| 摘要 |
In the manufacture of hydrazobenzenes by the reduction of the corresponding nitro compounds or reducible reduction products thereof by means of iron and caustic alkali solution, the concentration of the caustic alkali solution is maintained substantially at least at its initial value throughout the reaction. The initial concentration of the caustic alkali solution is advantageously 40-60 per cent by weight (preferably as low as possible in the range 40-50 per cent), and may be maintained or even increased (especially after the azobenzene stage has been reached) by adding caustic alkali solution of higher concentration or solid caustic alkali or by distilling off water during the reaction, or advantageously by a combination of both means. The reaction is desirably effected in the presence of a solvent for the hydrazobenzene produced. In examples: (1) iron filings or borings are added gradually to a heated mixture of nitrobenzene, mixed xylenes and 60 per cent caustic soda solution, in an apparatus fitted with a reflux condenser and water separator, and solid caustic soda is added when the azo stage is reached; (2) the caustic soda solution in (1) is replaced by a 40 per cent solution, solid caustic is added gradually commencing as soon as the addition of iron is complete, and water is distilled off at the azo stage; (3) iron which has been used repeatedly is employed in the process of (2), fresh iron and some water being added after water has been distilled off at the azo stage; (4) in the process of (3) the final addition of water is replaced by addition of 35 per cent caustic soda solution. Additional starting materials specified are o-nitroanisole, o - nitrochlorobenzene, o - nitro - toluene, 4 - chloro - 2 - nitroanisole, and the corresponding azoxy and azo compounds. Specifications 15706/01, [Class 2 (iii)], and 391,774 are referred to. |
