Exp-3: Cyclohexanone oxime and its
rearrangement to ε-caprolactam
INTRODUCTION:
An oxime is a compound belonging to imines family (RR1C = NOH). If R is an alkyl or an
aryl group, R1 may be a hydrogen atom (aldoxime) or an alkyl/aryl group (ketoxime)
(Figure 1). These compounds are usually synthesized by the addition of hydroxylamine
on an aldehyde or a ketone.
Figure 1. Types of oximes
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.
Oximes are the derivative of carbonyl group but they are less reactive as they are less
electrophillic due to less electronegativity of nitrogen as compare to oxygen in carbonyl.
In short, they are low respondents to nucleophillic attack. Generally, oximes are
generated by reacting hydroxylamine with aldehyde or ketone but it can also be made
by reacting nitrites with compounds containing acidic hydrogen.
Most of all of oximes are highly crystalline and the oximation is a very efficient method
for characterization and purification of carbonyl compounds. These compounds not only
represent a convenient series of derivatives of carbonyl compounds but also used
intermediate for the preparation of amides by the Beckmann rearrangement, nitrones,
hydroximinoyl chlorides, nitrile oxide and chiral α-sulfinyl oximes. The usual method for
the preparation of oximes involves treatment of hydroxyl amine hydrochlorides in a
basic aqueous medium with adjustment of pH.
