Amine-oxides

Amine oxides, known as A[-oxides of tertiary amines, are classified as aromatic or aliphatic, depending on whether the nitrogen is part of an aromatic ring system or not. This stmctural difference accounts for the difference in chemical and physical properties between the two types. 

The higher aUphatic amine oxides are commercially important because of their surfactant properties and are used extensively in detergents. Amine oxides that have surface-acting properties can be further categorized as nonionic surfactants however, because under acidic conditions they become protonated and show cationic properties, they have also been called cationic surfactants. Typical commercial amine oxides include the types shown in Table 1. 

Aromatic amine oxides, produced on a much smaller scale and having some pharmaceutical importance, do not demonstrate the surface-acting properties that the aUphatic amine oxides do. 

The physical properties of amine oxides are attributed to the semipolar or coordinate bond between the oxygen and nitrogen atoms with high electron density residing on oxygen. 

The N—O bond distances, found to be 0.133 to 0.139 nm for trimethyl amine oxide (1), are somewhat shorter than the single N—C bond distance of 0.147 nm ia methylamine. The N—C bond distance of 0.154 nm ia trimethyl amine oxide approaches that of the C—C bond. This is ia agreement with the respective absorptions ia the iafrared region valence vibrations of N—O bonds of aUphatic amine oxides are found between 970 920 cm (2). 

Amine oxides are the reaction products of tertiary amines and hydrogen peroxide. In aqueous solutions fatty amine oxides exhibit non-ionic or cationic properties depending on pH, and under neutral or alkaline conditions they exist as non-ionised hydrates. 

The oxides are produced from tertiary amines by adding the amine to 35% solutions of hydrogen peroxide over a period of 1 h at 60°C with very good mixing. During the addition period, small amounts of water must be added to prevent the formation of gel [38-40]. The 

Trade name Chemical structure Active level C8 C10 Cl 2 Cl 4 C16 Cl 8 

Amine Oxides, RN+(CH3)20 Usually, N-alkyldimethylamine oxides. These are usually classified as cationics, although they are actually zwitterionics, and will be so classified in the following chapters (including the tables). They are 

The determination of amine oxides is straightforward they can be titrated in acid solution with sodium dodecyl sulphate or NaTPB, either poten-tiometrically or in a two-phase system, for which purposes the solution must be at least 0.1 M in hydrogen ion, and they can be titrated with acid. However, for quality-control purposes it is necessary to determine the free tertiary amine content. This can be done by potentiometric titration, either in a solvent which permits discrimination on the basis of base strength, or before and after removal of the amine oxide. Methods are described for both of these. 

In the first method [31] the sample is titrated with hydrochloric acid in 50% propan-2-ol. In water or propan-2-ol alone only one point of inflection is observed, but in the mixture the tertiary amine is the stronger base and is titrated first, well separated from the amine oxide. 

Solvent 50% aqueous propan-2-ol, carbon dioxide free. Mix the solvents and either heat to boiling and cool (caution flammable vapour) or purge with a stream of nitrogen for half an hour. 

Weigh a sample containing about Imillimol amine oxide in a 250 ml beaker. Dissolve in 100 ml solvent. 

Titrate potentiometrically with aqueous 0.1 M hydrochloric acid. 

The A -oxides of pyrimidines have also been examined and compared with the pyridine A/-oxides by Wiley and Slaymaker [58] and by Katritzky [81]. The N- 0 absorptions occur in the 1300—1255 cm range and show the same sensitivity to substituent effects as the pyridine oxides. Pyrazine oxide absorbs at 1318 cm .  

Compounds related to amine oxides occur in the azoxy series 

These are prepared by oxidizing a tertiary nitrogen group with aqueous hydrogen peroxide at temperatures in the region of60-80 ° C. Several examples can be quoted, including N-alkyl amidopropyl-dimethyl amine oxide, N-alkyl bis(2-hydroxyethyl) 

C0C0CONHCH2CH2CH2N O Alkyl amidopropyl-dimethyl amine oxide 

CH12 H25N O Lautyl dimethyl amine oxide 

In acid solutions, the amino group is protonated and acts as a cationic surfactant, whereas in neutral or alkaline solution the amine oxides are essentially nonionic in character. Alkyl dimethyl amine oxides are water-soluble up to Cj, alkyl chain. Above pH 9, amine oxides are compatible with most anionics, but at pH 6.5 and below some anionics tend to interact and form precipitates. In combination with anionics, amine oxides can be used as foam boosters (e.g., in shampoos). 

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Cope Elimination- elimination of R2NOH from an amine oxide... 

For oximes, the word oxime is placed after the name of the aldehyde or ketone. If the carbonyl group is not the principal group, use the prefix hydroxyimino-. Compounds with the group Z = N—OR are named by a prefix alkyloxyimino- as oxime O-ethers or as O-substituted oximes. Compounds with the group r C=N(0)R are named by adding A-oxide after the name of the alkylideneaminc compound. For amine oxides, add the word oxide after the name of the base, with locants. For example, C5H5N—O is named pyridine A-oxide or pyridine 1-oxide. 

Fatty amides Fatty amine Fatty amine oxides Fatty amines... 

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