| 摘要 |
The reduction of nitro compounds and of reducible reduction products of nitro compounds (e.g. azoxy or azo compounds), especially to hydrazo compounds, preferably in alkaline media, is effected by the reducing action of iron having an extended surface in relation to its mass prepared from compounds of iron by methods which avoid sintering or fusion of the metal. Pyrophoric iron is particularly suitable whilst spongy iron may also be employed. The iron may be prepared by the reduction of precipitated iron p hydroxide or of iron oxide obtained by heating the nitrate, or by the decomposition of iron carbonyl, e.g. by heat. In the last case the iron may be produced in situ. The activity of the iron may, if desired, be enhanced by pretreatment with caustic soda or metal salt solutions or both. The reduction of nitro compounds may be carried out at elevated temperatures, e.g. 90-100 DEG C., preferably in the absence of oxygen, and if desired in the presence of diluents, e.g. hydrocarbons or alcohol. According to the Provisional Specification, it may be carried out in a neutral or reducing atmosphere, e.g. in nitrogen or hydrogen. When hydrazo compounds are produced they may be converted, after isolation if necessary, into benzidine or substituted benzidines by treatment with acid, e.g. hydrochloric acid, preferably without heating. Derivatives such as the acetyl or benzoyl derivatives of benzidine may be obtained directly by heating the hydrazo compound with the organic acid or anhydride or a mixture thereof. The process is also applicable to the production of amino, azo or azoxy compounds. In an example nitrobenzene is reduced by means of caustic soda and very finely divided iron obtained by reducing iron oxide with hydrogen or by thermal decomposition of iron carbonyl, yielding azoxybenzene, which is further reduced to azobenzene, and this in turn to hydrazobenzene. This product is converted into benzidine by stirring in the cold hydrochloric acid. Other starting materials specified are nitrotoluenes, nitroanisoles and nitroxylenes. The caustic soda may be replaced wholly or in part by alkaline earth oxides or hydroxides, e.g. lime.ALSO:Iron is obtained in a form having an extended surface in relation to its mass, particularly in finely divided form, by the reduction of precipitated iron hydroxide or of iron oxide prepared by the action of heat on the nitrate. In an example, iron oxide is reduced by means of hydrogen, yielding very finely divided iron. |
