According to one series of studies the mercury nitrate first takes benzene to the corresponding
nitroso compound and through the
diazonium salt to the
phenol. The presence of
nitrite is essential for the reaction; picric acid formation is prevented when
urea, a trap for nitrous acid, is added to the mixture. From then on the reaction proceeds as a regular aromatic
nitration.[5][6]
^The Mechanism of the Oxynitration of Benzene F. H. Westheimer, Edward Segel, and Richard Schramm
J. Am. Chem. Soc.; 1947; 69(4) pp 773 - 785;
doi:
10.1021/ja01196a011
^The Oxynitration of Benzene. I. Studies Relating to the Reaction MechanismsMarvin Carmack, Manuel M. Baizer, G. Richard Handrick, L. W. Kissinger, and Edward H. Specht
J. Am. Chem. Soc.; 1947; 69(4) pp 785 - 790;
doi:
10.1021/ja01196a012