MANUFACTURE OF PICRIC ACID^501Phenoltrisulphonic acid is formed only when using an excess of 20% oleum.
The second stage in the preparation of picric acid is the nitration of the phenol-sulphonic acid obtained in the first stage of the process.
“Sulphophenol”, which is the name of the starting material for the second stage,
is a mixture of 1,4-phenolsulphonic and 1,2,4-phenoldisulphonic acids.
For the nitration the following nitrating agents may be used:
(a) dilute (44-65%) nitric acid;
(b) mixture of dilute nitric acid and sodium nitrate;
(c) concentrated nitric acid.
A schematic presentation of the reactions occurring in the process of preparation
of picric acid acid via sulphonic acid is given below (Pascal [2]):