What are tarry oxidation products?

Hint: The loss of electrons by a molecule, an atom, or an ion during a reaction is known as oxidation. When the oxidation state of a molecule, an atom, or an ion is increased, it is called oxidation.

Complete step-by-step answer:
When nitric acid oxidizes aniline, tarry oxidation products form as a by-product, which may happen if aniline is not adequately protected during nitration. Even so, when not protonated, unprotected aniline will behave as a nucleophile and target protonated nitric acid, initiating what appears to be the tarry oxidation pathway. A nucleophile is a reactant that contributes a pair of electrons to the formation of a new covalent bond.

In addition to the nitro derivatives, direct nitration of aniline produces tarry oxidation products. Furthermore, in a strongly acidic environment, aniline is protonated to form the meta-directing anilinium ion. As a result, a considerable amount of meta derivative is produced in addition to ortho and para derivatives.

When nitrating unprotected aniline, sulfuric acid, which is the strongest acid present, can protonate both the nitric acid and the aniline, resulting in unwanted products. These unwanted products are known as tarry oxidation products. Aniline, anilinium, sulfuric acid, nitric acid, and protonated nitric acid will then be in the solution as aniline was not adequately protected.

Note: Oxidation decreases the biochemical oxygen demand (BOD) in wastewater, thereby decreasing the toxicity of specific impurities. Any impurities are converted to carbon dioxide, water, and bio-solids during this process. In addition to this, for disinfection, chemical oxidation is often used.