Acetyl cation/radical

Acetylchloride is a trapping agent that allows the reaction to go completion, transforming the product into a less oxidizable compound.The results of other reactions between indole (57) and substituted cyclohexa-1,3-dienes show that the photo-induced Diels-Alder reaction is almost completely regioselective. In the absence of 59 the cycloaddition did not occur the presence of [2+2] adducts was never detected. Experimental data support the mechanism illustrated in Scheme 4.14. The intermediate 57a, originated from bond formation between the indole cation radical and 58, undergoes a back-electron transfer to form the adduct 60 trapped by acetyl chloride. 

Various hydroxyl and amino derivatives of aromatic compounds are oxidized by peroxidases in the presence of hydrogen peroxide, yielding neutral or cation free radicals. Thus the phenacetin metabolites p-phenetidine (4-ethoxyaniline) and acetaminophen (TV-acetyl-p-aminophenol) were oxidized by LPO or HRP into the 4-ethoxyaniline cation radical and neutral V-acetyl-4-aminophenoxyl radical, respectively [198,199]. In both cases free radicals were detected by using fast-flow ESR spectroscopy. Catechols, Dopa methyl ester (dihydrox-yphenylalanine methyl ester), and 6-hydroxy-Dopa (trihydroxyphenylalanine) were oxidized by LPO mainly to o-semiquinone free radicals [200]. Another catechol derivative adrenaline (epinephrine) was oxidized into adrenochrome in the reaction catalyzed by HRP [201], This reaction can proceed in the absence of hydrogen peroxide and accompanied by oxygen consumption. It was proposed that the oxidation of adrenaline was mediated by superoxide. HRP and LPO catalyzed the oxidation of Trolox C (an analog of a-tocopherol) into phenoxyl radical [202]. The formation of phenoxyl radicals was monitored by ESR spectroscopy, and the rate constants for the reaction of Compounds II with Trolox C were determined (Table 22.1). 

Cation radicals containing three electrons in the field of four atoms or anion radicals with five electrons retained by four atoms represent a special group of multicentered ion radicals. Thus, nonclassical, cyclically delocalized 3e/4C cation radicals and 2e/4C (dication) radicals of substituted cyclobutadienes are known (Allen and Tidwell 2001). The 3e/4N cation radical and the 5e/4N anion radical depicted in Scheme 3-27 have also been discovered (Exner et al. 1998, 1999, 2000). The reactions in Scheme 3-27 illustrate such species as well as the corresponding dianion and acetylated products of the latter. 

A series of 5-oxides of phenothiazines and benzophenothiazines, some of which were iV-acetylated, have been polarographically reduced in ethanolic solution they displayed behavior similar to that of other aromatic jS-oxides. The reduction proceeds more easily in acid media, because at lower pH phenothiazine-5-oxides are in equilibrium with the corresponding phenazathionium salts, which undergo a one-electron reduction (see Section IV,B,1). The cation radical thus formed cannot be further reduced under these condi-... 

Upon electron donation to the hydroxyl radical (HO") to form OH-, melatonin gives rise to the melatoninyl cation radical, which is able with the superoxide anion radical (OjT to A/-acetyl-A/-formyl-5-methoxykynuramine [61]... 

Acetanilides Ketene elimination to yield the aniline radical cation (often base peak), which consecutively eliminates HCN (Am 27), and formation of the acetyl cation (m/z 43). 

There are many reports for nitration of alkenes using various nitrating agents, which proceeds via an ionic or radical addition process.49 Nitration of cyclohexene with acetyl nitrate gives a mixture of 3-and y-nitrocyclohexenes, 1,2-nitroacetate, and 1,2-nitronitrate. This reaction is not a simple ionic or radical process instead, [2+2] cycloaddition of nitryl cation is proposed.50... 

Amines are stable to electrochemical oxidation in acid solution because the nitrogen lone pair is protonated and inaccessible for reaction. This is not the case for N-acetylamines, which are oxidisable at a lead dioxide anode in aqueous sulphuric acid [99]. The primary electron tiansfer step involves the amide function and leads to a radical-cation, which loses a proton from the carbon atom adjacent to nitrogen. Subsequent steps lead to an acylimmonium ion, which is trapped by water. N-acetylated primaiy amines are converted to the corresponding carboxylic acid. 

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