Abstract
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 = NO
2
) involved in the hydrolysis of 2-chloro-3,5-dinitropyridine to the 2-pyridone by the nucleophilic ring-opening ring-closure mechanism. The ratio
k
1
/
k
2
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.