γ-Al2O3 catalyzed N-alkylation of amines with alcohols

Catalysis Communications 24 (2012) 30–33

Contents lists available at SciVerse ScienceDirect

Catalysis Communications journal homepage: www.elsevier.com/locate/catcom

Short Communication

Ni–Cu/γ-Al2O3 catalyzed N-alkylation of amines with alcohols Jian Sun, Xiaodong Jin, Fengwei Zhang, Wuquan Hu, Juntao Liu, Rong Li ⁎ The Key Laboratory of Nonferrous Metal Chemistry and Resources Utilization of Gansu Province, College of Chemistry and Chemical Engineering Lanzhou University, Lanzhou 730000, China

a r t i c l e

i n f o

Article history: Received 7 December 2011 Received in revised form 2 March 2012 Accepted 7 March 2012 Available online 16 March 2012 Keywords: A, Ni–Cu catalysts B, Alkylation C, Alcohols D, Amines

a b s t r a c t A γ-Al2O3 supported Ni and Cu bimetallic nanoparticles catalyst (45 wt.% Ni, Ni/Cu mass ratio = 4.5/1.0) is prepared by electroless plating method for the N-alkylation of amines with alcohols under base and Lewis acidic cocatalyst conditions. The catalyst afforded fast conversions, high selectivity for amines and alcohols with various structures under an Ar atmosphere in o-xylene. Furthermore, catalyst still has a stable catalytic activity after two consecutive cycles regenerated. © 2012 Elsevier B.V. All rights reserved.

1. Introduction Nitrogen-containing molecules, particularly amines and their derivatives are intermediates and products of enormous importance for chemical and life science applications [1,2]. The general synthetic methods for the synthesis of amines are amination of aryl/alkyl halides [3] and reductive amination of carbonyl compounds [4–7]. However, there can be problems with the toxicity of such alkylating agents and the need for activation of aryl/ alkyl halides. The use of alcohols instead of aryl/alkyl halides to achieve the N-alkyl amines is an attractive method because it does not generate harmful by-products. Alcohols are inexpensive, readily available and the selectivity of the reaction can be controlled with the catalyst. A variety of transition metals such as ruthenium [8–12], iridium [13–18], platinum [19], gold [20], silver [21,22], palladium [23,24], nickel [25,26], copper [27,28], and iron [29–31] catalysts have been reported for the N-alkylation of amines and alcohols. Although the majority of reported homogeneous catalysts are active for this reaction, they are significantly more expensive and non-recoverable. Consequently, the development of economical and easily recyclable heterogeneous catalysts is attracting more and more attention. In this context, heterogeneous systems have been employed for the N-alkylation of amines. Although there are several reports on the N-alkylation using heterogeneous catalysts [32–38] such as solid acids and

⁎ Corresponding author. Tel.: + 86 0931 891 2311; fax: + 86 0931 891 2582. E-mail address: [email protected] (R. Li). 1566-7367/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.catcom.2012.03.010

transition metal-based catalysts, most of them require long reaction time[27,28], high pressure [20], even special equipment [14,30]. Here, we report our results about Ni–Cu/γ-Al2O3 catalyzed coupling reaction of amine with alcohol in the presence of base and Lewis acidic additives at relatively short time. Meanwhile, it was found that the catalyst showed a high activity for the N-alkylation reaction, affording a high yield in all the case investigated. 2. Experimental 2.1. Preparation of catalysts Ni–Cu/γ-Al2O3 was prepared by electroless plating method [39], and a metal, such as Ag, was used to induce the plating. Ag/γ-Al2O3 was synthesized as follows: An aqueous solution (425 mL) containing AgNO3 (0.02 g, 0.118 mmol), ammonia (0.15 g, 8.824 mmol), NaOH (0.005 g, 0.125 mmol), and formaldehyde (0.002 g, 0.067 mmol) was prepared and then the Al2O3 (2.0 g) was added. After stirring at 40 °C for 4 h, the resulting Ag/γ-Al2O3 was washed with distilled water and dried at 50 °C for 12 h. The amount of Ag in the support was found to be 0.2% based on ICP analysis. For the preparation of Ni–Cu/γ-Al2O3, the Ag/γ-Al2O3 (4 g L− 1) support was added to the aqueous solution containing NiCl2·6H2O (16.8 g L− 1), NH3·H2O (10 g L− 1), N2H4·H2O (36 g L− 1), Cu(NO3)2·6H2O (3.4 g L− 1) and NaOH to maintain a pH of 10–13 for adjusting the particle size of Ni–Cu nanoparticles. After stirring at 70 °C for about 3 h until no significant bubbles were observed. The product was washed with distilled water thoroughly to give a pH of 7 and separated by filtration. The collected sample was dried in N2 flow (100 cm− 3 g− 1 min− 1) at 80 °C for 12 h, and then treated in a 20%

J. Sun et al. / Catalysis Communications 24 (2012) 30–33

31

(0.25 mmol), o-xylene (3.0 mL) and catalyst (0.1 g). The reaction was performed at 160 °C for 12 h and was monitored by GC analysis. Assignments of products were made by comparison with authentic samples. Selected products were also analyzed by GC/MS (Agilent 6,890 N/5,973 N). Since the ferromagnetic property of Ni component, the catalyst was recovered in a facile manner from the reaction mixture by using a permanent magnet. When the separated catalyst was used directly, the yield of mono-alkylated N-benzylaniline 3 was only 45%. This result may be due to the Ni–Cu nanoparticles on surface of catalyst were partially oxidized. For further use, the separated catalyst was washed with water for several times, followed by calcination in air at 500 °C for 20 min, and by the reduction with 20% H2/N2 at 350 °C for 30 min. 3. Results and discussion

Fig. 1. XRD patterns of the catalysts: (a) Al2O3; (b) Cu/Al2O3; (c) Ag/Al2O3; (d) Ni/Al2O3; (e) Ni–Cu/Al2O3.

H2/N2 flow (100 cm− 3 g− 1 min− 1) at 350 °C (ramping rate, 5 °C min− 1) for 2 h and passivation (0.1% O2/ N2, 40 cm− 3 g− 1 min− 1) at ambient temperature for 4 h. The amount of Ag in the obtained catalyst was found to be 0.02% based on ICP analysis. Ni–Cu nanoparticles exchanged most of the silver on the surface of Al2O3 and well-dispersed without aggregation. The Ni/Cu mass ratio of the obtained catalyst was 45:10 (with a loading amount of 45 wt.% Ni: 10 wt.% Cu), the catalyst was denoted as Ni45Cu10. Ni0Cu40, Ni5Cu5, Ni15Cu5, Ni30Cu5, Ni30Cu30, Ni40Cu20 and Ni50Cu0 were prepared using the same procedure. 2.2. Characterization of catalysts All of the reagents and solvents were commercially available and used without further purification. XRD measurements were performed on a Rigaku D/max-2400 diffractometer using Cu-Kα radiation as the X-ray source in the 2θ range of 10-80°. The conversion was estimated by GC (P.E. AutoSystem XL) or GC-MS (Agilent 6,890 N/5,973 N). Ni–Cu content of the catalyst was measured by inductively coupled plasma (ICP) on IRIS Advantage analyzer. The morphology of the catalyst was observed by a JEM-1200EX transmission electron microscopy and samples were obtained by placing a drop of a colloidal solution onto a copper grid and evaporating the solvent in air at room temperature. 2.3. Catalytic tests Under argon atmosphere, 10 mL round-bottomed flask was charged with amine (2.0 mmol), alcohol (5.0 mmol), NaOH (0.5 mmol), CaCl2

Fig. 1 shows the XRD patterns between 20 and 80° of the samples. Fig. 1a is the pattern of pure Al2O3. In comparison with Cu/Al2O3, Ni/ Al2O3 and Ni–Cu/Al2O3 exhibit three different peaks at 2θ = 44.6°, 52° and 76°, corresponding to the reflections of (111), (200) and (220) crystal planes of nickel, respectively. The diffraction pattern of the as prepared Ag/Al2O3 (metallic silver, 2θ = 38.2°, 44.3°, 64.6° and 77.6°) template is almost the same as that of Ni/ Al2O3. Fig. 2 presents the TEM images of Al2O3, Ag/Al2O3 and Ni–Cu/Al2O3. Ag nanoparticles synthesized by the reduction of Ag+ with formaldehyde are highly dispersed on Al2O3. The average particle size of metallic catalysts, Ag/Al2O3 and Ni–Cu/Al2O3, is 10 and 20 nm, respectively. It can be seen that Ni–Cu alloy nanoparticles are uniformly distributed on the support (Fig. 2c), which is advantageous for the catalytic activity. Initially, the reaction of aniline with benzyl alcohol was chosen as a test reaction to optimize reaction conditions. In order to promote the formation of the desired product, an excess amount of benzyl alcohol with respect to aniline was used (5:2). Using the Ni45Cu10 catalyst, the effect of temperature and base were studied (Table 1). Without any additives, the yield of mono-alkylated N-benzylaniline 3 was only 26% (Table 1, entry 5). A basic additive, NaOH, did markedly increase the yield of 3 (Table 1, entries 2–4). According to the experimental data, the yield of 3 at 160 °C is higher than 140 °C (Table1, entries 1–2). In contrast, the yield of 3 was increased by the addition of polyvalent metal salts, such as Lewis acidic additives (Table 2, entries 1–12). The result indicates that the hydrogenation of the imine 4 is slow under neutral to basic conditions and Lewis acidic additives promote the imine hydrogenation step. Among the co-catalysts tested, CaCl2, gave the best yield of 3, and the second recovered catalyst just showed a slightly lower yield of 3 (84%) than the first run (90%) (Table 2, entry 12). The same reaction condition only produces an increase in the reaction time (18 h), obtaining the yield of 3 (92%) has a slightly increased. The result confirmed that a longer reaction time can increase the selectivity. From an economic perspective, 12 h should be an optimal reaction time.

Fig. 2. TEM micrographs of (a) Al2O3, (b) Ag/Al2O3 and (c) Ni–Cu/Al2O3.

32

J. Sun et al. / Catalysis Communications 24 (2012) 30–33

Table 1 Effect of base and temperature.

Entry

T [°C]

Base

Conv. [%]

Yield [%] 3

4

1 2 3 4 5

140 160 160 160 160

NaOH NaOH tBuOK K2CO3 –

63 70 99 86 55

11 44 34 13 26

52 26 65 73 11

Reaction conditions: Ni45Cu10 (0.1 g), Alcohol (5 mmol), aniline (2 mmol), o-xylene (3 mL). Conversions and selectivities were determined by gas chromatography.

Then influence of various catalyst parameters on the catalytic activity for the N-alkylation of aniline 2 with benzyl alcohol 1 was studied under the optimized reaction conditions (Table 2). A series of Ni–Cu/Al2O3 catalysts with different Ni–Cu loading (Table 3, entries 2–9) were tested their activity for the reaction. Among the various catalysts (such as Ni45Cu10, Ni0Cu40, Ni5Cu5, Ni15Cu5, Ni30Cu5, Ni30Cu30, Ni40Cu20 and Ni50Cu0), Ni0Cu40 (Cu nanoparticles) and Ni50Cu0 (Ni nanoparticles) gave great conversions, but not good selectivity. Meanwhile, the yield of 3 increased with the enhancement of Ni/Cu mass ratio in obtained catalysts. When the Ni/Cu mass ratio up to 4.5/1.0, the catalyst (Ni45Cu10) showed the highest conversion (100%) and yield (90%) (Table 3, entry 7). Meanwhile, 0.1 g catalyst displays a higher yield in comparison to 0.05 g. Without catalyst, the yield of mono-alkylated N-benzylaniline 3 was only 53% (Table 3, entry 1). Various amines were allowed to react with alcohols under optimized conditions; the results are summarized in Table 4, from which it can be observed that the reactions of amine derivatives with benzyl

Table 2 Reaction of 1 with 2 in the presence of catalyst under various conditions.

alcohol (entries 2–5) proceeded efficiently. The reactions of amines with aliphatic alcohols (entries 6–9) proceeded to give moderate yields. The reaction using different 4-substituted benzylic alcohols with benzylamine gave nearly the same results (Table 4, entries 10, 14 and 15), independent of the electron-donating or withdrawing character of the substituent. Furthermore, the reaction of aniline with 4-chlorobenzyl alcohol (entries 12) gave a higher yield than benzylamine. The reaction can also be performed using electron-poor heteroaromatic amines: for instance, the reaction with the 2-pyridyl derivative gave quantitative yield, practically independent of the benzylic alcohol used (entries 5, 11, 13 and 16). From these essential observations and discussions on Ni–Cu based catalyst, we proposed a catalytic cycle in Scheme 1 for one-pot N-Alkylation of Amines with alcohols using Ni–Cu/Al2O3 catalyst, and named it as “borrowing hydrogen” mechanism [40–42]. The first step of the reaction would involve the oxidation of an alcohol to the corresponding carbonyl compound. Then the carbonyl intermediate would readily react with amine to afford an imine. The catalyst with NaOH significantly increased the initial step of the reaction. CaCl2 with higher Lewis acidity enables faster hydride transfer to immonium cation, and this effect result in the higher selectivity of amines.

Table 3 Reaction of 1 with 2 using various catalysts.

Entry

1 2 3 4 5 6 7 8 9 10 11 12

Additive

– CoCl2·6H2O FeCl3·6H2O SnCl4·5H2O FeCl2·4H2O CaF2 NiCl2·6H2O AgNO3 BaCl2·2H2O CuCl2·2H2O CuCl CaCl2

Conv. [%]

70 72 70 31 95 71 71 95 65 98 99 100 100a 96b

Yield [%] 3

4

44 64 56 16 35 60 59 54 60 77 88 90 92 84

26 8 11 15 60 3 10 41 5 17 8 5 4 4

Reaction conditions: Ni45Cu10 (0.1 g), Alcohol (5 mmol), aniline (2 mmol), o-xylene (3 mL), NaOH (0.5 mmol), additive (25 mmol%), reaction temperature 160 °C. Conversions and selectivities were determined by gas chromatography. a After 18 h. b Yield after second recycle.

Entry

Ni/Cu

1 2 3 4 5 6 7

– 0/40 5/5 30/30 40/20 15/5 45/10

8 9

30/5 50/0

Conv. [%]

59 99 93 91 93 96 100 97a 99 99

Yield [%] 3

4

53 82 71 71 78 73 90 85 88 12

6 12 18 20 9 21 5 4 6 87

Reaction conditions: Catalyst (0.1 g), Alcohol (5 mmol), aniline (2 mmol), o-xylene (3 mL), NaOH (0.5 mmol), CaCl2 (25 mmol%), reaction temperature 160 °C, under 1 atm of Ar. Conversions and selectivities were determined by gas chromatography. a Catalyst (0.05 g) was used.

J. Sun et al. / Catalysis Communications 24 (2012) 30–33 Table 4 N-alkylation of alcohols with amines. Entry

Alcohol

Amine

Conv. [%]

Yield [%] amine

Imine

1

100

90

5

2

100

98

2

33

(45 wt.% Ni, Ni/Cu mass ratio = 4.5/1.0) for the direct N-alkylation of amines with alcohols in the presence of base and a catalytic amount of Lewis acid. The catalyst system shows excellent selectivity and high yield in the N-alkylation of amines with aliphatic/aromatic alcohols to provide the corresponding alcohols. References

3

99

99

0

4

99

96

1

5

98

80

6

6

99

73

27

7

100

72

29

8

94

86

8

9

86

83

0

10

99

76

21

11

100

98

1

12

99

91

8

13

99

99

0

14

99

77

17

15

99

68

31

16

97

93

3

Reaction conditions: Ni45Cu10 (0.1 g), Alcohol (5 mmol), amine (2 mmol), o-xylene (3 mL), NaOH (0.5 mmol), CaCl2 (25 mmol%), reaction temperature 160 °C, and reaction time 12 h. Conversions and selectivities were determined by GC or GC-MS.

4. Conclusions In conclusion, we demonstrated that γ-Al2O3 supported Ni and Cu bimetallic nanoparticles act as a recyclable heterogeneous catalyst

Scheme 1. Borrowing hydrogen in amine alkylation.

[1] J.S. Bradshaw, K.E. Krakowiak, R.M. Izatt, Tetrahedron 48 (1992) 4475–4515. [2] R.N. Salvatore, C.H. Yoon, K.W. Jung, Tetrahedron 57 (2001) 7785–7811. [3] A. Dhakshinamoorthy, P. Visuvamithiran, V. Tharmaraj, K. Pitchumani, Catalysis Communications 16 (2011) 15–19. [4] S.J. Bhattacharyya, Organic Chemistry 60 (1995) 4928–4929. [5] A.F. Abdel Magid, K.G. Carson, B.D. Harris, C.A. Maryanoff, R.D. Shah, The Journal of Organic Chemistry 61 (1996) 3849–3862. [6] S. B hn, S. Imm, L. Neubert, M. Zhang, H. Neumann, M. Beller, ChemCatChem 3 (2011) 1853–1864. [7] T. Mizuta, S. Sakagushi, Y. Ishii, The Journal of Organic Chemistry 70 (2005) 2195–2199. [8] J.Y. Luo, M.Y. Wu, F.H. Xiao, G.J. Deng, Tetrahedron Letters 52 (2011) 2706–2709. [9] J.W. Kim, K. Yamaguchi, N. Mizuno, Journal of Catalysis 263 (2009) 205–208. [10] M.H.S.A. Hamid, C.L. Allen, G.W. Lamb, A.C. Maxwell, H.C. Maytum, A.J.A. Watsom, J.M.J. Williams, Journal of the American Chemical Society 131 (2009) 1766–1774. [11] S. Naskar, M. Bhattacharjee, Tetrahedron Letters 48 (2007) 3367–3370. [12] R. Cano, D.J. Ramón, M. Yus, The Journal of Organic Chemistry 76 (2011) 5547–5557. [13] D. Gnanamgari, E.L.O. Sauer, N.D. Schley, C. Butler, C.D. Incarvito, R.H. Crabtree, Organometallics 28 (2009) 321–325. [14] W.X. Zhang, X.C. Dong, W.L. Zhao, Organic Letters 13 (2011) 5386–5389. [15] K. Fujita, Y. Enoki, R. Yamaguchi, Tetrahedron 64 (2008) 1943–1954. [16] R. Yamaguchi, S. Kawagoe, C. Asai, K. Fujita, Organic Letters 10 (2008) 181–184. [17] R. Kawahara, K. Fujita, R. Yamaguchi, Journal of the American Chemical Society 132 (2010) 15108–15111. [18] B. Blank, M. Madalska, R. Kemape, Advanced Synthesis and Catalysis 350 (2008) 749–758. [19] J.J. Brunet, N.C. Chu, M. Rodriguezo-Zubiri, European Journal of Inorganic Chemistry 30 (2007) 4711–4722. [20] L. He, X.B. Lou, J. Ni, Y.M. Liu, Y. Cao, H.Y. He, K.N. Fan, Chemistry – A European Journal 16 (2010) 13965–13969. [21] B. Sreedhar, P.S. Reddy, M.A. Reddy, B. Neelima, R. Arundhathi, Tetrahedron Letters 48 (2007) 8174–8177. [22] K. Shimizu, M. Nishimura, A. Satsuma, ChemCatChem 1 (2009) 497–503. [23] M.S. Kwon, S. Kim, S. Park, W. Bosco, R.K. Chidrala, J. Park, The Journal of Organic Chemistry 74 (2009) 2877–2879. [24] Y. Zhang, X.J. Qi, X.J. Cui, F. Shi, Y.Q. Deng, Tetrahedron Letters 52 (2011) 1334–1338. [25] R.G. Rice, E. Kohn, Journal of the American Chemical Society 77 (1955) 4052–4054. [26] J.L. Garcia-Ruano, A. Parra, J. Aleman, F. Yuste, V.M. Mastranzo, Chemical Communications (2009) 404–406. [27] A. Martínez-Asencio, D.J. Ramón, M. Yus, Tetrahedron Letters 51 (2010) 325–327. [28] A. Martínez-Asencio, D.J. Ramón, M. Yus, Tetrahedron 67 (2011) 3140–3149. [29] X.J. Cui, F. Shi, Y. Zhang, Y.Q. Deng, Tetrahedron Letters 51 (2010) 2048–2051. [30] C. Gonzalez-Arellano, K. Yoshida, R. Luque, P.L. Gai, Green Chemistry 12 (2010) 1281–1287. [31] Y.S. Zhao, S.W. Foo, S. Saito, Angewandte Chemie International Edition 50 (2011) 3006–3009. [32] F. Valotl, F. Fachel, R. Jacquot, M. Spagnol, M. Lemairel, Tetrahedron Letters 40 (1999) 3689–3691. [33] J.M. Campelo, D. Luna, J.M. Marinas, A.A. Romero, Journal of Molecular Catalysis A: Chemical 269 (2007) 190–196. [34] A. Baiker, J. Kijenski, Catalysis Reviews, Science and Engineering 27 (1985) 653–697. [35] P.R. Likhar, R. Arundhathi, M.L. Kantam, P.S. Prathima, European Journal of Organic Chemistry 31 (2009) 5383–5389. [36] R.E. Vultier, A. Baiker, A. Wokaun, Applied Catalysis 30 (1987) 167–176. [37] D.M. Roundhill, Chemical Reviews 92 (1992) 1–27. [38] T. Yamakawa, I. Tsuchiya, D. Mitsuzuka, T. Ogawa, Catalysis Communications 5 (2004) 291–295. [39] Z.J. Wu, Z.F. Zhao, M.H. Zhang, ChemCatChem 2 (2010) 1606–1614. [40] H. Kimura, K. Matsutani, S.-i. Tsutsumi, S. Nomura, K. Ishikawa, Y. Hattori, M. Itahashi, H. Hoshino, Catalysis Letters 99 (2005) 119–131. [41] M.H.S.A. Hamid, J.M.J. Williams, Chemical Communications (2007) 725–727. [42] G. Guillena, D.J. Ramon, M. Yus, Chemical Reviews 110 (2010) 1611–1641.