OXIMES, in organic chemistry, compounds containing the grouping >C:N.OH and obtained by the action of hydroxylamine on compounds containing the >CO group. They were first pre pared by Victor Meyer in 1882. The commonest are those of the general formulae RHC:NOH and RR'C:NOH where R and R' are alkyl or aryl groups ; the former, prepared from aldehydes, are known as aldoximes, and the latter, from ketones, as ketox imes.
The lower alkyl aldoximes and ketoximes are readily soluble in water, but the solubility decreases with increase in molecular weight ; if an aryl group be present, the compounds are usually sparingly soluble in water. Generally the oximes are readily soluble in the common organic solvents and may be extracted from aqueous solutions by their means ; they are weak acids and dissolve in aqueous solutions of alkali hydroxides to form salts which are decomposed, with liberation of the oxime, by carbon dioxide or by ammonium chloride. At the same time ethereal solu tions of most oximes yield with hydrogen chloride precipitates of hydrochlorides, and sulphates may be obtained by dissolving the oximes in concentrated sulphuric acid; both hydrochlorides and sulphates are rapidly decomposed by water with regeneration of the oxime. Oximes are hydrolysed by boiling with dilute acids
(the parent aldehyde or ketone being formed) ; on reduction with sodium amalgam in alcoholic acetic acid, or in the vapour phase by hydrogen in the presence of nickel (see HYDROGENA TION), they yield primary amines ; on oxidation they yield a number of products, aldoximes giving hydroxamic acids R.C(OH) :NOH or peroxides R.CH:NO.ON :CHR, and ketoximes nitro-hydrocarbons Dehydrating agents convert aldoximes into nitriles With phorus pentachloride ketoximes undergo the Beckmann change (see below).
Aldoximes and ketoximes are generally prepared by the action of hydroxylamine (liberated from the hydrochloride in situ by sodium carbonate or sodium hydroxide) upon the aldehyde or ketone ; they are also formed by the oxidation of primary amines with Caro's acid, (E. Bamberger, 1902), and by the reduction of primary or second ary nitro-hydrocarbons with stannous chloride and hydrochloric acid : RWCHNO-- RR'C:N.OH. Aldoximes are formed by the reduction of unsaturated nitro-hydrocarbons with aluminium amalgam in dilute acetic acid.