Chromic acid carboxylic acids

Chromic acidfacetic acid Carboxylic acids from alcohols s. 12, 223... 

Chromic acid/sulfuric acid Carboxylic acids from methyl groups... 

Thiazolecarboxaldehydes are very easily oxidized to carboxylic acids by most oxidizing agents, the most common being KMn04 in cold pyridine or boiling acetone. Thiazolecarboxylic acids are obtained in 50% yield (29). Other oxidizing agents such as Ag 0 in dioxane and water (29, 103), chromic acid, and so forth are also used. 

Chromic acid (H2Cr04) is a good oxidizing agent and is formed when solutions containing chromate (Cr04 ) or dichromate (Cr207 ) are acidified Sometimes it is possible to obtain aldehydes m satisfactory yield before they are further oxidized but m most cases carboxylic acids are the major products isolated on treatment of primary alco hols with chromic acid... 

A primary or secondary alkyl side chain on an aromatic ring is converted to a carboxyl group by reaction with a strong oxidizing agent such as potassium permanga nate or chromic acid... 

Oxidation of primary alcohols (Section 15 10) Potassi um permanganate and chromic acid convert primary al cohols to carboxylic acids by way of the corresponding aldehyde... 

Oxidation of aldehydes (Section 17 15) Aldehydes are particularly sensitive to oxidation and are converted to carboxylic acids by a number of oxidizing agents in eluding potassium permanganate and chromic acid... 

Oxidation by Chromic Acid. Under mild conditions, e.g., in acetic acid at atmospheric temperature this converts the dihydric alcohol or keto-alcohol bases to diketo-bases, e.g., the lelobanidines, Ci3H2902N, to lelobanines, C13H25O2N. Under more vigorous action the keto-alcohol and the diketo-bases are oxidised to benzoic acid (side-chain, Ph. CO. ), acetic and i iropionic acids (side-chain, C2H5. CO. ) and either scopolinic acid l-methylpiperidine-2 6-dicarboxylic acid (IV)) or methylgranatic acid (l-methylpiperidine-2-carboxylic-6-acetic acid) or both, these being from the methylpiperidine nucleus with residues of the two side-chains. 

In the early 1930 s, when the prime research aim was the commercial synthesis of the sex hormones (whose structures had just been elucidated), the principal raw material available was cholesterol extracted from the spinal cord or brain of cattle or from sheep wool grease. This sterol (as its 3-acetate 5,6-dibromide) was subjected to a rather drastic chromic acid oxidation, which produced a variety of acidic, ketonic and hydroxylated products derived mainly by attack on the alkyl side-chain. The principal ketonic material, 3j -hydroxyandrost-5-en-17-one, was obtained in yields of only about 7% another useful ketone, 3 -hydroxypregn-5-en-20-one (pregnenolone) was obtained in much lower yield. The chief acidic product was 3j -hydroxy-androst-5-ene-17j -carboxylic acid. All three of these materials were then further converted by various chemical transformations into steroid hormones and synthetic analogs ... 

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—... 

We can control how far we oxidize by carefully choosing our reagents. If we want to go all the way up to a carboxylic acid, then we just use chromic acid ... 

The kinetics of the initial stages of the oxidation of some a-hydroxy-carboxylic such as lactic, malic and mandelic acids by chromic acid have been studied by Bakore and Narain . The initial reaction resembles the oxidation of a secondary alcohol to ketone. The authors concluded that the rate determining step involves C-H bond rupture at the a-carbon atom. The rate of oxidation of these acids is reduced to one-half by the addition of manganous ions, when the concentration of the latter is commensurable with that of the acids. 

This procedure, coupled with the procedure described on p. 41, illustrates the Barbier-Wieland method for systematically degrading carboxylic acids. foxwor-Desoxycholic acid may be prepared from wor-desoxycholic acid by repetition of this procedure. If the chromic acid oxidation product is not sufficiently solid to filter after dilution with water, the mixture must be extracted with ether and washed with dilute hydrochloric acid before the alkaline extraction. Wxwor-Desoxycholic acid may be crystallized from ethyl alcohol. It melts at 239-241°. 

An organic compound (A) (molecular formula C8H16O2) was hydrolysed with dilute sulphuric acid to give a carboxylic acid (B) and an alcohol (C). Oxidation of (C) with chromic acid produced (B). (C) on dehydration gives but-l-ene. Write equations for the reactions involved. 

Oxidation of nicotine with chromic acid led to the isolation of pyridine-3-carboxylic acid, which was given the trivial name nicotinic acid. We now find that nicotinic acid derivatives, especially nicotinamide, are biochemically important. Nicotinic acid (niacin) is termed vitamin B3, though nicotinamide is also included under the umbrella term vitamin B3 and is the preferred material for dietary supplements. It is common practice to enrich many foodstuffs, including bread, flour, corn, and rice products. Deficiency in nicotinamide leads to pellagra, which manifests itself in diarrhoea, dermatitis, and dementia. 

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