Flash-Photolysis Studies of α- and γ-(2,4-Dinitrobenzyl)pyridine

Abstract

From flash-photolysis experiments it has been determined that the blue, phototropically produced substance from α-(2,4-dinitrobenzyl)pyridine fades to the colorless form by at least two mechanisms. The rate of the slower process, which is controlling in neutral and slightly basic solution, is first order in the blue substance and is apparently independent of the nominal hydrogen-ion concentration. The faster process is rate controlling in the acidity range, [H+]=5×10—7 to at least 5×10—1, and follows a rate constant which is linear in [H+] over some 5 or 6 orders of magnitude, i.e., a half-life from ∼10 to ∼3.5×10—5 sec. Similar behavior is displayed by the γ isomer. The large solvent dependence reported earlier is now ascribed to slight acid impurities in the sensitive 10—6—10—7[H+] range. These and related findings are discussed in terms of possible structural and mechanistic details.