Methods for extrapolating rates for nitrations in aqueous sulphuric acid to different temperatures and acidities are discussed. A standard procedure to obtain k, values at 25" and Ho -6.6 is applied t o literature data for 131 nitration rates. Allowance is made where necessary for minority species concentrations.NITRATION is perhaps the most common of the electrophilic substitution reactions of aromatic rings. It is widely used preparatively, and has been extensively studied kinetically in this and in other lab~ratories.~-~ Comparison of nitration rates of different compounds is complicated by their variation with solvent and acidity. Because of the considerable acidity dependence, kinetic rates can be obtained for compounds of widely differing reactivity in aqueous sulphuric acid of appropriate concentration. In this respect nitration kinetics resemble those for acid-catalysed hydrogen exchange : in previous work, we have given reasons for choosing pH = 0 and t The Kinetics and Mechanism of the Electrophilic Substitution
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