Abstract:
Hie photochemical reduction of thionine by N-phenyl
glycine, N-allylurea, N -phonylurea and thiourea in absolute me¬
thanol ms investigated. An apparatus for the irradiation of
air free solutions, with known intensities of monochromatic
light was constructed. Double walled glass reaction cell was
deviced in which nitrogen inlet/outlet, water inlet/outlet ar¬
rangements were made. Acidities of the reaction solutions were
controlled using buffer solutions. Acidities determined spec-
trophotometrically using basic indicator were expressed in
terms of a Hamnett acidity function. Variations of quantum ef¬
ficiencies in absolute methanol have been determined at various
concentrations of thionine, reductants, and acidities. The oxy¬
gen free reaction solutions were irradiated and the react ions
were followed by measuring the intensity of light transmitted.
The quantum efficiency, in yellow light, for the dis¬
appearance of thionine, was found to be a function of reductant
concentration, acidity and temperature. The quantum efficiency
was found to be independent of the concentration of thionine. The
results have been interpreted in terms of a reaction mechanism
Ratios of the certain rate constants for the proposed mec banian
have been evaluated. It was found that the quantum efficiency
is controlled by two equilibriums between: i) triplet state of
thionine with proton, and protonated triplet state of thionine,
and ii) protonated triplet state of thionine with reductant, and
associated complex of thionine with reductant.
