Amination

Amination. It is the process of introducing an amino group (–NH ₂ ) in an organic compound, such as for obtaining aniline (C ₆ H ₅ NH ₃ 2) by reducing nitrobenzene (C ₆ H ₅ NO ₂ ) in phase liquid or vapor phase using a fluidized bed reactor. Throughout several decades, the only method to locate an amino group in an aryl nucleus, involves the primary addition of a nitro group (–NO ₂ ), and then proceeded to reduce it until obtaining the amino group (- NH ₂ ).

Summary

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• 1 Reducing agents
• 2 Hydrogenation in liquid and gas phase
• 3 Replacement of a constituent by an amino
• 4 Equipment
• 5 Use of amination
• 6 Oxygenated compounds
• 7 Production of methylamines
• 8 Sources

Reducing agents

Without the presence of high pressure resistant containers and catalyst compounds , the reduction must be done using reagents that can perform their function at atmospheric pressure. The most common reducing agents available under these restrictions are:

1. Iron and acid .
2. Zinc and alkalis.
3. Sodium sulfide or polysulfide .
4. Sodium hydrosulfite .
5. Electrolytic hydrogen.
6. Metal hydrides.

Hydrogenation in liquid and gas phase

Currently, hydrogenation in the liquid and gaseous phase can be carried out using a wide variety of construction materials.

In those processes where metals are used to produce the reducing hydrogen , various problems may arise during processing. The expense is so great that it is necessary to find some useful use for the material obtained. The iron used can sometimes be used for the separation of pigment, or also to absorb hydrogen sulfide . Shaking a container that contains a lot of metal is difficult.

On a small scale, the thermal decomposition of ammonia can produce the hydrogen required to effect reduction. The transport and storage of hydrogen in the form of ammonia is compact, and the thermal disintegration (cracking) procedure involves only a pipeline packed with a catalyst , which is immersed in a molten salt bath. The nitrogen that accompanies the generated hydrogen is inert.

Amination is also accomplished using ammonia (NH ₃ ) in a process called ammonolysis. As an example, the production of aniline (C ₆ H ₅ NH ₂ ) can be described from the reaction of chlorobenzene (C ₆ H ₅ Cl) with ammonia (NH ₃ ). The reaction will only occur under the application of high pressures.

Replacement of a constituent by an amino

The replacement of a constituent such as a hydroxyl (–OH), chlorine (–Cl) or sulfonic acid (–SO ₃ H) group with an amino (–NH ₂ ) using ammonia (ammonolysis) has been practiced for a certain time , using feeds that have reactive groups present, which makes replacement easier.

For example, 1,4-dichloro-2-nitrobenzene can be changed very easily to 4-chloro-2-nitroaniline by treatment with aqueous ammonia. Other molecules offer more difficulties during processing, and high pressure resistant containers are then required for the production of aniline from chlorobenzene or phenol.

equipment

Ammonia is a low-cost reagent, and the process can be balanced to obtain the desired amine. The other routes for manufacturing amines using reduction employ expensive reagents ( Iron , Zinc , or Hydrogen ), which makes the costs associated with ammonolysis very attractive. The substituted amines can be produced using substituted ammonia (amines) instead of simple ammonia.

The equipment consists of a high pressure resistant iron container with stirring; although stainless steel can also be used for its construction. Reduction amination is usually carried out in cast iron vessels (1600 gallon capacity or more) while alkali reduction is carried out in carbon steel vessels of all desired sizes.

The container is usually equipped with a spout at the base so that the sodium oxide sludge or the entire charge can be removed after the reaction is complete. In some reducers, a vertical axis supports a set of cast iron stirrers in order to keep the iron particles in suspension in the lowest part of the container, and so that all the components of the reaction are in intimate contact.

Furthermore, the stirrer aids in the diffusion of the amino compounds away from the metal surface, thus making it possible for there to be more extensive contact between the nitro body and the catalytic surface.

Use of amination

In this way, amination, or reaction with ammonia, is used to form both aromatic and aliphatic amines. Reduction of nitro compounds is the most traditional method of producing amines today, although ammonia or substituted ammonia can react directly to form amines. The production of aniline through amination at this time exceeds that obtained through reduction (of nitrobenzene ).

Oxygenated compounds

Oxygenated compounds may also be subject to ammonolysis, for example:

1. The methanol over aluminum phosphate catalyst yields monomethylamine (CH3NH2), di-methylamine [(CH ₃) ₂ NH] and tri-methylamine [(CH ₃ ) ₃ N].
2. The 2-naphthol plus sodium ammonium sulfate catalyst (NaNH ₃SO ₃ ), which is nothing but the Bucherer reaction, yields 2-naphthylamine.
3. Ethylene oxide yields monoethanolamine (HOCH ₂CH ₂ NH ₂ ), di-ethanolamine [(HOCH ₂ CH ₂ ) ₂ NH)], and tri-ethanolamine [(HOCH ₂ CH ₂ ) ₃ N)]
4. Glucose plus nickel catalyst yields glucosamine.
5. Cyclohexanone plus nickel catalyst yields cyclohexylamine.

Production of methylamines

Methylamines are produced by reacting gaseous methanol with a catalyst at a temperature of 350-400 ºC, and 290 lb / in2 (2.0 Mpa) of pressure. Then the reaction mixture is distilled. Any possible ratio of mono-, di-, or trimethylamines can be obtained by recycling the undesirable products.

When ethylene oxide is bubbled through 28% gaseous ammonia at 30 or 40 ° C temperature, an equilibrium mixture of the three ethanolamines occurs. The recirculation of the reaction products, the alteration of the reaction temperatures and pressures, as well as the variation of the initial ratio of ammonia / ethylene oxide (taking care whenever there is an excess of ammonia) will allow the desired amine to predominate . The diluent gas will also alter the ratio of the final product.

• monoethanolamine
• di-ethanolamine
• tri-ethanolamine

After the reaction, which is highly exothermic, has taken place, the reaction products are recovered and separated by means of instantaneous distillation, recycling the ammonia and then fractionating the produced amines.

Monoethanolamine is used in the manufacture of explosives, insecticides, and surfactants. Di-methylamine is used to make di-methylformamide and acetamide, pesticides, and for water treatment. For its part, tri-methylamine is used to make biocides and pesticides.

Other alkyl-amines can be obtained similarly from alcohol and ammonia. Methyl-, ethyl-, isopropyl-, cyclohexyl- and combination amines have small markets and are usually manufactured by reacting the correct alcohol with anhydrous ammonia, in the vapor phase.