Solvent-free Reduction of Aromatic Nitro Compounds ...

6 downloads 931 Views 62KB Size Report
1, No. 2, April 2010. 16. Solvent-free Reduction of Aromatic Nitro Compounds with. Alumina supported Iron powder and Acetic acid under. Microwave Irradiation.
Canadian Journal on Chemical Engineering & Technology Vol. 1, No. 2, April 2010

Solvent-free Reduction of Aromatic Nitro Compounds with Alumina supported Iron powder and Acetic acid under Microwave Irradiation Dr. Pranjit Barman, Tirtha Bhattacharjee Chemistry Department, National Institute of Technology, Silchar, Assam, PIN: - 788010, India Phone No: +91-9859804536 & +91-9864371762 E-mail ID: [email protected] & [email protected] Abstract: This work describes an easy, rapid and convenient method for the reduction of aromatic nitro compounds on alumina supported iron powder and acetic acid under microwave irradiation without using any solvent. Key words: Nitro compounds, Reduction, Microwave irradiation, Acidic condition. Introduction: The reduction of aromatic nitro compounds to corresponding aromatic amines is one of the most important transformations in synthetic organic chemistry. The availability of aromatic nitro compounds easily prepared by nitration1 of simple aromatic compounds, allows the easiest way for synthesis of substituted anilines, which serve as starting material in synthesis of other important industrial products such as dyes,2 pharmaceuticals etc. Further more amino group can easily be replaced with other groups such as H,3 F,4 Cl,5 Br,6 I,7 OH8 etc via corresponding diazonium salts. In conventional methods, iron, tin, zinc,9 iron oxide hydroxide10-11 etc are used as catalyst for the reduction of aromatic nitro compounds mostly under acidic conditions and the reaction condition is vigorous and time consuming mechanical stirring and refluxing is needed. When zinc is used as catalyst for the reduction of nitrobenzene under acidic conditions mono chloroanilines12 (25%) are formed as by-products. In case of newly developed reduction method using iron oxide hydroxide catalyst/hydrazine hydrate, though reflux time is reduced to 20-50 minutes but solvent emission is still there and time consuming catalyst preparation is involved. Other conventional reagents are hydrogenation over platinum–alumina catalyst at ca. 10–30 atm pressure of hydrogen,13 decaborane (B10H14) in presence of palladium on carbon and drops of acetic acid,14 sulfurated calcium borohydride [Ca (BH2S3)2] in THF15 etc. But as a whole all these require excess time for reflux, large excess of solvent, less yields, sometimes catalyst poisoning and most important factor is the harmful emissions. Thus environmental protection requirement is not fulfilled.

16

Canadian Journal on Chemical Engineering & Technology Vol. 1, No. 2, April 2010

Now a days, solvent free microwave accelerated reductions are studied,16because of selective absorption of MW energy by polar molecules, rapid synthetic transformations at ambient pressure, enhanced reaction rates, higher yields and reduction of harmful emissions. In this paper, we wish to report a high effective environmentally friendly method for the synthesis of aromatic amines by the reduction of their corresponding aromatic nitro compounds using iron powder (electrolytic 100 mesh) over active alumina (neutral) as solid support and drops of glacial acetic acid as hydrogen donor under microwave irradiation. Advantage of this process is that it requires no solvent, lesser time, comparative yields, with no or very less impurities, as compared to conventional methods. We here used iron powder because it is inexpensive, abundant and harmless to the environment and it has a high functional group tolerance. Experimental Section: General: Melting point was recorded on a Reico melting point apparatus. All reactions were carried out in a commercially available LG MG-557B Grill microwave oven having a maximum power output of 900W operating at 2450 MHz. IR spectra were recorded on Perkin-Elmer 73633 FTIR Spectrometer as KBr Pellet. 1H NMR spectra were recorded on Varian 400MHz FT NMR Spectrometer, using TMS as internal standard and CDCl3 as solvent. Mass spectra were recorded on Perkin-Elmer Clarus500 GCMS. All the chemicals used are of Merck. General procedure for reduction reaction under microwave conditions: Aromatic nitro compound (7.5 mmol), iron powder (0.6367g, 11.4 mmol) and neutral alumina (3.0g) were taken in an agate mortar. Then glacial acetic acid (2mL) was added drop wise, mixed properly and grinded with a pestle. The mixture was then taken in an Erlenmeyer flask with a funnel as a loose top and irradiated in a microwave oven for an appropriate time (Table I) at 180W. A sealed tube (made of Teflon) can also be used as reaction vessel. After cooling, it was diluted with hydrochloric acid solution (5mL, 20%), filtered and then was made alkaline (PH= 8-9) by adding sodium hydroxide or ammonium hydroxide solution (20%). It was filtered and the desired product was obtained by extraction of the filtrate by diethyl ether followed by evaporation. The yield was found to be 78-85%. Structure of the products was confirmed by 1H NMR, IR and Mass spectral analysis. Regeneration of solid support: After separating the aromatic amines, alumina containing iron powder and other impurities was washed several times with sodium hydroxide solution (50%) and then with water to remove iron contents.

17

Canadian Journal on Chemical Engineering & Technology Vol. 1, No. 2, April 2010

Organic fraction was washed with absolute alcohol. Then alumina fraction was washed several times with dilute acid and water and filtered. Finally alumina was heated in a furnace at about 800°C for 1 hour, allowed to cool to room temperature, which was then re-used.

NO2

NH2 Fe-Al2O3/CH3COOH

R

MW, 180W(1-2min)

R

R= o-CH3, m-CH3, p-CH3, o-Cl

68-82%

Scheme 1: Reduction of aromatic nitro compounds with iron powder and glacial acetic acid on solid support under microwave irradiation.

Results and Discussion: One of the aims of our work was to develop green chemistry by performing reduction reaction under solvent free conditions. In this regard, we have performed convincingly the reduction of aromatic nitro compounds using iron powder as catalyst and acetic acid as hydrogen donor over neutral alumina as solid support without using any solvent in much shorter time and with moderate to high yields. In order to study the reaction we have taken five different aromatic nitro compounds and the results were satisfactory.

Table 1: Reduction of substituted aromatic nitro compounds to their corresponding aromatic amines under microwave irradiation. Substrate Product Reaction time (s) Yield (%)

NO2

NH2

NO2

NH2

NO2

NH2

18

95

72

95

74

90

82

Canadian Journal on Chemical Engineering & Technology Vol. 1, No. 2, April 2010

Cl

Cl NO2

NH2

NO2

NH2

100

68

100

80

Formations of all five aromatic amines were confirmed by azo dye test, presence (M+―1) and (M+―27) peaks in mass spectra and also by 1H NMR and ir spectral analysis. Spectral Data: 2-Methylaniline: IR Cm-1: 3450, 3378, 1623, 1272; 1H─NMR (CDCl3, 400MHz) δ: 3.5 (s, 2H), 2.1 (s, 3H), 6.4 (d, 1H), 7.0 (d, 1H), 6.7 (t, 1H), 7.0 (t, 1H); m/z (%): 107[M+.], 106[M+―1], 80[M+―27]; Anal. calcd. for C7H9N : C, 78.46; H, 8.47; N, 13.07. Found: C, 78.52; H, 8.42; N, 13.06.

3-Methylaniline: IR Cm-1: 3465, 3377, 1621, 1287; 1H─NMR (CDCl3, 400MHz) δ: 3.5 (s, 2H), 2.2 (s, 3H), 6.5 (d, 1H), 6.6 (d, 1H), 7.0 (t, 1H), 6.5 (s, 1H); m/z (%):107[M+.], 106[M+―1], 80[M+―27]; Anal. calcd. for C7H9N : C, 78.46; H, 8.47; N, 13.07. Found: C, 78.48; H, 8.44; N, 13.08 4-Methylaniline: IR Cm-1: 3471, 3384, 1622, 1291; 1H─NMR (CDCl3, 400MHz) δ: 3.5 (s, 2H), 2.2 (s, 3H), 7.0 (d, 2H), 7.6 (d, 2H); m/z (%): 107[M+.], 106[M+―1], 80[M+―27]; Anal. calcd. for C7H9N: C, 78.46; H, 8.47; N, 13.07. Found: C, 78.51; H, 8.46; N, 13.03 2-Chloroaniline: IR Cm-1: 3471, 3380, 1617, 1306; 1H-NMR (CDCl3, 400MHz) δ: 3.9(s, 2H), 6.7(d, 1H), 7.0(t, 1H), 6.6(t, 1H), 7.2(d, 1H); m/z (%):127[M+.], 126[M+―1], 100[M+―27]; Anal. calcd. for C6H6NCl: C, 56.49 ; H, 4.74; N, 10.98; Cl, 27.79. Found: C, 56.45; H, 4.79; N, 10.97; Cl, 27.79 1-naphthylamine: IR Cm-1: 3476, 3395, 1620, 1288; 1H-NMR (CDCl3, 400MHz) δ: 4.0(s, 2H), 6.7(d, 1H), 7.2(t, 1H), 7.3(d, 1H), 7.8(d, 1H), 7.5(t, 1H), 7.4(t, 1H), 7.7(d, 1H); m/z (%): 143[M+.], 142[M+―1], 116[M+―27]; Anal. called. for C10H9N: C, 83.88; H, 6.33; N, 9.79. Found: C, 83.87; H, 6.30; N, 9.83

19

Canadian Journal on Chemical Engineering & Technology Vol. 1, No. 2, April 2010

Conclusion: To summarize, solvent free reduction of aromatic nitro compounds using iron powder and glacial acetic acid on solid support (active neutral alumina) under microwave irradiation are not only of interest from an ecological view point but also offers considerable synthetic advantages in terms of yields, cost, safety, time saving and simplicity. Acknowledgements: We thank Director of NIT, Silchar for laboratory facilities and to CSIR, New Delhi for the award of a junior research fellowship to one of us (T.Bhattacharjee). References: [1] J.P. Adams, J.R. Paterson. J. Chem. Soc. Perkin Trans.1, 3695 (2000) [2] Y.C. Chao, T.S. Lee, S.Y. Chang. Dyes and Pigments. 37, 255 (1998) [3] L.A. Bigelow, J.R. Johnson, L.T. Sandborn. Organic Syntheses. 1, 133 (1941) [4] D.T. Flood, Fluorobenzene. Organic Syntheses. 2, 295 (1943) [5] C.S. Marvel, S.M. Mcelvain. Organic Syntheses.1, 170 (1941) [6] L.A. Bigelow. Organic Syntheses. 1, 136 (1941). [7] H.J. Lucas, E.R. Kennedy. Organic Syntheses. 2, 351(1943) [8] H.E. Ungnade, E.F. Orwoll. Organic Syntheses. 3, 130(1955) [9] E.L. Martin. Organic Syntheses. 2, 501 (1943) [10] M. Lauwiner, R. Roth, P. Rys. Applied catalysis A: General. 177, 9 (1999). DOI: 10.1016/S0926-860X (98)00247-6 [11]M. Lauwiner, P. Rys, J. Wissmann. Applied Catalysis A: General. 172, 141 (1998), DOI: 10.1016/S0926-860X (98)00110-0 [12] G.R. Robertson, R.A. Evans. J.Org.Chem.5, 142 (1940), DOI: 10.1021/jo01208a008 [13] V.V. Zhandarev, V.N. Kazin and G.S. Mironov. Russ. J. Org. Chem. 37, 673 (2001) [14] J.W. Bae, Y.J. Cho, S.H. Lee, C.M. Yoon. Tetrahedron Lett. 41, 175 (2000), DOI: 10.1016/S0040-4039(99)02048-1 [15] H. Firouzabadi, B. Tamami, A.R. Kiasat. Synth. Commun. 30, 587 (2000), DOI: 10.1080/00397910008087360 [16] A. Vass, J. Dudas, J. Toth, R.S. Varma. Tetrahedron Lett. 42, 5347 (2001). DOI: 10.1016/S0040-4039(01)01002-4

20