Fixation of CO2 as a carboxylic acid precursor by microcrystalline cellulose (MCC) supported Ag NPs: A more efficient, sustainable, biodegradable and eco-friendly catalyst

Article abstract of DOI:10.1039/c8nj06373g

Silver nanoparticles supported on microcrystalline cellulose (Ag NPs@MCC), an active catalyst, has been discovered for the direct carbonylation of terminal alkynes with CO₂ into carboxylic acid under mild and sustainable reaction conditions. The stabilized Ag NPs show higher distribution with a uniform particle size. The catalyst was characterized by PXRD, SEM, TEM, HR-TEM, EDS, EDX, ICP-AES and XPS analysis. The Ag NPs@MCC material was found to be more efficient, shows excellent dispersion in various solvents and is biodegradable. The solvent effects on carbonylation of terminal alkynes were well studied both experimentally and computationally. Furthermore, the present catalyst can be recycled in up to five catalytic cycles without significant loss of its activity and is also applicable for the gram scale carbonylation of terminal alkynes.

Full text of DOI:10.1039/c8nj06373g

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PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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Fixation of CO as Carboxylic Acid Precursor by Microcrystalline
DOI: 10.1039/C8NJ06373G
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Cellulose (MCC) Supported Ag NPs: A More Efficient, Sustainable,
Biodegradable and Eco-friendly Catalyst
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Dharmesh J Shaha, Anuj S Sharmab, Akshara P Shahc, Vinay S Sharma*a, Mohd
Athard, Jigar Y.Sonia
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a:Department of Chemistry, Faculty of Basic and Applied Science, Madhav University,
Sirohi, Rajasthan, India
b:Department of Chemistry, School of Science, Gujarat University, Ahmedabad, India
c: Department of Chemistry, University of Mumbai, Santacruz (East), Mumbai, India
d:Department of Chemistry, School of Chemical Sciences, Central University of Gujarat,
Gandhinagar, India
Email of corresponding author: vinaysharma3836@gmail.com
ABSTRACT
Silver Nanoparticles supported on microcrystalline cellulose (Ag NPs@ MCC), an
active catalyst has been discovered for the direct carbonylation of terminal alkynes with CO2
in to carboxylic acid at mild and sustainable reaction conditions. The stabilized Ag NPs
shows higher distribution with uniform particle size. The catalyst was characterized by
PXRD, SEM, TEM, HR-TEM, EDS, EDX, ICP-AES and XPS analysis. Ag NPs@ MCC
material were found to be more efficient, shows excellent dispersion in various solvents and
biodegradable. The solvents effects on carbonylation of terminal alkynes were well studied
by experimentally and computationally. Further, the present catalyst can be recyclable up to
five catalytic cycles without significant loss in its activity and also applicable for the gram
scale carbonylation of terminal alkynes.
KEYWORDS: Microcrystalline Cellulose (MCC), Carboxylic acid, CO2
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INTRODUCTION
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Carbon dioxide is an abundant greenhouse gas, renewable carbon source and an
environmentally friendly chemical reagent present on earth. However, its atmospheric
concentration has risen day by day which contributes in growing problems such as climate
change and global warming. To mitigate the emission reduction, CO2 capture and its
utilization in to various applications is one of the best solutions. Importantly, CO2 constitutes
a highly attractive C1- building block in synthetic organic chemistry due to its abundant
supply from industries and easy handling. In contrast, only few industrial-scale catalysis
processes have been developed that use carbon dioxide as a carbon source.1-6 This is
attributed due to the fact that CO2 is low in energy, thermodynamically stable, chemically
inert, less reactive, highly symmetrical and more difficult to activate for bond formation.
Thus, strong nucleophiles or harsh reaction conditions were usually required when carbon
dioxide is utilized in organic syntheses. Significant efforts have been developed to transform
carbon dioxide into high-value chemicals.7-9
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The transition-metal-catalyzed carboxylation reactions of various carbon nucleophiles
with C–C bond formation have been actively developed for the preparation of fine chemicals.
In this regards, the demand of more efficient, robust and sustainable catalyst material increase
due to its ability to activate as well as convert CO2 in to some valuable organic chemicals
more effectively.10-12 Silver, is a coinage metal, which has been widely utilized in various
organic syntheses. In present time, silver catalyzed activation of inactivated C-H bonds into
desired functionalities has emerged as a powerful method in organic synthesis. Moreover, the
transition-metal-catalyzed C-H bond functionalization could offer green and sustainable
methodology to construct diverse organic molecules starting from simple and easily available
compounds.13-16
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Propiolic acids are belongs to the more valuable intermediates and successVfiuewllAyrticle Online
DOI: 10.1039/C8NJ06373G
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applied in the various biological important molecules (Figure 1). Traditionally, the syntheses
of propiolic acids carried out by the oxidation of propargylic alcohols or aldehyde,
deprotonation of alkynes with strong bases such as alkali metal hydrides or organometallic
reagents. However, these methods are not environmental friendly.17-19 Literature reports
indicate that different homogeneous catalysts have been well developed to afford the higher
yield of Propiolic acid.20-22 However, major bottleneck of these catalysts are its recyclability
issues and its metal contamination in to the desired product that made this protocol less
sustainable and applicable. To overcome this issues, metal nanoparticles (NPs) are intensely
researched in the field of catalysis, as they combine the recyclability of heterogeneous
catalytic systems and the activity and selectivity of homogeneous ones.25-30 After that, several
supported metal nanocatalyst (heterogeneous catalysts) have been well reported for the
synthesis of Propiolic acid. In 2014, Cheng and co-worker have synthesized Ag NPs/MIL-
101 (zeolite-type metal-organic framework) material and demonstrated its applicability for
the synthesis of Propiolic acid. However, the need of higher loading and recyclability issues
would render its applicability.31 Previously, Huang and co-worker have developed a silica
supported Schiff-base based silver catalyst and its shows higher activity towards the synthesis
of Propiolic acid. However, the aggregation of silver nanoparticles that affect its catalytic
performance.32 In recent report, similar group have reported mesoporous knitting aryl
network polymers supported silver nanoparticles (Ag NPs/KAPs). It has noted that the
materials exhibits narrow size distribution of Ag NPs and achieved higher yield of desired
product. However, this strategy required tedious workup for the preparation of the catalyst
material.33
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Figure 1. Various important organic molecules synthesis from the Propiolic Acids.
Thus, the development of a more efficient, sustainable, low cost, easily available and
bio-degradable supported silver nanocatalyst is must require for the fixation of CO2 into
corresponding to Propiolic acid under milder and greener reaction conditions. In the present
work, we have synthesized Ag NPs supported on MCC (Ag NPs/MCC) and investigated its
performance towards the fixation of CO2 via C-H bond activation of terminal alkyne. The
present catalyst shows excellent dispersion, higher activity, scalability, and recyclability.
Importantly, the solvents effects on carbonylation of terminal alkynes were well studied by
experimentally and computationally. Further, the applicability of the Propiolic acid was
exploded for the synthesis of aminoindolines, pyrrolo [1,2a] quinoline and arylacetylenic
sulfones.
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RESULT AND DISCUSSION
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Synthesis and Characterization of Ag NPs/MCC material
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Microcrystalline Cellulose (MCC) is an interesting conjugated polymer and composed
of glucose units connected with a 1, 4-β glycosidic bond. It exhibits unique properties
including such as renewable, biodegradable, non-toxic, thermally stable, superior mechanical
strength, inexpensiveness, excellent dispersion, controllable surface chemistry and
environmental sustainability made this material highly favourable for the catalysis support. 34-
35 The catalyst was synthesized by sorption reduction method. After impregnation of Ag NPs
the colour of support material changed from white to light reddish brown. The catalyst was
centrifuged, washed with water, dried and isolated as a light reddish brown coloured powder.
The catalyst system was characterize by different sophisticated analytical techniques such as
energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), X-ray
photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), powder X-ray
diffraction (PXRD), inductively coupled plasma atomic emission spectrometry (ICP-AES),
and transmission electron microscopy (TEM) and high-resolution-transmission electron
microscopy (HR-TEM).
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The crystalline phase of the Ag NPs/MCC was characterized by powder XRD. The
finely amorphourous powdered MCC did not show any peak, only a broad hump was
observed at 2θ value at 15.73˚ and 22.61˚ which indicated the amorphous nature of the
carbon matrix. (Figure S1). When this MCC material was impregnated with silver
nanoparticles, it showed four characteristic peaks at 38.37˚, 44.51˚, 64.69 ˚ and 77.61˚ in the
XRD spectrum and conferring (111), (200), (220) and (311) facets of the face centered cubic
(fcc) symmetry. It confirmed Ag NPs pattern agreed as per JCPDS card no. 04-0783 and
suggesting that the Ag NPs were crystalline in nature as represented in Figure 2 (A).36 The
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average particles size of Ag NPs calculated from the Scherrer’s equation was found to be 5-
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10 nm. The oxidation state and surface property of silver nanoparticles supported on MCC
was also investigated by X-ray photoelectron spectroscopy. The 3d orbital of silver clearly
resolved in to Ag 3d5/2 and Ag 3d3/2 contributions centred at 368.4 eV and 374.4 eV
respectively depicted in Figure 2 (B), which are in good agreement with the binding energies
of metallic silver Ag (0).37
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Figure 2. PXRD of Ag NPs/MCC (A) and deconvoluted XPS spectra of Ag3d (B).
The FT-IR spectra shown in Figure 3 exhibit the patterns of the functional groups
present in both MCC and Ag NPs/MCC. The observed peaks in the range of 3660-2900 cm-1
is characteristic peak for stretching vibration of O-H and C-H bonds present in
polysaccharides. In addition, the broad peak observed at 3331 cm-1 is the characteristic for the
confirmation of the stretching vibration of the hydroxyl group present in polysaccharides.
The band observed at 2864 cm-1 is mainly attributed due to the C-H stretching vibration of all
hydrocarbons in polysaccharides. The peaks found at 1633 cm-1 correspond to the vibration of
water molecules that absorbed in micro crystalline cellulose. Apart from that, the absorption
bands observed at 1428, 1367, 1334, 1027 cm-1 and 896 cm-1 belong to stretching and
bending vibrations of –CH2, -CH, -OH and C-O bonds in micro crystalline cellulose. The
band around 1420-1430 cm-1 is associated due to the amount of the crystalline structure of the
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cellulose, while the band at 897cm-1 is assigned to the amorphous region in cDeOllIu: 1l0o.1s0e3.93/8C-83N9J06373G
After impregnation of MCC with Ag NPs, all absorption peak positions are almost similar to
those present in the case of MCC, which indicated that the structure of MCC is not much
changed after the impregnation with Ag NPs.
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Figure 3. FT-IR spectrum of MCC and Ag NPs/MCC.
Scanning electron microscopy (FE-SEM) was used to study the composition and
surface morphology of Ag NPs/MCC. The results clearly show that there is a no change in
the morphology of Ag NPs/MCC shown in Figure 4 as compared with MCC (Figure S2).
The EDS mapping (Figure 5) and EDX spectra (Figure 6) evaluated the presence of Ag and
also indicate the homogenous distribution of Ag NPs. Total quantity of Ag loaded on to MCC
was investigated by ICP-AES analysis. 500 mg of catalyst material was incinerated in a
crucible for 2h at 550 ˚C. The residue was dissolved in 1 mL aqua regia and diluted to 5 mL
with distilled water. The average concentration of silver (3 trials) as determined by ICP-AES
was found to be 0.0275 mmol/ 500 mg (0.8 mg/ 500 mg).
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Figure 4. SEM images of Ag NPs/MCC.
Figure 5. EDS mapping of Ag NPs/MCC.
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Figure 6. EDX spectrum of Ag NPs/MCC.
Furthermore, the internal morphology and size of Ag NPs were characterized from
transmission electronic microscopy (TEM). TEM images of the Ag NPs/MCC catalyst
material are represented in Figure 7. As shown, all of the Ag NPs were spherical in shape
and well dispersed into the support without any aggregation. The particle sizes of Ag NPs
were between 2-10 nm as illustrated in histogram. TGA studies for MCC and Ag NPs/MCC
were carried out and the graph of the percentage weight loss versus temperature is
represented in Figure S3 and Figure S4. In case of MCC, slow initial weight loss was
attributed to moisture or monomers thereafter, the degradation was rapid between 200 and
380 ˚C which was mainly due to the concurrent cellulose degradation processes including de-
polymerization, dehydration and decomposition of glycosyl unit followed by the formation of
charred residue. (Figure S3). Final residue at 650 ˚C was 6.910 %. TGA of Ag NPs/MCC
showed similar pattern however; in comparison the residue left at 650 ˚C was large (9.684
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%). This large increase in the amount of residue was mainly attributed to Ag NPs (Figure
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S4).
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Figure 7. TEM and HR-TEM images of Ag NPs/MCC.
Catalyst potential for Ag NPs/MCC material
Our main objective was to design and develop an active silver based biodegradable,
non-toxic and heterogeneous catalyst that can facilitate the carboxylation of phenyl acetylene
via C-H bond activation under milder and sustainable reaction conditions. In this regard,
microcrystalline cellulose based catalyst would not only render the procedure greener but also
applicable in industries and academia in large scale synthesis due to its several promises.
Thus, microcrystalline cellulose (MCC) was successfully used as support material for the
stabilization of silver nanoparticles (Ag NPs). The silver nitrate (AgNO3) was immobilized
over MCC surface via noncovalent interaction with MCC. At initial stage, the comparative
catalytic potential of this material (Ag NPs/MCC) were evaluated for the carbonylation of
acetylene in to propiolic acid via C-H bond activation reaction. For our initial study, we
selected carboxylation of phenyl acetylene as a model reaction (Scheme 1). The experimental
set up was represented in Figure S5.
The investigation of the effect of various parameters such as catalyst quantity,
solvents, reaction time and temperature were also studied on this reaction to achieve the best
optimization reaction condition. It has shown that, when the reaction was performed with
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AgNO3 or microcrystalline cellulose (MCC) alone as catalyst, trace conversion were
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observed (Entries 1, 2, Table 1). However, the Ag NPs/MCC catalyst shows excellent yield
of product (99 %) at 50 ˚C after 16h in DMSO (Entry 4, Table 1). In addition, the reaction
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was also carried out with absence of catalyst and observed no progress of the reaction. (Entry
3, Table 1). These results revealed that the catalyst was necessary to proceed the reaction.
Scheme 1. Carbonylation of Phenyl acetylene via C-H bond activation catalyzed by Ag
NPs/MCC.
Importantly, the effect that a solvent exerts on a rate of heterogeneously catalyzed
reaction mainly depends on reaction substrates and support material of catalyst. It has shown
that the solvents do not merely acts as diluent in which the reactants are dissolved; they can
also interact with the catalyst surface and modify the extent to which different kind of
substrates are absorbed on the surface of catalyst [40]. The solvents used in the experiments
were methanol (MeOH), dimethyl sulphoxide (DMSO), dimethyl formamide (DMF), toluene
and acetonitrile. The best yield of phenyl propiolic acid (99 %) was obtained in DMSO
(Entry 4, Table 1). However, 50 % yield was found in DMF (Entry 6, Table 1), 20 % yield
in MeOH (Entry 5, Table 1) and trace yield of desired product in case toluene and MeCN
respectively.
Further, the effects of various bases such as sodium carbonate (Na2CO3), potassium
carbonate (K2CO3) and trimethyl amine (NEt3) were screened. It has concluded that the poor
yield was noticed in all these bases (Entries 12-14, Table 1). Literature reports indicate that
the caesium carbonate (Cs2CO3) is one of the most commonly used bases to precede the
reaction with well product yield. In our studied, the best yield of product was formed in case
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of Cs2CO3. Importantly, it has shown that the combination of Cs2CO3 with DMSO plays a
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crucial role to boost the conversion to the desired product with high yield. In addition, the
stronger polar solvent (DMSO) may promote the dissolution of Cs2CO3 in the liquid phase,
which was responsible for alkynes to free the terminal protons by forming the Ag-C
intermediates for further carboxylation. 33, 41
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After successfully optimization of the base and solvent, the effect of temperature on
the carbonylation of phenyl acetylene was investigated by changing the reaction temperature
from 40 ˚C to 50˚C. In our delight, the yield of phenyl propiolic acid was increased from 67
% to 99 %. In addition, the reaction was also conducted at room temperature and observed
that the poor yield of product be formed (Entry 17, Table 1). Therefore, 50 ˚C was selected
as an optimal temperature. It was also shown that the yield of phenyl propiolic acid was
increased from 42 % to 99 % as increasing the reaction time from 5h to 16 h. The maximum
yield of product was achieved after 16 h. After successfully achieved the optimum reaction
time, the effect of catalyst dose was examined by changing the amount of catalyst while
keeping the other parameters constant. As we increased the catalyst dose from 20 mg to
30mg, the product yield increased from 82.7 to 99.0 %. We found that the best yield of
product was obtained with 30 mg of catalyst (2.0 mol % of Ag). Further increasing the
catalyst quantity from 30 mg to 50 mg, the yield was drastically decreased from 99 % to 58.7
%.
Table 1. Catalyst Screening and Reaction optimizationa.
Entry
Catalyst
Solvent
Base
Time (h)
Yield (%)a, b
T (˚C)
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AgNO3
MCC
DMSO
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
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Trace
N.R
99
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DOI: 10.1039/C8NJ06373G
DMSO
DMSO
DMSO
MeOH
DMF
No Catalyst
Ag NPs/MCC
Ag NPs/MCC
Ag NPs/MCC
Ag NPs/MCC
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CH3CN
Traces
8
Ag NPs/MCC
Ag NPs/MCC
Ag NPs/MCC
Ag NPs/MCC
Ag NPs/MCC
Toluene
DMSO
DMSO
DMSO
DMSO
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Na2CO3
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Traces
82.7
55.9
58.7
02 %
9c
10d
11e
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Ag NPs/MCC
Ag NPs/MCC
Ag NPs/MCC
Ag NPs/MCC
Ag NPs/MCC
Ag NPs/MCC
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
K2CO3
NEt3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
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10
16
16
50
50
50
50
RT
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Traces
Traces
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65
Traces
67
a Reaction Conditions: Alkyne (1 mmol), Catalyst (30 mg), Cs2CO3 (1.5 mmol), CO2 (1 atm),
DMSO (5 mL), 16 h, = Reaction was performed by Ag NPs/MCC ( 30 mg). = Reaction
was performed by Ag NPs/MCC (20 mg), d = Reaction was performed by Ag NPs/MCC (40
mg), e = Reaction was performed by Ag NPs/MCC (50 mg)
b
c
A wide substrate scope was subjected to C-H activation of terminal alkyne to
corresponding to carboxylic acid derivatives catalyzed by Ag NPs/MCC. In our delight, the
carboxylation of phenyl acetylene and its derivatives (electron withdrawing and electron
donating) were preceded smoothly leading to the formation of corresponding carboxylic
derivatives. In case of Cyclopropyl acetylene and 1-hexyne derivatives, gave lower yield of
product as compare to phenyl acetylene and its different substituents. Therefore, it is revealed
that the Ag NPs/MCC catalyst can be widely and efficiently used for CO2 fixation by
terminal alkynes as carboxylic acids precursor.
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Table 2. Scope of Carbonylation of various terminal alkynes catalyzed by Ag NPs/MCC.
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Entry
1
Reactant
Product
Yield (%)
99
COOH
COOH
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98
2
3
COOH
OCH3
OCH3
COOH
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4
NO2
NO2
COOH
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6
98
99
Br
Br
COOH
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F
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COOH
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98
7
8
OH
OH
COOH
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92
Cl
Cl
COOH
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90
99
COOH
10
11
F
F
O
O
F3C
F3C
COOH
85
87
COOH
12
13
COOH
92
90
S
S
COOH
14
F3C
CF3
F3C
CF3
a Reaction Conditions: Alkyne (1 mmol), Ag NPs/MCC (30 mg), CS2CO3 (1.5 mmol), CO2 (1
atm), 50 ˚C, DMSO (5 mL), 16 h, Isolated yield.
Based on the literature reports, we have proposed the reaction mechanism for the
selective C-H carbonylation of terminal acetylene with CO2 catalyzed by Ag NPs/MCC. At
initial stage, the C-H bond (sp hybridization) of terminal alkyne was first coordinated to the
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Ag NPs present on MCC. After that, it was deprotonated by the presence of Cs2CO3 to form
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silver acetylide intermediate (Figure S6, 1). Then the electrophilic attack of carbon dioxide
taking place to the silver acetylide complex to demonstrate the transition state (Figure S6, 2).
Afterwards, the formation of the silver carboxylate (Figure S6, 3) followed by the
transmetallation in presence of Cs2CO3 and terminal alkyne molecules to form cesium
carboxylate (Figure S6, 4). Subsequently, the reaction mixture was acidified with
concentrated HCl up to pH = 1 to afford the desired product (Figure S6, 5). Importantly, it
was noticed that the synergistic effect between silver NPs and Cs2CO3 can play a more
crucial role to enhance the activity of present catalyst material (Ag NPs/MCC).
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Here, the key transition state (Figure S6, 2) in the solvent was investigated by density
functional theory (DFT) calculations. In this following step, the complex of deprotonated
phenyl acetylene is considered as the reactant molecule. The following Figure S7 displays the
relative free energy profiles for the Ag NPs catalyzed carbonylation of phenyl acetylene with
CO2 via C-H bond activation in different solvents such as DMSO, DMF, MeOH, Toluene and
acetonitrile solvent. In case of DMSO, deprotonated phenylacetylene coordinates with CO2
with the alkynyl C≡C triple bond by a moderate energy barrier of 13.75 kcalmol-1 (EDMSO).
The desired product was formed by the coordination of PhC≡C-COO to the Ag NPs with
decreasing energy (-4.74 Kcalmol-1) in comparison to the complex of deprotonated
phenylacetylene (Figure S7, Table S1). Therefore, the result obtain from DFT calculation
indicates that the Ag NPs could be an effective catalyst for the carbonylation of phenyl
acetylene via C-H bond activation. In addition, based on the literature and our finding
indicates that the higher polar solvent (DMSO) may be more beneficial and efficient for the
synthesis of propiolic acid.32
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Further, to investigate the scalability of our optimized reaction conditions, aDOgIr: a10m.10-3s9c/Ca8leNJ06373G
reaction was conducted by using 0.348 g of phenyl acetylene. In our delight, the scale-up
reaction afforded the phenyl propiolic acid with 85 % yield after 16 h (Scheme 2).
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Scheme 2. Gram-Scale Synthesis of Phenyl propiolic acid catalyzed by Ag NPs/MCC.
Phenyl propiolic acid was further derivatized into useful heterocyclic compounds and
organo sulfone such as aminoindolines, pyrrolo[1,2a] quinoline and arylacetylenic sulfones
(Scheme 3). Aminoindolizine and pyrrolo[1,2-a] quinolines are the most significant structural
frameworks found in various natural products as well as in various drugs.42 In further, the
present catalyst material Ag NPs/MCC was successfully applied for the synthesis of
aminoindolizine and pyrrolo [1,2a] quinoline via A3 coupling reaction with decarboxylative
pathway. The desired products such as aminoindolines and pyrrolo [1,2a] quinoline were
obtained with excellent yield (96-98 %) in ethylene glycol as recyclable and biodegradable
solvent. Furthermore, the arylacetylenic sulfone was synthesized by the treatment of phenyl
propiolic acid with iodine and tert-butyl hydroperoxide (TBHP) to form the desired product
with 92 % yield.43
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Scheme 3. Synthetic Application of the Phenyl propiolic acid.
Further, to investigate the stability and reusability of the present catalyst from the
viewpoint of industrial application, a set of experiments was performed at 1 mmol scale of
phenyl acetylene using the model reaction and optimization reaction conditions. After the
completion of reaction, the catalyst was recovered using a filtration, washed with hot acetone
to remove the sorbed product, and further reused for the next cycle. The results indicated that
the Ag NPs/MCC catalyst could be recycled and reused up to five cycles with slightly
decrease its activity (Figure 8). In addition, the absence of metal leaching was further
confirmed by using ICP-AES analysis of the catalyst before and after completion of the
reaction. The concentration of silver present in fresh catalyst was found to be 2.5 mol %. It
was observed that the concentration of elemental silver was found to be almost constant up to
the three runs (2.41 mol %). However, its concentration was decreased after fifth run (2.2 mol
%). This is mainly due to the loss of catalyst mass during the mechanically operation;
separation, filtration and drying process.
To evaluate the effect of particle size and morphology of the silver nanoparticles,
TEM analysis was carried out for the recovered catalyst after five cycles. The results
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indicated that the most of the particles were found between 5-12 nm. Slightly agDgOloI: m10.e10r3a9t/iCo8nNJ06373G
was found that results some bigger size particles mainly due to the migration and coalescence
of silver nanoparticle that were usually possible at the exposed surface of the MCC (Figure
S8). The IR and XRD spectrum of the recycled catalyst was also performed and it has found
that no other peaks were recorded (Figure S9, Figure S10). These results illustrate that the Ag
NPs/MCC catalyst behaves as a heterogeneous catalyst for the carbonylation of terminal
acetylene via C-H bond activation reaction. The catalytic activity of Ag NPs/MCC for the
synthesis of phenyl propiolic acid was compared with that of previous work related to silver
based catalysts with different supports material (Table S2). The Ag NPs/MCC shows higher
yield of desired product with good substrate scope. Further, the catalyst was also more
effective for the scalable synthesis of propiolic acid (3 mmol), easier to synthesized, cost-
effective, biodegradable, non-toxic and recyclable.
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Figure 8. Reusability of Ag NPs/g-C3N4 towards the Carboxylation of phenyl acetylene.
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CONCLUSIONS
In conclusion, we have developed a greener and sustainable protocol for the carboxylation of
terminal alkynes with CO2 corresponding to propiolic acid via C-H bond activation of the
terminal alkyne catalyzed by Ag NPs/MCC catalyst. The silver nanoparticles can be
introduced homogeneously into the micro crystalline cellulose (MCC) material. Importantly,
the synergy between the Ag NPs and the MCC shows higher activity for the carboxylation of
terminal alkynes. Moreover, the present catalyst material shows higher thermal stability, non-
toxicity, inexpensiveness, excellent dispersion, easily synthesize and provide researcher a
sustainable catalyst material for the development of higher yield of propiolic acid under mild
reaction condition. In addition, the following catalyst material also shows higher recyclability
and stability and can further reused up to five cycles without significant loss of its activity
under the optimization reaction conditions.
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Acknowledgments
DS, VS, JS acknowledge thanks to Department of Chemistry, Faculty of Basic and
Applied Science, Sirohi, Rajasthan for providing lab facility. AP is thankful to the University
Grants Commission, New Delhi, India for providing financial support under the MANF
(Maulana Azad National Fellowship). MA gratefully acknowledges the financial assistance
provided by Department of Science & Technology (DST)-Innovation in Science Pursuit for
Inspired Research (INSPIRE), (New Delhi). The authors also acknowledge thanks to Oxygen
Healthcare-Ahmedabad (O2h), MNIT Jaipur for providing analytical and spectral services.
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GRAPHICAL ABSTRACT
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