Reduction of Nitrogenous Compounds

The biggest problem with this is that the RNH2 molecule is also nucleophilic so that it reacts with more alkyl halide to give a secondary or tertiary amine molecule. The end result is that there will be a mixture of primary, secondary, and tertiary amines, and quaternary ammonium salts unless a large excess of ammonia is used (which favors a primary amine). Note, this reaction cannot be done with aryl halides because they do not undergo simple nucleophilic substitution.

REDUCTION OF NITROGENOUS COMPOUNDS

First of all, what is an azide? It is a RN3 molecule, in which an alkyl chain is attached to a nitrogen, that is attached to another nitrogen, that is attached to still another nitrogen. This will have a positive charge on one nitrogen and a negative charge on the other but it is still unstable and easily reduced to a RNH2 molecule through the reduction process shown in figure 102:

Figure 102.

Figure 102 shows the reduction of nitriles as well, which also gives rise to a primary amine molecule. These are oxidation-reduction reactions that get reduced through the addition of different reagents. With RN3, the reducing agent is either LiAlH4 (lithium aluminum hydride) or catalytic hydrogenation with hydrogen gas and palladium.

Nitriles, which are RCN molecules can be reduced to a primary amine, adding four hydrogen ions to make RCH2NH2. This will also take a hydrogenating compound such as lithium aluminum hydride or a combination of hydrogen gas and palladium as catalysts. The alkyl nitrile itself can be made by substituting a CN- cyanide ion onto an alkyl halide molecule. In addition, it is possible to reduce an aryl nitrile to an aryl amine.

It is also possible to reduce a nitro compound, which is a RNO2 molecule, to make a RNH2 molecule. This can be accomplished with the R side chain being an aryl group. It is a simple oxidation-reduction reaction. The reducing agents can be iron/H+, selenium/H+, or catalytic hydrogenation using H2 gas plus palladium as a catalyst. This is called the reduction of nitroarenes. Nitroarenes themselves are prepared by the nitration of aromatics with HNO3 (nitric acid) in H2SO4. The ArNH2 molecule is called an aniline.

An amine compound can also be made by mixing lithium aluminum hydride with an amide, which is RCONH2. This can remove the oxygen and add two hydrogen molecules to the carbonyl carbon in a nucleophilic acyl substitution plus a nucleophilic addition reaction, the summary of which is seen in figure 103:

Figure 103.

This is accomplished by reducing the CO double bond, which starts in an amide with a +3-oxidation number and reduces it to a -1-oxidation number (which is -2 from the hydrogen atoms and +1 from the nitrogen atom). It involves the leaving of oxygen rather than nitrogen because oxygen is a better leaving group when compared to nitrogen.

You should know also that there can be primary, secondary, or tertiary amides, depending on the number of side chains on the nitrogen atom. The example in figure