Nitrobenzene ions, decomposition

The last two reactions, which are extremely fast, account for the stoichiometric relationship 2 ArN2 + H2Q. The reaction is second order kinetically, however, because only one molecule of diazonium ion is consumed up to the rate-determining step of the reaction. The solvent isotope effect is attributed to the fact that the for deuterated hydroquinone, DO—CgH4—OD, is 4.16 times less than that of hydroquinone. The absence of deuterium in the nitrobenzene when the reaction is done in D2O indicates that the decomposition of the Ar—N2 to product does not involve hydroquinone and that hydroquinone is not the source of the hydrogen that is added to the benzene ring in the final step of the reaction. In fact, the partial deuteration of the nitrobenzene suggests that the decomposition of the aryldiazenyl radical occurs by two pathways (equation 56), where SH is the solvent for the reaction. 

The nitrations of benzene and nitrobenzene by dinitrogen pentaoxide in carbon tetrachloride have been studied. It was concluded that dinitrobenzenes could be formed directly from benzene without the intermediacy of nitrobenzene. It was suggested that the initially attacking species is NOs and that dinitrobenzenes could be formed by the reaction of the intermediate formed by such attack reacting with NO2, formed by N2O5 decomposition above 25 °C. The reactions of 2-nitrotoluene, l-chloro-2-nitrobenzene, and l-chloro-4-nitrobenzene with dinitrogen pentaoxide in dichloromethane at 0°C are catalysed by certain zeolites giving near quantitative yields. In this process the activated site on the zeolite may provide an incipient nitronium ion for reaction. 

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