Haloketones

Haloketones are organic compounds in which a halogen is attached to the carbon atom adjacent to the carbonyl group of a ketone. The most common are alpha-haloketones, with the general structure R-CO-CHX-R', where X is a halogen such as F, Cl, Br, or I. The halogen can influence reactivity, enabling various substitution and rearrangement reactions. Some sources also use haloketone to refer more broadly to halogenated ketones, but alpha-haloketones are the best known subgroup.

Preparation generally involves halogenation at the alpha position of a ketone. Enol or enolate intermediates react with halogen sources such as Cl2, Br2, or N-bromosuccinimide under acidic or basic conditions. Methyl ketones can yield dihalogenated alpha-ketones with sequential halogenation. The resulting alpha-haloketones vary in reactivity with the choice of halogen and substituents.

Chemically, the alpha-haloketone carbon is activated toward nucleophilic substitution, allowing substitution of X by a wide range of nucleophiles (for example, thiols, amines, or alkoxides). Under basic conditions, alpha-haloketones can undergo the Favorskii rearrangement, forming carboxylic acids or ring-contracted products. Haloform reactions can occur with methyl ketones in the presence of base and excess halogen, producing haloform and a carboxylate.

Haloketones are versatile intermediates in organic synthesis and in medicinal chemistry. They are used to prepare enones, heterocycles, and other functionalized molecules, and serve as building blocks for pharmaceuticals and natural product derivatives. Chloroacetone and bromoacetone are among the best-known examples and are often cited for their reactivity as alkylating agents.

Safety: many haloketones are toxic, lachrymatory, and potentially carcinogenic; they should be handled with appropriate precautions in a well-ventilated laboratory.