Reaction Reduction of a Nitro-Compound to an Amine

A mixture of 90 grammes of granulated tin and 50 grammes of nitrobenzene is placed in a 1 -litre round flask. To this are gradually added 200 grammes of concentrated hydrochloric acid 

To the nitro-compounds of the aromatic series, as well as those of the aliphatic series, belongs the property of being converted into primary amines on energetic reduction. For the reduction of every nitro-group, 

For the reduction of nitro-compounds on the small scale in the laboratory, it is most convenient to use, as the reducing agent, granulated tin and hydrochloric acid, or stannous chloride and hydrochloric acid  

To 1 molecule of a mononitro-compound, i atoms of tin, or 3 molecules of stannous chloride, are therefore used. In calculating tire amount of the latter necessary for a reaction, it is to be remembered that the salt crystallises with two molecules of water (SnCl,+ 2H,0). If the reduction is to be effected by metallic tin, double the above quantity is frequently used, i.e. to 1 nitro-group, 3 atoms of tin. In this case, the tin is not converted into stannic chloride, but into stannous chloride  

in the cases mentioned, hydrochloric acid is always present in excess, and the amines unite with it to form soluble salts, the end of the operation occurs when no more of the insoluble nitro-compound is present, and the reaction-mixture dissolves clear in water. In order to get the free amine from the add mixture, various methods may be employed. If, as in the above example, the amine is volatile with Steam, and insoluble in alkali, then the acid solution is treated with caustic potash, or caustic soda, until the oxide of tin which separates out at first is redissolved in the excess of alkali the liberated amine is driven over with steam. Further, volatile or non-volatile amines can be extracted from an alkaline solution by a proper solvent, like ether. But this process is often troublesome, since the alkaline tin solution forms an emulsion with ether, which subsides with great difficulty. If the free amine is solid, it may be obtained by filtering off the alkaline liquid. In many cases, where a non-volatile amine is under examination, it is advisable to predpitate the tin before liberating the amine. This is done by diluting the add solution with much water, heating on the water-bath, and as soon as the liquid has reached the temperature of the bath, hydrogen sulphide is passed into it. The tin is predpitated as stannous or stannic sulphide this is separated from 

---