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a class of organic compounds containing a carbonyl group bonded with two organic radicals, RCOR’. Ketones are classified as aliphatic (fatty), alicyclic, aromatic, or heterocyclic, depending on the nature of R and R’. For example, acetone (dimethyl ketone), CH3COCH3, is the simplest ketone of the fatty series, while benzophenone, C6H5COC6H5, is the simplest aromatic ketone. In contrast to the given symmetrical forms, asymmetrical (mixed) ketones also exist, which contain different R and R’ radicals, for example, fatty-aromatic ketones, such as acetophenone, C6H5COCH3. Numerous cyclic ketones are known in which a CO group enters the ring, for example, cyclohexanone
The designation of ketones belonging to the fatty series in accordance with the Geneva nomenclature is derived from the name of the corresponding hydrocarbons, adding the “-one” ending and indicating the position of the carbonyl group; for example, diethyl ketone, CH3CH2COCH2CH3, is known as pentanone-3.
Lower aliphatic ketones are colorless liquids with a pleasant odor; they mix readily with water. Higher aliphatic ketones are solid substances. All ketones are soluble in organic solvents.
Ketones are similar to aldehydes in properties and methods of preparation, although ketones exhibit a lower degree of reactivity and are considerably more resistant to oxidation. Two types of reactions are characteristic of ketones, both determined by the presence of the carbonyl group: (1) addition with the carbonyl group and (2) substitution of the carbonyl oxygen with another group. For example, hydrocyanic acid, HCN, adds readily to ketones to form oxynitriles, RC(OH)R’CN; sodium bisulfite, NaHSO3, chloroform, CHCL3, and others react with ketones in a similar manner. Secondary alcohols are produced during ketone hydrogenation:
RCOR’ + H2 → RCH(OH)R’
Tertiary alcohols are formed during the interaction of ketones and organometallic compounds and subsequent hydrolysis:
RCOR’ + RʺMgX → RR’C(Rʺ)OMgX → RR’RʺCOH
Upon interaction with PCl5, two chlorine atoms are substituted for the oxygen atom in the ketone. Ketones react with hydroxylamine to form ketoximes:
RCOR’ + NH2OH → RC(̿NOH)R’
This reaction, as well as the formation of other crystalline oxygen substitution products (such as hydrazones, 2,4-dinitrophenyl hydrazones), is used in the identification of ketones. Hydrolysis of these products is used to prepare pure ketones. The reduction of the group to (Kizhner-Wolff reaction) is of great importance.
Industrial preparation of ketones involves the dehydrogenation of secondary alcohols
RCH(OH)R’ → RCOR’ + H2
and the thermal dissociation of calcium salts of carboxylic acids
(RCOO2)Ca → R2CO + CaCO3
or the passage of carboxylic acid vapors over thorium oxide, barium oxide, and calcium carbonate catalysts. Aromatic and fatty-aromatic ketones are obtained during the action of acid chlorides on aromatic hydrocarbons in the presence of aluminum chloride, for example,
C6H6 + CH3COCl → C6H5COCH3 + HCl
Many ketones can be prepared by oxidizing hydrocarbons with oxygen in the presence of catalysts—acetophenone from ethylbenzene, C6H5CH2CH3; cyclohexanone from cyclohexane.
Ketones find diverse application. For example, cyclohexanone is a primary product in the manufacture of synthetic caprone fibers; Michler’s ketone is used in the manufacture of triarylmethane dyes. Some ketones are used in the perfume industry.