Cocamidopropyl betaine

Anionic surfactants are the most commonly used class of surfactant. Anionic surfactants include sulfates such as sodium alkylsulfate and the homologous ethoxylated versions and sulfonates, eg, sodium alkylglycerol ether sulfonate and sodium cocoyl isethionate. Nonionic surfactants are commonly used at low levels ( 1 2%) to reduce soap scum formation of the product, especially in hard water. These nonionic surfactants are usually ethoxylated fatty materials, such as H0CH2CH20(CH2CH20) R. These are commonly based on triglycerides or fatty alcohols. Amphoteric surfactants, such as cocamidopropyl betaine and cocoamphoacetate, are more recent surfactants in the bar soap area and are typically used at low levels (<2%) as secondary surfactants. These materials can have a dramatic impact on both the lathering and mildness of products (26). 

These surfactants, in conjunction with soap, produce bars that may possess superior lathering and rinsing in hard water, greater lather stabiUty, and improved skin effects. Beauty and skin care bars are becoming very complex formulations. A review of the Hterature clearly demonstrates the complexity of these very mild formulations, where it is not uncommon to find a mixture of synthetic surfactants, each of which is specifically added to modify various properties of the product. Eor example, one approach commonly reported is to blend a low level of soap (for product firmness), a mild primary surfactant (such as sodium cocoyl isethionate), a high lathering or lather-boosting cosurfactant, eg, cocamidopropyl betaine or AGS, and potentially an emollient like stearic acid (27). Such benefits come at a cost to the consumer because these materials are considerably more expensive than simple soaps. 

Cocamidopropyl betaine is an amphoteric detergent, a detergent that can act as an acid or a base. It does not irritate the skin or mucous membranes. It is used to thicken shampoos, and to reduce the irritation that would result if only more irritating detergents were used. It has antibiotic effects, and is used in personal sanitary products. It also has antistatic properties, making it an effective conditioning agent in shampoos. 

In addition to the soaps and fatty acids, some bars contain cocamidopropyl betaine, a mild amphoteric detergent that is added to control irritation without decreasing suds or cleaning power, and benzine sulfonate detergents such as sodium dode-cylbenzinesulfonate. Other detergents, such as sodium isethion-ate and sodium cocoyl isethionate, are also common. 

Amphoteric surfactants are those that are an acid and a base at the same time (like water is). Cocamidopropyl betaine, for example, is used in shampoos to stabilize foam and thicken the mixture. 

Cocamidopropyl betaine (Table 1.4) is the most prominent representative of the class of amphoteric surfactants. Due to the synergism with other surfactants and its gentleness to the skin and mucous membranes, cocamidopropyl betaine performs well in shampoo and cosmetics where its dosage lies in the order of 1-5% [27]. 

Cocamidopropyl betaine is manufactured by a two-step reaction coconut oil-derived fatty acid is reacted with dimethylaminopropyl-amine to yield the cocamide that is subsequently converted to the betaine by the addition of monochloroacetate. The acyl group in the amide linkage ranges in length from 8 to 16 carbon atoms with C12 and C14 as the predominant components [44]. 

The components of a technical cocamidopropyl betaine (CAPB Fig. 2.13.1) mixture were separated under reversed phase conditions in the order of increasing length of the alkyl chain (Fig. 2.13.2) [1]. Since the hydrophobic moiety of the surfactant molecule is derived from coconut oil, the two homologues Ci2 and C14 form the major constituents according to the distribution in the natural raw product containing approximately 49% of Ci2- and 19% of C14-fatty acid [2],... 

Only limited data have been published on the degradability of betaines, such as cocamidopropyl betaine (CAPB, Fig. 5.1.22), and the limited information available is somewhat contradictory. Swisher reported that total degradability was rather poor (45-58%) [10], whilst Brunner et al. [138] obtained mixed results with a series of the amphoteric surfactants in an extended OECD 302B test and a laboratory trickling test filter. While the two compounds cocoampho diacetate and cocoampho dipropionate were mineralised only to a minor extent, CAPB and cocoampho acetate proved to be nearly totally degradable. 

Chloroxylenol 3% and cocamidopropyl PG-dimonium chloride phosphate 3%. Inactive ingredients water, sodium lauryl sulfate, cocamide DEA, propylene glycol, cocamidopropyl betaine, citric acid, tetrasodium EDTA,... 

The wide availability of relatively inexpensive dimethylaminopropylamine (DMAPA) allows surfactant producers to convert economic triglycerides, fatty acids and methyl esters into amido -functional tertiary amines that may then be quaternized with sodium chloroacetate to produce alkylamidopropyl betaines (see Figure 6.15). The most economically significant of these is cocamidopropyl betaine which can be produced from a variety of feedstocks and lauramidopropyl betaine which is generally produced from lauric acid. These are widely used secondary surfactants in consumer products such as shampoos, bath products, washing up liquids and other cleaners. 

Over the past decade, studies by DeGroot [6] and others have indicated that free amines present in cocamidopropyl betaine appear to be sensitizers. It has not been clear as to whether the problem was due to free DMAPA or cocamidopropyl dimethylamine but recent evidence suggests it maybe due to both. The producers of these products reacted to the problem and the typical alkylamidopropyl betaine produced today contains less than 10 ppm of free DMAPA and less than 0.5% of cocamidopropyl dimethylamine (Table 6.9). 

Table 6.9 Comparison of an older commercial cocamidopropyl betaine product with a modern one...

Property Older cocamidopropyl betaine Modern cocamidopropyl betaine... 

The production of cocamidopropyl betaine has traditionally been based on two feedstocks coconut oil and topped or stripped (C-8 and 10 removed) coconut fatty acid or methyl ester. These products are still widely used but, to achieve better colors and odors, hydrogenated feedstocks are now very frequently used, either fully hydrogenated coconut oil triglyceride or stripped, hydrogenated, distilled coconut fatty acid. These products are most frequently sold as aqueous solutions with 35% nonvolatile matter. If made from triglyceride, the betaine surfactant will contain about 2.5% glycerin by-product and 5% sodium chloride by-product in addition to the active surfactant. Products made from fatty acid or methyl ester are approximately 30% active product and slightly more than 5% sodium chloride. 

Cocamidopropyl betaine and cocamidopropyl hydroxysultaine, discussed later, are also used in petroleum production. Their relatively high foaming nature, electrolyte tolerance and hydrolytic stability make them useful for foam acidizing and foam fracturing fluids. 

As the use of cocamidopropyl betaine increased as a secondary surfactant in anionic systems, the relatively low concentration of about 35% nonvolatiles at which it is normally sold became an issue. At this concentration, betaines are somewhat susceptible to bacterial growth so a preservative is often needed and the low concentration also increases freight costs so that several patented technologies were developed to address this [7]. Typically, the inclusion of about 2% of one of the patented additives allows the producers to prepare an aqueous solution of 45% nonvolatiles which is hostile to microbial growth without... 

De Groot, A.C. (1997) Cocamidopropyl betaine a new important cosmetic allergen. Dermatosen in Berufund Umwelt, 45(2), 60-3. 

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