Resumen de Photo-pk of indoline-2-thione

C.G. Araya-Hernández, U. E. Steiner

• The photochemistry and photokinetics of indoline-2-thione (1) has been investigated by continuous illumination at 334 nm and flash photolysis in aqueous solutions as a function of pH. The photokinetic behaviour and product distribution were almost independent on the presence of oxygen in the solution. Whereas indole is formed as the main product in acidic solutions biindolyl was found as the main product in unbuffered solution. For the quantum yield f of photodegradation of 1 a marked increase was observed in acidic solutions. The pH dependence follows a Henderson-Hasselbalch relation with a pKa of 2.2. This photo-pK does note correspond to a pKa in the ground state. It is tentatively assigned to the protolytic equilibrium ³1 + H+ ®³1H+ in the excited triplet state, evidence for which is found in the pH-dependence of transient absorption observed in laser flash photolysis experiments. Our findings support the intermediacy of a 2-mercapto-indole tautomer of 1 in the photochemical desulfurization mechanism as suggested previously by Nishio.11