Solvent effects on aromatic nucleophilic substitution by the ANRORC mechanism. Hydrolysis of 2-chloro-3,5-dinitropyridine

Added organic solvents (dimethyl sulfoxide is an exception) have opposite effects on the rates of formation and disappearance of the open-chain intermediate 4(R = NO2) involved in the hydrolysis of 2-chloro-3,5-dinitropyridine to the 2-pyridone by the nucleophilic ring-opening ring-closure mechanism. The ratio k1/k2 increases from 8 in water to over 1000 in 80% tetrahydrofuran at 25 °C and above. The effects are too complex to be analysed in terms of a single parameter, but an approach using the Kamlet–Taft solvatochromic parameters is applied successfully to six mixed aqueous solvent systems.