Kinetics of the reaction of p-dinitrobenzene with cyanide in dimethylformamide

Abstract

The anion radical (pDNB^–) is formed in the reaction of p-dinitrobenzene (pDNB) with cyanide in dry and oxygen-free dimethylformamide (DMF). The rate of the radical formation was studied spectrophotometrically in the concentration range 10^–4≤c_pDNB≤ 2 × 10^–3 mol dm^–3 and 10^–4≤c_CN≤10^–2 mol dm^–3. The rate was first order in p-dinitrobenzene. For c_CN10^–3 mol dm^–3 the reaction was also first order in CN^– with a second-order rate constant of (3.65 ± 1.2)× 10^–2 dm³ mol^–1 s^–1, an activation energy of (66 ± 7) kJ mol^–1, and an Arrhenius factor of 8.1 × 10⁹ dm³ mol^–1 s^–1(0–40 °C). Radical formation is assumed to proceed via an intermediate Meisenheimer complex which reacts with a second cyanide ion to produce pDNB^– and CN^–. The formation of the Meisenheimer complex is assumed to be rate determining.