.

5. References

The reaction was catalyzed by the basic sites of RH-MCM41, which were associated with the framework oxygen[5] J.S. Beck, C. Vertuli, W.J. Roth, C.T. Kresge, Family ofmesoporous molecular sieves prepared with liquid crystal
templates, J. Am. Chem. Soc. 114 (1992) 10834–10843.

φH

φCN
C

O + H2 C
CO 2 EtCNC

H2OH[1] “Rice husk ash market styudy”, BronzeoakLtd.,UK2003[2] L.P. Hunt, J.P. Dismukes, J.A. Amick, Rice hull as araw material forproducing silicon, J. Electrochem. Soc.
131 (1984) 1683–1686.
[3] H. Halimaton, N.M.M. Mohd, E. Salasiah, L. Endang,R. Zainab, 29Si MAS NMR, XRD and FESEM studies ofrice husk silica for the synthesis of zeolites, J. Non-Cryst.
Solids 211 (1997) 126–131.
[4] N. Yalcin, V. Sevinc, Studies on silica obtained fromrice husk,Ceramic Int. 27 (2001) 219–224

CCO2 Et

7th International Symposium on Feedstock Recycling of Polymeric Materials (7th ISFR 2013)
New Delhi, India, 23-26 October 2013

[6] N. Grisdanurak, S. Chiarakorn, J. Wittayakun,
Utilization of mesoporous molecular sieve synthesizedfrom natural source rice husk silica to chlorinated volatileorganic compounds (CVOCS) adsorption, Korean J. Cem.
Eng. 20 (2003) 950–955.
[7]Kalapathy U., Protor A. and Shultz J., “A simple method
for production of pure silica from rice hull ash”,Bioresource Technology, Vol. 73, (2000), pp 257-264.

7th International Symposium on Feedstock Recycling of Polymeric Materials (7th ISFR 2013)
New Delhi, India, 23-26 October 2013