pubs.acs.org/Langmuir © 2009 American Chemical Society
New Catalytic Liquid-Phase Ammoxidation Approach to the Preparation of Niacin (Vitamin B3) )
Robert Raja,*,† Richard D. Adams,*,‡ Douglas A. Blom,‡ William C. Pearl, Jr.,‡ Enrica Gianotti,§ and John Meurig Thomas*, † Department of Chemistry, University of Southampton, Highfield, Southampton SO17 1BJ, U.K., Department of Chemistry and Biochemistry at the USC Nanocenter, University of South Carolina, Columbia, South Carolina 29208, §Department of Chemistry, IFM and NIS - Centre of Excellence, University of Turin, v.P. Giuria 7, 10125 Torino, Italy, and Department of Materials Science, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ, U.K. )
‡
Received March 5, 2009. Revised Manuscript Received April 2, 2009 New highly dispersed bimetallic nanoscale catalysts based on rhenium combined with antimony or bismuth have been shown to be highly effective for the ammoxidation of 3-picoline to nicotinonitrile (precursor for vitamin B3) under mild conditions in the liquid phase.
The use of niacin (3-picolinic acid or nicotinic acid) in foodstuffs and as a cholesterol-lowering agent is extensive.1 Until very recently, it has been been produced commercially by using procedures2 that are environmentally aggressive and have serious ecological drawbacks (Schemes 1 and 2). Gas-phase ammoxidation (Scheme 3) of 3-picoline to nicotinonitrile (cyanopyridine) followed by hydrolysis to either nicotinamide or nicotinic acid using vanadium oxide catalysts has proved effective and offers an industrially viable strategy for the production of nicotinamide.2,3 More recently,4 liquid-phase oxidation processes that involve reacting 3-picoline with homogeneous cobalt and manganese acetates with hydrobromic acid at relatively high temperatures (483 K) and high pressures (100 atm) have been reported. The yields and selectivities are, however, quite low (32% conversion with 19% selectivity for nicotinic acid). Recent studies have also revealed that combinations of rhenium and antimony exhibit activity for the ammoxidation of certain hydrocarbons.5 Recently, two of us demonstrated6 that by using a benign source of solid oxygen, namely, acetyl peroxy borate, in conjunction with a single-site microporous catalyst (MnIIIAlPO-5) a viable, one-step, solvent-free, environmentally benign preparation of niacin could be formulated. Herein we report a catalytic approach to the synthesis of niacin: an ammoxidation, under mild conditions in the liquid phase with good yields and high selectivities involving compositionally simple (three- or four-atom) *Corresponding authors. (R.R.) Fax: +44-2380-593781, e-mail: r.raja@ soton.ac.uk. (R.D.A) Fax: +1-803-777-6781, e-mail:
[email protected]. sc.edu. (J.M.T.) Fax: +44-1223-740360, e-mail:
[email protected]. (1) (a) Kirk-Othmer Encyclopedia of Chemical Technology, 4th ed.; Wiley: New York, 1998; Vol. 25, pp 83-89.(b) Ullmann’s Encyclopedia of Industrial Chemistry, 5th ed.; VCH: Weinheim, Germany, 1986; Vol. A27, p 581. (2) Chuck, R. Appl. Catal. A 2005, 280, 75–82. (3) (a) Heveling, J.; Armbruster, E.; Utiger, L.; Rohner, M.; Dettwiler, H.-R. (Lonza) U.S. Patent 5,719,045, 1998. (b) Beschke, H.; Dahm, F. L.; Friedrich, H. (Degussa), Patent DE-OS 3107755, 1982. (4) Hatanaka, M; Tanaka, N. (Nissan Chemical Ind. Ltd.), Patent WO 9305022, 1993. (5) (a) Gaigneaux, E. M.; Liu, H.; Imoto, H.; Shido, T.; Iwasawa, Y. Top. Catal. 2000, 11/12, 185–193. (b) Liu, H.; Gaigneaux, E. M.; Imoto, H.; Shido, T.; Iwasawa, Y. Catal. Lett. 2001, 71, 75–79. (c) Liu, H.; Imoto, H.; Shido, T.; Iwasawa, Y. J. Catal. 2001, 200, 69–78. (6) Raja, R.; Thomas, J. M.; Greenhill-Hooper, M.; Ley, S. V.; Paz, F. A. A. Chem.;Eur. J. 2008, 14, 2340–2348.
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nanocluster precursors consisting of Re and either Sb or Bi, in which considerable synergy exists between the constituent elements. In the parlance of industrial chemists, ammoxidation is regarded as synonymous with the conversion of propylene (usually in a fluid-bed reactor) to acrylonitrile using oxygen and ammonia in the presence of a solid catalyst.7 Of late, however, a major breakthrough has occurred in the direct ammoxidation of propane to acrylonitrile using a solid catalyst consisting of Mo, V, Nb, Sb, and O.8 The catalysts used for such purposes are both compositionally and structurally complex, as illustrated by the work of Murayama et al8a and in a recent U.S. patent by Miyaki et al7a who describe a catalyst comprising Mo, Bi, at least one element from Ni, Co, Zn, Mg, Mn, and Cu, and at least one element from La, Ce, Pr, and Nd. Trifiro and colleagues9 have designed a family of rutile-based solid oxide catalysts, typified by Cr3+V4+Sb5+O6, that are promising ammoxidation catalysts for converting alkanes directly to nitriles. The method that we describe below is benign, but it first entails the formation of the intermediate, nicotinonitrile, which is easily converted to niacin and niacinamide by hydrolysis. Whereas the single-site heterogeneous catalysts (SSHC) that we used formerly6 took advantage of the regioselectivity (7) (a) Miyaki, K.; Yanagita, M.; Mori,K. (Dia-Nitrix Co. Ltd) U.S. Patent 20,044,248,734, 2008. (b) Grasselli, R. K. In Turning Points in Solid-State, Materials and Surface Science; Harris, K. D. M., Edwards, P. P., Eds.; RSC Publishing: London, 2008; pp 577-587(c) Grasselli, R. K.; Buttrey, D. J.; De Santo, P.; Burrington, J. D.; Lugmair, C. G.; Volpe, A. F.; Weingand, T. Catal. Today 2004, 91, 251–258. (d) Sadakane, M.; Ueda, W. In Turning Points in SolidState, Materials and Surface Science, Harris, K. D. M., Edwards, P. P., Eds.; RSC Publishing: London, 2008; pp 507-518; (e) Guliants, W.; Bhandari, R.; Swaminathan, B.; Vasudevan, V. K.; Brongersma, H. H.; Knoester, A.; Gaffney, A. M.; Han, S. J. Phys. Chem. B 2005, 109, 24046–24055. (f) Grasselli, R. K. Catal. Today 1999, 49, 141–153. (g) Moro-Oka, Y.; Ueda, W. Adv. Catal. 1994, 40, 233–273. (8) (a) Murayama, H.; Vitny, D.; Ueda, W.; Fuchs, G.; Anne, M .; Dubois, J. L. Appl. Catal. A 2007, 318, 137–142. (b) De Santo, P.; Buttrey, D. J.; Grasselli, R. K.; Lugmair, C. G.; Volpe, A. F.; Toby, B. H.; Vogt, T. Z. Kristallogr. 2004, 219, 152–165. (9) (a) Ballarini, N.; Berry, F. J.; Cavani, F.; Cimini, M.; Ren, X.; Tamoni, D.; Trifiro, F. Catal. Today 2007, 128, 161–167. (b) Trifiro, F. In Fourth International Workshop on Oxide-Based Materials: Novelties and Perspectives; Gamba, A., Fois, E., Tobacchi, G., Eds.; Como, July 6-10, 10; 2008.(c) Ballarini, N.; Cavani, F.; Cimini, M.; Trifiro, F.; Millet, J. M. M.; Cornaro, U.; Catani, R. J. Catal. 2006, 241, 255–267.
Published on Web 05/22/2009
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Letter Scheme 1. Chromic Acid Oxidation of Nicotine
Scheme 2. Oxidation of 3-Picoline with Permanganates
Scheme 3. Gas-Phase Ammoxidation of 3-Picoline to Niacinamide and Niacin
Table 1. Ammoxidation of 3-Picoline Using New Rhenium-Based Nanocluster Catalysts Supported on Silicaa product selectivity (mole %) catalyst
catalyst activation temp (K)
reaction temp (K)
conv mole %
3-cyanopyridine (nicotinonitrile)
niacinamide
niacin
pyridine
others
473 403 21.3 86.5 2.9 1.7 3.4 5.3 Re2Sb 473 423 37.0 78.9 3.5 3.0 4.3 10.5 Re2Sb Re2Sb recycle test 473 423 36.4 78.0 3.0 2.8 4.5 11.7 473 403 25.0 87.3 1.5 1.5 5.0 4.8 Re2Sb2 473 423 41.5 75.0 5.0 4.5 4.9 10.5 Re2Sb2 Re2Sb2 recycle test 473 423 40.3 77.3 3.7 3.5 5.0 10.5 473 403 47.8 85.5 5.3 3.7 6.7 Re2Bi2 473 423 65.0 75.0 8.8 6.9 9.5 Re2Bi2 Re2Bi2 recycle test 473 423 67.0 78.0 9.6 5.4 6.9 573 423 70.4 65.4 8.6 6.5 20.0 Re2Bi2 Re 573 423 12.5 75.3 5.7 3.2 15.0 Bi 573 423 7.9 43.4 4.5 51.9 a Reaction conditions: 3-picoline = 5 g; NH3 = 20 bar; air = 40 bar; toluene solvent (25 g); catalyst (Re2Sb/Re2Sb2/Re2Bi2) supported on Davison silica (38 A˚) = 100 mg; tetralin (internal standard) = 0.5 g; t = 8 h; others = mainly coupling and high-molecular-weight condensation products of pyridine and niacinamide.
of a nanoporous catalyst, here we show that single-site, multinuclear bimetallic catalysts, supported on a high-area silica, present a particularly promising new approach to the synthesis of niacin. The three new rhenium-based nanocluster catalysts (Re2Sb2, Re2Bi2, and Re2Sb) were investigated for the liquid-phase ammoxidation of 3-picoline at moderate temperatures (403-423 K). All three exhibit high activities and selectivities for the formation of the nicotinonitrile (Table 1). These catalysts were derived from the organometallic precursor complexes: Re2(CO)8(μ-SbPh2)(μ-H) (1), Re2(CO)8(μ-SbPh2)2 (2), and Re2(CO)8(μ-BiPh2)2 (3).10 We have not yet sought to optimize the conditions (e.g., (10) Adams, R. D.; Captain, B.; Pearl, W. C.Jr. J. Organomet. Chem. 2008, 693, 1636–1644.
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by varying the pH, hydrolysis methods, etc) or the loadings of the catalyst, but we decided to use compositionally simple catalysts (containing elements such as Re, Sb, and Bi, known to be active in the ammoxidation of alkenes). Precursor complex 1 (Figure 1A) was prepared as previously reported.10 New complexes 2 (16% yield) and 3 (10% yield) were prepared expressly for this study; see Experimental Section in the Supporting Information. Compounds 2 and 3 were characterized by single-crystal X-ray diffraction analyses. These compounds are isomorphous, isostructural, and centrosymmetrical (see ORTEP diagrams Figure 1b,1c). Compounds 2 and 3 each contain two MPh2 ligands, M = Sb or Bi, that bridge two Re(CO)4 groups. There is no metal-metal bond between the two rhenium atoms, Re 3 3 3 Re = 4.343(1) A˚ for 2 and 4.483(1) A˚ for 3. DOI: 10.1021/la900803a
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Figure 1. (A) Precursor complex Re2(CO)8(μ-SbPh2)(μ-H) (1). (B, C) ORTEP diagram of the similar molecular structures of 2 (M = Sb) and 3 (M = Bi) showing 30% thermal ellipsoid probability. Selected bond distances (angstroms) and angles (deg) are as follows: For 2, Re(1)-Sb (1) = 2.7648(5), Re(1)-Sb(1) = 2.7650(4), Re(1) 3 3 3 Re(10 ) = 4.343(1); Sb(1)-Re(1)-Sb(10 ) = 76.496(14), Re(1)-Sb(1)-Re(1) = 103.505 (14). For 3, Re(1)-Bi(1) = 2.8403(3), Re(1*)-Bi(1) = 2.8422(3), Re(1) 3 3 3 Re(10 ) = 4.483(1); Bi(1)-Re(1)-Bi(10 ) = 75.840(8), Re(1)-Bi (1)-Re(10 ) = 104.160(8).
Figure 2. Kinetic plot of the ammoxidation of 3-picoline at 423 K by the Re2Sb2 catalyst supported on the mesoporous silica.
The compounds were deposited separately (approximately 3% metal loading) on mesoporous silica (Davison 911) and activated so as to remove the CO and Ph ligands by heating to 200 °C for 2 h in vacuo. Catalytic tests were carried out as described in the Experimental Section. The results are listed in Table 11, from which it is seen that the principal product in all cases was nicotinonitrile (75-87% selectivity). Our objective in this work was to achieve high yields of nicotinonitrile in the liquid phase at low temperatures. A typical kinetic plot for this ammoxidation at 423 K by the silica-supported Re2Sb2 catalyst is shown in Figure 2. The desired product, nicotinonitrile, reaches a maximum approximately 8 h into the reaction, and it is apparent that the byproducts grow in the latter stages of the reactions largely as a result of hydrolysis of the cyano group of the nicotinonitrile. There is only a small difference in activity between catalysts derived from 1 and 2. Interestingly, the catalyst derived from 3 exhibited at least 50% greater activity than either of the ReSb catalysts for the ammoxidation of 3-picoline with similar selectivity. The catalysts exhibited good long-term stability. The ReBi catalyst showed no significant loss in activity after six consecutive runs. To probe the 7202 DOI: 10.1021/la900803a
bimetallic character of the reaction further, the catalytic activity of silica-supported rhenium and bismuth nanoparticles in their pure forms was also investigated under similar conditions. Although rhenium and bismuth both showed some activity (Table 1), it was only a small fraction (12.5% conversion for Re and 7.9% conversion for Bi) of the activity of the ReBi combination (70.4 conversion). This result confirms that significant synergistic effects are operative when the two elements are combined. A comparison of the performance of all three catalysts is shown in the bar chart in Figure 3. The catalysts were characterized both before and after catalysis by high-angle annular dark field (HAADF) high-resolution scanning transmission electron microscopy (HRSTEM).11,12 (11) (a) Thomas, J. M.; Johnson, B. F. G.; Raja, R.; Sankar, G.; Midgley, P. A. Acc. Chem. Res. 2003, 36, 20–36. (b) Thomas, J. M.; Adams, R. D.; Boswell, E. M.; Captain, B.; Gronbeck, H.; Raja, R. Faraday Discuss. 2007, 138, 301–315. (c) Hungria, A. B.; Raja, R.; Adams, R. D.; Captain, B.; Thomas, J. M.; Midgley, P. A.; Golovko, V.; Johnson, B. F. G. Angew. Chem., Int. Ed. 2006, 45, 4782–4785. (d) Adams, R. D.; Boswell, E. M.; Captain, B.; Hungria, A. B.; Midgley, P. A.; Raja, R.; Thomas, J. M. Angew. Chem., Int. Ed. 2007, 46, 8182–8185. (12) Nellist, P. D.; Pennycook, S. J. Adv. Imaging Electron. Phys. 2000, 113, 147–203.
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Figure 3. Graphical representation of the ammoxidation activity of the new rhenium nanocatalysts at 423 K after 8 h use.
Figure 4. ReSb (A1 and A2) and ReBi (B1 and B2) nanoparticles derived from 1 and 3: before catalysis (left) and after catalysis (right).
An image of the nanoparticles derived from 1 on the silica support is shown in Figure 4. Most of the particles were ca 1 nm in diameter. Similar images were obtained for the Re2Sb2 particles Langmuir 2009, 25(13), 7200–7204
obtained from 2 and the Re2Bi2 particles obtained from 3 (Figure 4). An analysis of the ReBi samples after catalysis by using X-ray emission spectroscopy in the HRSTEM instrument DOI: 10.1021/la900803a
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confirmed the bimetallic composition in the ranges of 27-44% Re and 56-73% Bi, which is similar to the composition of precursor 3. To monitor the sites exposed at the catalyst surface, CO was used as a probe molecule so as to reveal both the oxidation state and the dispersion of the metal centers. CO is irreversibly adsorbed on the three activated catalysts, and the FTIR spectra (Supporting Information) of the Re2Sb sample produced a large number of intense and quite definite bands at 2130, 2062, 2039, 2010, and 1967 cm-1. The 2130 cm-1 band is assigned to the stretching mode of the CO molecule adsorbed on partially reduced Ren+ sites, which indicates the presence of Re in higher oxidation states.13 The bands present at lower wavenumbers, which are due to CO adsorbed on reduced Re sites, suggest that the coordination geometry of these sites is intrinsically different, which indicates interactions with the residual complex ligands, and is therefore not as uniform as for Re2Sb2 and Re2Bi2. Only weak bands are formed for Re2Sb2 (2062 and 2052 cm-1) and Re2Bi2 (2052 cm-1). These bands can be assigned13,14 to CO adsorbed on Re0, and in the case of Re2Bi2, the band is quite symmetric, indicating the presence of well-defined single-site Re0 exposed at the surface of the metal nanoparticles, as further evidenced by HRSTEM (Figure 4). These spectroscopic results are in good agreement with the catalytic trends observed in Table 1 and Figure 3. The presence of (13) Daniell, W.; Weingand, T.; Knozinger, H. J. Mol. Catal. A 2003, 204-205, 519–526. (14) Solymosi, F.; Bansagi, T. J. Phys. Chem. 1992, 96, 1349–1355.
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Re in mixed oxidation states with Re2Sb leads to a lower degree of activity as compared to that for Re2Sb2 and Re2Bi2 which confirms that the presence of well-defined single-site Re0 centers is crucial for achieving high catalytic performance. It is possible that the stoichiometry of the cluster and the nature of the oxophile employed also play a key role in enhancing the activity and selectivity (as observed earlier with Ru-Sn clusters).11c Our results demonstrate that bimetallic nanocluster catalysts anchored on silica surfaces offer a promising new low-temperature route for the production of niacin. Bi is clearly a superior cocatalyst to Sb in the presence of Re for enhancing the activity for the liquid-phase ammoxidation of 3-picoline to nicotinonitrile. Much remains to be learned about the mechanistic aspects of this novel kind of ammoxidation catalysis. However, it is not surprising, in view of the recent computations by Goddard et al15 and from the early survey of Grasselli and Burrington16 that bismuth may play a key role in the selective activation of C-H bonds during ammoxidation. Supporting Information Available: Experimental details on the synthesis, elemental composition, spectroscopic characterization, crystallographic analyses of Re2(CO)8(μSbPh2)2 and Re2(CO)8(μ-BiPh2)2, and catalytic protocols. This material is available free of charge via the Internet at http://pubs.acs.org. (15) (a) Goddard, W. A.III; Chenoweth, K.; Pudar, S.; van Duin, A. C. T.; Cheng, M. J. Top. Catal. 2008, 50, 2–18. (b) Jang, Y. H.; Goddard, W. A.III J. Phys. Chem. B 2002, 106, 5997–6013. (16) Grasselli, R. K.; Burrington, J. D. Adv. Catal. 1981, 30, 133–163.
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