Dichromate oxidation, degradation

Oxidative degradations of aldehyde derived enamines with ozone (4) or sodium dichromate (485-487) have been applied to the formation of progesterone from 3-ketobisnor-4-cholenaldehyde. 

Dichromate anions are readily absorbed under acidic conditions by wool that has been dyed with chrome dyes. The chromium(VI) on the fibre is then gradually reduced by the cystine residues in wool keratin to chromium(III) cations, which react with the dye ligands to form a stable complex. In this way the cystine disulphide bonds are destroyed, resulting in oxidative degradation of the wool fibres [71]. 

The result of this oxidative degradation can be explained by an initial fragmentation leading to formaldehyde, and a cation that can be trapped by reaction with dichromate, resulting in a chromate ester that yields a lactone. The authors of this reaction pursued as much fragmentation as possible, and found that best yields of fragmented product were obtained by the use of AC2O as accelerant. 

Degradation of the carbon chain does not always occur. Dichromate oxidation of triisobutylenes gives acids with the same carbon content as the olefins. The keto acid, benzoylformic acid (55%), is made by hot alkaline permanganate oxidation of styrene. ° ... 

Experiments on the oxidative degradation of PVA with potassium permanganate [103], potassium dichromate [104], hydrogen peroxide [105], and ozone [106] were carried out in detail. It was observed that a random scission of the PVA chain occurs. The scission product was fractionated, and the determination of the DP and end groups was carried out. It was found that the main end groups formed by the scission are either carbonyls or carboxyls. Radiation-induced oxidative degradation has also been studied [107]. 

The structures of thaliglucine methochloride and thaliglucinone metho-chloride were confirmed by a standard chemical sequence. Northalphenine prepared by a photochemical route (see Sec. 10.2.1) was quaternized with methyl iodide to furnish thalphenine and subsequent Hofmann degradation produced the phenanthrene base thaliglucine (see below). Dichromate oxidation of thaliglucine leads to the phenanthrene lactone thaliglucinone. ... 

Oxidation of acridine by dichromate in acetic acid yields 9-acridone (14) permanganate in an alkaline medium gives oxidative degradation to quinoline-2,3-dicarboxyUc acid (15) ... 

Potassium dichromate/acetic acid Oxidative degradation of side chains... 

Chromones are readily oxidized by permanganate or dichromate with opening of the pyran ring and the formation of a salicylic acid (402). Flavones and isoflavones are also degradatively oxidized for example oxidation of munetone (403) with alkaline hydrogen peroxide yields 2-methoxybenzoic acid and 4-hydroxy-2-isopropylbenzofuran-5-carboxylic (isotubaic) acid. 

It is known that preparation of the oxidant salt under anhydrous conditions is explosion-prone [1], but during repetition of a supposedly safe preparative method [2], recommended for large-scale use [3], ignition and a violent explosion occurred. Use of more water to dissolve completely the chromium trioxide, and a reaction temperature below 25°C, are recommended [4], During a study by TGA of the thermal degradation of the salt, too-rapid heating of the samples led to explosions with fire [5]. See other DICHROMATE SALTS OF NITROGENOUS BASES, OXIDANTS... 

No dialdehyde groups are detectable in modified celluloses obtained by oxidation of cellulose with persulfate, hypobromite, hypochlorite, permanganate, nitric acid, or dichromate. " Alkaline-hypochlorite oxidized starches, which have already been partially degraded by alkali, are more resistant to alkaline degradation than are unmodified starches, and the alkali-lability slowly decreases with increasing oxidation because of the resulting oxidation of reducing ends."... 

Other chemical oxidants that have been examined include ceric ammonium sulfate,74 potassium dichromate,75 and hydrogen peroxide,76 although it is reported that optimal conductivities are obtained when (NH4)2S208 is used as oxidant. It has been suggested that the polymerization process is less dependent on the oxidation potential of the particular oxidant (see Table 4.1) than on the degradation processes associated with each. 

Accelerating the rate of chemical reactions with oxidants, e.g., hydrogen peroxide, oxygen, peroxydisulfate, dichromate and nitric acid [136]. The free radicals formed are used to break down organic molecules and the addition of a TiC>2 suspension as a photocatalyst [139] further enhances degradation. 

Sulfo and nitro substituents also often make it harder to degrade the side chain. For the preparation of nitrobenzoic acids from nitrotoluenes a dichromate-sulfuric acid mixture is superior to chromic acid alone in glacial acetic acid trinitrotoluene is converted into trinitrobenzoic acid by the former but is not attacked by the latter reagent. o-Toluenesulfonamide (obtained from the acid by way of the chloride) is oxidized by alkaline permanganate solution... 

This picture has been broadly validated, and in some respects refined, by other work in which coal was depolymerized by acid-catalyzed transalkylation [as by interaction of coal with phenol and BF3 (23-27)] or by similar, less clearly defined, phenolation reactions (28-31), or selectively degraded by specific oxidants, such as dichromates (32-34), hypohalites (35-38), or peroxy-acids (39-43). But these studies have also revealed some previously unsuspected features. Buffer-controlled oxidation with Na2Cr207 (34) and KMn04 (44) have indicated an occasionally significant presence of straight-chain (up to C21) and branched-chain (up to C8) aliphatic compounds in coal. Oxidation with performic acid (41-43) has yielded substituted compounds that are clearly related to the microbial or chemical degradation products of lignin or flavonoids. And when applied to supposedly very similar coals, virtually identical depolymerization or oxidation procedures often furnished distinctly different product slates (45). 

Acridine is oxidized by dichromate in acetic acid giving 9-acridone 13 and degraded by permanganate in an alkaline medium forming quinoline-2,3-dicarboxylic acid 14 ... 

Degradable organic matter determined by oxidation with potassium dichromate Total nitrogen... 

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