Oxime generally refers to the presence ofcarbonylAldehydes and ketoneschemical compoundAndhydroxylamineAn organic compound produced by action.The general formula of oxime has the structure of C=NOH.The oxime formed by aldehyde is called aldehyde oxime, and the oxime formed by ketone is called ketoxime.Oxime channelhydrolysisCan get the originalaldehydeorketone。In addition, oxime can participate in many organic chemical reactions, such as the classicbeckmann rearrangement Namely, oxime is used as substrate to rearrange to form amide under acidic conditions（Lactam）The product of.[1]
Chinese name
oxime
Foreign name
oxime
Meaning
Organic compounds generated by the reaction of aldehydes and ketones containing carbonyl groups with hydroxylamine
General Structural Formula of Aldoxime and Ketoxime
Oxime is a kind of important organic compound, its English name is oxime, and its general formula can be written as R-C=NOH.Benzaldehyde oximeThe English version of is benzaldoxime,Acetone oximeIs acetaxime.Most oximes have good crystallization and definite melting points, such asAcetaldoxime47 ℃, tablet ketoxime 75 ℃, acetone oxime 61 ℃,Cyclohexanone oxime90 ℃, so its melting point can be used to identify aldehyde or ketone.Some oximes are importantAnalytical reagent, such asDimethylglyoximeIt is a common reagent for qualitative and quantitative determination of nickel in analytical chemistry.
Compounds with general structure R-CH=N-OH or RR ′ C=N-OH are usually called "oximes", and further classified as "aldoximes" and "ketoximes" respectively.According to the principle of naming functional groups, they can be named by adding the class name "oxime" after the name of aldehyde (RCHO) or ketone (RR ′ C=O);Or name it according to the substitution method, and connect the prefix "hydroxyamino -" to the name of the parent hydride or parent substituent prefix.Compounds containing=N-OR group can be namedO-Substitute oxime or alkoxy substituted imine.IUPAC-2013 suggested that oxime be named as the hydrocarbon subunit derivative of hydroxylamine according to the substitution method.[3]
Tautomerism
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Oxime can be used withNitroso compoundTautomerism has the following balance:
Tautomerism of oxime
Nitroso compounds are stable only when there is no α - hydrogen. If there is α - hydrogen, the above balance will be in the direction of oxime.[1]
There are two isomers of oxime, Z and E, but usually only one isomer can be obtained.Z configuration is generally unstable and easy to change to E configuration. For example, benzaldoxime has two isomers, and the melting point of Z configuration isomer is 35 ℃. Dissolve it in alcohol and add a little acid to change it into E configuration isomer, and the melting point is 132 ℃.The reaction equation and structural formula of two isomers are shown in Figure 1:
Figure 2 General formula of Beckmann rearrangement
The reaction mechanism is as follows:
Reaction mechanism of Beckmann rearrangement
The above reaction mechanism shows that the catalytic effect of acid is to help hydroxyl leave.This reaction has three characteristics:
One is that the leaving group and the migrating group are in the trans form, which is inferred from the structure of the product.
The second is that the departure of the group is synchronous with the migration of the group. If not, the hydroxyl group leaves first in the form of water to form a nitrogen positive ion. At this time, two groups on the adjacent carbon can migrate to get a mixture, but the experimental results show that there is only one product, so the reaction is synchronous.[1]
The third is that the configuration of the migration group remains unchanged before and after migration.(As shown in Figure 3)
Fig. 3 The configuration of oxime rearrangement reaction remains unchanged
In addition, industrial productionCaprolactamThat is to use this reaction, while caprolactam is producednylon-6.Using this reaction, the configuration of oxime can also be inferred from the hydrolysate.The preparation process is shown in Figure 4:
Fig. 4 Synthesis of caprolactam
Lactam is the product of dehydration of carboxyl and amino groups in the molecule.Caprolactam can be polymerized by ring opening in the presence of sulfuric acid or phosphorus trichloride to obtain nylon-6.Since amide hydrolysis can produce carboxylic acid and amine, this rearrangement reaction also provides a way to prepare carboxylic acid and amine from ketone.Since only the group in the reverse position with the hydroxyl can migrate, the group always in the reverse position of the hydroxyl will finally generate amine, and the group in the cis position of the hydroxyl will finally generate carboxylic acid.(as shown in Figure 5).Oxime can also beSodium amalgamorhydrogenationReduction to produce amine.[2]
