Introduction
An amine oxide, also known as amine-N-oxide and N-oxide, is a chemical compound that contains the functional group R3N+−O−, an N−O coordinate covalent bond with three additional hydrogen and/or hydrocarbon side chains attached to N. It is worth mentioning that the use of amine oxide has been improperly extended to other N–O-bond containing compounds, such as nitrones, nitrile oxides, and substituted dialkylhydroxylamines. Amine oxides possess a distinctive common fragment: an oxygen atom that is datively.
Applications
Industry use: Amine oxides are surfactants commonly used in consumer products such as shampoos, conditioners, cleansers and hard surface cleaners. Alkyl dimethyl amine oxide is the most commonly used amine oxide on the market. In North America, more than 95% of amine oxides are used as household cleaning products. They can be used as stabilizers, thickeners, emollients, emulsifiers and conditioners. The rest is used for personal care, institutional, commercial products and for unique patented applications such as photography.
Organic chemistry: Pyrolysis of amine oxides yields olefins and hydroxylamines. This procedure constitutes an efficient route to the preparation of olefins. Due to the requirement for higher reaction temperature, Cope elimination usually proceeds under thermodynamical control. The reversibility of the Cope elimination can be seen in many examples of reverse Cope cyclization, especially intramolecular variants, which can lead to the synthesis of useful cyclic oxides. O'Neil used the Cope-retro Cope sequence to allow highly diastereoselective syntheses of six-membered cyclic hydroxylamines.
Fig.1. Syntheses of cyclic amine oxide
Since amine oxides with various transition metal complexes exhibit the characteristic reactivity, they have been extensively studied as non-explosive oxidants. In particular, amine oxides such as N-methylmorpholine-N-oxide (NMO) are stoichiometric oxidants for many oxidation reactions. NMO monohydrate has a melting point of 70℃, and is stable under normal conditions. It is soluble in polar solvents, especially in water. NMO has been proved to be a very effective terminal oxidant in the osmium-catalyzed dihydroxylation. The reaction efficiency can allows demanding or unusual substrates to participate. For example, the use of olefins allows cis-dihydroxylation of alkyl- and aryltrifluoroborates that containing olefins in moderate to good yields. The resulting diols are coupling partners with alkenyl and aryl bromides that are effective in Suzuki-Miyaura type reactions.
Fig.2. Osmium-catalyzed dihydroxylation
Reference
- Bagley M C, Tovey J. Diastereoselective synthesis of cis-2,5-disubstituted pyrrolidine N-oxides by the retro-Cope elimination[J]. Tetrahedron Letters, 2001, 42(2): 351-353.
