Question

What happens when aniline reacts with the following:-
Fuming sulphuric acid

Answer 1

Hint: As we know that aniline is an organic compound that consists of a phenyl group attached to an amino group. It is the simplest aromatic amine available. It is industrially very significant and used as a starting reaction in organic synthesis of various compounds. So here we are to tell the compound formed when aniline reacts with fuming sulphuric acid.

Complete answer:
 Let us discuss about reactive nature of aniline followed by the reaction as follows:-
Just like phenols, aniline does give electrophilic substitution reaction. Due to its high reactivity, it can also be categorized as an enamine. This is because aniline has a good electron donating ability to the electrophilic species. This can be seen in the reaction of aniline with fuming sulphuric acid as follows:-
-Formation of anilinium hydrogen sulphate:-

When aniline reacts with concentrated sulphuric acid (${{H}_{2}}S{{O}_{4}}$), the lone pair of nitrogen donates its electron to proton of acid. This leads to the formation of anilinium hydrogen sulphate due to the ionic interaction between phenyl ammonium ion and hydrogen sulphate ion.
-Reaction of anilinium hydrogen sulphate with concentrated sulphuric acid at high temperature:-

When concentrated sulphuric acid reacts with anilinium hydrogen sulphate, electrophilic substitution reaction takes place which leads to the formation of sulphanilic acid.
-Equilibrium of sulphanilic acid:-

Sulphanilic acid is in constant equilibrium condition to its respective zwitterion because the H atom attached to the –OH part of $-S{{O}_{3}}H$ keeps on moving between oxygen atom and nitrogen atom of amino group.
-From the above data we can say that when aniline reacts with fuming sulphuric acid, the product obtained is Sulphanilic acid which is also known as p-aminobenzene sulfonic acid.

Note:
-Remember that zwitterion is a neutral species which contains an equal number of positive and negative charges to make it an ion at the same time.
-Also study and learn all types of reaction shown by aniline as it is an important reactant in most of the organic synthesis.