Ketoximes

Ketoximes are oximes derived from ketones, formed by the condensation of a ketone with hydroxylamine. The general structure is R1R2C=NOH, where the carbonyl carbon bears two carbon substituents (R1 and R2) from the parent ketone. Ketoximes can exist as E and Z isomers about the C=N bond, and the isomer distribution can influence reactivity and properties.

Preparation methods typically involve reacting a ketone with hydroxylamine or hydroxylamine hydrochloride in the presence of a base, such as Na2CO3, in a protic solvent like methanol or ethanol. Water is removed to drive formation of the oxime. Variants include forming O-substituted ketoximes by using O-substituted hydroxylamines.

Key reactions and transformations of ketoximes include dehydration to nitriles, using dehydrating reagents such as POCl3, SOCl2, or strong acids. They can undergo Beckmann rearrangement under acidic conditions to give amides, with migration of the substituent anti to the oxime OH. Reductive methods convert ketoximes to primary amines (R1R2CH-NH2). Ketoximes also serve as carbonyl protecting groups in synthesis, being convertible back to the ketone under suitable conditions. In modern chemical biology, oxime formation is exploited in oxime ligation, a chemoselective reaction between aminooxy groups and carbonyl compounds to form stable oxime linkages.

Representative examples include acetone oxime (CH3)2C=NOH and benzophenone oxime Ph2C=NOH. Ketoximes thus function as versatile intermediates in organic synthesis, enabling access to nitriles, amides, amines, and protected carbonyl species.