Oxime

Oximes are organic chemical compounds which contain a functional group to group C = N-OH. The name is derived from oxidation and imine, ie an oxidized imine. The compounds are closely related to hydroxylamines, from which they differ by the imino double bond. Depending on the nature of the residues at the C atom, a distinction is

  • Ketoximes: both radicals (R1, R2 ) are organic radicals: R1R2C = N-OH
  • Aldoxime: one of the two radicals is a hydrogen atom: RHC = N-OH

The simplest is the oxime formaldoxime, wherein the two radicals are hydrogen atoms.

According to IUPAC naming is allowed by prepending " hydroxyimino ".

Production

Oxime can be obtained from hydroxylamine, or its hydrochloride, and carbonyl compounds such as aldehydes and ketones.

Isomerism

All aldoximes (except formaldoxime ) and unsymmetrical ketoximes (i.e., R1 ≠ R2), there are two different isomers, the (E ) - or ( Z)- form, which have different reactivities. The (E)- form and trans - form (Z) - form referred to as cis-form.

Use

1,2- dioxime as chelator. With dimethylglyoxime to nickel (II ) ions can be detected as a water-insoluble, bright raspberry -colored complex. By oxime titration to aldehydes and ketones can be quantitatively detected.

Formaldoxime used for complexation of metal ions for photomerische provisions.

Oximes as anti -skinning agents (English: anti- skinning agents ) are used. These substances, also referred to as a retarder or skinning agents prevent skinning during storage of coatings. Be used for this purpose usually volatile oximes such as acetone or 2 -butanone oxime.

Furthermore, oximes in organic synthesis interesting because they can be easily reduced to the amine. Aldoximes can be dehydrated to nitriles or oxidized to nitrile oxides. The industrially most important oxime is cyclohexanone oxime, which reacts in a Beckmann rearrangement in the presence of an acid catalyst to form caprolactam, an intermediate in the production of polyamides.

Ketoximes can be tosylated at the oxygen atom, and then interact by base exposure in a Neber rearrangement to the alpha- amino ketone.

Some oximes find application in the treatment of poisoning with phosphoric acid esters, such as the pesticide E605 or military nerve agents such as sarin, tabun, soman or VX. The toxic effects of these phosphoric esters based on an irreversible inhibition (phosphorylation ) of the esteratischen center of acetylcholinesterase and thus leads initially to an acetylcholine - flooding of the body. In the following, it comes through continuous nerve impulses to paralysis and eventually death from respiratory paralysis. Oximes, such as pralidoxime or obidoxime can reactivate acetylcholinesterase to a limited extent. The effect is based on a Umphosphorylierung and release of cholinesterase. The effect of therapy is determined by the type of nerve agent. Phosphoric acid esters according to lose the toxic release a side chain and are thereby insensitive to the effect of the oxime, however, remain toxic. VX never decomposes. Tabun over a longer period sarin in 3-5 hours. Soman disintegrates within about two minutes.

Halogenated oximes were developed and supported between the two world wars as nettle substances to combat purposes.

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