Ketone
In
Nomenclature and etymology
The word ketone is derived from Aketon, an old German word for acetone.[2][3]
According to the rules of
The derived names of ketones are obtained by writing separately the names of the two
Although used infrequently, oxo is the
Structure and properties
The ketone carbon is often described as
The carbonyl group is
Classes of ketones
Ketones are classified on the basis of their substituents. One broad classification subdivides ketones into symmetrical and unsymmetrical derivatives, depending on the equivalency of the two organic substituents attached to the carbonyl center. Acetone and benzophenone ((C6H5)2CO) are symmetrical ketones. Acetophenone (C6H5C(O)CH3) is an unsymmetrical ketone.
Diketones
Many kinds of diketones are known, some with unusual properties. The simplest is
Unsaturated ketones
Ketones containing
Cyclic ketones
Many ketones are cyclic. The simplest class have the formula (CH2)nCO, where n varies from 2 for cyclopropanone ((CH2)2CO) to the tens. Larger derivatives exist. Cyclohexanone ((CH2)5CO), a symmetrical cyclic ketone, is an important intermediate in the production of nylon. Isophorone, derived from acetone, is an unsaturated, asymmetrical ketone that is the precursor to other polymers. Muscone, 3-methylpentadecanone, is an animal pheromone. Another cyclic ketone is cyclobutanone, having the formula (CH2)3CO.
Keto-enol tautomerization
Ketones that have at least one
Acid/base properties of ketones
C−H bonds adjacent to the carbonyl in ketones are more acidic
Ketones are also weak bases, undergoing
Characterization
An aldehyde differs from a ketone in that it has a hydrogen atom attached to its carbonyl group, making aldehydes easier to oxidize. Ketones do not have a hydrogen atom bonded to the carbonyl group, and are therefore more resistant to oxidation. They are
Spectroscopy
Ketones (and aldehydes) absorb strongly in the infra-red spectrum near 1750 cm−1, which is assigned to νC=O ("carbonyl stretching frequency"). The energy of the peak is lower for aryl and unsaturated ketones.[8]
Whereas
Qualitative organic tests
Ketones give positive results in
Synthesis
Many methods exist for the preparation of ketones in industrial scale and academic laboratories. Ketones are also produced in various ways by organisms; see the section on biochemistry below.
In industry, the most important method probably involves
For specialized or small scale organic synthetic applications, ketones are often prepared by oxidation of secondary alcohols:
- R2CH(OH) + "O" → R2C=O + H2O
Typical strong
Many other methods have been developed, examples include:[10]
- By geminal halide hydrolysis.[11]
- By hydration of alkynes.[12] Such processes occur via enols and require the presence of an acid and mercury(II) sulfate (HgSO4). Subsequent enol–keto tautomerization gives a ketone. This reaction always produces a ketone, even with a terminal alkyne, the only exception being the hydration of acetylene, which produces acetaldehyde.
- From Weinreb Amides using stoichiometric organometallic reagents.
- Aromatic ketones can be prepared in the
- Ozonolysis, and related dihydroxylation/oxidative sequences, cleave alkenes to give aldehydes or ketones, depending on alkene substitution pattern.[15]
- In the peroxidesand base.
- In the Ruzicka cyclization, cyclic ketones are prepared from dicarboxylic acids.
- In the Nef reaction, ketones form by hydrolysis of salts of secondary nitro compounds.[16]
- In the Fukuyama coupling, ketones form from a thioester and an organozinc compound.
- By the reaction of an organocopper compounds.
- The Dakin–West reaction provides an efficient method for preparation of certain methyl ketones from carboxylic acids.[17]
- Ketones can be prepared by the reaction of
- By carboxylic anhydride.
- Ketones can be prepared from haloketones in reductive dehalogenation of halo ketones.
- In ketonic decarboxylation symmetrical ketones are prepared from carboxylic acids.[12][19]
- diketones (the acetoacetic ester synthesis).
- Acid-catalysed rearrangement of 1,2-diols,[12] or Criegee oxidation of the same.
Reactions
Ketones engage in many organic reactions. The most important reactions follow from the susceptibility of the carbonyl carbon toward nucleophilic addition and the tendency for the enolates to add to electrophiles. Nucleophilic additions include in approximate order of their generality:[10]
- With water (hydration) gives geminal diols, which are usually not formed in appreciable (or observable) amounts
- With an hydroxyalkyne
- With primary amine gives an imine
- With secondary amine gives an enamine
- With tertiary alcohol
- With an alcohols or ketal. This reaction is employed to protect ketones.
- With sodium amide resulting in C–C bond cleavage with formation of the amide RCONH2 and the alkane or arene R'H, a reaction called the Haller–Bauer reaction.[21]
- With strong oxidizing agents to give carboxylic acids. Ketones are generally oxidized under vigorous conditions, i.e., strong oxidizing agents and at elevated temperatures. Their oxidation involves carbon-carbon bond cleavage to afford a mixture of carboxylic acids having lesser number of carbon atoms than the parent ketone.
- Electrophilic addition, reaction with an electrophile gives a resonance stabilized cation
- With phosphonium ylides in the Wittig reaction to give the alkenes
- With thiols to give the thioacetal
- With hydrazine or 1-disubstituted derivatives of hydrazine to give hydrazones.
- With a ketone reduction
- With haloketone, a reaction that proceeds via an enol (see Haloform reaction)
- With deuteratedketone
- Fragmentation in photochemical Norrish reaction
- Reaction of 1,4-aminodiketones to oxazoles by dehydration in the Robinson–Gabriel synthesis
- In the case of aryl–alkyl ketones, with sulfur and an amine give amides in the Willgerodt reaction
- With hydroxylamine to produce oximes
- With reducing agentsto form secondary alcohols
- With peroxy acids to form esters in the Baeyer–Villiger oxidation
Biochemistry
Ketones are pervasive in nature. The formation of organic compounds in
In medicine,
Applications
Ketones are produced on massive scales in industry as solvents, polymer precursors, and pharmaceuticals. In terms of scale, the most important ketones are
Toxicity
Although it is difficult to generalize on the toxicity of such a broad class of compounds, simple ketones are, in general, not highly toxic. This characteristic is one reason for their popularity as solvents. Exceptions to this rule are the unsaturated ketones such as methyl vinyl ketone with LD50 of 7 mg/kg (oral).[23]
See also
- Diketone
- Ketone bodies
- Thioketone
- Triketone
- Ynone
- Ketosis
References
- ^ Raymond, Kenneth W. (2010). General Organic and Biological Chemistry (3rd ed.). Wiley. p. 297.
- ^ Harper, Douglas. "ketone". Online Etymology Dictionary.
- ^ The word "ketone" was coined in 1848 by the German chemist Leopold Gmelin. See: Leopold Gmelin, ed., Handbuch der organischen Chemie: Organische Chemie im Allgemeinen … (Handbook of organic chemistry: Organic chemistry in general … ), 4th ed., (Heidelberg, (Germany): Karl Winter, 1848), volume 1, p. 40. From page 40: "Zu diesen Syndesmiden scheinen auch diejenigen Verbindungen zu gehören, die als Acetone im Allegemeinen (Ketone?) bezeichnet werden." (To these syndesmides*, those compounds also seem to belong, which are designated as acetones in general (ketones?).") [*Note: In 1844, the French chemist Auguste Laurent suggested a new nomenclature for organic compounds. One of his new classes of compounds was "syndesmides", which were compounds formed by the combination of two or more simpler organic molecules (from the Greek σύνδεσμος (syndesmos, union) + -ide (indicating a group of related compounds)). For example, acetone could be formed by the dry distillation of metal acetates, so acetone was the syndesmide of two acetate ions. See: Laurent, Auguste (1844) "Classification chimique," Comptes rendus, 19 : 1089–1100 ; see especially p. 1097.
- ^ List of retained IUPAC names retained IUPAC names Link Archived 9 July 2023 at the Wayback Machine
- ISBN 0-534-16218-5
- ^ Evans, David A. (4 November 2005). "Evans pKa table" (PDF). Evans group website. Archived from the original (PDF) on 19 June 2018. Retrieved 14 June 2018.
- ISBN 978-0-470-46259-1.
- ^ Smith, Brian. "The C=O Bond, Part VIII: Review". Spectroscopy. Archived from the original on 13 February 2024. Retrieved 12 February 2024.
- ISBN 0-582-22628-7
- ^ ISBN 978-0-471-72091-1
- .
- ^ ISBN 9780582462366.
- .
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- ^ Haller–Bauer Reaction. homeip.net
- ISBN 1-57259-153-6.
- ^ ISBN 9783527306732.)
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External links
- Media related to Ketones at Wikimedia Commons