Ketone
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Ketones are organic compounds having at least one RC(=O)R' group, where R and R' can be a variety of carbon-containing substituents, like alkanes, alkenes, alkynes, or aromatics. Compounds with non-carbon substituents like H, OH, NH2 or halogens are not ketones, but aldehydes, carboxylic acids, amides or acyl halides respectively.
Properties
Ketones are colorless liquids, with a mildly pleasant odor. Of all ketones, only acetone is miscible with water, while the rest are soluble or miscible with various organic solvents.
Ketones are reactive both directly at the carbonyl and at their alpha-carbon positions. Nucleophilic addition upon the carbonyl is common, as in the reaction of Grignard reagents with ketones. They form adducts with bisulfite and hydroxylamine, a property useful for isolating them (along with aldehydes) from biological samples and other impure sources.
Preparation
Ketones can be easily prepared through the Jones oxidation of secondary alcohols, using chromium trioxide or potassium dichromate dissolved in dilute sulfuric acid. Potassium permanganate can also be used.
A more convenient route involves the pyrolysis of carboxylic acid salts, process known as ketonic decarboxylation. However, this process leads to mixed products. A few examples below:
- 2 CH3COONa → (CH3)2CO + Na2CO3
- CH3COONa + CH3CH2COONa → (CH3)CO(CH3CH2) + Na2CO3
- CH3COONa + C6H5COONa → (CH3)CO(C6H5) + Na2CO3
Other synthesis routes are hydration of alkynes, reaction of Grignard reagents with nitriles, followed by hydrolysis, decarboxylation of carboxylic anhydrides, oxidation of amines with iron(III) chloride, Friedel–Crafts acylation, etc.
Safety
Unlike aldehydes, ketones have low toxicity and low carcinogenic potential. They are however very flammable.
