Oxidation methyl group, chromic acid

The fact that the side-chain methyl group is oxidized, hut the aromatic ring is unchanged, illustrates the remarkable chemical stahihly of the aromatic ring. Halogen and nitro substituents on an aromatic ring are unaffected by these oxidations. For example, chromic acid oxidizes 2-chloro-4-nitrotoluene to 2-chloro-4-nitrobenzoic acid. Notice that in this oxidation, the nitro and chloro groups remain unaffected ... 

By oxidation with chromic acid, this is converted into cyclohexanone-3-carboxylic acid, in which the —CH. OH— group is converted into the —CO— group. This is converted into its ethyl ester and treated with magnesium methyl iodide, and the product, on hydrolysis, yields l-methyl-cyclohexane-l-ol-3-carboxylic acid, which is converted byhydro-bromic acid into 1-bromo-l - methyl - cyclohexane - 3 - carboxylic acid. When this is digested with pyridine, hydrobromic acid is eliminated and yields l-methyl-A -cyclohexane-3-carboxylic acid of the formula—... 

A method for the determination of carbon-linked methyl groups (and, by extension, used in the analysis of chiral methyl groups in stereochemical studies of enzyme-catalyzed reactions acting on methyl groups). In this procedure, the methyl groups are converted to acetic acid by oxidation of the metabolite with chromic and sulfuric acids. Milder versions are also available. 

The dibenzopyranone ring system may be viewed as a chromone with an additional fused benzene ring and thus generally related to the antiasthmatic mediator release inhibitor cromolyn (see Chapter 11). Two dibenzopyranones have in fact been investigated for this indication in the clinic. Friedel-Crafts cyclization of the substituted cresyloxybenzoic acid (2-1) in sulfuric acid leads to the dibenzopyranone (2-2). The methyl group is then oxidized to a carboxylic acid by means of chromic acid. The acid is then converted to its sodium salt, xanoxate sodium (2-3) [2]. 

Reaction C. Oxidation of the Side Chain in Aromatic Compounds. (A., 122,184 133, 41 137, 308 141,144 147, 292 B., 7,1057 19, 705 Z. Ch., 4, 119) (Fittig).—When aromatic compounds containing aliphatic side chains attached to the nucleus are treated with certain oxidising agents (potassium permanganate, dilute nitric acid, and chromic acid), the side chain is oxidised until only a carboxylic group attached to the nucleus remains the end methyl group, if there are several carbon atoms... 

Then, by oxidizing one of the methyl groups to a carboxyl group with chromic acid, he obtained a carboxylic acid which on losing C02 was converted to a- trinitrotoluene. 

Oxidations with chromic oxide encompass hydroxylation of methylene [544] and methine [544, 545, 546] groups conversion of methyl groups into formyl groups [539, 547, 548, 549] or carboxylic groups [550, 55i] and of methylene groups into carbonyls [275, 552, 553, 554, 555] oxidation of aromatic hydrocarbons [556, 557, 555] and phenols [559] to quinones, of primary halides to aldehydes [540], and of secondary halides to ketones [560, 561] epoxidation of alkenes [562, 563,564, and oxidation of alkenes to ketones [565, 566] and to carboxylic acids [567, 565, 569]. 

Not only methyl groups but practically any other alkyl groups attached to aromatic rings are oxidized to carboxyls by sufficiently strong oxidants, such as nitric acid [460, 461, 462, 463, 464, 891], chromic acid and its derivatives [550, 551, 624, 633, 634, 1129, 1130], and potassium permanganate [503, 841, 880, 881, 882, 883, 1131]. Occasionally, such oxidations have been effected by other reagents, such as ozone [68], sulfomonoperacid (Oxone) [205], sodium hypochlorite [696], and nickel dioxide [933], or by electrooxidation [117] (equation 181). 

Destructive oxidation of any methyl-group-containing compound to acetic acid is accomplished by heating the compound with chromic acid and sulfuric acid at 165-170 °C for 30-60 min. The oxidation is known as the Kuhn-Roth determination of methyl groups [1181]. Its significance waned with the advent of nuclear magnetic resonance techniques. 

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