ketonic /ki ton"ik/, adj.
/kee"tohn/, n. Chem.
1. any of a class of organic compounds containing a carbonyl group, CO, attached to two alkyl groups, as CH3COCH3 or CH3COC2H5.
2. containing the ketone group.
[1850-55; < G Keton, aph. alter. of Aceton ACETONE]

* * *

Any of a class of organic compounds containing a carbonyl group (―C=O; see functional group) bonded to two carbon atoms.

Ketones can participate in many chemical reactions, though to a lesser extent than the related aldehydes. Many more complex organic compounds have ketones as building blocks. Their chief industrial use is as solvents and in the manufacture of explosives, lacquers, paints, and textiles. Acetone is the most important ketone; several sugars and some natural and synthetic steroids are ketones. In ketosis, ketones produced by lipid metabolism accumulate in the blood and urine in abnormal amounts, usually because of starvation or a metabolic disease such as diabetes mellitus.

* * *

 any of a class of organic compounds (organic compound) characterized by the presence of a carbonyl group in which the carbon atom is covalently bonded to an oxygen atom. The remaining two bonds are to other carbon atoms or hydrocarbon radicals (R):

      Ketone compounds have important physiological properties. They are found in several sugars (sugar) and in compounds for medicinal use, including natural and synthetic steroid hormones (steroid hormone). Molecules of the anti-inflammatory agent cortisone contain three ketone groups.

      Only a small number of ketones are manufactured on a large scale in industry. They can be synthesized by a wide variety of methods, and because of their ease of preparation, relative stability, and high reactivity, they are nearly ideal chemical intermediates. Many complex organic compounds are synthesized using ketones as building blocks. They are most widely used as solvents, especially in industries manufacturing explosives (explosive), lacquers, paints (paint), and textiles (textile). Ketones are also used in tanning, as preservatives, and in hydraulic fluids.

      The most important ketone is acetone (CH3COCH3), a liquid with a sweetish odour. Acetone is one of the few organic compounds that is infinitely soluble in water (i.e., soluble in all proportions); it also dissolves many organic compounds. For this reason—and because of its low boiling point (56 °C [132.8 °F]), which makes it easy to remove by evaporation when no longer wanted—it is one of the most important industrial solvents, being used in such products as paints, varnishes (varnish), resins (resin), coatings, and nail-polish removers.

nomenclature of ketones
      The International Union of Pure and Applied Chemistry (IUPAC) name of a ketone is derived by selecting as the parent the longest chain of carbon atoms that contains the carbonyl group. The parent chain is numbered from the end that gives the carbonyl carbon the smaller number. The suffix -e of the parent alkane (paraffin hydrocarbon) is changed to -one to show that the compound is a ketone. For example, CH3CH2COCH2CH(CH3)2 is named 5-methyl-3-hexanone. The longest chain contains six carbon atoms and numbering of the carbon must begin at the end that gives the smaller number to the carbonyl carbon. The carbonyl group is on carbon 3, and the methyl group is on carbon 5. In cyclic ketones, numbering of the atoms of the ring begins with the carbonyl carbon as number 1. Common names for ketones are derived by naming each carbon group bonded to carbon as a separate word followed by the word “ketone.”

      The simplest ketone, CH3COCH3, whose IUPAC name is 2-propanone, is almost always called by its common name, acetone, which is derived from the fact that it was first prepared by heating the calcium salt of acetic acid.

Reactions (chemical reaction) of ketones
      Ketones are highly reactive, although less so than aldehydes (aldehyde), to which they are closely related. Much of their chemical activity results from the nature of the carbonyl group. Ketones readily undergo a wide variety of chemical reactions. A major reason is that the carbonyl group is highly polar; i.e., it has an uneven distribution of electrons (electron). This gives the carbon atom a partial positive charge, making it susceptible to attack by nucleophiles (nucleophile), which are species attracted to positively charged centres. Typical reactions include oxidation-reduction (oxidation–reduction reaction) and nucleophilic addition. The polarity of the carbonyl group affects the physical properties of ketones as well.

      Secondary alcohols (alcohol) are easily oxidized to ketones (R2CHOH → R2CO). The reaction can be halted at the ketone stage because ketones are generally resistant to further oxidation. Oxidation of a secondary alcohol to a ketone can be accomplished by many oxidizing agents, most often chromic acid (H2CrO4), pyridinium chlorochromate (PCC), potassium permanganate (KMnO4), or manganese dioxide (MnO2). With a few exceptions (such as oxidative cleavage of cyclohexanone, C6H10O, to adipic acid, HO2C[CH2]4CO2H, a compound used to make nylon-6,6), the oxidation of ketones is not synthetically useful.

      The treatment of an aromatic hydrocarbon with an acyl halide or anhydride in the presence of a catalyst composed of a Lewis acid (i.e., a compound capable of accepting an electron pair), most often aluminum chloride (AlCl3), gives an aryl alkyl or diaryl ketone (ArH → ArCOR or ArCOAr′), where Ar represents an aromatic ring. This reaction is known as Friedel-Crafts acylation.

      Nitriles (nitrile) (RCN) react with Grignard reagents (Grignard reagent) to produce ketones, following hydrolysis (RCN + R′MgX → RCOR′).

      Ketones possessing α-hydrogens can often be made to undergo aldol reactions (also called aldol condensation) by the use of certain techniques. The reaction is often used to close rings, in which case one carbon provides the carbonyl group and another provides the carbon with an α-hydrogen. An example is the synthesis of 2-cyclohexenone. In this example, the aldol product undergoes loss of H2O to give an α, β-unsaturated ketone.

William H. Brown

* * *

Universalium. 2010.

Игры ⚽ Нужно решить контрольную?

Look at other dictionaries:

  • Ketone — group …   Wikipedia

  • Ketone — Ketone, eine Gruppe von organischen Verbindungen, die den Aldehyden (s.d.) sehr nahe stehen und gleich diesen die Karbonylgruppe CO enthalten. Während aber in den Aldehyden diese Gruppe einerseits mit einem Wasserstoffatom, anderseits mit einem… …   Lexikon der gesamten Technik

  • Ketone —   [Kurzwort], Singular Keton das, s, umfangreiche Klasse von organischen Verbindungen, die als charakteristische Gruppe mindestens eine an zwei Kohlenwasserstoffreste gebundene Carbonylgruppe (Carbonyl...) enthalten, allgemeine Formel R CO R ,… …   Universal-Lexikon

  • Ketone — Ke tone (k[=e] t[=o]n), n. [Cf. {Acetone}.] (Chem.) One of a large class of organic substances resembling the aldehydes, obtained by the distillation of certain salts of organic acids and consisting of carbonyl ({CO}) united with two hydrocarbon… …   The Collaborative International Dictionary of English

  • Ketone — (Chem.), eine Reihe homologer Zersetzungsproducte, welche bei der trockenen Destillation der lipogenen Säuren (Säuren von der allgemeinen Formel Cn Hn–1 O3) mit Alkalien od. alkalischen Erden unter Austritt von 1 Atom Kohlensäure entstehen, ihre… …   Pierer's Universal-Lexikon

  • Ketōne — (Acetone), organische Verbindungen, die wie die Aldehyde die zweiwertige Karbonylgruppe CO enthalten, die in den Aldehyden mit einem Wasserstoffatom und einem einwertigen Alkyl (CH3.CO.H), in den Ketonen aber mit zwei einwertigen Alkylen… …   Meyers Großes Konversations-Lexikon

  • Ketone — Ketōne, Azetone, organische Verbindungen, entstehen durch Oxydation sekundärer Alkohole und durch trockne Destillation organisch saurer Kalziumsalze; z.B. Azeton (s.d.) aus essigsaurem Kalzium; natürlich vorkommende K. sind zum Teil wichtige… …   Kleines Konversations-Lexikon

  • ketone — chemical group, 1851, from Ger. keton, coined in 1848 by German chemist Leopold Gmelin (1788 1853) from Ger. Aketon, from Fr. acétone (see ACETONE (Cf. acetone)). Its comb. form is keto …   Etymology dictionary

  • ketone — ► NOUN Chemistry ▪ an organic compound containing the group =C=O bonded to two alkyl groups, e.g. acetone. ORIGIN from German Aketon acetone …   English terms dictionary

  • ketone — [kē′tōn΄] n. [Ger keton, arbitrary var. of Fr acétone: see ACETONE] an organic chemical compound containing the carbonyl group, CO, in combination with two hydrocarbon radicals …   English World dictionary

  • Ketone — Allgemeine Struktur der Ketone [R1 und R2 sind organische Reste (Alkyl, Aryl o. ä.)]. Die Carbonylgruppe ist blau markiert. Ketone sind chemische Verbindungen, die als funktionelle Gruppe eine nicht endständige Carbonylgruppe (>C=O)… …   Deutsch Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”