The Isolation of Nitro Compounds

Isolation of Nitro Compounds.—Nitro compounds in many cases separate in the liquid or solid form from the residual acid ( Waste acid ). Since these are usually somewhat soluble in waste acid a further yield can be obtained by diluting the latter with water. Liquid nitro compounds are isolated in a separating funnel, while solids are removed by filtration. Steam distillation is sometimes adopted as in Preparation 232. 

The temperature is kept at 60°—70° until nitration is complete (2 hours). 

When nitration is complete the mixture is run into a separator, diluted with water and allowed to settle. After a time the layers are separated, the nitrobenzene being washed with a little dilute sodium carbonate solution. 

After settling, the nitrobenzene is run ofE from the bottom, and freed from water by anhydrous calcium chloride until it is clear. The water and any unchanged benzene may also be removed by distillation. The nitrobenzene is then distilled, distillation being stopped when the contents of the flask turn dark in colour, the fraction 208°—212° being collected. The residue in the flask contains dinitrobenzene. 

Preparation 226.—o- and p-Nitrotoluenes (l-Methyl-2-nitrobenzene and 1 -methyl-i-nitrobenzene). 

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