Ketone (chemistry)
A ketone is an organic compound that has a carbonyl functional group attached to two carbon atoms, unlike an aldehyde, in which the carbonyl group is attached to at least one hydrogen atom. When the carbonyl functional group is the most relevant in said organic compound, ketones are named by adding the suffix -one to the hydrocarbon from which they come (hexane, hexanone; heptane, heptanone; etc). It can also be named by postponing ketone to the radicals to which it is attached (for example: methylphenyl ketone). When the carbonyl group is not the priority group, the prefix oxo- is used (example: 2-oxopropanal).
The carbonyl functional group consists of a carbon atom covalently double bonded to an oxygen atom.
Having 2 organic radicals attached to the carbonyl group is what differentiates it from carboxylic acids, aldehydes, esters. The double bond with oxygen is what differentiates it from alcohols and ethers. Ketones tend to be less reactive than aldehydes since the alkyl groups act as electron donors due to an inductive effect.
Classification
Aliphatic ketones
They result from the moderate oxidation of secondary alcohols. If the alkyl radicals R are the same, the ketone is called symmetrical, otherwise it will be asymmetrical, as long as there is a covalent atom with another.
- I'd think.
- Cetons are isomers of aldehydes of equal carbon number.
- Cetons of more than four carbons present isomery of position. (In specific cases)
- Cetons present tautomeria
Aromatic Ketones
Quinones stand out, derived from benzene and carbon.
Mixed Ketones
When the carbonyl group is coupled to an aryl and an alkyl radical, such as phenylmethylbutanone.
To name the ketones we have two alternatives:
- The name of the hydrocarbon from which it is finished in -ona. The oxo prefix should be used as a substitute.
- Cite the two radicals that are attached to the Carbonilo group by alphabetical order and then the word cetona.
Physical properties
Carbonyl compounds have lower boiling points than alcohols of the same molecular weight. There are no major differences between the boiling points of aldehydes and ketones of the same molecular weight. Short-chain carbonyl compounds are soluble in water and as the chain length increases, solubility decreases.
Chemical properties
- When the carbonyl group is found in a secondary carbon, they are less reactive than the aldehydes.
- They can only be oxidized by strong oxidants such as potassium permanganate, giving as products two acids with fewer carbon atoms.
- By reduction they give secondary alcohols.
- They do not react with the reactive of Tollens to give the silver mirror as the aldehydes, which is used to differentiate them.
- They don't react to Fehling and Schiff's reagents either.
Summary
Due to change of functional group
- Oxidation of secondary alcohols
- Car rental
- Gemmalian dihalogenide hydrolysis
- Nef reaction
By joining carbon skeletons
- Synthesis of Gilman
- Synthesis of Weinreb
- Synthesis of Fukuyama
- Friedel-Crafts and Houben-Hoesch
- Haworth Reaction
- Cylonic convictions
- Bally-Scholl Synthesis
- Benzoinian transition
- Synthesis of Blaise
- Condensation of Dieckmann Claisen and Condensation
- Chelotropic reaction of a cetene with diazometan
- Cicloading of a batch with olefins
- Reaction of Diels Alder with blinds
- Ruzicka Cycling
- Dakin-West reaction
- Grignard reagents with nitriles
- Reaction of Darzens
- Reaction of Darzens-Nenitzescu
- Pauson-Khand's Reaction for 2-cyclopentens
By transposition
- Transposition of Claisen
- Carroll transition
- Transposition of Fries
- Transposition of Kornblum-DeLaMare
- Baker-Venkataramane Transposition
- Transposition of Criegee
- Meyer-Schuster Transposition and Favorskii Reaction
By breaking carbon skeletons
- Harris Ozonolysis
- Reaction of Malaprade
Ketone Reactions
The reactions of aldehydes and ketones are essentially of three types; nucleophilic addition, oxidation and reduction.
Nucleophilic addition: Due to the resonance of the carbonyl group, the most important reaction of aldehydes and ketones is the nucleophilic addition reaction whose mechanism is as follows:
This scheme is followed by the reaction with hydrides (NaBH4, LiAlH4) where Nu- = H- and the reaction with organometallics (RMgLi, RLi) where Nu- = R-.
- nucleophilic addition of alcohols.
- Addition of primary amine.
- Hydroxylamine Addendum.
- Hydracin addition.
- Addendum of Cyanideic Acid.
Examples of ketone reactions are the Grignard reaction, the Reformatski reaction, the Baker-Venkataraman rearrangement.
Ketones can be oxidized to form esters in the Baeyer-Villiger Oxidation.
Ketones that have hydrogens in the α position to the carbonyl group also undergo condensation reactions through a mechanism in which a strong base subtracts an α hydrogen from the ketone, generating an enolate, which (in its carbanionic form) acts as a nucleophile on the group. carbonyl of another molecule of the same ketone or of another carbonyl compound (another ketone, aldehyde, ester, etc). After the nucleophilic addition of the carbanion to the carbonyl group, an aldol is generated by acidifying the medium, which can be dehydrated by heating the reaction mixture, obtaining an α,β-unsaturated carbonyl compound. It should be noted that acidification of the reaction medium is not always necessary and that in many condensation reactions the dehydrated product is obtained spontaneously (this depends on the relative stability of the possible condensation products).
The carbonyl of ketones can react with alkenes in [2 + 2] cycloadditions to form oxetanes (Paterno-Büchi Reaction)
Ketone nomenclature
For more details, see Ketone nomenclature
Substitute nomenclature
In the nomenclature of ketones, to name them, the number of carbon atoms is taken into account and the ending is changed to ONA, indicating the carbon that carries the carbonyl group (CO). In addition, the longest chain that contains the carbonyl group must be taken as the main chain and then numbered in such a way that it takes the lowest locant.
Radiofunctional nomenclature
Another type of nomenclature for ketones consists of naming the chains as substituents, ordering them alphabetically, naming the radicals and adding the word KETONE. If the two radicals are the same, it is a symmetrical ketone, and if the radicals are different, it is an asymmetrical ketone.
Nomenclature in special cases
In cases where there are two or more carbonyl groups in the same chain, the substitutive nomenclature can be used. In this nomenclature, if there are two or more CO groups, we increase the prefixes (di, tri, tetra, etc.), before the ending -one.
As in the substitutive nomenclature, also in the radiofunctional nomenclature, if there are two or more CO groups in the same chain, the radicals are normally named and the prefix (di, tri, tetra, etc) to the word ketone.
For some compounds in which the carbonyl group CO is directly attached to a benzene or naphthalene ring, the aforementioned nomenclatures can be used, as well as this other type of nomenclature that consists of indicating the groups:
- CH3-CO-
- CH3-CH2-CO-
- CH3-CH2-CH2-CO-, etc.
using the names aceto, proper, butyro, etc. and adding the ending phenone or naphthone.
Nomenclature of ketones that act as radicals within the chain
The nomenclature already mentioned above is taken for cases considered in which the ketone function has priority, but when the ketone is not the main functional group, but there is another function or other functions with greater preference, this nomenclature is used: To indicate the group CO, the prefix OXO is used.