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The position alpha to the carbonyl group (C=O) in a ketone is easily halogenated. This is due to its ability to form an enolate (C=C−O −) in basic solution, or an enol (C=C−OH) in acidic solution. An example of alpha halogenation is the mono-bromination of acetone ((CH 3) 2 C=O), carried out under either acidic or basic conditions, to ...
Remarkably, ketone halogenation also occurs in biological systems, particularly in marine algae, where dibromoacetaldehyde, bromoacetone, 1, l,l -tribromoacetone, and other related compounds have been found. The halogenation is a typical α-substitution reaction that proceeds by acid catalyzed formation of an enol intermediate. [1]: 846
(Benzylideneacetone)iron tricarbonyl is an organoiron compound with an η 2 ketone ligand. Some η 2-aldehyde complexes insert alkenes to give five-membered metallacycles. [5] η 1-Complexes of alpha-beta unsaturated carbonyls exhibit enhanced reactivity toward dienes. This interaction is the basis of Lewis-acid catalyzed Diels-Alder reactions.
A common route for enamine production is via an acid-catalyzed nucleophilic reaction of ketone [7] or aldehyde [8] species containing an α-hydrogen with secondary amines. Acid catalysis is not always required, if the pK aH of the reacting amine is sufficiently high (for example, pyrrolidine, which has a pK aH of 11.26).
In carbohydrate chemistry, the Lobry de Bruyn–Van Ekenstein transformation also known as the Lobry de Bruyn–Alberda van Ekenstein transformation is the base or acid catalyzed transformation of an aldose into the ketose isomer or vice versa, with a tautomeric enediol as reaction intermediate. Ketoses may be transformed into 3-ketoses, etcetera.
For example, hexanoyl chloride 1 can be brominated in the alpha-position by NBS using acid catalysis. [11] The reaction of enolates, enol ethers, or enol acetates with NBS is the preferred method of α-bromination as it is high-yielding with few side-products. [12] [13]
Bromoacetone is prepared by combining bromine and acetone, [4] with catalytic acid. As with all ketones, acetone enolizes in the presence of acids or bases. The alpha carbon then undergoes electrophilic substitution with bromine. The main difficulty with this method is over-bromination, resulting in di- and tribrominated products.
Adding boric acid to the acid-catalyzed reaction mixture increases the yield of phenol product over phenyl carboxylic acid product, even when using phenyl aldehyde or ketone reactants with electron-donating groups meta to the carbonyl group or electron-withdrawing groups ortho or para to the carbonyl group. Boric acid and hydrogen peroxide form ...