The photophysics and the mechanisms of the photochemical and chemical aroma
tization of 1,2,3,4-tetrahydro-7H-pyrido/3,4-b/indole (THBC) in 40% v/v met
hanol-water media have been investigated. The primary photophysical process
es of THBC resemble those of indoles and related alkaloids. The photochemic
al oxidation has been carried out in the presence of atmospheric oxygen and
light. The chemical oxidation has been studied using sodium peroxodisulpha
te (PDS) as the electrophilic agent. In both cases, strong acid media, i.e.
, sulphuric acid concentrations higher than 0.5 mol dm(-3) are needed for t
he dehydroderivative (DR) to be formed. In the photochemical oxidation, the
rate constants for the disappearance of THBC increase linearly with the co
ncentration of acid and the intensity of the exciting radiation. However, t
he formation of DH only depends on the acidity of the media. In the chemica
l oxidation a similar behaviour is observed. In this case, the rate constan
ts for the disappearance of THBC increase linearly with both PDS and acid c
oncentrations, and the appearance of DH solely varies with the acid concent
ration. A two step mechanism is proposed for these oxidation reactions. In
the first step, excited or ground state THBC reacts with ground state oxyge
n or PDS, respectively, to give an indolenine intermediate. This intermedia
te slowly rearranges, in a second acid catalysed step to yield DH. (C) 2000
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