Sodium dichromate carboxylic acids

Sodium dichromate/sulfuric acid Carboxyl from methyl groups N-Oxldes as intermediates... 

This procedure illustrates a general method for the preparation of aromatic carboxylic acids by oxidation of the corresponding alkylarenes.2 For example, 2-naphthoic acid (360 g., 93% yield m.p. 184-185°) was obtained from 2-methylnaphthalene (320 g., 2.25 moles), sodium dichromate (975 g., 3.26 moles, 45% excess), and water (1.81.). 

Sodium cyclopentadienide, 41, 96 Sodium dichromate for oxidation of alkylarcncs to aromatic carboxylic acids, 43, 80 Sodium iodide, in conversion of 2,4-di-nitrochlorobenzene to 2,4-dinitro-iodobenzene, 40, 34 reduction of peroxide with, 41,... 

MethyIanlhraquinane and Related Compounds. 2-Methylanthraqui-none and its derivatives are important as intermediates for manufacturing various kinds of vat dyes and brilliant blue (turquoise blue] disperse dyes 2-Methylanthraquinone is prepared from phthalic anhydride and toluene via a benz.oylbenzoic acid. I -Nitroanthraquinone-2-carboxylic acid is of great importance as an intermediate for manufacture of vat dyes as well as disperse dyes. It is conventionally prepared from 2-melhyl-l-nitatanlhraquinone, by oxidation in sulfuric acid with sodium dichromate. 

Primary trialkylboranes were directly converted into carboxylic acids by the oxidation with pyridinium dichromate in dimethylformamide, sodium dichromate in aqueous sulfuric acid, or chromium trioxide in 90% aqueous acetic acid (Equation (106)).509... 

Sodium dichromate in sulfuric acid ( chromic acid, H2Cr04) is the traditional laboratory reagent for oxidizing secondary alcohols to ketones. Bleach (NaOCl) is an inexpensive, chromium-free alternative that also oxidizes secondary alcohols to ketones. Primary alcohols are usually over-oxidized to carboxylic acids under these conditions. 

Sodium dichromate, Na C O Oxidizes primary alcohols to yield carboxylic acids and secondary alcohols to yield ketones (Sections 17.7 and 19.2). 

Sidechain Oxidation Products. Dissolve 0.2 g of sodium dichromate in 0.6 mL of water and add 0.4 mL of concentrated sulfuric acid. Add 50 mg of the unknown and boil for 30 min. Cool, add 0.4 to 0.6 mL of water, and then remove the carboxylic acid by filtration. Wash the crystals with water and recrystallize from methanol-water. 

Sodium dichromate hydroxylates tertiary carbons [620] and oxidizes methylene groups to carbonyls [622, 623, 625, 626, 631] methyl and methylene groups, especially as side chains in aromatic compounds, to carboxylic groups [624, 632, 633, 634, 635] and benzene rings to quinones [630, 636, 637] or carboxylic acids [638]. The reagent is often used for the conversion of primary alcohols into aldehydes [629, 630, 639] or, less frequently, into carboxylic acids or their esters [640] of secondary alcohols into ketones [621, 629, 630, 641, 642, 643, 644] of phenylhydroxylamine into nitroso-benzene [645] and of alkylboranes into carbonyl compounds [646]. 

The degradation of benzene rings to carboxyls is facilitated by the presence of electron-donating groups. m-Trifluoromethylaniline is converted into trifluoroacetic acid in 90-95% yield on heating with sodium dichromate and dilute sulfuric acid for 30-40 min at 70-170 °C [638]. 

Homologues of naphthalene are oxidized to naphthalenecarboxylic acids on heating in an autoclave at 250 °C for 18 h with an aqueous solution of sodium dichromate. p-Methylnaphthalene affords (3-naphthoic acid in 93% yield [633], and 2,3-dimethylnaphthalene, 2,3-naphthalenedicar-boxylic acid in 87-93% yield [1130]. Methylanthracenes and methylphen-anthrenes are similarly converted into the corresponding carboxylic acids in yields well over 90% [633]. 

When sodium or potassium dichromate in the presence of dilute sulfuric acid is used, care must be taken to prevent overoxidation of the products to carboxylic acids. Lower boiling aldehydes can be removed by concomitant steam distillation and thus escape from further oxidation. The disadvantage of dichromate oxidations is the need for rather high reaction temperatures, often those of refluxing aqueous solutions 639, 653. ... 

The oxidation of a methyl ketone to a carboxylic acid with one less carbon by oxidants other than hypohalites is exemplified by the oxidation of 2-acetylfluorene with sodium dichromate. In addition to the methyl keto group, the methylene group is also oxidized (equation 432) [626]. 

Reaction of the C-0 and O-H Bonds Primary alcohols oxidize to carboxylic acids secondary alcohols oxidize to ketones with chromium trioxide or sodium dichromate. Tertiary alcohols do not oxidize under mild conditions. With pyridinium chlorochromate (PCC) the oxidation of primary alcohols can be stopped at aldehydes. 

The particular value of the method is for converting methyl and polymethyl derivatives of polycyclic aromatic compounds into mono- and poly-carboxylic acids. For instance, 1-methylnaphthalene with a 42% excess of aqueous sodium dichromate solution in an autoclave at 240-250° gives 95% of 1-naphthoic acid in 18 h 2-methylnaphthalene with a 55% excess gives a 93% yield of 2-naphthoic acid the methyl group in fluoro-, bromo-, chloro-, nitro-, and methoxy-toluene as well as in xylenes and heterocycles can usually be oxidized smoothly to a carboxyl group. An excess of Na2Cr207 acts as a buffer and favors smooth reaction. With 1.5 moles of Na2Cr207 the reaction occurs in accord with the equation ... 

A common way to change reaction conditions for the oxidation of alcohols is to modify the acid that is added to the medium. Indeed, chromium trioxide will have different oxidizing abilities in different acids. Since most organic compounds are insoluble in water, a cosolvent is usually required to dissolve not only the chromium reagent but also the alcohol substrate. This solvent must be resistant to oxidation, and acetic acid or acetone are commonly used. For the alcohol - carbonyl conversion several Cr(VI) reagents can be used, including chromium trioxide in water or aqueous acetic acid catalyzed by mineral acid, sodium dichromate in aqueous acetone catalyzed by mineral acid, sodium dichromate in acetic acid, the Cr03 pyridine complex, and err-butyl chromate.Both primary and secondary alcohols can be oxidized to the aldehyde or ketone, respectively. Aldehydes may be oxidized to the carboxylic acid under some conditions. 

Eq. (a) shows the oxidation ofp-nitrotoluene by sodium dichromate in an acidic medium (with H2S0 ) to yield p-nitro benzoic acid (I) whereby the methyl function in the starting material gets oxidized to the corresponding carboxylic moiety due to the evolution of 3-moles of nescent oxygen as given in Eq. (a) iii). 

Acidified sodium dichromate is an example of an oxidizing agent which will bring about the oxidation of primary alcohols through to carboxylic acids and secondary alcohols to ketones. If an aldehyde is required as the product of oxidation of a primary alcohol, the apparatus must be designed so that the aldehyde will be distilled off as it is formed. 

Aldehydes are formed by oxidizing a primary alcohol. In the laboratory potassium dichromate(VI) is used in sulfuric acid. They can be further oxidized to carboxylic acids. Reduction (using a catalyst or nascent hydrogen from sodium amalgam in water) produces the parent alcohol. 

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