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Concept
Bétaïne de cocamidopropyle
Résumé
Cocamidopropyl betaine (CAPB) is a mixture of closely related organic compounds derived from coconut oil and dimethylaminopropylamine. CAPB is available as a viscous pale yellow solution and it is used as a surfactant in personal care products and animal husbandry. The name reflects that the major part of the molecule, the lauric acid group, is derived from coconut oil. Cocamidopropyl betaine to a significant degree has replaced cocamide DEA.
Despite the name cocamidopropyl betaine, the molecule is not synthesized from betaine. Instead it is produced in a two step manner, beginning with the reaction of dimethylaminopropylamine (DMAPA) with fatty acids from coconut or palm kernel oil (lauric acid, or its methyl ester, is the main constituent). The primary amine in DMAPA is more reactive than the tertiary amine, leading to its selective addition to form an amide. In the second step chloroacetic acid reacts with the remaining tertiary amine to form a quaternary ammonium center (a quaternization reaction).
CH3(CH2)10COOH + H2NCH2CH2CH2N(CH3)2 → CH3(CH2)10CONHCH2CH2CH2N(CH3)2
CH3(CH2)10CONHCH2CH2CH2N(CH3)2 + ClCH2CO2H + NaOH → CH3(CH2)10CONHCH2CH2CH2N+(CH3)2CH2CO2− + NaCl + H2O
CAPB is a fatty acid amide containing a long hydrocarbon chain at one end and a polar group at the other. This allows CAPB to act as a surfactant and as a detergent. It is a zwitterion, consisting of both a quaternary ammonium cation and a carboxylate.
Cocamidopropyl betaine is used as a foam booster in shampoos. It is a medium-strength surfactant also used in bath products like hand soaps. It is also used in cosmetics as an emulsifying agent and thickener, and to reduce irritation purely ionic surfactants would cause. It also serves as an antistatic agent in hair conditioners, which most often does not irritate skin or mucous membranes. However, some studies indicate it is an allergen.
CAPB is obtained as an aqueous solution in concentrations of about 30%.
Typical impurities of leading manufacturers today:
Sodium monochloroacetate < 5 ppm
Amidoamine (AA) < 0.
Source officielle
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