Amine oxide
3432792
203810464
2008-04-06T19:14:05Z
V8rik
195918
/* Reactions */Polonovski reaction
[[Image:amine oxide.png|thumb|right|100px|General structure of an amine oxide]]
An '''amine oxide''', also known as '''amine-''N''-oxide''' and '''''N''-oxide''', is a [[chemical compound]] that contains the [[functional group]] R<sub>3</sub>N<sup>+</sup>-O<sup>−</sup> (sometimes written as R<sub>3</sub>N=O or R<sub>3</sub>N→O). In the strict sense the term ''amine oxide'' applies only to oxides of tertiary [[amine]]s including [[nitrogen]]-containing [[simple aromatic ring|aromatic compounds]] like [[pyridine]], but is sometimes also used for the analogous derivatives of primary and secondary amines.
Amine oxides are used as [[protecting group]] for amines and as [[chemical synthesis|chemical]] intermediates. Long-chain [[alkyl]] amine oxides are used as [[nonionic]] [[surfactant]]s and [[foam]] stabilizers.
Amine oxide are highly [[polar molecule]]s have a high [[polarity]] close to that of [[quaternary ammonium salt]]s. Small amine oxides are very [[hydrophilic]] and have an excellent [[water (molecule)|water]] [[solubility]] and a very poor solubility in most organic [[solvent]]s.
Amine oxides are weak [[base (chemistry)|bases]] with a [[Acid dissociation constant|p''K''<sub>a</sub>]] of around 4.5 that form R<sub>3</sub>N<sup>+</sup>-OH, [[cation]]ic [[hydroxylamine]]s, upon [[protonation]] at a [[pH]] below their p''K''<sub>a</sub>.
'''Pyridine N-oxide''' is a crystalline solid with [[melting point]] 62-67°C and soluble in water [[N-Methylmorpholine N-oxide|''N''-Methylmorpholine ''N''-oxide]] is an oxidant.
== Synthesis ==
Amine oxides are prepared by [[oxidation]] of tertiary amines or pyridine analogs with [[hydrogen peroxide]] (H<sub>2</sub>O<sub>2</sub>), [[Caro's acid]] or [[peracid]]s like [[meta-Chloroperoxybenzoic acid|mCPBA]] in '''N-oxidation''' <ref>''Recent trends in the chemistry of pyridine N-oxides'' Shaker Youssif [[Arkivoc]] 2001 [http://www.arkivoc.com/home.aspx?VIEW=MANUSCRIPT&MSID=180 Link]</ref>.
== Reactions ==
*Pyrolytic elimination. Amine oxides, when heated to 150 to 200 °C eliminate a hydroxylamine, resulting in an [[alkene]]. This [[pyrolysis|pyrolytic]] syn-[[elimination reaction]] is known under the name [[Cope reaction]]. The mechanism is similar to that of the [[Hofmann elimination]].
*Reduction to amines. Amine oxides are readily converted to the parent amine by common [[redox|reduction]] [[reagent]]s including [[lithium aluminium hydride]], [[sodium borohydride]], [[catalytic reduction]], [[zinc]] / [[acetic acid]], and [[iron]] / acetic acid. Pyridine N-oxides can be deoxygenated by [[phosphorus oxychloride]]
* O-alkylation. Pyridine N-oxides react with [[alkyl halide]]s to the O-alkylated product
* In the '''Meisenheimer rearrangement''' certain N-oxides R<sub>1</sub>R<sub>2</sub>R<sub>3</sub>N<sup>+</sup>O<sup>-</sup> [[rearrangement reaction|rearrange]] to [[hydroxylamine]]s R<sub>2</sub>R<sub>3</sub>N-O-R<sub>1</sub> <ref>J. Meisenheimer, Ber. 52. 1667 (1919)
</ref> <ref>March's Advanced Organic Chemistry: Reactions, Mechanisms, and Structure Michael B. Smith, Jerry March Wiley-Interscience, 5th edition, 2001, ISBN 0-471-58589-0</ref>
* In the '''Polonovski reaction''' a tertiary N-oxide is cleaved by [[acetic acid anhydride]] to the corresponding [[acetamide]] and [[aldehyde]] <ref>M. Polonovski, M. Polonovski, Bull. Soc. Chim. France 41, 1190 ('''1927''').</ref> <ref>''Strategic Applications of Named Reactions in Organic Synthesis (Paperback)'' by Laszlo Kurti, Barbara Czako ISBN 0-12-429785-4</ref>:
:[[Image:PolonovskiReaction.svg|Polonovski reaction]]
== Metabolites ==
Amine oxides are common [[Metabolism|metabolite]]s of [[medication]] and [[psychoactive drug]]s. Examples include [[nicotine]], [[Zolmitriptan]], and [[morphine]].
Amine oxides of [[chemotherapy|anti-cancer drugs]] have been developed as [[prodrug]]s that are metabolized in the [[oxygen]] deficient [[cancer]] [[Biological tissue|tissue]] to the active drug.
== See also ==
* [[Functional group]]
* [[Amine]], NR<sub>3</sub>
* [[Hydroxylamine]], NR<sub>2</sub>OH
* [[Sulfoxide]], R<sub>2</sub>S=O
* [[Azoxy]], RN=N+(O–)R RN=N<sup>+</sup>RO<sup>−</sup>
* [[TEMPO]] (2,2,6,6-Tetramethylpiperidine-1-oxyl), a stable amine oxide radical
== External links ==
* [http://www.cem.msu.edu/~reusch/VirtualText/amine2.htm Chemistry of amine oxides]
* [http://nanoparticles.org/pdf/Salager-E300A.pdf Surfactants, types and uses] (pdf)
* [http://www.chm.bris.ac.uk/motm/proline/aminehomepage.html The amine oxides homepage]
* [http://www.chem.qmul.ac.uk/iupac/class/oneN.html Nomenclature of nitrogen compounds]
* [http://www.iupac.org/goldbook/A00273.pdf IUPAC definition] (pdf)
==References==
{{reflist}}
[[Category:Amine oxides]]
[[Category:Functional groups]]
[[ja:アミンオキシド]]