Oximes
An oxime is a chemical compound belonging to the imines, with the general formula R1R2C=NOH, where R1 is an organic side-chain and R2 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 RC(=NOH)(NRR').
Oximes are usually generated by the reaction of hydroxylamine and 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, the oxime can have two geometric stereoisomeric form: a syn isomer and an anti isomer, depending on which of the two side-chains is closer to 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, at wavenumbers 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 aldoxime, and ketoxime is 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
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