Cocamidopropyl betaine (CAPB) is a mixture of closely related

organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. T ...

s 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 Lauric acid, systematically dodecanoic acid, is a saturated fatty acid with a 12-carbon atom chain, thus having many properties of medium-chain fatty acids. It is a bright white, powdery solid with a faint odor of bay oil or soap. The salts and ...

group, is derived from coconut oil. Cocamidopropyl betaine to a significant degree has replaced cocamide DEA.

Production

Despite the name cocamidopropyl betaine, the molecule is not synthesized from

betaine A betaine () in chemistry is any neutral chemical compound with a positively charged cationic functional group, such as a quaternary ammonium or phosphonium cation (generally: onium ions) that bears no hydrogen atom and with a negatively charge ...

. 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 Palm kernel oil is an edible plant oil derived from the kernel of the oil palm tree ''Elaeis guineensis''. It is related to other two edible oils: ''palm oil'', extracted from the fruit pulp of the oil palm, and ''coconut oil'', extracted from ...

(

, 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 Chloroacetic acid, industrially known as monochloroacetic acid (MCA), is the organochlorine compound with the formula ClCH2CO2H. This carboxylic acid is a useful building block in organic synthesis. It is a colorless solid. Related compounds a ...

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

Chemistry

CAPB is a

fatty acid amide Fatty acid amides (FAAs) are amides formed from a fatty acid and an amine. In nature, many FAAs have ethanolamine as the amine component. Also known as ''N''-acylethanolamines, they contain the functionality RC(O)N(H)CH2CH2OH. A well known ex ...

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 In chemistry, a zwitterion ( ; ), also called an inner salt or dipolar ion, is a molecule that contains an equal number of positively- and negatively-charged functional groups. : With amino acids, for example, in solution a chemical equilibrium wil ...

, consisting of both a quaternary ammonium cation and a

carboxylate In organic chemistry, a carboxylate is the conjugate base of a carboxylic acid, (or ). It is an ion with negative charge. Carboxylate salts are salts that have the general formula , where M is a metal and ''n'' is 1, 2,...; ''carboxylat ...

Specifications and properties

Cocamidopropyl betaine is used as a foam booster in shampoos. It is a medium-strength surfactant also used in bath products like

hand soap Soap is a salt of a fatty acid used in a variety of cleansing and lubricating products. In a domestic setting, soaps are surfactants usually used for washing, bathing, and other types of housekeeping. In industrial settings, soaps are used as ...

s. It is also used in

cosmetics Cosmetics are constituted mixtures of chemical compounds derived from either natural sources, or synthetically created ones. Cosmetics have various purposes. Those designed for personal care and skin care can be used to cleanse or protect ...

as an emulsifying agent and

thickener A thickening agent or thickener is a substance which can increase the viscosity of a liquid without substantially changing its other properties. Edible thickeners are commonly used to thicken sauces, soups, and puddings without altering their t ...

, and to reduce irritation purely ionic surfactants would cause. It also serves as an

antistatic agent An antistatic agent is a compound used for treatment of materials or their surfaces in order to reduce or eliminate buildup of static electricity. Static charge may be generated by the triboelectric effect or by a non-contact process using a high ...

in hair conditioners, which most often does not irritate

skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different de ...

mucous membrane A mucous membrane or mucosa is a membrane that lines various cavities in the body of an organism and covers the surface of internal organs. It consists of one or more layers of epithelial cells overlying a layer of loose connective tissue. It i ...

s. 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) < 0.3% * Dimethylaminopropylamine (DMAPA) < 15 ppm *

Glycerol Glycerol (), also called glycerine in British English and glycerin in American English, is a simple triol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids known ...

< 3% The impurities AA and DMAPA are most critical, as they have been shown to be responsible for skin sensitization reactions. These by-products can be avoided by a moderate excess chloroacetate and the exact adjustment of pH value during betainization reaction accompanied by regular analytical control.

Niche Uses

CAPB is also used as a co-surfactant with

Sodium dodecyl sulfate Sodium dodecyl sulfate (SDS) or sodium lauryl sulfate (SLS), sometimes written sodium laurilsulfate, is an organic compound with the formula . It is an anionic surfactant used in many cleaning and hygiene products. This compound is the sodium salt ...

for promoting the formation of

gas hydrates Clathrate hydrates, or gas hydrates, clathrates, hydrates, etc., are crystalline water-based solids physically resembling ice, in which small non-polar molecules (typically gases) or polar molecules with large hydrophobic moieties are trapped i ...

. CAPB, as an additive, helps to scale-up the gas hydrates' formation process.

Safety

CAPB has been claimed to cause allergic reactions in some users, but a controlled pilot study has found that these cases may represent irritant reactions rather than true allergic reactions. Furthermore, results of human studies have shown that CAPB has a low sensitizing potential if impurities with amidoamine (AA) and dimethylaminopropylamine (DMAPA) are low and tightly controlled. Other studies have concluded that most apparent allergic reactions to CAPB are more likely due to amidoamine. Cocamidopropyl betaine was voted 2004 Allergen of the Year by the American Contact Dermatitis Society.History of Allergen of the Year
. contactderm.org

References