Nanoscience and NanotechnologyVol. 15, 8243–8250, 2015
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Synthesis and Characterization of AlCl3Impregnated Molybdenum Oxide as Heterogeneous
Nano-Catalyst for the Friedel-Crafts AcylationReaction in Ambient Condition
Arvind H. Jadhav, Amutha Chinnappan, Vishwanath Hiremath, and Jeong Gil Seo∗
Department of Energy and Biotechnology, Energy and Environment Fusion Technology Center, Myongji University,Myongjiro 116, Cheoin-gu, Yongin-si, Gyeonggi-do 449-728, South Korea
Aluminum trichloride (AlCl3� impregnated molybdenum oxide heterogeneous nano-catalyst was pre-pared by using simple impregnation method. The prepared heterogeneous catalyst was character-ized by powder X-ray diffraction, FT-IR spectroscopy, solid-state NMR spectroscopy, SEM imaging,and EDX mapping. The catalytic activity of this protocol was evaluated as heterogeneous catalystfor the Friedel-Crafts acylation reaction at room temperature. The impregnated MoO4(AlCl2�2 cata-lyst showed tremendous catalytic activity in Friedel-Crafts acylation reaction under solvent-free andmild reaction condition. As a result, 84.0% yield of acyl product with 100% consumption of reactantsin 18 h reaction time at room temperature was achieved. The effects of different solvents systemwith MoO4(AlCl2�2 catalyst in acylation reaction was also investigated. By using optimized reac-tion condition various acylated derivatives were prepared. In addition, the catalyst was separatedby simple filtration process after the reaction and reused several times. Therefore, heterogeneousMoO4(AlCl2�2 catalyst was found environmentally benign catalyst, very convenient, high yielding,and clean method for the Friedel-Crafts acylation reaction under solvent-free and ambient reactioncondition.
Keywords: MoO4(AlCl2�2 Nano-Catalyst, Friedel-Crafts Acylation, Solvent-Free and AmbientCondition, Green Chemistry.
1. INTRODUCTIONFriedel-Crafts acylation reactions of aromatic compoundswith acid chlorides are considered as fundamental andvery important processes in organic synthesis as wellas in industrial chemistry.1–4 Traditionally, these reac-tions require large amount of anhydrous strong Lewisacids, such as AlCl3, TiCl3, FeCl3, or SnCl4, more thanstoichiometric amounts.5–8 These methods suffer fromtoxicity and corrosion of the catalysts, generation ofa large amount of waste, and difficult purification ofproducts.9–11 Moreover, these catalysts are highly mois-ture sensitive and hence moisture-free reaction condi-tions are required to achieve the optimal yields of thedesired aromatic ketones.1–4 With the increasing emphasis
∗Author to whom correspondence should be addressed.
on green chemistry, environmentally benign processesshould be developed to improve the green credentialsof the reaction.12–18 For the development of greenerprocesses, moisture-insensitive and easy to handle solidacid catalysts are desired.19–22 Furthermore, the use ofsolid acid catalysts offers facile catalyst recovery andrecycling, as well as product separation. At the sametime, the catalyst recovery also decreases contamina-tion of the desired products with hazardous or harmfulmetals.8–13
Indeed, solid supported catalysts are attracting moreconsideration in organic reactions because of their easeof handling in work-up procedure, good selectivity,high yields, low cost, and reusability in compar-ison with their homogeneous catalysts for Friedel-Crafts acylation reaction.1–5 Several solid acid catalysts
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Synthesis and Characterization of AlCl3 Impregnated Molybdenum Oxide as Heterogeneous Nano-Catalyst Jadhav et al.
have been investigated for the Friedel-Crafts acylationreactions, such as metal triflate loaded SBA-15, meso-porous superacid catalyst, zeolite, hybrid zeolitic meso-structured materials, modified clay, nafion-silica compositematerials, mesoporous sulphated zirconia, and meso-porous AlKIT-5.14–25 Although interesting results havebeen achieved for the Friedel–Crafts acylation reaction,they have not led to any very important industrial applica-tion. Friedel-Crafts acylation reaction could be performedunder solvent-free reaction condition using a solid hetero-geneous catalyst without addition of co-catalysts in mildreaction conditions such process would be eco-friendly andsafe.19–22
New and improved catalytic protocols continue to attractthe attention of industries/chemical laboratories due to avery high importance of the aromatic ketones which arekey intermediates in several fields including fine chemi-cals and pharmaceuticals.1–5 Hence, there is still a demandfor developing new synthetic methods for carrying outthe Friedel-Crafts acylation, which deal with moisture-insensitive catalysts and efficient product/catalyst isola-tion procedure.14–25 Solvent-free Friedel-Crafts acylationreaction with impregnated heterogeneous catalyst leads tonew eco-benign reaction procedures that save and main-tain green reaction procedure.14–19 The Lewis acids suchas TiCl3 and FeCl3 impregnated with some other metalssuch as molybdenum which shows the complex formationwith Lewis acids are unique heterogeneous catalysts forthe Friedel–Crafts acylation reaction.14–25 These catalystshave their original Lewis acidity and they gain the het-erogeneous property with impregnation with other metalsand such catalysts were utilized in organic reactions.8–12
These reactions shows various advantages over traditionalreactions in organic solvents, such reactions are reducingthe load of organic solvent disposal and enhance the rateof many organic reactions and reuse of catalyst.5–12 There-fore, the development of an environmental benign het-erogeneous catalytic using impregnation method which ismore efficient, highly selective, and less expensive for theFriedel-Crafts acylation reaction under solvent-free condi-tion is highly anticipated.In the present study, we report preparation of heteroge-
neous AlCl3 impregnated molybdenum oxide nano-catalystand its application to Friedel-Crafts acylation reactionunder solvent-free condition. The prepared heterogeneouscatalyst was characterized by using different analytical andspectroscopic methods. The fruitfully prepared and char-acterized catalyst was utilized in acylation reaction. Asresults, the catalyst showed 84% yield of respective acy-lated product in 18 h reaction time at room temperaturein solvent-free condition. In addition, effect of amountof catalyst and other solvent effects with this protocolwere determined. We have also evaluated the possibilityof regeneration of catalyst and recyclability test in Friedel-Crafts acylation reaction.
2. EXPERIMENTAL DETAILS2.1. Preparation of MoO4(AlCl2)2 Catalyst by
Impregnation MethodEthanol (20 ml) was taken in a two necked round bot-tom flask under nitrogen atmosphere. Anhydrous alu-minum chloride (AlCl3� (1.89 g, 0.014 mol) (Aldrich,99.0%) was added into it and stirred at room temper-ature till a clear solution formed. Ammonium molyb-date (1.25 g, 0.0101 mol) (Aldrich, 99.0%) was added toit under nitrogen atmosphere. The reaction mixture wasstirred under reflux at 100 �C and kept under nitrogenatmosphere by passing nitrogen gas (99.999%) at the rateof 10 ml/min for 12 h. Ethanol was evaporated on rotaryevaporator at 80 �C and solid dry mass was obtained. Theobtained solid mass was calcined in nitrogen atmosphereat 400 �C up to two hours. The HCl gas librated dur-ing reflux process was determined by acid base titrationand librated amount of HCl in millimole was estimatedand then the catalyst was tested for the Friedel-Craftsreaction.
2.2. Catalyst CharacterizationFT-IR spectra of prepared catalysts were taken on aVarian 2000 IR spectrometer (Scimitar series) by usingKBr disc method. Powder X-ray diffraction (XRD) pat-terns of the catalysts were recorded on a Rigaku Mini-flex (Rigaku Corporation, Japan) X-ray diffractometerusing Ni filtered Cu K� radiation (� = 1�5406 Å) witha 2� min−1 scan speed and a scan range of 10–60�
at 30 kV and 15 mA. The surface morphology ofMoO4(AlCl2�2 catalyst was studied by scanning elec-tron microscopy (SEM) using a Hitachi, S-3500N SEMinstrument. Energy Dispersive X-Ray spectrometry (EDX)were determined using SEM instrument combined with anINCA instrument for energy dispersive X-ray spectroscopyscanning electron microscopy (EDX-SEM), with scan-ning electron electrode at 20 kV. The prepared acylated
0 500 1000 1500 2000 2500 3000 3500 4000 450050
60
70
80
90
100
110
120
130
140
Mo-
Al
Wavelength(cm–1)
Used MoO4(AlCl2)2 MoO4(AlCl2)2 Pure AlCl3 Pure ammonium molybdate
Figure 1. FT-IR analysis of MoO4(AlCl2�2 catalyst.
8244 J. Nanosci. Nanotechnol. 15, 8243–8250, 2015
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Copyright: American Scientific Publishers
Jadhav et al. Synthesis and Characterization of AlCl3 Impregnated Molybdenum Oxide as Heterogeneous Nano-Catalyst
Figure 2. EDX pattern of catalyst MoO4(AlCl2�2.
products were compared with the authentic samples andcharacterized by the 1H NMR and 13C NMR spec-troscopy on Bruker spectrometer 400 MHz at ambienttemperature.
Figure 3. Scanning electron microscopic analysis of MoO4(AlCl2�2 catalyst.
2.3. Friedel-Crafts Acylation ReactionThe Friedel-Crafts acylation of Anisole (1 g, 9.26 mmol)(Aldrich, 99.0%) with propionyl chloride (5 equiv.)(Aldrich, 99.0%) using the prepared MoO4(AlCl2�2(5 wt%, 10 mg) catalyst was carried out in a magnet-ically stirred two-necked round bottom flask fitted witha guard tube (CaCl2�, activated at 150 �C for 2 h. Thepresent reaction mixture stirred at room temperature up tothe completion of reaction. Reaction progress was mon-itored by thin layer chromatography (TLC). After com-pletion of the reaction, reaction mixture was filtered andsolid catalyst was separated out. The separated solid cat-alyst can be recycled in next attempt of Friedel-Craftsacylation reaction. The reaction mixture was washed withdichloromethane (DCM) and water, the same process wasdone triplicate and collected the organic layer. The organiclayer was then dried over anhydrous sodium sulfate andconcentrated on rotary evaporator and crude acylated prod-uct was obtained and purified on column chromatography.
3. RESULTS AND DISCUSSION3.1. Catalyst CharacterizationFTIR spectroscopic analysis of MoO4(AlCl2�2 catalyst,pure ammonium molybdate, and pure AlCl3 catalyst wereperformed in order to determine any alterations in the FT-IR pattern of MoO4(AlCl2�2 upon grafting process andresults are showed in Figure 1. The prepared catalystscanned IR range between 400–4000 cm−1 and showedmajor peaks at 1720, 1373, 1199, 910, 994, and 621. Thepeaks at 994 and 910 resembles the presence of Mo Oand Mo–O–Mo vibrational stretching in MoO4(AlCl2�2catalyst.26 In addition, the similar peaks we observed in
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Synthesis and Characterization of AlCl3 Impregnated Molybdenum Oxide as Heterogeneous Nano-Catalyst Jadhav et al.
pure ammonium molybdate spectra. On the other hand,the absence of broad band between 3400–3600 cm−1 andabsence of sharp peak at 900 cm−1 indicates the absenceof hydroxyl and amine groups in prepared MoO4(AlCl2�2catalyst.27 Peaks at 638, which attributed for the Al–Clbonding is present in the both pure AlCl3 spectrum and IRspectrum of catalyst.27 Which indicate the presence of alu-minum impregnation on prepared MoO4(AlCl2�2 catalyst.To study the structural modifications in recycled catalyst,we also carried out the IR spectra of recycled catalyst andall similar types of bands were also observed in recycledcatalyst after being used in 6th cycle.In order to determine the stoichiometry of
MoO4(AlCl2�2 we performed EDX scanning, Figure 2shows the EDX pattern of prepared catalystMoO4(AlCl2�2. At higher magnification, elemental com-position was obtained by EDX analysis. An extremelyhomogeneous distribution of Al, Mo, Cl, and O elementsthroughout the MoO4(AlCl2�2 catalyst was observed byEDX mapping. The weight percent ratio and atomic ratiocalculated from EDX analysis were equal to the expectedstoichiometry for MoO4(AlCl2�2. These results show thatthe aluminium grafted molybdenum catalyst was preparedsuccessesfully and it was agreed with the secondarysupport of IR, XRD diffraction and SEM analysis.The morphology and structure of MoO4(AlCl2�2 cata-
lyst were investigated using SEM analysis. Figure 3 showsthe morphology of catalyst, which exhibit well-definednanostructure with ten and five microns in size. TheSEM images show that well dispersed powder through-out the surface. In addition, we observed the surface ofour MoO4(AlCl2�2 catalyst which indicate the amorphousAlCl3 impregnated on molybdenum oxide, which exhib-ited the active component disperses very evenly on thesurface of MoO4(AlCl2�2 catalyst. In 100 �m and 50 �mpictures we can see the overall particle shapes of catalyst,these particles shapes can be seen close rambles in pic-ture 20 �m and 10 �m. At 10 �m and 5 �m we can seethe catalyst particle surface which specify the impregnatedMoO4(AlCl2�2 catalyst.
Figure 4. 27Al solid state NMR analysis of MoO4(AlCl2�2 catalyst.
Figure 5. XRD analysis of MoO4(AlCl2�2 catalyst.
The 27Al NMR in the solid state method is uniquelysuitable to the study of Al chemistry and thus for char-acterization of Al in various states of complexation andgood tool for the determination of the aluminium coordi-nation number in complexes. It is well known that 27AlNMR in the solid state shows a signal between −10 and+20 ppm for coordination number six and between +55and +85 ppm for coordination number four. The 27Al spec-trum of MoO4(AlCl2�2 catalyst represented in Figure 4.The 27Al solid state NMR spectrum of MoO4(AlCl2�2 cat-alyst at 25 �C showed a clear single line spectrum at−12.01 ppm, which showed the highly active tetrahedralform of 27Al is present in the catalyst. The absence of peakin the range of +55 and +85 ppm attributed the absence
Table I. Friedel-Crafts acylation reaction using MoO4(AlCl2�2 insolvent-free condition and effect of other solventsa .
Notes: aAll reactions were carried out on 1.0 mmol scale of substrate with 0.1–1.0equiv. of MoO4(AlCl2�2 catalyst, accordingly in 4.0 ml solvent and without solvent.bYield refers to the isolated product.
8246 J. Nanosci. Nanotechnol. 15, 8243–8250, 2015
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Jadhav et al. Synthesis and Characterization of AlCl3 Impregnated Molybdenum Oxide as Heterogeneous Nano-Catalyst
Table II. Preparation of various acylated derivatives using MoO4(AlCl2�2 catalyst in solvent-free conditiona .
Sr. No Ar-H Acid Halide Time (h) Product Yieldb(%)
1
18
2
16
3 14
4 16
5 22
6 8
7 12
8 6
9 9
10 14
11 18
84
72
72
80
67
87
81
76
71
69
76
Notes: aAll reactions were carried out on 1.0 mmol scale of substrate with catalyst (except Entry 1) and without addition of any co-catalyst and solvent;bYield refers to the isolated product.
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Synthesis and Characterization of AlCl3 Impregnated Molybdenum Oxide as Heterogeneous Nano-Catalyst Jadhav et al.
of octahedral form in the prepared MoO4(AlCl2�2 catalyst.According to a study, the peak at 0.0 ppm is attributedto six-coordinate Al species. This peak appears from aircontamination when the catalysts were placed in an NMRcell. This cell was manipulated under ambient air and itdoes not protect entirely the catalyst from moisture.Figure 5 shows the 2-D X-ray diffraction spectra of
MoO4(AlCl2�2 catalyst. We performed the XRD patternbetween 0–80�, to determine the crystalline structure ofcatalyst, unfortunately catalyst does not have any strongdiffraction peaks in the range of 2� = 0–80�. The broadhump at the range of 2� = 18–25� is belong to the molyb-denum oxide. It can be seen that all the XRD patternsof the catalysts are like crystalline and amorphous whichsuggest that AlCl3 is impregnated on molybdenum, inwhich molybdenum showed crystalline phase and AlCl3showed the amorphous phase in prepared impregnatedMoO4(AlCl2�2 catalyst.
Table I exhibits the Friedel-Crafts acylation reac-tion of anisole (1) with propionyl chloride (2) usingMoO4(AlCl2�2 in solvent-free condition as a model reac-tion using various reaction conditions with catalyst.Initially, we performed catalyst free and solvent-free acy-lation reaction of (1) and (2) at room temperature fortwo days and we observed that, this reaction fails to giveany desired product (entry 1). Further, to determine thecatalytic activity of MoO4(AlCl2�2 at room temperature,number of reactions were performed in solvent-free con-dition. Primarily, we discovered the minimum amount ofMoO4(AlCl2�2 required for rapid acylation reaction by car-rying out the catalyst dosage using 1, 0.5, 0.4, 0.3, 0.2, and0.1 equiv. of MoO4(AlCl2�2 at uniform reaction condition(entry 2-7) and we found that all reactions were progressedefficiently and provide excellent yield of respective acy-lated product (3) in 18 h reaction time, these reactionsshowed the significant catalytic activity of MoO4(AlCl2�2catalyst. In view of, the mole economy ratio of catalystwe selected to use 0.1 equiv. of MoO4(AlCl2�2 for fur-ther study of the Friedel-Crafts acylation reaction undersolvent-free condition.In addition, we also carried out Friedel-Crafts acyla-
tion reaction using various solvents with MoO4(AlCl2�2catalyst to study the effect of these solvents on acylationreaction of (1) and (2). Entries 8 and 9 show acylationreaction with prepared catalyst in benzene and tetrahy-drofuran and were observed very sluggish reaction andprovided only 27% and 48% yield of desired product inrespective reaction period. However, solvents such as 1,4-dioxane and methanol were also found to be inactive forthis protocol and showed only 22% and 48% yield (entry10 and 11). On the other hand, Entry 13 shows the acy-lation results in dichloromethane and acetonitrile in pres-ence of catalyst and was showed 31% and 24% yield
of respective acylated products. Therefore, from all theseresults we conclude that, prepared MoO4(AlCl2�2 cata-lyst is highly efficient for Friedel-Crafts acylation reactionunder solvent-free condition.Table II shows various Friedel-Crafts acylation reac-
tion products of structurally varied arenes and acid chlo-rides of using optimized reaction condition in presence ofMoO4(AlCl2�2 catalyst. Entry 1 shows the results of modelreaction products which were used to establish the opti-mized reaction condition. Entries 2, 3, 4, and 5 shows theresults of substituted anisole with different structures ofacid chlorides, all yields of respective products are effi-cient in corresponding reaction time with MoO4(AlCl2�2catalyst. In addition, we tried to determine the reactionwith five membered arenes “thiophene” with different acidchlorides. Results showed that, present catalyst is able toperform Friedel-Crafts acylation reaction efficiently withfive membered rings in good yield at ambient condition(Entries 6, 7, 8). Entries 9, 10, 11 shows the resultsof acylated products of substituted thiophene with differ-ent acid chloride, all reactions were performed smoothlyand obtained good to efficient yield with impregnatedMoO4(AlCl2�2 catalyst in solvent-free condition. Theseobservations encourage us to study the reaction mecha-nism with prepared MoO4(AlCl2�2 catalyst in solvent-freecondition.Figure 6 shows the plausible reaction mechanism
of Friedel-Crafts acylation reaction with impregnatedMoO4(AlCl2�2 catalyst under solvent-free condition.
2 Ar-H
C+O
2R-CH2 + Mo+4 ClCl
ArC
OH2C2R
+HCl
Mo+6
2R-CH2 C
O
Cl
Case-I Reaction Mechanism with Molybdate Oxide
2 Ar-H
C+
O
2R-CH2+
ArC
OH2C2R
+HCl
2R-CH2 C
O
Cl
AlCl(X+1)AlCl(X)
Case-II Reaction Mechanism with Aluminum Chloride
Figure 6. Plausible reaction mechanism of Friedel-Crafts acylationreaction with impregnated MoO4(AlCl2�2 catalyst under solvent-freecondition.
8248 J. Nanosci. Nanotechnol. 15, 8243–8250, 2015
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Copyright: American Scientific Publishers
Jadhav et al. Synthesis and Characterization of AlCl3 Impregnated Molybdenum Oxide as Heterogeneous Nano-Catalyst
0
20
40
60
80
100
1 2 3 4 5 6
Yie
ld (
%)
Cycles
Figure 7. Recyclability test of MoO4(AlCl2�2 catalyst in Friedel-Craftsacylation reaction under solvent-free condition.
We believed that the present catalyst could participate inmechanism in two different ways. In case-I, the Mo6+
present in MoO4(AlCl2�2 catalyst helps to the formationof acyl cation from the acid chloride and molybdenumcomplex, which on reaction with the aromatic substrateleads to the formation of the acylated product and Mo+6
is regenerated as showed in case-I. On the other hand, theAlClx present in the catalyst might be helping to the for-mation of acylated product in presence of MoO4(AlCl2�2catalyst as shown in case-II.
3.3. Recyclability Test of HeterogeneousMoO4(AlCl2)2 Catalyst
Catalyst reusability is one of the important factors for eco-nomical operation for organic transformation using het-erogeneous catalyst, as this can allow reduction in theoperating cost and environmental pollution. After first runof Friedel-Crafts acylation reaction, catalyst was removedfrom the reaction mixture by filtration process. The filteredcatalyst was reused directly after washing with ethanol.Catalyst was reused for the next six cycles with thesame reaction parameters which were used for fresh cat-alyst assisted acylation reaction. The results of catalystreusability study has been depicted in Figure 7 and itwas found that almost similar yield can be obtained up tofourth run i.e., acylated yield only marginally decreasedfrom 84 to 78%. After the fifth run, catalyst activitystarted decreasing significantly and 62% yield of respec-tive product was obtained in sixth run. Hence, the cat-alyst is efficiently recycled for up-to six cycles withoutconsiderable loss in its catalytic activity and selectivityin the Friedel-Crafts acylation reaction under solvent-freecondition.
4. CONCLUSIONSAluminum trichloride (AlCl3� impregnated molybdenumoxide heterogeneous nano-catalyst was prepared success-fully by using simple impregnation method. Properties and
morphology of prepared catalyst were characterized by FT-IR, XRD, SEM, EDX, and solid-state NMR spectroscopy.MoO4(AlCl2�2 catalyst after successful characterizationapplied as heterogeneous catalyst for the Friedel-Craftsacylation reaction. The present catalytic system showed100% conversion and achieved 84% yield of respectiveacylated product at room temperature using 0.1 equiv.of catalyst in solvent-free condition. Various acylatedderivatives were prepared by using optimized reactioncondition with MoO4(AlCl2�2 catalyst at optimized reac-tion condition. In addition, a proposed mechanism pathway also draw to understand the reaction path way withMoO4(AlCl2�2 catalyst. The prepared MoO4(AlCl2�2 cat-alyst can be recycled by simple filtration process at endof the reaction and reused several times without con-siderable loss of catalytic activity and selectivity. Theresults demonstrate that the impregnated MoO4(AlCl2�2catalyst is an excellent environmentally benign solid cat-alyst for the Friedel-Crafts Acylation reaction in ambientcondition.
Acknowledgment: This work was supported by BasicScience Research Program through the National ResearchFoundation of Korea (NRF) funded by the Ministry ofEducation (Grant number: NRF-2013R1A1A2060638) and2014 Research fund of Myongji University.
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Received: 30 July 2014. Accepted: 2 December 2014.
