Solvent-free synthesis of jasminaldehyde using double metal cyanide based solid acid catalysts

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1 Indian Journal of Chemistry Vol. 52A, December 2013, pp Solvent-free synthesis of jasminaldehyde using double metal cyanide based solid acid catalysts Mallikarjun V Patil, Sumeet K Sharma, Raksh V Jasra, * Discipline of Inorganic Materials and Catalysis, CSIR-Central Salt and Marine Chemicals Research Institute (CSMCRI), GB Marg, Bhavnagar, , Gujarat, India rakshvir.jasra@ril.com (RVJ)/ sumeetsharma036@gmail.com (SKS) Received 12 July 2013; revised and accepted 14 November 2013 The catalytic activity of Fe-Zn double metal cyanide catalysts is studied for the solvent-free synthesis of jasminaldehyde by liquid phase condensation of benzaldehyde and 1-heptanal at 433 K. The highest conversion of 1-heptanal (93%) with 77% selectivity to jasminaldehyde is achieved under the optimum reaction conditions. The presence of co-ordinatively unsaturated Zn 2+ in the structural framework of Fe-Zn double metal cyanide assists the condensation reaction. The effects of complexing and co-complexing agent, amount of catalyst, benzaldehyde to 1-heptanal molar ratio and temperature on the selectivity of jasminaldehyde is reported. Keywords: Catalysts, Double metal cyanide, Jasminaldehyde, Heptanal, Benzaldehyde, Solid acid catalyst, Aldol condensation Jasminaldehyde is a commercially important fine chemical that can be synthesized by condensation of benzaldehyde with 1-heptanal. Conventionally, this reaction is carried out in the presence of sodium or potassium hydroxide as a catalyst at moderate temperature. The limitation of this process is the formation of undesired products which reduce the yield of jasminaldehyde. The undesired byproduct, 2-pentyl-2-nonenal, is formed by the self-condensation of 1-heptanal. To overcome this limitation, there is need for new methodology for the synthesis of jasminaldehyde with high selectivity and conversion. Various solid base catalysts such as anionic exchange resins, mixed oxides, phase transfer catalysts have been reported for the synthesis of jasminaldehyde 1. Recently, Sharma et al. have reported magnesium organosilicates 2 and hydrotalcite 3 as solid base catalysts for synthesis of jasminaldehyde. The solid acids are also used as catalysts for synthesis of jasminaldehyde. Different solid acid catalysts such as large pore zeolites (HY and Beta), mesoporous aluminosilicates (Al-MCM-41), and amorphous aluminophosphates (ALPO) have been reported for synthesis of jasminaldehyde 4-7. In these reports, the zeolites showed lower activity and selectivity Present address: Reliance Technology Group, Reliance Industries Limited, Vadodara, , Gujarat, India. than mesoporous aluminosilicates (Al-MCM-41) 4-7, which was attributed to the confinement effects of the reactants and products inside the voids of the microporous materials, leading to self-condensation of 1-heptanal, as well as to the fast deactivation of catalyst. However, since lower selectivity is generally found on the use of acid catalysts as compared to base, studies are sparse for the synthesis of jasminaldehyde using solid acid catalysts. Recently double metal cyanides were reported as highly efficient solid acid catalysts for the trans-esterification reactions 8,9. More recently, we have reported Fe-Zn double metal cyanide (DMC) as a potential solid acid catalyst for Prins condensation of β-pinene and paraformaldehyde 10. In the present study, we are reporting the solvent-free synthesis of jasminaldehyde over Fe-Zn double metal cyanide catalysts which have Lewis acidic sites due to presence of coordinative unsaturated Zn 2+ in their structural framework. Materials and Methods Potassium ferrocyanide (K 4 [Fe(CN) 6 ].3H 2 O) purchased from Polypharm Pvt. Ltd., India, and, ZnCl 2 purchased from Rankem, India, were used as the starting materials for the catalyst preparation. n-butanol, iso-butanol and tert-butanol used as complexing agents were purchased from SD

2 PATIL et al.: SOLVENT-FREE SYNTHESIS OF JASMINALDEHYDE OVER Fe-Zn CYANIDE CATALYSTS 1565 Fine Chemicals. Ltd., India. Triblock copolymer, poly(ethylene glycol)-block-poly(propylene glycol)- block-poly(ethylene glycol) (Pluronic P123, m. wt. = 5800, EO 20 PO 70 EO 20 ), benzaldehyde and 1-heptanal were procured from Sigma-Aldrich, USA. All the chemicals were used as received without any further purification. Preparation and characterization of catalysts In a typical synthesis procedure for DMC-1 catalyst, solution 1 was prepared by dissolving 0.01 mol of potassium ferrocyanide, K 4 [Fe(CN) 6 ].3H 2 O in 40 ml doubly distilled water. In a separate beaker, solution 2 was prepared by dissolving 0.1 mol of ZnCl 2 in 100 ml distilled water and 20 ml n-butanol (complexing agent). The tri-block copolymer (co-complexing agent, 15 g) was dissolved in a third beaker containing 2 ml distilled water and 40 ml n-butanol to prepare solution 3. Solution 2 was slowly added to the solution 1 over an hour at 323 K at vigorous stirring speed. Then solution 3 was added to the stirred reaction mixture within 5 10 min and stirred for 1 h. The reaction mixture was filtered and the obtained solids were washed thoroughly with doubly distilled water to remove all the uncomplexed ions. The filter cake was dried at 298 K for 8 h and diagnosed as DMC-1. Effect of complexing agents on the catalytic activity was studied by preparing DMC-5 and DMC-6 catalysts using iso-butanol and tert-butanol, respectively as complexing agents and tri-block copolymer as co-complexing agents The catalysts, DMC-2, DMC-4 and DMC-7 were prepared using n-butanol, iso-butanol and tert-butanol, respectively as complexing agents without addition of any co-complexing agents (Table 1). No complexing and co-complexing agents were added during the synthesis of DMC-3 catalyst. The Lewis acidity of DMC samples were studied by DRIFT spectroscopic studies of adsorbed pyridine on a Thermoelectron Corporation (Nicolet 6700) FT-IR instrument equipped with the selector DRIFT accessory incorporating an environmental chamber (EC) assembly and an automatic temperature controller. Catalyst samples were activated at 120 C for 4 h and then exposed to pyridine vapors. In a vacuum desiccator, 5 ml of dry pyridine and 0.2 g of samples were kept under vacuum for 24 h. Subsequently, the samples were evacuated (10 2 Torr) for 30 min at room temperature to desorb physisorbed pyridine. The DMC samples were heated in situ at 100, 200, 300 and 400 C at atmospheric pressure and at a heating rate of 10 C/min using an automatic temperature controller connected with the EC. The sample was kept at the desired temperature for 30 min, thus allowing sufficient time for pyridine desorption, before recording the spectra. Vapors of desorbed pyridine were collected in dil. HCl solution. Typically 300 scans were co-added at a resolution of 4 cm 1. Fourier transform infrared spectra (FT-IR) were recorded on a Perkin-Elmer instrument (GX-FTIR) using KBr pellet. Synthesis of jasminaldehyde In a typical reaction procedure, 1-heptanal and benzaldehyde (mole ratio = 1:5) were taken with 0.1 g of n-decane as an internal GC standard in an oven dried double necked round bottom flask. One neck of the flask was fitted with 2.25 feet long refluxing condenser having spiral tube inside and the other neck of the flask was blocked with a silicon rubber septum. The top of the refluxing condenser was blocked by a standard cork. Water at 288 K was circulated in the refluxing condenser throughout the course of reaction from a water chiller at a flow rate of 6 L/min. The entire experimental setup was kept in an oil bath equipped with temperature and agitation speed controllers. The calculated amount of DMC catalyst was added to the flask and the reaction was carried out at 433 K for 12 h. The reaction mixture was cooled to room temperature, filtered and analyzed by gas chromatography (GC) (Shimadzu 17A, Japan) and Table 1 Characterization data of the studied double metal cyanide based catalysts Catalysts Fe(II) precursor Zn(II) precursor Complexing agent Co-complexing agent DMC-1 K 4 Fe(CN) 6.3H 2 O ZnCl 2 n-butanol EO 20 PO 70 EO 20 DMC-2 K 4 Fe(CN) 6.3H 2 O ZnCl 2 n-butanol nil DMC-3 K 4 Fe(CN) 6.3H 2 O ZnCl 2 nil nil DMC-4 K 4 Fe(CN) 6.3H 2 O ZnCl 2 iso-butanol nil DMC-5 K 4 Fe(CN) 6.3H 2 O ZnCl 2 iso-butanol EO 20 PO 70 EO 20 DMC-6 K 4 Fe(CN) 6.3H 2 O ZnCl 2 tert-butanol EO 20 PO 70 EO 20 DMC-7 K 4 Fe(CN) 6.3H 2 O ZnCl 2 tert-butanol nil

3 1566 INDIAN J CHEM, SEC A, DECEMBER 2013 GC-MS (mass spectrometer, Shimadzu QP2010, Japan). The GC was fitted with a 5% diphenyl and 95% dimethyl siloxane universal capillary column (60 m length and 0.25 mm dia.) and a flame ionization detector (FID). The initial column temperature was increased from 40 to 200 C at the rate of 10 C/min. Nitrogen gas at a flow rate of 100 ml/min was used as the carrier gas. The temperatures of the injection port and FID were kept constant at 473 K during the analysis. The retention times of different compounds were determined by injecting pure compound under identical gas chromatography conditions. Progress of the reaction was monitored in terms of consumption of 1-heptanal. However, the weights of initial reaction mixture and product mixture after the reaction were compared to ensure the absence of vapor loss in the reaction mixture. The conversion and selectivity were calculated by the following equations: moles of 1- heptanal reacted %Conv.of heptanal = 100 moles of 1- heptanal fed % Sel.to jasminaldehyde = moles of jasminaldehyde 100 moles of (jasminaldehyde pentyl- 2- nonenal) The 2-pentyl-2-nonenal was formed as a byproduct during the reaction. Formation of the products was also confirmed by GC-MS analysis of the reaction mixture. The standard fragmentation patterns of jasminaldehyde (m/z: 202, 173,145, 129, 117, 91, 65) and 2-pentyl-2-nonenal (m/z: 210, 181,153, 125, 97, 81, 69) were observed. It was also observed that the catalysts prepared without complexing and co-complexing agents gave 82% conversion and 77% selectivity for jasminaldehyde (DMC-3). The catalysts prepared using both complexing and co-complexing agents showed 1-heptanal conversion in the range of 84 89% with 73 75% selectivity to jasminaldehyde (DMC-1, DMC-5, DMC-6). The catalysts prepared with only complexing agent gave conversion of 1-heptanal in the range of 90 93% with 75 77% selectivity to jasminaldehyde (DMC-2, DMC-4, DMC-7). These data show that the complexing agents enhanced the activity of the DMC catalysts. The Results and Discussion Characterization of double metal cyanide complex catalysts The detailed characterization of Fe-Zn double metal cyanide catalysts and their precursor compounds, K 4 [Fe(CN) 6 ].3H 2 O and ZnCl 2 by P-XRD, FT-IR, diffuse reflectance UV-vis, SEM and TGA are discussed in detail elsewhere 10. Pyridine vibration bands appear in the IR region of cm 1. The bands at 1612 and 1450 cm 1 are due to the coordination of pyridine with Lewis acid sites The DRIFT spectra recorded at various temperatures after pyridine adsorption are shown in Fig. 1(a) and (b) for DMC-6 and DMC-7, respectively. DMC-6 shows pyridine vibration bands at 1450 and 1612 cm 1 confirming the presence of the Lewis acid Zn 2+ cations on the edge the of catalyst. FT-IR of DMC-7 shows bands at about 1450, 1490 and 1612 cm 1, which are attributed to pyridine associated with acid sites, i.e., Lpy + Bpy + Hpy 16,17. Effect of complexing and co-complexing agents on the catalytic activity The Fe-Zn double metal cyanide catalysts showed conversion of 1-heptanal in the range of 82 93% with selectivity to jasminaldehyde in the range of 73 77%. Fig. 1 DRIFT spectra of DMC catalysts. [(a) DMC-6; (b) DMC-7].

4 PATIL et al.: SOLVENT-FREE SYNTHESIS OF JASMINALDEHYDE OVER Fe-Zn CYANIDE CATALYSTS 1567 activity of DMC catalysts was observed to decrease slightly in the case of catalysts prepared with both complexing and co-complexing agents. The decrease in the activity may be due to the partial blockage of active sites by the co-complexing agent. Selectivity to jasminaldehyde was not observed without the catalyst. DMC-7 was selected as a representative catalyst for further study since its catalytic activity for jasminaldehyde synthesis was highest. Effect of varying reaction parameters Effect of reaction temperature was studied in the range of K. Faster rate of condensation was observed at higher temperatures. For example, 20% conversion of 1-heptanal with 65% selectivity to jasminaldehyde was obtained at 373 K and 50% conversion with 73% selectivity at 393 K. On further increasing the temperature to 433 K, 93% conversion of 1-heptanal with 77% selectivity to jasminaldehyde was achieved. The conversion of 1-heptanal and selectivity to jasminaldehyde remains same on further increasing the reaction temperature to 443 K. The conversion of 1-heptanal was observed to increase with increasing the 1-heptanal to benzaldehyde molar ratio from 1:1 to 1:5. Nearly 73% conversion of 1-heptanal was observed at 1-heptanal: benzaldehyde molar ratio 1:1 which increased to 93% at 1-heptanal: benzaldehyde molar ratio 1:5. Lower conversion of 1-heptanal at lower molar ratio is due to insufficient amount of benzaldehyde. Significant increase in selectivity to jasminaldehyde was also observed on increasing the 1-heptanal: benzaldehyde molar ratio. For example, selectivity to jasminaldehyde was increased from 62 to 77% on increasing the 1-heptanal: benzaldehyde molar ratio from 1:1 to 1:4. However, on increasing the ratio to 1:5, no significant change in the jasminaldehyde selectivity was observed. Furthermore, 2-pentyl-2-nonenal selectivity, which is a selfcondensation product of 1-heptanal, was observed to decrease on increasing 1-heptanal: benzaldehyde molar ratio. This confirms that the self-condensation of 1-heptanal is faster than the cross-condensation of 1-heptanal with benzaldehyde at higher concentration of 1-heptanal 3. The initial rate of self-condensation of 1-heptanal is faster than cross-condensation of 1-heptanal with benzaldehyde. About 29% conversion of 1-heptanal with 61% selectivity to jasminaldehyde was obtained in 1 h reaction time. On increasing the reaction time from 1 to 5 h, the conversion of 1-heptanal increased to 71% with 70% jasminaldehyde selectivity. Further increase in the reaction time to 12 h resulted in 93% conversion of 1-heptanal with 77% jasminaldehyde selectivity. Both reactions are competitive reactions and require similar nature of active sites (acidic/basic). Initially all the catalytic active sites are exposed to the reaction mixture in which adsorption of 1-heptanal would be significantly faster than the adsorption of benzaldehyde which leads to formation of the self-condensation product of 1-heptanal. The concentration of 1-heptanal in the reaction mixture decreases with progress of reaction. The probability of benzaldehyde adsorption/interaction with active sites would be higher than the 1-heptanal molecule at decreased concentration of 1-heptanal. Therefore, selectivity to jasminaldehyde increases on increasing the reaction time. The rate of formation of 2-pentyl-2- nonenal was observed to increase linearly on increasing the 1-heptanal concentration 18. Effect of catalyst amount on conversion of 1-heptanal and selectivity to jasminaldehyde was studied by varying the 1-heptanal: catalyst ratio from The conversion of 1-heptanal increased on increasing the amount of catalyst. The higher conversion of 1-heptanal (93%) with 77% selectivity to jasminaldehyde was obtained with 1-heptanal: catalyst weight ratio 10. On increasing the 1-heptanal:catalyst weight ratio 20, about 59% conversion of 1-heptanal with 86% jasminaldehyde selectivity was obtained. The decrease in conversion of 1-heptanal from 93 to 59% with decrease in catalyst amount is due to the decreased availability of active Zn 2+ sites in the reaction mixture. It was observed that a higher amount of catalyst favors the self-condensation of 1-heptanal to 2-pentyl-2-nonenal since the self-condensation of 1-heptanal is also catalyzed by the active acidic sites available on the surface of catalyst. On increasing the amount of catalyst, the number of active acidic sites is expected to increase significantly. Decrease in the selectivity to jasminaldehyde at higher amounts of catalyst is due to faster adsorption of 1-heptanal than that of benzaldehyde on the active acidic sites of the catalyst, which assists faster self-condensation of 1-heptanal to 2-pentyl-2-nonenal. A higher rate of selfcondensation of 1-heptanal than the condensation of 1-heptanal with benzaldehyde has been reported at higher amount of catalyst 6. Further optimization studies were carried out with 1-heptanal: catalyst weight ratio 10, since higher selectivity to

5 1568 INDIAN J CHEM, SEC A, DECEMBER 2013 Fig. 2 FT-IR spectra of DMC-7 catalyst. [1, spent catalyst after wash; 2, fresh catalyst; 3, spent catalyst without wash]. jasminaldehyde and conversion of 1-heptanal was obtained with this ratio. Recycling of the catalyst For reusability experiments, the crude reaction mixture was filtered and the solid catalyst (DMC-7) was washed with methanol (3 times) and dried at 373 K for 4 h. The results show that the catalyst could be recycled several times with a slight decrease in the catalytic activity of the catalyst after each cycle. For example, fresh DMC-7 catalyst gave 93% conversion of 1-heptanal with 77% selectivity to jasminaldehyde. The conversion decreased to 82% with 84% selectivity of jasminaldehyde at the third cycle. Apart from handling loss, the decrease in activity of the catalyst may be due to the adsorption of substrates or products on the catalyst surface which was confirmed by FT-IR spectra of spent catalyst. The bands at about cm 1 range in the FT-IR of spent catalyst are attributed to the aromatic compounds (Fig. 2). Reaction mechanism A tentative reaction mechanism for the synthesis of jasminaldehyde over Fe-Zn double metal cyanide is shown in Scheme 1. The role of weak acidic sites is to activate benzaldehyde molecule by attacking the Zn 2+ ions on the carbonyl group, favoring polarization of carbonyl group 12. Reaction mechanism of Fe Zn double metal cyanide catalyzed Prins condensation of β-pinene, trans-esterification of dimethylcarbonate and ring opening polymerization of propylene oxide has been reported previously 8,9,13. Similar reaction pathway is also expected in the present study, the co-ordinatively unsaturated Zn 2+ cations in the Tentative reaction mechanism for synthesis of jasminaldehyde using Fe 2+ -Zn 2+ double metal cyanide complexes as catalyst. [A] = Zn 2+ coordinated benzaldehyde, [B] = enolate of 1 heptanal, [C] = intermediate species Scheme 1 structure of Fe Zn double metal cyanide are the probable active sites for the formation of species [A] that involves the activation of benzaldehyde by polarization of carbonyl group on the acid sites. Then the formed carbanion attacks on the in situ generated enolate of 1-heptanal [B] to produce [C] species which on dehydration gives the α, β-unsaturated aldehyde (i.e. jasminaldehyde). Conclusions A novel application of double metal cyanide (DMC) as a highly active solid base catalyst is reported in the present study for solvent-free synthesis of jasminaldehyde by condensation of 1-heptanal with benzaldehyde. The catalysts containing Fe 2+ -Zn 2+ and complexing agents show higher activity for the synthesis of jasminaldehyde. The possible active sites for condensation reaction are the Zn 2+ cations (Lewis acidic sites) present on the surface of the catalyst. Acknowledgement Authors thank Council of Scientific and Industrial Research (CSIR), New Delhi, India, for Network Project on Catalysis. MVP and SKS acknowledge CSIR, for senior research fellowship.

6 PATIL et al.: SOLVENT-FREE SYNTHESIS OF JASMINALDEHYDE OVER Fe-Zn CYANIDE CATALYSTS 1569 References 1 Abenhaem D, Son C P N, Loupy A & Heip N B, Syn Commun, 24 (1994) Sharma S K, Patel H A & Jasra R V, J Mol Catal A: Chem, 280 (2008) Sharma S K, Parikh P A & Jasra R V, J Mol Catal A: Chem, 286 (2008) Chuah G K, Jaenicke S, Liu S H & Hu X C, Appl Surf Sci, 169 (2001) Climent M J, Corma A, Lopez R G, Iborra S & Primo J, J Catal, 175 (1998) Climent M J, Corma A, Garcia H, Lopez R G, Iborra S & Fornés V, J Catal, 197 (2001) Climent M J, Croma A, Fornés V, Lopez R G & Iborra S, Adv Synth Catal, 344 (2002) Srivastava R, Srinivas D & Ratnasamy P, J Catal, 241 (2006) Sreeprasanth P S, Srivastava R, Srinivas D & Ratnasamy P, Appl Catal A: Gen, 314 (2006) Patil M V, Yadav M K & Jasra R V, J Mol Catal A: Chem, 273 (2007) Kim I, Ahn J T, Lee S H, Ha C S & Park D W, Catal Today, (2004) Saravanamurugan S, Palanichamy M, Hartmann M & Murugesan V, Appl Catal A: Gen, 298 (2006) Kim I, Ahn J T, Ha C S, Yang C S & Park I, Polymer, 44 (2003) Corma A, Chem Rev, 95 (1995) Barzetti T, Selli E, Moscotti D & Forni L, J Chem Soc Faraday Trans, 92 (1996) Chevalier S, Franck R, Suquet H, Lambert J F & Barthomeuf D, J Chem Soc Faraday Trans, 90 (1994) Yadav M K & Jasra R V, Catal Commun, 7 (2006) Sudheesh N, Sharma S K, Khokhar M D & Shukla R S, J Mol Catal A: Chem, 339 (2011) 86.