pubs.acs.org/Langmuir © 2009 American Chemical Society
Investigation of Catalytic Characterization of Two-Dimensional Molecular Space with Regular Ammonium and Pyridine Groups Jianming Chen,† Ken Yao,*,† Wenfeng Shangguan,‡ and Jian Yuan‡ †
Department of Chemistry, Shanghai University, Shanghai 200444, P. R. China, and ‡Research Center for Combustion and Environment Technology, Shanghai Jiao Tong University, Shanghai 200240, P. R. China Received December 24, 2008. Revised Manuscript Received February 14, 2009
Novel two-dimensional molecular space with regular pyridine groups layered pyridine-4-amidepropylsilica (PAPS) and pyridine-4-amidephenylsilica (PAPhS) were successfully synthesized through grafting pyridine groups in the layer structure of two-dimensional molecular space with regular ammonium groups layered aminopropylsilica (ATMS-DS) and layered aminophenylsilica (APhTMS-DS). The two-dimensional structures were kept after grafting reaction of pyridine groups in PAPS and PAPhS. The catalytic potentials of two-dimensional molecular space with regular ammonium and pyridine groups were investigated. The catalytic capability of APhTMS-DS, PAPS, and PAPhS was confirmed through Knoevenagel condensation reactions. Knoevenagel condensation of aromatic aldehydes with malononitrile was not observed in the presence of ATMS-DS. Otherwise, the lower yield of Knoevenagel condensation of higher active 2-chlorobenzaldehyde with malononitrile in the presence of APhTMS-DS, PAPS, and PAPhS indicated the potential of the two-dimensional molecular space with regular catalyst molecules on influencing catalysis processes utilizing the chemical and geometrical limits.
Introduction Molecular reaction processes are usually influenced by the molecular environment due to the interaction between molecules. Thus, it is important to afford an appropriate reaction environment for molecular reaction processes. However, it is difficult to control the molecular environment in an open space due to the huge amount of molecules. A nanospace material with special chemical and geometrical structures can afford a reaction space with chemical and geometrical limits for molecules and influence the molecular reaction processes. Thus, it is important to develop nanospace materials with designed chemical and geometrical structures in order to influence and control molecular reaction processes.1,2 Two-dimensional layer spaces of layered materials are expandable with the size of the intercalated molecules. The intercalated molecules usually form monolayers or bilayers in the interlayer space of layered materials independent of molecular size due to the interaction between the layer plate and guest molecules. The molecular reaction process can be influenced by utilizing the geometrical and chemical limits of interlayer space of layered materials. Thus, two-dimensional layered materials are promising materials for influencing and controlling molecular reaction processes in the interlayer spaces by utilization of the interaction *Corresponding author: Tel +86-21-6613-4857; Fax +86-21-5638-8125; e-mail
[email protected]. (1) Ariga, K.; Hill, J. P.; Lee, M. V.; Vinu, A.; Charvet, R.; Acharya, S. Sci. Technol. Adv. Mater. 2008, 9, 014109. (2) Otani, W.; Kinbara, K.; Zhang, Q.; Ariga, K.; Aida, T. Chem.;Eur. J. 2007, 13, 1731. (3) Choy, J. H.; Jung, H.; Han, Y. S.; Yoon, J. B.; Shul, Y. G.; Kim, H. J. Chem. Mater. 2002, 14, 3823. (4) Hagerman, M. E.; Salamone, S .J.; Herbst, R. W.; Payeur, A. L. Chem. Mater. 2003, 15, 443. (5) Greenwell, H. C.; Stackhouse, S.; Coveney, P. V.; Jones, W. J. Phys. Chem. B 2003, 107, 3476. (6) Vaysse, C.; Guerlou-Demourgues, L.; Duguet, E.; Delmas, C. Inorg. Chem. 2003, 42, 4559. (7) Sasai, R.; Iyi, N.; Fujita, T.; Arbeloa, F. L.; Martınez, V. M.; Takagi, K.; Itoh, H. Langmuir 2004, 20, 4715.
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between the layer plate and guest molecules, and a series of functional materials are formed utilizing two-dimensional layered materials.3-25 Previously, we developed two kinds of two-dimensional organicsilica with regular ammonium groups in the structure: layered aminopropylsilica (ATMS-DS) and aminophenylsilica (APhTMS-DS), using 3-aminopropyltrimethoxysilane or p-aminophenyltrimethoxysilane with anionic surfactant (dodecyl sulfate, DS) template, under acidic conditions.26,27 The twodimensional lamellar organicsilica structures were also reported (8) Beaudot, P.; De Roy, M. E.; Besse, J. P. Chem. Mater. 2004, 16, 935. (9) Iyi, N.; Matsumoto, T.; Kaneko, Y.; Kitamura, K. Chem. Mater. 2004, 16, 2926. :: (10) Muller, R.; Hrobarikova, J.; Calberg, C.; Jer^ome, R.; Grandjean, J. Langmuir 2004, 20, 2982. (11) Reinholdt, M. X.; Kirkpatrick, R. J.; Pinnavaia, T. J. J. Phys. Chem. B 2005, 109, 16296. (12) Kooli, F.; Khimyak, Y. Z.; Alshahateet, S. F.; Chen, F. X. Langmuir 2005, 21, 8717. (13) Williams, G. R.; O’Hare, D. Chem. Mater. 2005, 17, 2632. (14) Hu, G.; O’Hare, D. J. Am. Chem. Soc. 2005, 127, 17808. (15) Allada, R. K.; Pless, J. D.; Nenoff, T. M.; Navrotsky, A. Chem. Mater. 2005, 17, 2455. (16) Moujahid, E. M.; Dubois, M.; Besse, J. P.; Leroux, F. Chem. Mater. 2005, 17, 373. (17) Fujita, S.; Sato, H.; Kakegawa, N.; Yamagishi, A. J. Phys. Chem. B 2006, 110, 2533. (18) Xu, Z. P.; Stevenson, G. S.; Lu, C. Q.; Lu, G. Q.; Bartlett, P. F.; Gray, P. P. J. Am. Chem. Soc. 2006, 128, 36. (19) Feng, Y. J.; Williams, G. R.; Leroux, F.; Taviot-Gueho, C.; O’Hare, D. Chem. Mater. 2006, 18, 4312. (20) Liu, Z. P.; Ma, R. Z.; Osada, M.; Iyi, N.; Ebina, Y.; Takada, K.; Sasaki, T. J. Am. Chem. Soc. 2006, 128, 4872. (21) Baker, S. E.; Sawvel, A. M.; Zheng, N.; Stucky, G. D. Chem. Mater. 2007, 19, 4390. (22) Galimberti, M.; Lostritto, A.; Spatola, A.; Guerra, G. Chem. Mater. 2007, 19, 2495. (23) Xiong, Z. G.; Xu, Y. M. Chem. Mater. 2007, 19, 1452. (24) Ide, Y.; Ogawa, M. Angew. Chem., Int. Ed. 2007, 46, 8449. (25) Mouawia, R.; Mehdi, A.; Reye, C.; R.; Corriu, J. P. J. Mater. Chem. 2008, 18, 2028. (26) Yao, K.; Imai, Y.; Shi, L. Y.; Abe, E.; Adachi, Y.; Nishikubo, K.; Tateyama, H. Chem. Lett. 2004, 33, 1112. (27) Yao, K.; Imai, Y.; Shi, L. Y.; Dong, A. M.; Abe, E.; Adachi, Y.; Nishikubo, K.; Tateyama, H. J. Colloid Interface Sci. 2005, 285, 259.
Published on Web 3/18/2009
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Scheme 1. Schematic Illustrations of (a) Vertical Cross-Section View of ATMS-DS and (b) Vertical Cross-Section View of APhTMS-DS
to be obtained by direct concentration of n-alkyltrichlorosilanes,28 organotrialkoxysilanes,29 3-aminopropyltrimethoxysilane,30 and cyanoalkyltrialkoxysilane.25 The inorganic part of layered ATMS-DS and APhTMS-DS was highly crystalline SiO hexagonal, and the ammonium groups were considered that alternately arranged on both sides of the sheet, as illustrated in Scheme 1a,b. The layered ATMS-DS and APhTMS-DS with regular ammonium groups exhibited stable layer structure and better intercalation response. The better XRD responses of various intercalation precipitates of layered ATMS-DS and APhTMS-DS were obtained.26,27 The better intercalation behaviors demonstrated the high regular arrangement of phenylamine and propylamine groups in the layer structure of layered ATMSDS and APhTMS-DS. The regular ammonium groups afforded regular reactable points in the two-dimensional structure, making it possible to develop a series two-dimensional molecular space with various chemical and geometrical structures.
(28) Parikh, A. N.; Schivley, M. A.; Koo, E.; Seshadri, K.; Aurentz, D.; Mueller, K.; Allara, D. L. J. Am. Chem. Soc. 1997, 119, 3135. (29) Loy, D. A.; Baugher, B. M.; Baugher, C. R.; Schneider, D. A.; Rahimian, K. Chem. Mater. 2000, 12, 3624. (30) Kaneko, Y.; Iyi, N.; Matsumoto, T.; Fujii, K.; Kurashima, K.; Fujita, T. J. Mater. Chem. 2003, 13, 2058.
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We have developed two-dimensional molecular space materials with regular double bonds (layered acrylamidephenylsilica, AAPhS),31 chlorine groups (layered chloroacetamidephenylsilica, CAAPhS),32 and carboxyl groups (layered carboxylpropylamidephenylsilica, CPAPhS)33 utilizing grafting reaction of layered APhTMS-DS. The two-dimensional structures had been retained in these materials after grafting reaction. The potential of twodimensional molecular space with regular molecular structures for influencing and controlling molecular reaction processes have been investigated using the polymerization process of acrylic acid in layered aminopropylsilica.34 The acrylic acid regularly fixed in layered aminopropylsilica was completely polymerized to form a novel organic-inorganic nanocomposite material named as polyacrylamidepropylsilica (ATMS-PAA) with monolayers of polyacrylamide in layer space of layered aminopropylsilica without initiator.34 (31) Yu, F. T.; Yao, K.; Shi, L. Y.; Wang, H. Z.; Fu, Y.; You, X. Q. Chem. Mater. 2007, 19, 335. (32) Yao, K.; Fu, Y.; Shi, L. Y.; Wan, W.; You, X. Q.; Yu, F. T. J. Colloid Interface Sci. 2007, 315, 400. (33) Yao, K.; You, X. Q.; Shi, L. Y.; Wan, W.; Yu, F. T.; Chen, J. M. Langmuir 2008, 24, 302. (34) Yu, F. T.; Yao, K.; Shi, L. Y.; Wan, W.; Zhong, Q. D.; Fu, Y.; You, X. Q. Chem. Mater. 2007, 19, 3412.
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It is known that the chemical and geometrical structures of catalysts are the key points to influencing the catalytic properties. The two-dimensional molecular spaces with regular catalyst molecules can afford reaction spaces with chemical and geometrical limits for catalytic processes, in which the special catalytic properties may be obtained. Thus, it is important to develop the two-dimensional molecular space with regular catalyst molecules and investigate the catalytic properties. Here, we report the development of novel two-dimensional molecular space materials with regular pyridine groups (layered pyridine-4-amidepropylsilica (PAPS) and pyridine-4-amidephenylsilica (PAPhS)) through grafting pyridine groups in the structure of layered ATMS-DS and APhTMS-DS using pyridine-4-acyl chloride and investigation of the catalytic potentials of two-dimensional molecular space with regular ammonium and pyridine groups using Knoevenagel condensation reactions. This research exhibited the catalytic potential of the novel two-dimensional molecular space with regular catalyst molecules. We hope to find special catalytic processes utilizing the molecular spaces with regular catalyst molecules in further research.
again. The identity of these compounds was easily established by comparison of their 1HNMR and IR spectra with those of authentic samples as reference.37-39 The same mole amount of layered ATMS-DS, APhTMS-DS, PAPS, and PAPhS was used in condensation reactions. The catalytic results were the average value of four times. The APhTMS-DS, PAPS, and PAPhS all were reusable, and the catalytic activity had not significantly decreased after eight times of catalytic reaction.
All the reagents were purchased from the Aldrich Chemical Co. and used as received. Layered aminopropylsilica (ATMS-DS) or aminophenylsilica (APhTMS-DS) was synthesized by the very slow titration (3 mL/min) of hydrochloric acid (0.5 mol dm-3) into 40 mL of aqueous solution of 3-aminopropyltrimethoxysilane (ATMS, 2.78 mmol) or p-aminophenyltrimethoxysilane (APhTMS, 2.78 mmol) and sodium dodecyl sulfate (SDS, 2.92 mmol). Then, the suspension was stirred at room temperature for 3 weeks, and the pH value was controlled between 2 and 3 as described previously.26,27 The precipitates were filtered and washed with deionized water and ethanol and then dried in vacuum. The pyridine-4-amidepropylsilica (PAPS) or pyridine4-amidephenylsilica (PAPhS) was synthesized as described below: first, 1.23 g of pyridine-4-carboxylic acid was treated with 10 mL of SOCl2 at 40 °C for 3 h to form pyridine-4-acyl chloride, and pyridine-4-acyl chloride was washed with benzene three times after the residual SOCl2 was removed under vacuum.35,36 Then, 0.37 g of ATMS-DS or 0.41 g of APhTMS-DS was added in pyridine solution of pyridine-4-acyl chloride at 50 °C for 48 h. The precipitate was filtered and washed with dichloromethane and then dried in vacuum. The 13C cross-polarization/magic angle spinning (CP/MAS) NMR spectra were recorded on a Bruker MSL-500WB spectrometer at 75.47 MHz for 13C. Chemical shifts for 13C NMR were referenced to tetramethylsilane (TMS) at 0 ppm. FTIR spectra were obtained by using an “Avatar 370” spectrophotometer of Nicolet, the preparation of the samples consisted in dispersing and gently grinding the powder in KBr. X-ray diffraction (XRD) data on the powder samples were recorded with an X-ray diffractometer (Rigaku, D\max-2550) using Cu KR radiation (0.1541 nm) under the conditions of 40 kV and 30 mA. Chemical analyses were performed by elementary organic microanalysis for C, N, and S in a “VerioEL” element analyzer. All Knoevenagel condensation reactions were carried out at 80 °C in solvent-free conditions. A typical Knoevenagel condensation reaction is as follows: A mixture of PAPS (0.08 g, 0.37 mol) or PAPhS (0.093 g, 0.37 mol), benzaldehydes (10 mmol), and malononitrile (10 mmol) was stirred at 80 °C for 1 h. Then the mixture was eluted with (Et)2O (2 30 mL) and filtered. Evaporation of solvent furnished the corresponding practically pure product, and the products were crystallized from ethanol
Results and Discussion Preparation of Two-Dimensional Molecular Space. The two-dimensional molecular space with regular ammonium groups (ATMS-DS and APhTMS-DS) was prepared as described before.26,27 The two-dimensional molecular space with regular pyridine groups (layered pyridine-4-amidepropylsilica, PAPS, and layered pyridine-4-amidephenylsilica, PAPhS) was synthesized through grafting pyridine groups in the structure of layered aminopropylsilica (ATMS-DS) and layered aminophenylsilica (APhTMS-DS) using pyridine-4-acyl chloride. First, the IR spectra were used to probe the formation of PAPS and PAPhS. Figure 1 showed the IR spectra of layered ATMS-DS and the reactive precipitates between aminopropylsilica and pyridine-4-acyl chloride. Spectral assignments for the IR spectrum of ATMS-DS shown in Figure 1a are made as follows. The peaks at 2851, 2926, and 2957 cm-1 were mainly assigned to symmetric C-H stretching vibrations of dodecyl sulfate (DS) and propylsilica; the peaks at 1379 and 1468 cm-1 were also assigned to the bending vibrations peaks of them; the peak at 1628 cm-1 corresponded to the vibrations of N-H in layered ATMS-DS. The IR spectrum of reactive precipitates between aminopropylsilica and pyridine-4-acyl chloride appeared as a new peak at 1707 cm-1 compared with layered ATMS-DS (Figure 1), which was assigned to the vibration of carbonyl in amide formed between amino groups of ATMS-DS and carboxyl of pyridine-4-acyl chloride. The IR absorption peaks due to CdO of the amido group over 1700 cm-1 were also observed in other grafting precipitate such as layered acrylamidephenylsilica, (AAPhS),31 layered carboxylpropylamidephenylsilica (CPAPhS),33 and polyacrylamidepropylsilica (ATMS-PAA),34 respectively. It is may be due to that the two-dimensional structure limited the vibration of organic molecules. The vibration of pyridine rings was observed around 1659-1500 cm-1, while a vibration peak observed at 3046 cm-1 was assigned to the vibration of C-H in pyridine rings (Figure 1b). The vibration peaks observed at 2934 and 2882 cm-1 in the IR spectrum of reactive precipitates between aminopropylsilica and pyridine-4acyl chloride (Figure 1b) were assigned to symmetric C-H stretching in the methylenes of propylsilica, instead of the stronger vibration peaks of methyl and methylenes (2957, 2926, and 2851 cm-1) of DS (dodecyl sulfate ions) in the IR spectrum of layered ATMS-DS (Figure 1a). The results of IR spectrum of reactive precipitates between aminopropylsilica and pyridine-4-acyl chloride indicated that the DS in layered ATMSDS disappeared, and pyridine rings were successfully grafted in layered aminopropylsilica due to the ammonium groups in layered ATMS-DS reacted with acyl chloride groups of pyridine-4-acyl chloride to form amide. The same results were also obtained in the reactive precipitates between aminophenylsilica and pyridine-4-acyl chloride. The IR spectra of layered APhTMS-DS and the reactive
(35) Hoogboom, J.; Garcia, P. M. L.; Otten, M. B. J.; Elemans, J. A. A. W.; Sly, J.; Lazarenko, S. V.; Rasing, T.; Rowan, A. E.; Nolte, R. J. Am. Chem. Soc. 2005, 127, 11047. (36) Yan, Z.; Li, G.. T.; Mu, L.; Tao, S. Y. J. Mater. Chem. 2006, 16, 1717.
(37) Naota, T.; Taki, H.; Mizuno, M.; Murahashi, S. J. Am. Chem. Soc. 1989, 111, 5954. (38) Kaupp, G.; Naimi-Jamal, M. R.; Schmeyers, J. Tetrahedron 2003, 59, 3753. (39) Gawande, M. B.; Jayaram, R. V. Catal. Commun. 2006, 7, 931.
Experimental Section
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Figure 1. IR spectra of (a) ATMS-DS and (b) PAPS.
Figure 3.
13
C CP/MAS NMR spectra of (a) ATMS-DS and (b)
PAPS.
Figure 2. IR spectra of (a) APhTMS-DS and (b) PAPhS.
precipitates between aminophenylsilica and pyridine-4-acyl chloride are shown in Figure 2. The peaks at 2851, 2920, and 2953 cm-1 were assigned to symmetric C-H stretching vibrations of dodecyl sulfate (DS). The peaks at 1600 and 1507 cm-1 were assigned to the vibration peaks of benzene ring; the peak at 1638 cm-1 corresponded to the vibrations of N-H in layered APhTMS-DS. The IR spectrum of reactive precipitates between aminophenylsilica and pyridine-4-acyl chloride appeared a new peak at 1660 cm-1 compared with layered APhTMS-DS, which was assigned to the vibration of carbonyl in amide formed between amino groups of APhTMS-DS and acyl chloride groups of pyridine-4-acyl chloride (Figure 2). The weaker vibration peaks observed around 3040 cm-1 in the IR spectrum of reactive precipitates between aminophenylsilica and pyridine4-acyl chloride (Figure 2b), instead of the stronger vibration peaks of methyl and methylenes (3000-2800 cm-1) of DS (dodecyl sulfate ions) in the IR spectrum of layered APhTMSDS (Figure 2a), were assigned to the vibrations of C-H in pyridine rings. It is also considered that the DS in layered APhTMS-DS disappeared, and the pyridine groups successfully grafted in layered aminophenylsilica due to the ammonium groups in layered APhTMS-DS were reacted with acyl chloride groups of pyridine-4-acyl chloride to form amide. To further affirm the results, the reactive precipitates between aminopropylsilica and pyridine-4-acyl chloride and between aminophenylsilica and pyridine-4-acyl chloride were characterized by 13C CP/MAS NMR spectra. The 13C CP/MAS NMR spectrum of ATMS-DS showed a series of resonance peaks assigned to methyl and methylenes of dodecyl sulfate (DS) and propyl groups of layered aminopropylsilica (Figure 3a). The wider low resonance peaks at 10, 21.5, and 42.7 ppm were assigned to three carbon species from ATMS (Si-CH2-CH2CH2-NH+ 3 ) in ATMS-DS. The other sharp resonance peaks were assigned to methyl and methylenes of dodecyl sulfate. The resonance peaks at 68.9 and 31.2 ppm were assigned to carbon 5996
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species connected to sulfate group and in the middle of alkyl chain in dodecyl sulfate, respectively. The 13C CP/MAS NMR spectrum of the reactive precipitates between aminopropylsilica and pyridine-4-acyl chloride appeared a resonance peak at 172.5 ppm (Figure 3b), which was assigned to carbonyl in amide -C (dO)-NH- formed between amino groups of ATMS-DS and acyl chloride groups of pyridine-4-acyl chloride, as shown in Scheme 2a. The resonance peaks at 122.5, 144, and 150.6 ppm were attributed to the resonances of carbon species in the pyridine rings (Figure 3b). The resonance peaks at 49.6, 23, and 11.1 ppm were assigned to three carbon species of propylsilica (Si-CH2-CH2-CH2-) in PAPS. The other sharp resonance peaks assigned to the methyl and methylenes of dodecyl sulfate (Figure 3a) were not observed in the 13C CP/MAS NMR spectrum of PAPS (Figure 3b). The result of 13C CP/MAS NMR spectrum of the reactive precipitates between aminopropylsilica and pyridine-4-acyl chloride indicated that dodecyl sulfate completely disappeared due to the ammonium groups in layered ATMS-DS completely reacted with acyl chloride groups of pyridine-4-acyl chloride to form amide, and the pyridine groups were successfully grafted in layered aminopropylsilica to form a novel two-dimensional molecular space materials pyridine-4amidepropylsilica (PAPS) with regular pyridine. The same results were also obtained in 13C CP/MAS NMR spectrum of the reactive precipitates between aminophenylsilica and pyridine-4-acyl chloride. The 13C CP/MAS NMR of spectrum of reactive precipitates between aminophenylsilica and pyridine-4acyl chloride appeared a resonance peak at 164.8 ppm (Figure 4b), which was assigned to carbonyl in amide -C (dO)-NH- formed between amino groups of APhTMS-DS and acyl chloride groups of pyridine-4-acyl chloride, as shown in Scheme 2b. The resonance peaks at 127 and 136 ppm observed in the 13C CP/MAS NMR spectrum of reactive precipitates between aminophenylsilica and pyridine-4-acyl chloride (Figure 4b), similar to 125 and 135 ppm obtained in APhTMS-DS (Figure 4a), were attributed to the superposition of resonances of carbon species in the aromatic rings of aminophenylsilica due to the aromatic rings fixed in the framework of silica as a layer plate. The resonance peaks of carbon species Langmuir 2009, 25(10), 5993–5999
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Figure 5. Powder XRD patterns of (a) ATMS-DS and (b) PAPS.
Figure 4.
13
C CP/MAS NMR spectra of APhTMS-DS and (b)
PAPhS.
Scheme 2. Schematic illustrations of Vertical Cross-Section View of (a) PAPS and (b) PAPhS
Figure 6. Powder XRD patterns of APhTMS-DS and (b) PAPhS.
in pyridine were observed at 121.8, 139, and 150 ppm (Figure 4b). The resonance peaks at 5-70 ppm in the 13C CP/ MAS NMR spectrum of APhTMS-DS (Figure 4a) attributed to the methyl and methylenes of dodecyl sulfate (DS) were not observed in reaction precipitates between aminophenylsilica and pyridine-4-acyl chloride. The result of the 13C CP/MAS NMR spectrum of reactive precipitates between aminophenylsilica and Langmuir 2009, 25(10), 5993–5999
pyridine-4-acyl chloride also indicated that dodecyl sulfate completely disappeared in PAPhS due to the ammonium groups in layered APhTMS-DS reacted with acyl chloride groups of pyridine-4-acyl chloride to form amide, and the pyridine groups were successfully grafted in layered aminophenylsilica to form a novel two-dimensional molecular space materials layered pyridine-4-amidephenylsilica (PAPhS) with regular pyridine. The X-ray diffraction spectra were used to examine the twodimensional structure of pyridine-4-amidepropylsilica (PAPS) and pyridine-4-carboxylpropyl-amidephenylsilica (PAPhS). The good XRD responses were observed in the XRD patterns of PAPS and PAPhS. The XRD patterns of ATMS-DS and PAPS are shown in Figure 5. The X-ray diffraction peak of PAPS assigned to the 001 reflection was shifted from 2θ = 2.2° in ATMS-DS to 2θ = 4.4°, corresponding to the interlayer distance shifted from 4.1 nm in ATMS-DS to 2 nm in PAPS. Figure 6 showed the XRD patterns of APhTMS-DS and PAPhS. The X-ray diffraction peak of PAPhS assigned to the 001 reflection was shifted from 2θ = 2.2° in APhTMS-DS to 2θ = 3.5°, corresponding to the interlayer distance shifted from 4 nm in APhTMS-DS to 2.7 nm in PAPhS. The change of the interlayer distance was consistent with the change of the molecular length from APhTMS-DS (Scheme 1b) to PAPhS (Scheme 2b). The interlayer distance of PAPS was obviously smaller than the structural model as shown in Scheme 2a. The smaller interlayer distance in PAPS was considered that the twodimensional layer of PAPS was compressed due to the fact that propyl chains in PAPS were flexible compared with benzene rings in PAPhS and might tend to be interdigitated. The good XRD responses indicated that the two-dimensional structure had been retained in the layered PAPS and PAPhS after the DOI: 10.1021/la8042523
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sample
C (wt %)
N (wt %)
S (wt %)
attempted formula
PAPS
50.09
12.20
0
SiO1.5C3H6NHCOC5H4N
Table 3. Knoevenagel Condensation of Benzaldehyde with Malononitrile Catalyzed by PAPS at Different Times aldehyde
Table 2. Elemental Analytical Results of PAPhS sample C (wt %)N (wt %)S (wt %) PAPhS 49.46
9.46
grafting reaction of pyridine groups, and the pyridine groups were regularly arranged in the two-dimensional structure. The elemental analytical results of layered PAPS and PAPhS are shown in Tables 1 and 2, respectively. No sulfur atom was observed in PAPS and PAPhS. The result of no sulfur element in the PAPS and PAPhS further indicated that DS in the twodimensional molecular space of ATMS-DS and APhTMS-DS was completely replaced by pyridine-4-acyl chloride. The elemental analytical results of layered PAPS and PAPhS indicated that almost 100% of the ammonium groups in layered ATMSDS and APhTMS-DS reacted with acyl chloride of pyridine-4acyl chloride to form amide, and pyridine rings were successfully grafted in layered aminopropylsilica and layered aminophenylsilica. The near 100% grafting rate of pyridine groups in the twodimensional structure of ATMS-DS and APhTMS-DS also agreed with the analysis of molecular size. The distance of rightand left parallel sides of pyridine ring is about 0.43 nm, which was smaller than the molecular distance of amino groups from each other on the same side of one sheet (about 0.52 nm) in ATMS-DS and APhTMS-DS,34,35 which contained hydrogen atoms similar to the benzene ring. Thus, the pyridine ring can be grafted in the two-dimensional structure of ATMS-DS and APhTMS-DS near 100%. The almost 100% grafting yield between layered ATMS-DS and pyridine-4-acyl chloride and between layered APhTMS-DS and pyridine-4-acyl chloride further confirmed that the pyridine groups were regularly arranged in the layer structure of PAPS and PAPhS. Knoevenagel Condensations in the Presence of Two-Dimensional Molecular Space Materials. It is known that the pyridine and pyridine ramification widely been applied in coordination chemistry, catalysis chemistry, and biochemistry. The two-dimensional molecular space with regular pyridine groups as a novel regular reaction space will have huge potential in the research of coordination chemistry, catalysis chemistry, and biochemistry. In this research, the catalytic potential of twodimensional molecular space with regular ammonium (ATMSDS and APhTMS-DS) and pyridine groups (PAPS and PAPhS) was investigated using Knoevenagel condensations of aromatic aldehydes with malononitrile in solvent-free conditions.37-39 catalyst, 80 °C ArCHO þ CH2 ðCNÞ2 ! ArCHdCðCNÞ2 without solvent
The reaction times and the corresponding yields of benzaldehyde reacted with malononitrile at 80 °C in the presence of layered PAPS are shown in Table 3. The yields of condensation reactions of benzaldehyde with malononitrile were about 63.7% 74.7%, 80.4%, and 83.0% at 15 min, 30 min, 1 h, and 3 h, respectively, in the presence of layered PAPS. The two-dimensional molecular space with regular pyridine groups showed a catalytic potential for Knoevenagel condensation reactions. The condensation reactions condition of 80 °C for 1 h was adopted for other layered catalysts. The yields of aromatic aldehydes reacted with malononitrile at 80 °C for 1 h in the presence of 5998
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reaction time
PAPS PAPS PAPS PAPS
15 min 30 min 1h 3h
yield (%) 63.7 74.7 80.4 83.0
attempted formula SiO1.5C6H4NHCOC5H4N 3 2.4H2O
0
benzaldehyde benzaldehyde benzaldehyde benzaldehyde
catalyst
Table 4. Knoevenagel Condensation of Aromatic Aldehydes with Malononitrile in the Presence of Layered ATMS-DS, APhTMS-DS, PAPS, and PAPhS aldehyde
catalyst
benzaldehyde 4-methoxybenzaldehyde 4-(dimethylamino)benzaldehyde 2-chlorobenzaldehyde benzaldehyde 4-methoxybenzaldehyde 2-chlorobenzaldehyde benzaldehyde 4-methoxybenzaldehyde 4-(dimethylamino)benzaldehyde 2-chlorobenzaldehyde benzal dehyde 4-methoxybenzaldehyde 4-(dimethylamino)benzaldehyde 2-chlorobenzaldehyde
ATMS-DS ATMS-DS ATMS-DS ATMS-DS APhTMS-DS APhTMS-DS APhTMS-DS PAPS PAPS PAPS PAPS PAPhS PAPhS PAPhS PAPhS
reaction time yield (%) 1h 1h 1h 1h 1h 1h 1h 1h 1h 1h 1h 1h 1h 1h 1h
0 0 0 0 86.5 59 75 80.4 62.8 50.1 74.2 84.1 57.5 48.1 73.0
layered ATMS-DS, APhTMS-DS, PAPS, and PAPhS are listed in Table 4. Knoevenagel condensations of aromatic aldehydes with malononitrile were not observed in the presence of layered ATMS-DS. However, condensation reactions of aromatic aldehydes with malononitrile occurred in presence of layered APhTMS-DS at 80 °C for 1 h in solvent-free condition (Table 4). The IR spectrum of APhTMS-DS after condensation reactions showed that the symmetric C-H stretching vibrations of dodecyl sulfate (DS) for 3000-2800 cm-1 obviously decreased and almost disappeared after 3 times condensation reactions (Supporting Information). The change of IR spectra indicated that the DS existed in interlayer space of APhTMS-DS before condensation reactions almost disappeared after 3 times condensation reactions. The IR spectral results of APhTMS-DS before and after condensation reactions indicated that the most accepted mechanism of Knoevenagel condensation reactions was that aromatic aldehydes first form intermediate with phenylammonium groups in two-dimensional molecular space of APhTMS-DS and then took place proton transfer and dehydration reaction with active methylene groups of malononitrile. The DS anions existed in interlayer space of APhTMS-DS were replaced due to the formation of intermediate between aromatic aldehydes and phenylammonium groups. No any change of IR spectrum of ATMS-DS during condensation reactions was observed. It is considered that Knoevenagel condensation reactions could not occur in the presence of layered ATMS-DS due to the fact that the propylammonium groups in ATMS-DS could not form an intermediate with aromatic aldehydes. The lower reaction capacity of propylammonium groups in ATMSDS also was confirmed in the formation of layered polyacrylamidepropylsilica (ATMS-PAA)34 and carboxylpropylamidephenylsilica (CPAPhS).33 It was confirmed that the chemical structures and layer structures of PAPS and PAPhS did not change because similar XRD patterns and IR spectra were observed after catalytic reaction. The similar XRD pattern and IR spectrum with APhTMS-DS were obtained after DS intercalated in APhTMS again after catalytic reaction (Supporting Information). Langmuir 2009, 25(10), 5993–5999
Yao et al.
It indicated that the layer structures of PAPS, PAPhS, and APhTMS were preserved during catalytic reaction. The yields of 4-methoxybenzaldehyde and 4-(dimethylamino)benzaldehyde reacting with malononitrile in the presence of layered APhTMSDS, PAPS, and PAPhS were lower than that of benzaldehyde in the same reaction conditions. It is considered that electrondonating groups such as -OCHH3 and -N(CH3)2 in the aromatic ring decreased the activity of aldehydes. It is known that electron-withdrawing groups such as -Cl in the aromatic ring increased the activity of aldehydes.37-39 However, the yields of 2-chlorobenzaldehyde reacted with malononitrile in the presence of layered APhTMS-DS, PAPS, and PAPhS were obviously lower than that of benzaldehyde in the same reaction conditions. Apparently, the two-dimensional structure of layered APhTMSDS, PAPS, and PAPhS influenced the Knoevenagel condensation of 2-chlorobenzaldehyde with malononitrile. The lower yields of Knoevenagel condensation of 2-chlorobenzaldehyde with malononitrile were considered that 2-chlorobenzaldehyde molecules with bigger molecular size were more difficult to form an intermediate with the ammonium and pyridine groups fixed in twodimensional molecular space due to the geometrical limits of the two-dimensional molecular spaces of layered APhTMS-DS, PAPS, and PAPhS. The results of Knoevenagel condensations in the presence of layered APhTMS-DS, PAPS, and PAPhS showed a potential on influenced catalytic reaction processes utilizing the chemical and geometrical limits of two-dimensional molecular spaces with regular catalyst molecules.
Langmuir 2009, 25(10), 5993–5999
Article
Conclusions Novel two-dimensional molecular space materials with pyridine groups (layered pyridine-4-amidepropylsilica, PAPS, and pyridine-4-amidephenylsilica, PAPhS) was synthesized through grafting pyridine groups in the layer structure of layered aminopropylsilica and layered aminophenylsilica, using pyridine-4-acyl chloride. The catalytic capability of two-dimensional molecular space APhTMS-DS, PAPS, and PAPhS was confirmed utilizing Knoevenagel condensation. Knoevenagel condensation reactions of aromatic aldehydes with malononitrile were not observed in the presence of ATMS-DS due to that propylammonium groups in ATMS-DS could not form intermediate with aromatic aldehydes. The potential of two-dimensional molecular space with regular catalyst molecules on influencing catalysis reaction processes utilizing the geometrical limits was confirmed. Acknowledgment. This work was supported by National High Technology Research and Development Program of China (863 Program) (2007AA05Z155), National Natural Science Foundation of China (20873082), and Shanghai Natural Science Foundation (08ZR1407900). Supporting Information Available: IR spectrum of APhTMS after three times Knoevenagel condensation reactions and XRD pattern of sample after DS intercalated in APhTMS again after condensation reaction. This material is available free of charge via the Internet at http://pubs.acs.org.
DOI: 10.1021/la8042523
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