Oximes
Oximes are derivatives of aldehydes or ketones that contain the group C = N − OH as a functional group . The name is formed with the syllables Oxi- and Im and thus indicates an oxidized imine . The oximes are formed by reactions of hydroxylamines with aldehydes or ketones. A distinction is made depending on the type of residues on the C atom
- Ketoxime
- Both radicals (R 1 , R 2 ) are organic radicals: R 1 R 2 C = N-OH
- Aldoximes
- One of the two residues is an H atom: RHC = N-OH
The simplest oxime is formaldoxime , in which both residues are hydrogen atoms.
According to IUPAC , naming is also allowed by prefixing “Hydroxyimino-”.
Manufacturing
Oximes can be obtained from hydroxylamine or its hydrochloride and carbonyl compounds such as aldehydes and ketones .
Isomerism
Of all aldoximes (except formaldoxime) and unsymmetrical ketoximes (i.e. R 1 ≠ R 2 ) there are two different isomers, the ( E ) or ( Z ) form, which are differently reactive. The ( E ) form is also known as the trans form, the ( Z ) form as the cis form.
use
1,2-Dioximes are used as chelating agents . With dimethylglyoxime , nickel (II) ions can be detected as a water-insoluble, bright raspberry-colored complex. Aldehydes and ketones can be quantitatively detected by oxime titration .
Formaldoxime is used to complex metal ions for photometric determinations.
Oximes are used as anti-skinning agents . These substances, also known as retarders or skin contraceptives , prevent skin formation when paints are stored . Most volatile oximes such as acetone oxime or 2-butanone oxime are used for this purpose .
Furthermore, oximes interest in organic synthesis, as they can easily become the amine can be reduced. 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 acidic catalyst to form caprolactam , an intermediate product for the production of polyamides .
Ketoximes can be tosylated at the oxygen atom and then react by the action of bases in a Neber rearrangement to form the alpha-aminoketone.
Some oximes are used in the therapy of poisoning with phosphoric acid esters, for example with the pesticide E605 or military neurotoxins such as sarin , tabun , soman or VX . The toxic effect of these phosphoric acid esters is based on an irreversible inhibition ( phosphorylation ) of the esteratic center of acetylcholinesterase and thus initially leads to acetylcholine flooding of the body. In the following, constant nerve impulses lead to paralysis and ultimately death from respiratory paralysis. Oximes such as pralidoxime or obidoxime can reactivate acetylcholinesterase to a limited extent. The effect is based on a rephosphorylation and release of the cholinesterase. The effect of the therapy is determined by the type of neurotoxin. The toxic phosphoric acid esters lose a side chain after being released and are thus insensitive to the action of the oxime, but remain toxic. VX never disintegrates. Tabun over a longer period of time, sarin in 3 - 5 hours. Soman disintegrates within around two minutes.
Halogenated oximes were developed and stored as nettles for combat purposes between the two world wars .
The oxime of 3-nitrobenzaldehyde can be converted into an explosive by reacting it with dinitrogen tetroxide ( Ponzio reaction ).
Individual evidence
- ^ Siegfried Hauptmann : Organic Chemistry , VEB Deutscher Verlag für Grundstoffindindustrie, Leipzig, 1985, 2nd edition, page 361, ISBN 3-342-00280-8 .
- ↑ Charles G. Hurst, Jonathan Newmark, James A. Romano: Chemical Terrorism , in Dan L. Longo, Anthony S. Fauci, Dennis L. Kasper, Stephen A. Hausser, J. Larry Jameson, Joseph Localzo (Eds.): Harrison's Principles of Internal Medicine , 18th Edition, Volume 1, New York, p. 1786.