Amine oxide

From Wikipedia, the free encyclopedia

An amine oxide, also known as amine-N-oxide and N-oxide, is a chemical compound that contains the functional group R₃N⁺-O⁻ (sometimes written as R₃N=O or R₃N→O). In the strict sense the term amine oxide applies only to oxides of tertiary amines including nitrogen-containing 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 intermediates. Long-chain alkyl amine oxides are used as nonionic surfactants and foam stabilizers.

Amine oxide are highly polar molecules have a high polarity close to that of quaternary ammonium salts. Small amine oxides are very hydrophilic and have an excellent water solubility and a very poor solubility in most organic solvents.

Amine oxides are weak bases with a pK_a of around 4.5 that form R₃N⁺-OH, cationic hydroxylamines, upon protonation at a pH below their pK_a.

Contents 1 Synthesis 2 Reactions 2.1 Pyrolytic elimination 2.2 Reduction to amines 3 Metabolites 4 Prodrugs 5 See also 6 External links

[edit] Synthesis

Amine oxides are prepared by oxidation of tertiary amines or pyridine analogs with hydrogen peroxide (H₂O₂) or peracids like mCPBA in N-oxidation.

[edit] Reactions

[edit] Pyrolytic elimination

Amine oxides, when heated to 150 to 200 ºC eliminate a hydroxylamine, resulting in an alkene. This pyrolytic syn-elimination reaction is known under the name Cope reaction. The mechanism is similar to that of the Hofmann elimination.

[edit] Reduction to amines

Amine oxides are readily converted to the parent amine by common reduction reagents including lithium aluminum hydride, sodium borohydride, catalytic reduction, zinc / acetic acid, and iron / acetic acid.

[edit] Metabolites

Amine oxides are common metabolites of medication and psychoactive drugs. Examples include nicotine, Zolmitriptan, and morphine.

[edit] Prodrugs

Amine oxides of anti-cancer drugs have been developed as prodrugs that are metabolized in the oxygen deficient cancer tissue to the active drug.

[edit] See also

• Functional group
• Amine, NR₃
• Hydroxylamine, NR₂OH
• Sulfoxide, R₂S=O
• Azoxy, RN=N+(O–)R RN=N⁺RO⁻
• N-Methylmorpholine N-oxide, an amine oxide
• TEMPO (2,2,6,6-Tetramethylpiperidine-1-oxyl), a stable amine oxide radical

[edit] External links

• Chemistry of amine oxides
• Surfactants, types and uses (pdf)
• The amine oxides homepage
• Nomenclature of nitrogen compounds
• IUPAC definition (pdf)