Oxime

An oxime is a chemical compound belonging to the imines, with the general formula RR'C=NOH, where R is an organic side-chain and R' may be hydrogen, forming an aldoxime, or another organic group, forming a ketoxime. O-substituted oximes form a closely related family of compounds. Amidoximes are oximes of amides with general structure R1C(=NOH)NR2R3. Oximes are usually generated by the reaction of hydroxylamine with aldehydes or ketones. The term oxime dates back to the 19th century, a combination of the words oxygen and imine. If the two side-chains on the central carbon are different from each other—either an aldoxime, or a ketoxime with two different 'R' groups—the oxime can often have two different geometric stereoisomeric forms according to the E/Z configuration. An older terminology of syn and anti was used to identify especially aldoximes according to whether the R group was closer or further from the hydroxyl. Both forms are often stable enough to be separated from each other by standard techniques. Oximes have three characteristic bands in the infrared spectrum, whose wavelengths corresponding to the streching vibrations of its three types of bonds: 3600 cm−1 (O−H), 1665 cm−1 (C=N) and 945 cm−1 (N−O). In aqueous solution, aliphatic oximes are 102- to 103-fold more resistant to hydrolysis than analogous hydrazones. Oximes can be synthesized by condensation of an aldehyde or a ketone with hydroxylamine. The condensation of aldehydes with hydroxylamine gives aldoximes, and ketoximes are produced from ketones and hydroxylamine. In general, oximes exist as colorless crystals and are poorly soluble in water. Therefore, oximes can be used for the identification of ketone or aldehyde. Oximes can also be obtained from reaction of nitrites such as isoamyl nitrite with compounds containing an acidic hydrogen atom. Examples are the reaction of ethyl acetoacetate and sodium nitrite in acetic acid, the reaction of methyl ethyl ketone with ethyl nitrite in hydrochloric acid. and a similar reaction with propiophenone, the reaction of phenacyl chloride, the reaction of malononitrile with sodium nitrite in acetic acid A conceptually related reaction is the Japp–Klingemann reaction.