How would you convert aniline into nitrobenzene?

Hint: Aromatic compounds are those compounds which contain one or more than one rings with delocalized $\pi $ electrons. Benzene is the most common aromatic compound having the chemical formula ${{C}_{6}}{{H}_{6}}$. Aromaticity is not only based on benzene rings but also defined by $(4n+2)\pi $ rule named as Huckel’s rule.

Complete Solution :
Aniline is an organic compound represented by the chemical formula ${{C}_{6}}{{H}_{5}}N{{H}_{2}}$. It is also kept in the category of aromatic compounds in which the phenyl group is attached with the amino group. Aniline is mainly used in the manufacturing of dyes and other industrial chemicals. It has a rotten fish-like smell. On the other hand Nitrobenzene is also an organic compound represented by the chemical formula ${{C}_{6}}{{H}_{5}}N{{O}_{2}}$, it is generally pale yellow oil and have almond like smell.
Aniline is converted into nitrobenzene via diazotization. It is generally a step by step process which can be discussed as follows:
1. First aniline is converted into diazonium chloride with the help of $NaN{{O}_{2}}$and $\text{HCl}$and the reaction can be shown as:
${{C}_{6}}{{H}_{5}}N{{H}_{2}}+NaN{{O}_{2}}+HCl\to {{C}_{6}}{{H}_{5}}{{N}_{2}}Cl$

2. By using ${{H}_{3}}P{{O}_{3}}$ we remove ${{N}_{2}}Cl$ group from diazonium chloride and this results in the formation of simple benzene which can be shown as:
${{C}_{6}}{{H}_{5}}{{N}_{2}}Cl+{{H}_{3}}P{{O}_{3}}\to {{C}_{6}}{{H}_{6}}$

3. Now in the final step we can convert the benzene into nitrobenzene with the help of nitrating mixture i.e. $HN{{O}_{3}}+{{H}_{2}}S{{O}_{4}}$ and reaction can be shown as:
${{C}_{6}}{{H}_{6}}+HN{{O}_{3}}+{{H}_{2}}S{{O}_{4}}\to {{C}_{6}}{{H}_{5}}N{{O}_{2}}$
In this way we get the desired product.

Note: Nitrobenzene is generally used in the production of aniline, rather than this it is also used to make unpleasant odors in shoe and floor polishes, leather dressings and in paint solvents. Nitrobenzene is highly toxic in nature and readily absorbed through skin.