Sulfonitric mixture

Nitration, are highly exothermic (30-70 kcal/mole)5,6 and have to be conducted with great care. Usually they are performed using the classic sulfonitric mixtures ("mixed acid"), in which a slight molar excess of concentrated nitric acid toward substrate and a molar equivalent of concentrated sulfuric acid are used5,7,9. 

Nitration - Nitro groups are introduced onto the carbon surface by the sulfonitric mixture or nitronium tetrafluoroborate and their concentration is determined. 

The case of nitration with at 70 % sulfonitric mixture seems particular. In this zone of acidity, the main specy is neither the nitronium ion neither nitric acid but protonated nitric acid H2NCb+ (ref. 13). In this case one can invoque a cyclic transition state to explain the ortho selectivity that is observed. 

The determination of arsenic in these derivatives is imperatively required by the pharmacopeia. To achieve it, the molecule is first mineralized by the sulfonitric mixture, which has strong oxidizing properties. The organic arsenic of the initial sample becomes mineralized and transformed into arsenic acid H3ASO4. The latter is brought in the presence of a solution of iodide ions in concentrated hydrochloric acid. In these conditions, As(+V) quantitatively oxidizes iodide ions to give iodine. The reaction evolves in the direction As(+V) As(+III). The liberated iodine is titrated later with an arsenious acid solution in hydrogen carbonate medium. Therefore, at this time, the reaction As(+III) As(+V) is used. 

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