An elegant synthesis of chitosan grafted hydrotalcite nano-bio composite material and its effective catalysis for solvent-free synthesis of jasminaldehyde

Article abstract of DOI:10.1039/c5ra16927e

A novel nano-bio composite of chitosan and a layered double hydroxide was elegantly synthesized by a co-precipitation method. The nano-bio composite material (CMA) was thoroughly characterized by FTIR, TGA, XRD, SEM and TEM. The composite material CMA showed efficient catalytic activity for selective synthesis of jasminaldehyde under solvent free conditions by condensation of benzaldehyde and 1-heptanal. In typical employed conditions, 39.5 mmol benzaldehyde, 7.9 mmol 1-heptanal, 100 mg catalyst, 160°C and 700 rpm, a maximum selectivity of 89% with 99% conversion was obtained. The investigations were performed in detail as a function of the amount of catalyst, temperature and molar ratio of 1-heptanal to benzaldehyde to observe the effect of these reaction parameters on the conversion, selectivity and rate of the formation of the condensation products. All these parameters were found to influence the performance of the catalyst. The initial rate of formation of jasminaldehyde was found to be ～20% more than the rates with individual chitosan and hydrotalcite. The rate of formation of 2-pentyl-2-nonenal with CMA was found to be lower in comparison with individual catalysts, chitosan and hydrotalcite. The determined activation energy was 16.3 kJ mol^-1. The catalyst was elegantly separated, washed and dried, and found to be effectively recycled six times without any substantial loss in its activity.

Full text of DOI:10.1039/c5ra16927e

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An elegant synthesis of chitosan grafted hydrotalcite nano-bio composite material and its
effective catalysis for solvent-free synthesis of jasminaldehyde
a,b
a,b
a,b,
Jacky H. Adwani , Noorꢀul H. Khan and Ram S. Shukla
*
a
Academy of Scientific and Innovative Research (AcSIR), CSIRꢀCentral Salt and Marine
Chemicals Research Institute (CSIRꢀCSMCRI), G. B. Marg, Bhavnagarꢀ364002, Gujarat, India.
b
Inorganic Materials and Catalysis Division, CSIRꢀCentral Salt and Marine Chemicals Research
Institute (CSIRꢀCSMCRI), G. B. Marg, Bhavnagarꢀ364002, Gujarat, India.
*Corresponding author: Tel.: +91 278 2567760; Fax: +91 278 2566970.
Email: ramshukla55@yahoo.in

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Abstract
A novel nanoꢀbio composite of chitosan and a layered double hydroxide was elegantly
synthesized by coꢀprecipitation method. The nanoꢀbio composite material (CMA) was
thoroughly characterized by FTIR, TGA, XRD, SEM and TEM. The composite material CMA
had shown efficient catalytic activity for selective synthesis of jasminaldehyde under solvent free
conditions by condensation of benzaldehyde and 1ꢀheptanal. In typical employed conditions,
39.5 mmol benzaldehyde, 7.9 mmol 1ꢀheptanal, 100 mg catalyst, 160 °C and 700 rpm, a
maximum selectivity of 89% with 99% conversion was obtained. The investigations were
performed in detail as a function of amount of the catalyst, temperature and molar ratio of 1ꢀ
heptanal to benzaldehyde to observe the effect of these reaction parameters on the conversion,
selectivity and rate of the formation of the condensation products. All these parameters were
found to influence the performance of the catalyst. The initial rate of formation of
jasminaldehyde was found to be ~20% more than those of the rates with individual chitosan and
hydrotalcite. The rate of formation of 2ꢀpentylꢀ2ꢀnonenal with CMA was found to be less in
comparison of individual catalyst, chitosan and hydrotalcite. The determined activation energy
was 16.3 kJ/mol. The catalyst was elegantly separated, washed and dried, and found to be
effective for its recycling for six times without any substantial loss in its activity.

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1. Introduction
The cross aldol reaction has proved to be an important synthetic tool for C–C bond formation for
the synthesis of α, β –unsaturated carbonyl products. Conventionally, this reaction is carried in
presence of strong liquid alkali bases like NaOH or KOH taken more than in stoichiometric
quantities. The use of these alkalies results in increase in the cost of synthesis, environmental
pollution, lack of thermal stability, reusability of catalyst and post reaction workꢀup. Apart from
1
2
3
the conventional bases, several weak bases like amines , ammonium salts and amino acids are
used in a homogenized system. Later numerous heterogeneous acid and base catalysts like
4
,5
6,7
8,9
10
alkaline earth metal oxides , alumina supported hydroxide , ionꢀexchange resins , zeolites ,
1
1
12
amino group immobilized silica gel , amino acid supported gold nanoparticles , silica
1
3
14
15
immobilized piperazine , amino modified Zr–terephthate MOF and synthetic talc have been
used. These catalysts have shown the potential advantages of ease of separation, robustness, long
operating life, reusability and environmentally benign nature over the homogeneous catalysts.
The heterogeneous catalysts find their importance in the large number of processes in the
1
6
chemical industries .
The incorporation of various active components into the supports that exemplifies an increase in
1
7ꢀ19
efficiency of catalyst as a result of cooperative effect is investigated in detail
. The work by
climent et al. showed that the amorphous aluminophosphates containing acidꢀbase pairs increases
2
0,21
the selectivity without affecting the activity of the catalyst
. Using this approach, Kadib et
2
2
al. functionalized chitosan microspheres by inorganic mono metal (lewis acid) oxide clusters
for the synthesis of jasminaldehyde wherein the basic –NH sites adjacent to acidic metal center
2
accounts for the increase in the selectivity.
2
3
24
The use of solid base catalysts chitosan and hydrotalcite are reported for the synthesis of
jasminaldehyde. These catalyst systems were found to have efficient catalytic activities via an
environmental friendly route in which the hazardous liquid base KOH/NaOH was successfully
replaced with these green solid base catalysts under solvent free conditions. These two catalysts
are individually studied in detail wherein kinetic aspect of chitosan catalyzed reaction is also
dictated. Both these catalysts have shown efficient recyclability up to six times. The present
study is to have an synergic insight of the composite effect of these two chitosan and hydrotalcite
catalytic materials for selective synthesis of jasminaldehyde. The composite material of chitosan
and Mg/Al hydrotalcite had been elegantly synthesized by simple coꢀprecipitation route. This
nanoꢀbio composite material CMA had been thoroughly characterized and investigated in detail
for the synthesis of jasminaldehyde as shown in scheme 1. A kinetic insight is also substantiated
in the present work for the synthesis of jasminaldehyde by evaluating the rates of formation of
selective major product, jasminaldehyde and minor product, 2ꢀpentylꢀ2ꢀnonanal. The effects of
various parameters namely amount of catalyst, temperature and molar ratio of benzaldehyde to 1ꢀ
heptanal on the rate of the formation of jasminaldehyde were investigated.

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2
. Experimental
.1. Materials
2
Magnesium nitrate (Mg(NO ) ꢁ6H O; 98.9%), aluminum nitrate (Al(NO ) ꢁ9H O; 99.1%),
3
2
2
3 3
2
sodium hydroxide (NaOH; 99.99%) and hydrochloric acid (HCl; 35.4%) were purchased from S.
D. Fine Chemicals, India. Lowꢀmolecular weight chitosan, 1ꢀheptanal and benzaldehyde were
procured from SigmaꢀAldrich and used without further purification.
2.2. Synthesis of chitosan-hydrotalcite nano-bio composite
The chitosanꢀhydrotalcite nanoꢀbio composite was prepared by coꢀprecipitation method. In the
typical synthesis of CMA, an aqueous solution (A) of 10 g Mg(NO ) ꢁ6H O and 4.18 g
3
2
2
Al(NO ) ꢁ9H O was prepared in 100 mL of double distilled millipore water. The solution A was
3
3
2
added dropwise into second solution (B) containing lowꢀmolecular weight chitosan (5 g)
completely dissolved in 0.1 M HCl (325 mL) under vigorous stirring at room temperature for 24
h. The temperature of the bath was slowly raised to 70 °C for 2 h. The pH of the solution was
adjusted to 10 by adding 0.2 M NaOH solution whereby the initial pale yellow color solution
changed to white precipitates. The content was aged for 16 h without stirring at room
temperature and then filtered. After filtration the precipitates formed were washed with excess
millipore water until filtrate became neutral. The obtained precipitates were dried at 70 °C and
then were powdered by using mortar and pestle. The powdered material was stored in a vial
simply under atmospheric conditions.
2.3. Characterization of the catalyst
The structural studies of the catalyst were carried out by Rigaku MINIFLEXꢀII (FD 41521)
°
powder Xꢀray Diffractometer. The samples were scanned in the 2θ range of 10–80 using CuKα
(λ=1.54178 Å) radiation and a Ni filter. FTꢀIR spectra of the catalyst were recorded with Perkinꢀ
ꢀ
Elmer GX spectrophotometer system using KBr pellets in the wavelength range of 400ꢀ4000 cm
1
.
Thermogravimetric Analysis (TGA) was carried out on a Mettler TGA/DTA 851e instrument
at a nitrogen flow rate of 50mL/min. N sorption analysis was carried out at 77.4 K in
2
sorptometer (ASAP 2010, Micromeritics). The sample was degassed at 120 °C for 4 h prior to
the sorption analysis. The morphology of the composite was determined using a LEO series 1430

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VP scanning electron microscope (SEM). The size and shape of the particles were analyzed
using Transmission Electron Microscopy (JEOL JEM 2100 microscope).
2.4. Condensation reaction
The desired amounts of benzaldehyde, 1ꢀheptanal and catalyst were taken into a oven dried
double neck round bottom flask with 0.01 g tetradecane as internal standard. One neck of the
flask was fitted with refluxing condenser with spiral tube inside and other neck was blocked
using a silicon rubber septum. Water at 15 °C was circulated in the spiral tube of the condenser
and the flask was kept in an oil bath equipped with temperature controller and magnetic stirring
unit. The reaction was carried out under nitrogen atmosphere to inhibit formation of
corresponding acids from aldehydes. The reaction was carried out at 125 °C. The product
mixture was cooled down to room temperature after the completion of the reaction. The progress
of the reaction was monitored in terms of consumption of 1ꢀheptanal by taking aliquots at
different time intervals. The conversion was evaluated by considering the subsequent decrease in
concentration of 1ꢀheptanal. The analysis of product mixture was carried out by GC (Bruker 450
GC, Japan), and GCꢀMS (Shimadzu, QPꢀ2010, Japan). The GC has a 5% diphenylꢀ and 95%
dimethyl siloxane universal capillary column and a flame ionization detector (FID). The
quantification of the FID response was done by using a standard calibration curve. To ensure the
reproducibility of the reaction, repeated experiments were carried out under identical reaction
conditions. Selected representative chromatograms are given in the Supporting information (Fig.
S1 to S5). The results obtained including conversion and selectivity were found to be in the
range of 5% variation. For recyclability studies, the catalyst used after each cycle was separated
by Whatman filter paper (Grade 41), washed thrice with methanol, dried and crushed. Thus
obtained catalyst was reused under selected identical conditions of 7.9 mmol heptanal, 39.6
o
mmol benzaldehyde, 125 C, 700 rpm for 8 h reaction time.
3. Results and Discussion
3.1. Characterization of the catalyst
The characterization of the catalyst was carried out by N Sorption, FTIR, TGA, XRD, SEM and
2
2
TEM. The BET surface area of CMA composite was found to be 3.77 m /g.
3.1.1. FTIR

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The FTIR spectrum of hydrotalcite (HT), pure chitosan powder (CT) and nanoꢀbio composite
CMA) are shown in Fig 1. The typical characteristic bands in the FTIR spectrum of CT
(
2
3
24
powder as well as HT were obtained. The FTIR spectra of CT powder showed a wide OH
ꢀ1
vibrational stretching peak at 3450 cm indicating the hydrogen bonding of hydroxyl groups.
ꢀ1
The peak at 1602 cm indicates the presence of –NH group resulting from deacetylation of
2
ꢀ1
chitin. The band that appeared at 2886ꢀ2929 cm is due to the C–H stretching vibration of
ꢀ1
aliphatic CH groups and that at 1083 cm is due to the C–O–C bond stretching vibrations. The
ꢀ1
25
band at 1660 cm corresponds to amide stretching vibration . The FTIR spectrum of HT
ꢀ1
showed absorption at 3500ꢀ3600 cm which is attributed to the Hꢀbonding vibrations in the
2
ꢀ
layers of the LDH material. The characteristic shoulder bands for H O and CO3 were observed
2
ꢀ1
at 1637 and 1450 cm respectively. The shoulder due to the interlayer carbonates appeared at
ꢀ1
ꢀ1
1
380 cm . The bands obtained at 659 cm is attributed to the in plane carbonate bonding in the
ꢀ1
ꢀ
LDH. For the spectrum of CMA, a broad peak between 3100ꢀ3700 cm and centered at 3442 cm
1
was obtained and attributed to the O–H and N–H stretching vibrations. The hydroxyl groups of
ꢀ1
the brucite layer overlapped with O–H and N–H of chitosan. The band location at 1602 cm and
ꢀ1
1
560 cm changed after the composition. These results indicated strong hydrogen bonding
2
6
between the N–H groups of chitosan and O–H groups of LDH brucite layer . The bands at 420
ꢀ1
and 630 cm was due to M–O or O–M–O bonds in CMA.
3.1.2. TGA
The TGA profile (Fig. 2) for the CMA showed three step weight loss. The first weight change
11%) was observed in the range of 40ꢀ190 °C due to physically adsorbed water molecules
without any change in the structure. The second weight loss (20%) observed in the range of 210ꢀ
10 °C is attributed to the decomposition of polysaccharide chain in the nanoꢀbio composite. The
(
3
third weight loss (22%) observed in the range of 320ꢀ570 °C is due to the removal of condensed
water molecules and carbonate anion entrapped in the residual brucite layer.
3.1.3. XRD
The XRD pattern of HT, CT and CMA are shown in Fig 3. The XRD pattern of HT showed
sharp, intense and symmetric peaks at lower diffraction angles (2 = 10ꢀ25°) and a broad
asymmetric reflection at higher diffraction angles (2 = 30ꢀ50°) which are characteristic of highly
θ
θ

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2
4
crystalline layered structure . The broad diffraction peaks at 2
θ
= 10° and 21° for semicrystalline
2
7
chitosan were present in the XRD pattern of the nanoꢀbio composite. The XRD pattern of CMA
showed no significant change in the characteristic planes of HT which indicated retention of the
structure. However after the formation of the composite, a slight shift towards lower 2θ values
for peaks corresponding to (003) and (006) planes was observed which is due to concurrent
decrease of the positive charge of the layers of HT. The XRD pattern was also indicative of a
slight intercalation of the biopolymer into the LDH layer as observed by marginal shift of (001)
peak relative to parent LDH along with the retention of both the phases (CT and HT).
3.1.4. SEM
The morphology of the CMA nanobiocomposite was investigated by SEM (Fig. 4). The SEM
image revealed the grafting of the biopolymeric part over inorganic layered nanoplatelet
material. Also it showed that the nanoplatelets are spread over the polymer in the composite.
3.1.5. TEM
The TEM of the CMA composite showed that the polymer is grafted over LDH material (Fig.
a). The Fig. 5b reveals the presence of an interplanar distance of approximately 1.4 nm
5
indicating some exfoliation of the LDH material. The inset in Fig. 5b shows presence of single
LDH layers in the composite sample. The Fig. 5c shows the presence of the small particles of the
layered structure whilst the Fig 5d shows the lattice fringes of the LDH material. The inset in Fig
5d shows the electron diffraction pattern of the composite. It confirms the presence of pure
composite material.
3.2. Catalytic activity
Catalytic activity of the catalyst was investigated for the synthesis of jasminaldehyde by the
condensation of benzaldehyde with 1ꢀheptanal. A 97% conversion of 1ꢀheptanal with 80%
selectivity to jasminaldehyde was obtained within 7 h of reaction at 160 °C. On increasing the
time to 14 h, a maximum selectivity of 89% was obtained. The effect of reaction parameters like
reaction time, temperature, the catalyst amount and the heptanal to benzaldehyde molar ratio on
the conversion of 1ꢀheptanal and selectivity to jasminaldehyde has been investigated in detail.
3.2.1. Effect of catalyst amount

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The effect of the catalyst amount on condensation of benzaldehyde and 1ꢀheptanal was studied
by varying the catalyst amount from 10 to 300 mg and the corresponding results are tabulated in
Table 1. On increasing the catalyst amount from 10 to 100 mg conversion and selectivity both
increased from 40 to >99% and 76 to 86% respectively. Further increase in catalyst amount to
200 mg gave no significant change in conversion and selectivity. On increasing the amount of
catalyst to 300 mg, conversion of 1ꢀheptanal started declining with increase in selectivity
towards jasminaldehyde. As the reaction proceeds the conversion increase with decrease in the
amount of 1ꢀheptanal. As the concentration of 1ꢀheptanal decreases, benzaldehyde competes
with 1ꢀheptanal to favor the selectivity towards jasminaldehyde.
3.2.2. Effect of reaction temperature
The effect of temperature on the condensation reaction was studied by selecting the temperature
in a range of 80 to 180 °C (Table 2) maintaining other reaction parameters under identical
conditions. The conversion of 1ꢀheptanal and selectivity to jasminaldehyde were determined at
different time intervals i.e. 3, 7 and 14 h and the results are listed in Table 2. The conversion of
1
ꢀheptanal and selectivity to jasminaldehyde both increased with an increase in the temperature
from 80 °C to 160 °C. Further increase of temperature resulted in a decrease in the selectivity. A
5% conversion with 76% selectivity towards jasminaldehyde was observed at 100 °C (Entry 2)
which increased to >99% with 86% selectivity with increase in the temperature to 125 °C (Entry
). A maximum selectivity with >99% conversion of 1ꢀheptanal was observed at 160 °C which
decreased to 85% on increasing temperature to 180 °C without any change in conversion.
9
3
3.2.3. Effect of 1-heptanal to benzaldehyde molar ratio
In the effect of molar ratio of 1ꢀheptanal to benzaldehyde, the study performed in the range of the
molar ratio of 1:1 to 1:10, it was observed that the conversion increased with time and reached
up to 99% at 14 h and remained the same for the molar ratios of 1:1 to 1:5 (Entries 1ꢀ5). Further
increase in the molar ratio resulted in a decrease in conversion (Entries 6 and 7). A drop in the
conversion was observed from 99% for the molar ratio of 1:5 to 89% for the molar ratio of 1:10.
The increase in molar ratio hinders the active sites on the catalyst thus reducing the conversion.
A 59% selectivity to jasminaldehyde at 1:1 molar ratio of 1ꢀheptanal to benzaldehyde increase to
66% selectivity on increasing the molar ratio to 1:2. The selectivity was increased till molar ratio

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of 1:4 and then remained the same i.e. 86% for higher molar ratio. The selfꢀcondensation of 1ꢀ
heptanal befits lower selectivity to jasminaldehyde at lower heptanal to benzaldehyde ratios.
Thus the optimum molar ratio of heptanal to benzaldehyde was 1:5 giving >99% conversion with
86% selectivity.
3.2.4. Kinetic studies
The condensation between benzaldehyde and 1ꢀheptanal using CMA as catalyst was carried out
with respect to reaction time and the kinetic profile (Fig. 6) was obtained in terms of
consumption of 1ꢀheptanal and formation of the aldol products, jasminaldehyde and 2ꢀpentylꢀ2ꢀ
nonenal. There was a decrease in amount of 1ꢀheptanal with increase in formation of cross aldol
product, jasminaldehyde for entire time of the reaction. The decrease in the amount of 1ꢀheptanal
and formation of jasminaldehyde were almost linear upto initial 4 h of the reaction and major
conversion (~75%) occurred. After that the conversion became slow. The formation of selfꢀ
condensation product 2ꢀpentylꢀ2ꢀnonenal was increased upto 2 h and gave a slow decreasing
trend with time. It is of interest to have an insight in this decreasing trend of the selectivity of 2ꢀ
pentylꢀ2ꢀnonenal with CMA composite in comparison of the performance of the individual
2
3
24
components, CT and HT , used as catalysts for this reaction. In case of the reported individual
CT system for aldol condensation of 1ꢀheptanal and benzaldehyde, the rate of formation of the
selfꢀcondensed product, 2ꢀpentylꢀ2ꢀnonenal was observed to be continuously increasing along
with the desired cross aldol product, jasminaldehyde with respect to time. In case of individual
HT catalyzed system, the rate of formation of 2ꢀpentylꢀ2ꢀnonenal gave an initial increase
followed by decrease in the trend with respect to time. Contrary to these systems, for the present
composite system, the rate of formation of 2ꢀpentylꢀ2ꢀnonenal is observed to decrease (Fig. 6)
continuously with respect to time after 2 h, unlike the trend followed by the individual
component systems. It is believed that the composite system facilitates the suppression of the
undesired selfꢀaldol condensation which may be due to the dominant competency of the
benzaldehyde in comparison to 1ꢀheptanal present in the system. Also, this byproduct molecule
being branched may have comparatively less possibility for its egress with respect to the linear
product, jasminaldehyde. It is quite possible that unlike the individual catalyst systems, the
composite system may possess some space constraint as a result of the compactness of the
composite structure. The initial rates of formation of jasminaldehyde (equation 1) and 2ꢀpentylꢀ

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2ꢀnonenal (equation 2) were calculated from the plots of Fig. 6, from their increasing
concentration from early linear portion of the plots upto 4 h. The initial rate of consumption of 1ꢀ
heptanal (equation 3) was calculated from its decreasing concentration.
ꢂ[ꢃꢄꢅꢆꢇꢈꢄꢉꢂꢊꢋꢌꢂꢊ]
vꢀ =ꢁ
vꢎ =ꢁ
(1)
(2)
(3)
ꢂꢍ
ꢂ[ꢎꢏꢐꢊꢈꢍꢌꢉꢏꢎꢏꢈꢑꢈꢊꢈꢄꢉ]
ꢂꢍ
ꢏꢒ[ꢀꢏꢋꢊꢐꢍꢄꢈꢄꢉ]
ꢒꢓ
v =ꢁ
The rates v , v and v were divided by the employed amount of the catalyst and expressed in
1
2
2
8
terms of mmol of product per unit time per gram of the catalyst . The determined rates
mmol/h/g ) v, v and v were found to be 14.65, 13.25 and 1.25 repectively. The summation of
(
cat
1
2
the rates v +v (14.50) was found to be almost identical to v (14.65) indicating a fine rate balance
1
2
between amount of the consumption of 1ꢀheptanal and formation of the aldol products.
The variation of rate of aldol condensation with respect to catalyst amount ranging from 10 to
200 mg is shown in Fig.7. The rate of formation of jasminaldehyde linearly increased upto 100
mg of the catalyst and on further increasing the amount of the catalyst, the rates started to attain
saturation. This represented the first order dependence with respect to catalyst towards its lower
amounts. The rate of the formation of the selfꢀcondensed product increased upto 50 mg of the
23
catalyst followed by decrease in the rate. In the individual CT catalyzed synthesis of
jasminaldehyde, the rate of formation of 2ꢀpentylꢀ2ꢀnonenal was observed to increase on
increasing the catalyst amount. Thus the CMA composite catalyzed reaction here dictated its
more influence in suppressing the rate of formation of 2ꢀpentylꢀ2ꢀnonenal as shown in Fig.7 in
comparison of CT catalyzed reaction, thereby showing its potential advantage to contribute
better towards the selectivity of jasminaldehyde. The effect of rate on the temperature between
80 and 180 °C is shown in Fig. 8. On increasing the temperature the rate of formation of
jasminaldehyde increased upto 125 °C and further increase in temperature could not influence
the rate. The rate of formation of 2ꢀpentylꢀ2ꢀnonenal was increased from 80 to 100 °C and after
that a decreasing trend was observed on increasing the temperature. The temperature dependence
23
24
performances with individual catalysts, CT and HT for the aldol condensation of 1ꢀheptanal
and benzaldehyde reported are observed to be different particularly for the selectivity of the selfꢀ

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2
3
condensation product, 2ꢀpentylꢀ2ꢀnonenal. With individual CT catalyzed reaction , the rate of
formation of both the aldol products were almost linearly increased with temperature in the range
of 80ꢀ180 °C with higher rate of jasminaldehyde than 2ꢀpentylꢀ2ꢀnonenal. Like the individual
CT, similar trend of increase in selectivity with temperature was observed in individual HT
2
4
catalyzed reaction also, however the selectivity of jasminaldehyde was not much influenced.
Thus CMA composite catalyzed reaction had demonstrated a potential over both the individual
CT and HT catalyzed systems wherein the rate of 2ꢀpentylꢀ2ꢀnonenal was decreased with
temperature (Fig. 8). It is of interest to mention here that the rates v were 13.25, 10.3 and 10.1
1
2
3
for CMA, HT (calculated from ref. 24) and CT catalyzed aldol reaction respectively whereas
the rate V were 1.25, 1.80 and 2.80 for these respective catalysts. This indicated that the
2
composite based catalyst CMA afforded >20% enhancement in the rate of formation of
jasminaldehyde in comparison of the individual components, HT and CT. Also, the rate of
formation of 2ꢀpentylꢀ2ꢀnonenal was slower with CMA than that of HT/CT. The activation
energy determined from the temperature dependence from the Arrhenius plot was found to be
23
1
6.3 kJ/mol. The reported activation energy for this reaction with individual CT catalyst is 20.1
kJ/mol, which is greater than that for CMA catalyzed reaction. The lower activation energy with
CMA is again in the line of the higher reaction rate with this composite catalyst. The effect of
rate on benzaldehyde was studied with benzaldehyde amounts ranging from 7.9 and 79 mmol
(Fig. 9). With increase in the amount of the benzaldehyde the rate of formation of
jasminaldehyde increased giving the highest rate for 1ꢀheptanal to benzaldehyde ratio of 1:5. On
further increasing the amount of the benzaldehyde the rate of formations were remained almost
uninfluenced.
3.3. Catalyst recycling
The condensation reaction was performed at two different times for 3 h and 14 h in order to
observe the recyclability of the catalyst (Table 4). For the fresh catalyst, a 64% conversion with
74% was observed in 3 h of the reaction. The conversion increased to >99% along with 86%
selectivity on increasing the time to 14 h. The fresh catalyst separated by filtration was washed
thrice with methanol and dried. The catalyst was reused under identical conditions. A decrease in
the conversion from 64% to 61% for 3 h recycling was observed in the first cycle (Entries 1 and
2). The conversion and selectivity both remained almost constant up to the fourth recycle. A

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similar trend was observed for the recycling of the catalyst for 14 h. The catalyst was effectively
recycled up to six cycles without much loss in its activity and selectivity.
4. Conclusion
The chitosanꢀhydrotalcite nanoꢀbio composite (CMA), synthesized, thoroughly characterized and
investigated for the aldol condensation of 1ꢀheptanal with benzaldehyde was found to be
efficient catalyst for the selective synthesis of jasminaldehyde. The catalyst is operative under
solventꢀfree conditions, giving the highest selectivity to jasminaldehyde 89%, with >99%
conversion with 100 mg catalyst at 160 °C under optimized reaction conditions. The reaction
investigated as a function of catalyst amount, temperature and the 1ꢀheptanal to benzaldehyde
ratio was found to influence the conversion, selectivity and rate of the reaction. On increasing the
catalyst amount the rate of formation of jasminaldehyde was effectively increased while that of
2ꢀpentylꢀ2ꢀnonenal, increased first and then showed a decreasing trend. On increasing the
temperature the rate of formation of jasminaldehyde increased while the rate of formation of 2ꢀ
pentylꢀ2ꢀnonenal tended to decrease. The initial rates of the formation of jasminaldehyde (v1)
were found to be more while the rate of formation of 2ꢀpentylꢀ2ꢀnonenal (v ) were less with
2
CMA as compared to the individual catalysts, CT and HT. The activation energy (16.3 kJ/mol)
with CMA was found to be less than that of the reported (20.1 kJ/mol) with the individual CT
catalyst.
5. Acknowledgement
CSMCRI communication No. IMCꢀ03 CSIRꢀCSMCRI – 143/2015. The authors thank Council
of Scientific and Industrial Research (CSIR), New Delhi, India for financial supports for
Network project for the Innovate Develop and Up Scale Modular, Agile, Intensified and
Continuous Processes and Plants (INDUS MAGIC) and the Analytical Division and Central
Instrumentation Facility of CSIRꢀCentral Salt and Marine Chemicals and Research Institute,
Bhavnagar, for providing instrumental analysis.

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Scheme 1. Synthesis of jasminaldehyde.
Fig. 1. FTIR Spectra of HT, CT, and CMA.
Fig. 2. TGA profile of CMA.
Fig. 3. XRD pattern of HT, CT, and CMA.
Fig. 4. SEM images of CMA.
Fig. 5. TEM images of CMA.
Fig. 6. Kinetic profile: catalyst = 100 mg, heptanal = 7.9 mmol, benzaldehyde = 39.5 mmol,
temperature = 125 °C and 700 rpm.
Fig. 7. Dependence of rate on the amount of catalyst: heptanal = 7.9 mmol, benzaldehyde = 39.5
mmol, temperature = 125 °C and 700 rpm.
Fig. 8. Dependence of rate on the temperature: catalyst =100 mg, heptanal = 7.9 mmol,
benzaldehyde = 39.5 mmol and 700 rpm
Fig. 9. Dependence of rate on the benzaldehyde: catalyst =100 mg, heptanal = 7.9 mmol,
temperature = 125 °C and 700 rpm.
Table 1 Effect of catalyst amount on the selectivity of jasminaldehyde
Table 2 Effect of reaction temperature on the selectivity of jasminaldehyde
Table 3 Effect of 1ꢀheptanal (H) to Benzaldehyde (B) ratio on the selectivity of jasminaldehyde
Table 4 Reusability of the catalyst

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Scheme 1. Synthesis of jasminaldehyde

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CMA
CT
1
602
4
20
6
30
1660
1602
3
442
1
083
HT
3
450
1
637
450
1
1
380
6
59
4000
3500
3000
2500
2000
1500
1000
500
-1
wavelength (cm )
Fig. 1. FTIR Spectra of HT, CT and CMA.

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100
9
8
7
6
5
0
0
0
0
0
100
200
300
400
500
600
700
o
Temperature C
Fig. 2. TGA profile of CMA.

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CMA
CT
HT
10
20
30
40
50
60
70
2
θ
Fig. 3. XRD pattern of HT, CT and CMA.

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Fig. 4. SEM images of CMA.

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Fig. 5. TEM images of CMA.

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8
7
6
5
4
3
2
1
0
1
ꢀheptanal
Jasminaldehyde
ꢀpentylꢀ2ꢀnonenal
2
0
2
4
6
8
10
12
14
Reaction time (h)
Fig. 6. Kinetic profile: catalyst = 100 mg, heptanal = 7.9 mmol, benzaldehyde = 39.5 mmol,
temperature = 125 °C and 700 rpm.

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1.4
1.2
1.0
0.8
0.6
0.4
0.2
Jasminaldehyde
ꢀpentylꢀ2ꢀnonenal
2
0
50
100
150
200
Catalyst amount (mg)
Fig. 7. Dependence of rate on the amount of catalyst: heptanal = 7.9 mmol, benzaldehyde = 39.5
mmol, temperature = 125 °C and 700 rpm.

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1
1
1
4
2
0
8
6
4
2
0
Jasminaldehyde
ꢀpentylꢀ2ꢀnonenal
2
80
100
120
140
160
180
o
Temperature ( C)
Fig. 8. Dependence of rate on the temperature: catalyst =100 mg, heptanal = 7.9 mmol,
benzaldehyde = 39.5 mmol and 700 rpm

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1
1
1
4
2
0
8
6
4
2
0
Jasminaldehyde
2ꢀpentylꢀ2ꢀnonenal
0
10
20
30
40
50
60
70
80
Benzaldehyde (mmol)
Fig. 9. Dependence of rate on the benzaldehyde: catalyst =100 mg, heptanal = 7.9 mmol,
temperature = 125 °C and 700 rpm.

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Table 1 Effect of catalyst amount on the selectivity of jasminaldehyde
Conversion (%)
Selectivity (%)
Catalyst
amount
Entry
Jasminaldehyde
2ꢀpentylꢀnonꢀ2ꢀenal
3
h
7 h
14 h
(mg)
3
h
7 h
68
14 h
76
3 h
48
7 h
32
14 h
24
1
2
3
4
5
6
7
10
30
50
20
22
47
64
80
84
85
27
34
60
85
92
95
97
40
55
52
61
68
74
75
78
65
72
71
78
78
79
71
78
78
86
85
85
79
39
32
26
25
22
35
28
29
23
22
21
29
22
22
14
15
15
21
85
100
150
200
300
>99
>99
100
100
o
Reaction conditions: heptanal=7.9 mmol, benzaldehyde=39.6 mmol, temperature=125 C

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Table 2 Effect of reaction temperature on the selectivity of jasminaldehyde
Conversion (%)
Selectivity (%)
Temp.
Entry
Jasminaldehyde
2ꢀpentylꢀnonꢀ2ꢀenal
o
(
C)
3 h
7 h
14 h
3
h
7 h
29
14 h
3 h
7 h
71
14 h
65
1
2
3
4
5
6
80
53
56
64
68
80
90
77
80
85
90
97
98
90
0
35
76
86
88
89
85
100
100
125
140
160
180
95
54
74
76
77
83
67
78
79
80
85
46
26
24
23
17
33
23
21
20
15
24
14
12
11
15
>99
>99
>99
>99
Reaction conditions: heptanal=7.9 mmol, benzaldehyde=39.6 mmol, catalyst=100 mg

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Table 3 Effect of 1ꢀheptanal (H) to Benzaldehyde (B) ratio on the selectivity of jasminaldehyde
Conversion (%) Selectivity (%)
Jasminaldehyde 2ꢀpentylꢀnonꢀ2ꢀenal
Entry
H:B
3
h
7 h
14 h
3
h
7 h
54
14 h
59
3 h
57
7 h
46
14 h
41
1
2
3
4
5
6
7
1:1
1:2
1:3
1:4
1:5
1:7
1:10
78
95
97
97
88
85
76
59
99
99
43
55
57
71
74
69
68
84
80
75
64
46
34
61
72
74
78
72
71
66
73
80
86
86
86
45
43
29
26
31
32
39
28
26
23
28
29
34
27
20
14
14
14
99
99
>99
93
89
o
Reaction conditions: heptanal=7.9 mmol, catalyst= 100 mg, temperature=125 C

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Table 4 Reusability of the catalyst
Conversion (%)
Selectivity (%)
Jasminaldehyde 2ꢀpentylꢀnonꢀ2ꢀenal
Catalyst
recycle
Entry
3
h
14 h
3
h
14 h
86
3 h
26
14 h
14
1
2
Fresh
64
61
>99
99
74
72
First
recycle
85
85
28
30
15
15
Second
recycle
3
4
5
6
59
58
58
56
95
92
89
85
70
67
67
65
Third
recycle
83
80
78
33
33
35
17
20
Fourth
recycle
Fifth
recycle
22
o
Reaction conditions: heptanal=7.9 mmol, benzaldehyde=39.6 mmol, temperature=125 C