The reactions of indoles in aqueous solution initiated by one-electron oxidation

Abstract

By pulse or gamma radiolysis in the presence of Br-, 1 -methylindole (1 b) is oxidized to its radical cation (2b), which adds to (lb) to form a radical dimer (8b). Species (2b) also reacts with OHto yield the pseudo-base, proposed to be the C,-OH adduct (4b). Identical end-product yields and spectral comparison reveal that the addition of OH' radicals to (lb) also produces (2b) and ( 4b) but virtually no other OH' adducts to (lb). The selectivity of OH towards the C, position appears to apply to the other indoles as well. The neutral indolyl radicals (3) disappear both by coupling and dismutation. Discrimination between these modes is governed by the substituent. A methyl group at the C, position favours C,-C,' coupling. Molecular oxygen adds to neutral indolyl radicals at the C, position. The measured and estimated rates of 0, addition relate to the redox potentials of the indolyl radicals. The reaction between 0,-* and the indolyl radical cation (2) produces (1) and 0,. On the other hand, 02-* couples to (3) to yield C,-OOH hydroperoxides (14). The latter decompose into C,-C3 opened amides (1 3) with concomitant chemiluminescence. Early photophysical and pulse radiolysis studies '-' aimed at Paper 9/03860D

Access to 3‐Oxindoles from Allylic Alcohols and Indoles

“…Outer‐sphere approach of nucleophilic indole 1 on π–allylic ruthenium(IV) intermediate II is followed by proton transfer and ligand exchange on IV with allylic alcohol 2 to release allylated indole 3 . Concerning pseudoindoxyls 6 , according to previous reports on the oxidation of 2,3‐disubstituted indoles and related compounds, hydroperoxide A tends to be the key intermediate ,. Homolysis of this hydroperoxide followed by reduction through comproportionation with 3 , water, or the surface involving hydroxy radicals might explain the formation of hydroxyindolenine B .…”

Colloidal CdS-induced photocatalytic reaction of 2-methylindole?mechanistic analysis of oxidation of indoles

“…Indolyl radical is known to couple with O 2 À to yield hydroperoxide. 19 Hence the initial step in CdS-sensitized reaction of 2-MI may consist of its oxidation to produce 2methylindolyl radical cation. The pK a of this radical cation is 5.7 AE 0.1, 20 and at pH 10.5 it will be converted largely into 2-methylindolyl radical.…”

“…The higher reactivity of 2methylindolyl radical with molecular oxygen in comparison with that of indole radical can be explained by the difference in their reduction potentials. 17,19 In case of indole the initially produced radical cation mainly forms an adduct with OH À at the electron-deficient C-2 position, 9b in contrast to 2-MI, in which the C-2 position is blocked by a methyl group. The OH adduct is then oxidized by the photogenerated hole to give 3-hydroxyindole, which is known to autooxidize readily to indigo in the presence of oxygen.…”

Flow-injection chemiluminescence determination of tryptophan through its peroxidation and epoxidation by peroxynitrous acid

“…The results showed that the proposed method has good selectivity. Although indole-based compound such as indole-3-acetic acid caused positive interference to a certain degree, which was due to the similarity of indole-3-acetic acid and tryptophan in chemical characteristics and molecular structure [38], dole-3-acetic acid at 0.5 times the tryptophan concentration was tolerable. Besides, 50 times aniline did not caused interference.…”

“…These chemiluminescence phenomena were considered as they originated from peroxidation and epoxidation of tryptophan by singlet oxygen and peroxynitrite [36,37]. Thus, The emitting species should be excited-state oxidation product resulted from decomposition of the formed dioxetane, epoxidized product of tryptophan by peroxynitrous acid [38,39], rather than the weak chemiluminescence of excited-state ONOOH * enhanced by tryptophan.…”