Physicochemical properties of amine oxides

1. Water solubility: due to the polar bond N → 0 in the amine oxide molecule, the dipole moment is 4138D, so the compound has the characteristics of high polarity and high melting point, and is easily soluble in polar solvents such as water and low-carbon alcohols , while insoluble in non-polar solvents such as mineral oil and benzene. In aqueous solution, amine oxides exist in the form of hydrate (R1R2R3NO · XH2O) in large quantities, but with the change of pH value, the polarity will change. For example, in alkaline solution with pH> 7, it is mainly anionic surfactant. But in acidic solutions at pH < 3, amine oxides exist mainly in the form of the cation [R1R2R3NOH]+. The aqueous solution of amine oxide has a weak oxidizing property, and its weak oxidizing property is used in cosmetics to achieve the purpose of whitening the skin.
2. Surface activity: (1) After adding amine oxide to the surface tension, the surface tension of water will be greatly reduced. For example, the surface tension of pure water is 72180 × 10 - 3 N/m. The surface tensions at the critical micelle concentration (cmc) of various amine oxides are all around 30 × 10 - 3N/m. The surface tension of amine oxides at cmc is much lower than that of quaternary ammonium salts, so the surface activity of amine oxides is much better than that of quaternary ammonium salts. (2) Detergent amine oxides have a synergistic effect on decontamination when mixed with AES or AS, but have little synergistic effect when mixed with LAS. The product of washing lip balm uses 12% fatty acid (C12:C18 = 12:1), 13% non-ionic surfactant, 12% LAS, such as adding a certain amount of amine oxide, the cleaning effect will be very good. (3) Emulsifying power Emulsifying power is an indicator to measure the quality of emulsifiers. For example, the amine oxide aqueous solution and the petroleum solvent were emulsified under the same conditions at 70 °C, and then the volume changes after emulsification were observed statically. The results show that among the amine oxide homologues, the emulsifying ability increases with the carbon number of the long-chain alkyl groups. Another feature of amine oxide as an emulsifier is that it can emulsify in a wide pH range, especially in acidic media, it can be compatible with quaternary ammonium salt cations as preservatives and fungicides, not only will not hinder The preservative properties of preservatives can be enhanced. This is beyond the reach of other nonionic surfactants. (4) Foaming and foam stabilization Amine oxide is an efficient foam stabilizer. C12~14N(CH3) 2O is commonly used in laundry detergents or dishwashing detergents. The product with an dosage of 1%~5% has mild performance, no irritation to eyes, and good resistance to hard water. It can be used in hard water at pH 9, 300 mg/kg. The medium bubble is higher. (5) Thickening effect Amine oxide has better thickening effect.
3. Physiological toxicity: The biodegradability of amine oxide is good, 88% can be degraded after 2 weeks, and 93% after 4 weeks. Amine oxide is essentially non-toxic, and it is extremely irritating to skin and eyes. According to KLein, the LD50 of amine oxide is 2 000 mg/kg to 6 000 mg/kg, which is almost equivalent to the LD 504 000 mg/kg of table salt. Amine oxides are anti-irritant when combined with other active agents and can be used in anti-dandruff shampoos to reduce the irritation of ZPT. In addition, in acidic shampoos and acidic solutions, amine oxides can interact with carboxyl groups on hair and skin corners to condition the hair, reduce fluff, ease wet combing, and improve skin roughness.

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