Everything about Haloketone totally explained
A
haloketone in
organic chemistry is a
functional group consisting of a
ketone group or more general a
carbonyl group with a α-
halogen substituent. The general structure is RR'C(X)C(=O)R where R is an alkyl or aryl residue and X any one of the halogens. The preferred
conformation of a haloketone is that of a
cisoid with the halogen and carbonyl sharing the same plane as the
steric hindrance with the carbonyl alkyl group is generally larger .
Haloketone synthesis
Asymmetric synthesis
Efforts are reported in
asymmetric synthesis of halocarbonyls through
organocatalysis. In one study an
acid chloride is converted into an α-halo-ester with a strong base (
sodium hydride), a bromine donor and an organocatalyst based on
proline and
quinine :
In the proposed
reaction mechanism the base first converts the acid chloride to the
ketene, the organocatalyst then introduces
chirality through its quininoid
tertiary amine, forming a ketene adduct.
Haloketone reactions
Haloketones take part in several reaction types. In reaction with a
nucleophile 2 electrophilic sites are available and in reactions with a
base several acidic protons exist due to the presence of two
electron withdrawing groups. The carbon halogen bond experiences increases
polarity from the
inductive effect of the carbonyl group making the carbon atom more electropositive.
In nucleophilic aliphatic substitution reactions with potassium iodide in acetone, 1-chloro-2-propanone reacts faster than n-propylchloride by a factor of 36000.
In the Favorskii rearrangement a base abstacts first an acidic α-proton and the resulting carbanion then displaces the halogen.
The same sequence is observed in the Bingel reaction with fullerenes
In crossed Aldol reactions between haloketones and aldehydes the initial reaction product is an halohydrin which can subsequently form a oxirane in the presence of base.
Haloketones are important in heterocyclic chemistry. An example is the use of haloketones in the Hantzsch Pyrrole Synthesis and the Hantzsch thiazole synthesis.
Haloketones react with phosphites in the Perkow reaction.Further Information
Get more info on 'Haloketone'.
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