Nitration: reaction of Phenol

Phenol reacts with dilute nitric acid at low temperature (298 k) to yield a mixture of ortho nitro phenl (15 %) and para nitrophenol (30-40 %).

The ortho and para isomers of nitrophenol can be separated by steam distilation. O-Nitrophenol is steam volatile due to intra molecular hydrogen bonding while p-nitrophenol is less volatile due to intermolecular hydrogen bonding which causes the association of molecules.

But, when nitration is carried out using concentrated nitric acid, phenol is converted to 2,4,6-trinitrophenol known as picric acid. In this reaction nitration is accompanied by oxidation of phenol.

Preparation of Picric acid

Industrially, picric acid is prepared by treating phenol, first with concentrated H2SO4 which converts it to phenol-2,4-disulphuric acid. This yields picric acid on treating it with conc. HNO3

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