Reduction of aromaticompound with hydrazine hydrate in the presence of iron oxide hydroxide catalyst.docx

1、Reduction of aromaticompound with hydrazine hydrate in the presence of iron oxide hydroxide catalystReduction of aromatic nitro compounds with hydrazine hydrate in the presence of an iron oxide hydroxide catalyst. I. The reduction of monosubstituted nitrobenzenes with hydrazine hydrate in the presen

2、ce of ferrihydriteMax Lauwiner, Paul Rys*, Jorg WissmannChemical Engineering and Industrial Chemistry Laboratory, Swiss Federal Institute of Technology, ETH Zentrum, CH-8092 Zurich, SwitzerlandReceived 30 December 1997; received in revised form 26 March 1998; accepted 27 March 1998AbstractA great va

3、riety of monosubstituted nitrobenzene derivatives has been reduced in good yield to the corresponding anilines with hydrazine hydrate in the presence of an iron oxide hydroxide catalyst prepared by precipitation from an aqueous iron(III) solution with sodium hydroxide. The dependence of the rate of

4、reduction on the nature and the position of additional substituents other than the nitro group was determined by measuring the reaction kinetics. The rate is enhanced by electron- attracting substituents and decreased by electron-donating groups, which results in a positive slope of =0.546 for the H

5、ammett plot. Competitive reduction experiments with mixtures of two differently substituted nitrobenzene derivatives revealed that the nitro compound with the more electron-attracting substituent is reduced first. # 1998 Elsevier Science B.V. All rights reserved.Keywords: Reduction; nitroarenes; Hyd

6、razine hydrate; Iron oxide ferrihydrite; H-transfer catalysis1. IntroductionAromatic amines are important starting materials and intermediates for the manufacture of a great variety of chemicals, such as dyestuffs, pharmaceu- tical products, agricultural chemicals, photographic chemicals, additives,

7、 surfactants, textile auxiliaries, chelating agents and polymers. They are generally synthesized by the reduction of nitroarenes. Aromatic amines can be prepared by a great variety of reduction methods. Probably the oldest industrially applied method is the reduction of nitrobenzenes with metal (usu

8、ally iron, but also tin, zinc and aluminium can be employed) and water in the presence of small amounts of acid, first described by Bechamp in 1854 1. It would certainly have been replaced much earlier by an alternative reduction method, if it had not been possible to obtain iron oxide pigments as a

9、 by-product of the reduction step. The reactions with metals and acid are the most vigorous reduction methods produ-cing merely the amino products. Therefore, if thearomatic moiety contains additional substituents prone to being reduced (as e.g. cyano, azo or further nitro groups), this drastic redu

10、ction method will pro-duce a significant amount of by-products. In those cases, the reduction can be carried out selectively by employing sulphides (Zinin-reduction 2). This selec-tive sulphide reduction is more expensive than the reduction by iron and acid, but is nevertheless widely applied for th

11、e selective reduction of nitro functions in azo and anthraquinone dyes. The Zinin-method 2 has a severe drawback, however,because in industry it is accompanied by the produc-tion of a large amount of waste products that have to be disposed in an ecologically unfavourable way. More-over, at low pH va

12、lues, the evolving of H2S gas might endanger the operating personnel. These problems with process security and more rigorous environmen-tal legislation in the handling of useless waste products required the development of a safe, econom-ically and ecologically beneficial alternative to these non-cat

13、alytic reduction methods still employedin industry. Nowadays, most large-scale aromatic amines are being produced by catalytic hydrogenation of the corresponding nitroarenes. With a large variety of catalysts (e.g. Ni, Cu, Co, Cr, Fe, Sn, Ag, Pt, Pd,Zn, Ti, Mo, metal oxides and sulphides) ,in most c

14、ases the corresponding amine is obtained quantitatively with-out the production of waste products. Because of the exothermic nature of the reaction and the need for a closed high-pressure system, numerous safety precau-tions have to be taken.The reduction of aromatic nitro compounds with hydrazine o

15、r hydrazine hydrate represents a special variation of the catalytic reduction, where hydrazine is the source of the hydrogen. The hydrogen can be generated by a variety of H-transfer catalysts 35. Especially with the use of noble metal catalysts, such as Pd, Pt or Ru, but also with the application o

16、f Ni or Cu, the catalytic hydrazine reduction gives high yields comparable to or better than the catalytic hydrogena-tion. In the past, the relatively high costs for hydrazine hydrate and for the noble metal catalysts preventedthis reduction method from being applied at an indus-trial scale. However

17、, there are two main reasons which are currently enhancing the attractivity of this catalytic H-transfer reduction: (a) It has been observed repeat-edly that several cheap iron(III) compounds, espe-cially a series of iron oxide or hydroxide modifications, exhibit an appreciable activity with regard

18、to catalytic H-transfer 68, the best results being obtained with -FeO(OH) 7,9 in methanol or ethanol 8; (b) In cases where the catalytic hydro-genation is not the method of choice, this method offers a safe as well as an ecologically and economic-ally beneficial alternative, above all for small prod

19、uct volumes in fine chemical manufacture, where the reaction can be carried out in multi-use batches under normal pressure.Fig. 1. Reduction of nitroarenes with hydrazine hydrate and an iron oxide hydroxide catalyst.This prompted us to investigate the H-transfer activity of these cheap and easily sy

20、nthesizable iron oxide hydroxide catalysts 10 by examining the infiuence of additional substituents on the rate of the reduction 11 and determining the selectivity 12 of the catalytic reduction for a selection of monosubstituted nitrobenzenes (Fig. 1).The catalyst was prepared by precipitation of an

21、 iron oxide hydroxide from an aqueous iron(III) chlor-ide solution with sodium hydroxide. It showed a much higher activity than the _-FeO(OH) used by Miyata et al. 7 and Ayyangar et al. 8. This most active iron oxide hydroxide modification was found 10 to be the ferrihydrite Fe5HO84H2O 9.2. Experime

22、ntal2.1. Preparation, characterization and handling of the catalyst The iron oxide hydroxide modification was preci-pitated from an aqueous solution of 32 g iron(III) chloride dissolved in 4 l of distilled water. 300 ml of 2 M sodium hydroxide were added dropwise to adjust the pH to 78. The temperat

23、ure of the reddish-brown mixture was raised slowly to 608C in 2 h and kept at this level for 12 h and a pH value of less than 8.After centrifugation and drying the catalyst was redis-persed and milled to a fine powder. The iron oxide hydroxide catalyst was characterized by Benz and Prins. They also

24、examined the inuence of its surface structure on the H-transfer activity 10.Half an hour before the reaction used to be started, the catalyst was activated by adding some drops of distilled water to develop its full catalytic activity in organic solvents. After the reaction the catalyst can be filte

25、red off, and is washed and reused for further reductions. At temperatures above 708C the catalyst changes its colour from reddish-brown to black. This colour change is accompanied by almost a complete loss of activity. The changes in surface structure and the loss of activity at higher temperatures

26、were inves-tigated by Mossbauer spectroscopy 10. Obviouslythe catalytically active ferrihydrite is transformed into a thermodynamically more stable modication with a lower surface and a weaker H-transfer activity.2.2. General procedure for the reductions at preparative scale A solution of 10 mmol of

27、 the nitro compound in 100 ml ethanol or water is heated to reaction tempera-ture. During this heating the reaction solution is purged with a nitrogen stream. The catalyst is weighed and activated as described in Section 2.1. and added to the reaction mixture. The reaction is started by adding a sto

28、ichiometric amount (15 mmol) of hydrazine hydrate and monitored by thin layer chromatography and GC-MS. After all starting material has dis-appeared, the catalyst is filtered off. The amine is isolated by evaporating the solvent, purified by recrys- tallization, destillation or sublimation and chara

29、cter-ized by GC-MS, NMR (1H,13C and 19F) andelementary microanalyses.2.3. Kinetic measurements All experiments were carried out in a 100 ml ther-mostatted glass vessel with a cooling jacket. The reaction solution was stirred vigorously with a mag-netic stirrer at 1000 rpm. The kinetic measurements f

30、or the determination of Hammetts &-relationship were run in ethanol at 558C and with a tenfold excess of hydrazine hydrate. The concentrations were 0.1 M of substituted nitrobenzenes with 0.1 g catalyst per 100 ml ethanol. Under these reaction conditions no diffusion effects could be observed 11. Af

31、ter addition of the catalyst to the reaction solu-tion, the reactions were started by adding hydrazine hydrate. For the evaluation of the reduction kinetics samples from the reaction mixture were drawn at different times. After ltering off the catalyst by a microlter with a pore diameter of 0.2 mm,

32、the com-position of the reaction mixtures was monitored by UV-VIS spectroscopy or gas chromatography. The concentrations of the nitrobenzenes and the corre-sponding anilines were determined by measuring the absorbance of the ltrate between 270 and 350 nm. The molar extinction coefcients of the nitro and amino compounds were determined with pure reference compounds. The kinetic measurements for the competitive experiments were carried out under the same reaction conditions except that the concentrations of the nitro-benzenes were 0.05 M for each substituted nitro-benzene. Only for the