Amine oxide

In chemistry, an amine oxide, also known as an amine N-oxide or simply N-oxide, is a chemical compound that has the chemical formula R₃N⁺−O⁻. It contains a nitrogen-oxygen coordinate covalent bond with three additional hydrogen and/or substituent-groups attached to nitrogen. Sometimes it is written as R₃N→O or, alternatively,^[1] as R₃N=O.

In the strict sense, the term amine oxide applies only to oxides of tertiary amines. Sometimes it is also used for the analogous derivatives of primary and secondary amines.

Examples of amine oxides include pyridine-N-oxide, a water-soluble crystalline solid with melting point 62–67 °C, and N-methylmorpholine N-oxide, which is an oxidant.

Amine oxides are surfactants commonly used in consumer products such as shampoos, conditioners, detergents, and hard surface cleaners.^[2] Alkyl dimethyl amine oxide (chain lengths C10–C16) is the most commercially used amine oxide.^[3] They are considered a high production volume class of compounds in more than one member country of the Organisation for Economic Co-operation and Development (OECD); with annual production over 26,000, 16,000 and 6,800 tonnes (28,700, 17,600 and 7,500 short tons) in the US, Europe, and Japan, respectively.^[2] In North America, more than 95% of amine oxides are used in home cleaning products.^[4] They serve as stabilizers, thickeners, emollients, emulsifiers, and conditioners with active concentrations in the range of 0.1–10%.^[2] The remainder (< 5%) is used in personal care, institutional, commercial products^[5] and for unique patented uses such as photography.^[2]

Amine oxides are used as

Amine oxides exhibit many kinds of reactions.[7]

• Pyrolytic elimination. Amine oxides, when heated to 150–200 °C undergo a Cope reaction to form a hydroxylamine and an alkene. The reaction requires the alkyl groups to have hydrogens at the beta-carbon (i.e. works with ethyl and above, but not methyl)
• Reduction to amines. Amine oxides are readily converted to the parent amine by common
  phosphorus oxychloride
• Sacrificial catalysis. Oxidants can be regenerated by reduction of N-oxides, as in the case of regeneration of osmium tetroxide by N-methylmorpholine N-oxide in the Upjohn dihydroxylation.
• O-Alkylation. Pyridine N-oxides react with
  alkyl halides
  to the O-alkylated product
• Bis-ter-pyridine derivatives adsorbed on silver surfaces are discussed to react with oxygen to bis-ter-pyridine N-oxide. This reaction can be followed by video-
  scanning tunneling microscopy with sub-molecular resolution.^[8]
• In the Meisenheimer rearrangement (after Jakob Meisenheimer) certain N-oxides R¹R²R³N⁺−O⁻ rearrange to hydroxylamines R²R³N−O−R^1[9][10]

in a 1,2-rearrangement:

or a 2,3-rearrangement:

• In the Polonovski reaction, a tertiary N-oxide is cleaved by
  acetic acid anhydride to the corresponding acetamide and aldehyde:^[11][12][13]

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

Amine oxides of

Amine oxides (AO) are not known to be carcinogens, dermal sensitizers, or reproductive toxicants. They are readily metabolized and excreted if ingested. Chronic ingestion by rabbits found lower body weight, diarrhea, and lenticular opacities at a lowest observed adverse effect levels (LOAEL) in the range of 87–150 mg AO/kw bw/day. Tests of human skin exposure have found that after 8 hours less than 1% is absorbed into the body. Eye irritation due to amine oxides and other surfactants is moderate and temporary with no lasting effects.^[2]

Amine oxides with an average chain length of 12.6 have been measured to be water-soluble at ~410 g/L. They are considered to have low bioaccumulation potential in aquatic species based on log K_ow data from chain lengths less than C14 (bioconcentration factor < 87%).^[2] Levels of AO in untreated influent were found to be 2.3–27.8 ug/L, while in effluent they were found to be 0.4–2.91 ug/L. The highest effluent concentrations were found in oxidation ditch and trickling filter treatment plants. On average, over 96% removal has been found with secondary activated sludge treatment.^[3] Acute toxicity in fish, as indicated by 96h LC50 tests, is in the range of 1,000–3,000 ug/L for carbon chain lengths less than C14. LC50 values for chain lengths greater than C14 range from 600 to 1400 ug/L. Chronic toxicity data for fish is 420 ug/L. When normalized to C12.9, the NOEC is 310 ug/L for growth and hatchability.^[3]

• Functional group
• Amine, NR₃
• Hydroxylamine, NR₂OH
• Phosphine oxide, PR₃=O
• Sulfoxide, R₂S=O
• Azoxy
  , RN=N⁺(O⁻)R RN=N⁺RO⁻
• Aminoxyl group, radicals with the general structure R₂N–O•
• Category:Amine oxides, containing all articles on specific amine-oxide compounds