The NO3Radical-Mediated Liquid Phase Nitration of Phenols with Nitrogen Dioxide

Phenols are transformed into nitrophenols by the combined action of ozonized oxygen and nitrogen dioxide ( Kyodai nitration) in different solvents. Dipole moments of the solvents were correlated with the ortho/para nitration ratio with phenol, showing an influence of the polarity of the solvent on the ortho/para nitration selectivity. A Hammett ρ of −0.72 was obtained in the Kyodai nitration of 4-substituted phenols. These facts suggest the formation of a charge-transfer complex which evolves to the addition of NO 3 to phenols followed by elimination of nitric acid to give the final nitrophenols. The position of the nitro group in nitrophenols found in air samples may be indicative of a gas- or a liquid-phase nitration occurring in the troposphere.