Page 20 - Chemical and process design handbook

Speight_Part 1_A 11/7/01 3:04 PM Page 1.6

AMINATION

Amination is the process of introducing the amino group (–NH ) into an
2
organic compound as, for example, the production of aniline (C H NH )
6 5 2
by the reduction of nitrobenzene (C H NO ) in the liquid phase (Fig. 1)
6 5 2
or in the vapor phase in a fluidized bed reactor (Fig. 2). For many
decades, the only method of putting an amino group on an aryl nucleus
involved adding a nitro (–NO ) group, then reduction to the amino
2
(–NH ) group.
2
Without high-pressure vessels and catalysts, reduction had to be done
by reagents that would function under atmospheric pressure. The common
reducing agents available under these restrictions are:

1. Iron and acid
2. Zinc and alkali
3. Sodium sulfide or polysulfide
4. Sodium hydrosulfite
5. Electrolytic hydrogen
6. Metal hydrides
Now liquid- and gas-phase hydrogenations can be performed on a vari-
ety of materials.
RNO + 3H → RNH + 2H O
2 2 2 2
Where metals are used to produce the reducing hydrogen, several difficult
processing problems are created. The expense is so great that it is necessary
to find some use for the reacted material. Spent iron can sometimes be used
for pigment preparations or to absorb hydrogen sulfide. Stirring a vessel con-
taining much metal is quite difficult.
On a small scale, cracking ammonia can produce hydrogen for reduc-
tion. Transport and storage of hydrogen as ammonia is compact, and the
cracking procedure involves only a hot pipe packed with catalyst and

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