Novel chemoselective reduction of aromatic nitro compounds over ferric hydroxide supported subnano Au catalyst with CO in the presence of H

PC-75

Fig. 1 TEM images of 1.5 wt%

Au/Fe(OH) x

Novel chemoselective reduction of aromatic nitro compounds over ferric hydroxide supported subnano Au catalyst with CO in the presence of H

2

O

Lequan Liu, Botao Qiao, Zhengjian Chen, Juan Zhang, Youquan Deng*

Centre for Green Chemistry and catalysis, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou,730000. *Fax: +86-931-4968116, E-mail: ydeng@lzb.ac.cn

Abstract

1. Introduction Nano-catalysts, especially supported Au,

^[1]

have attracted much attention after its unique activity for CO oxidation at lower temperatures had been found. Herein, we firstly report that chemoselective reduction of aromatic nitro compounds to its corresponding amines could be effectively achieved over ferric hydroxide supported subnano Au catalyst with CO in the presence of H

2

O, Scheme 1.

2. Results and discussion Chemoselective reductions of a series of nitro aromatic compounds with functional groups such as carbonyl, chlorine, methoxyl and bromine were

tested, Table 1. 95-99% conversions with high selectivities were successfully achieved over 1.5 wt% Au/Fe(OH)

x

with CO in the presence of H

2

O, and the only byproducts were small amount of azoxy or azo compounds. Relatively lower activities were observed with H

2

as reductive reagent. The activity decreased sharply over 4.4% Au/Fe

2

O

3

-W, and it may be attributed to the relatively enlarged Au particle sizes when being treated at elevated temperatures although Au loading was high enough. TEM characterization of the catalysts suggested that the Au particles may be in subnano level, Fig. 1. A water-gas shift reaction and Au particles with subnano size may be the main reason for such high activities. The effectiveness of other supported noble metal (e.g. Pd or Pt) catalysts for this kind of reaction is under investigation.

This work was financially supported by the National Sciences Foundation of China (No. 20773146).

References

[1] A. S. K. Hashmi and G. J. Hutchings, Angew. Chem., Int. Ed., 2006, 45, 7896.

R R

NO2

H2O Au/Fe(OH)x

NH2

R= CH, C-CH3, Cl, OCH3, Br O O

3CO 3CO2

Scheme 1. Selective hydrogenation of aromatic nitro compounds

Table1 Comparison of the catalytic performances for chemoselective reduction of aromatic nitro-compounds

Substrates Catalysts Au

loadings (wt %)

Reductive Gas

Tem.

(^oC) Time (h)

Con.

(%) Sel.

(%)

Other products (%)

p-Nitro acetophenone Fe(OH)x -- CO 100 1.5 0 -- --

Au/Fe(OH)x 1.5 CO 100 1.5 >99 99.6 4,4'-Diacetyl-azoxybenzene (0.4) Au/Fe(OH)x 1.5 H2 100 1.5 89 99.2 4-Ethylbenzenamine (0.8) Au/Fe2O3-W 4.4 CO 100 1.5 58 98.5 4,4'-Diacetyl-Azoxybenzene (1.5) 4-Nitrobenzaldehyde Au/Fe(OH)x 1.5 CO 120 5.5 >99 97.5 Azoxybenzene-4-aldehyde (2.5)

Au/Fe(OH)x 1.5 H2 120 5.5 95 99.3 (4-Aminophenyl)methanol (0.7) 2-Chloronitrobenzene Au/Fe(OH)x 1.5 CO 100 1.5 98 98.6 2-Chloro-n-ethylbenzenamine (1.1)

1-Chloro-2-nitrosobenzene (0.3) Au/Fe(OH)x 1.5 H2 100 1.5 86 96.0 2-Chloro-N-ethylbenzenamine (4.0) 1-Methoxy-2-nitrobenzene Au/Fe(OH)x 1.5 CO 100 1.4 >99 99.5 2,2'-Dimethoxy-Azoxybenzene (0.5)

Au/Fe(OH)x 1.5 H2 100 1.4 96 99.1 2,2'-Dimethoxy-Azoxybenzene (0.9) 4-Bromonitrobenzene Au/Fe(OH)x 1.5 CO 120 6 95 99.4 1,2-Bis(4-bromophenyl)diazene (0.6)

Au/Fe(OH)x 1.5 H2 120 6 90 95.4 1,2-Bis(4-bromophenyl)diazene (4.6)

All catalysts were prepared by co-precipitation and treated at 200 ^oC for 5 h except for Au/Fe2O3-W bought from World Gold Council.

Reaction conditions: 7.5 mmol substrate, 0.005g catalyst, 1.5 MPa CO, 2-ethoxyethanol/H2O = 7/3 ml (12/4 ml for 4-Bromonitrobenzene)

259