Oximes

aldehyde and ketone derivatives that are obtained upon action of hydroxylamine (H2NOH). Aldoximes have the general formula RHC=N—OH, and ketoximes RR’C=N—OH. Oximes are colorless liquids or crystalline solids with low melting points and low solubility in water but high solubility in organic solvents. Aldoximes and asymmetrical ketoximes occur in two stereoisomeric forms, syn- and anti-. Highly reactive, oximes interact with alkalis to form salts (for example, RR’C=NONa) and hydrolize upon heating with aqueous solutions of mineral acids to yield the original carbonyl compounds—aldehydes and ketones. One important property of ketoximes is their ability to undergo the Beckmann rearrangement—isomerization into the substituted carboxylic-acid amides upon action of acidic dehydrogenating agents. Under similar conditions, aldoximes generally undergo dehydration and subsequent conversion into nitriles.

Oximes form intermediate products during certain syntheses, for example, cyclohexanoneoxime is formed during the preparation of caprolactam, from which nylon-6 fibers are manufactured. Diacetyl dioxime, or dimethylglyoxime, is used in analytical chemistry as a reagent for nickel. One of the methods for quantitatively analyzing aldehydes and ketones is based on the formation of oximes from the salts of hydroxylamines and carbonyl compounds.