The solution is then acidified, and the phenols are'liberated and form an oily layer on the surface of the acid.
Nitro-phenols are readily obtained by the action of nitric acid on phenol.
The rationale of this treatment is not fully understood, but the action appears to consist in the separation or decomposition of the aromatic hydrocarbons, fatty and other acids, phenols, tarry bodies, &c., which lower the quality of the oil, the sulphuric acid removing some, while the caustic soda takes out the remainder, and neutralizes the acid which has been left in the oil.
The introduction of hydroxyl groups into the benzene nucleus gives rise to compounds generically named phenols, which, although resembling the aliphatic alcohols in their origin, differ from these substances in their increased chemical activity and acid nature.
The phenols more closely resemble the tertiary alcohols, since the hydroxyl group is linked to.