Amphoacetates
Amphoacetates are a class of amphoteric surfactants which, depending on the pH value , can be present as anionic , cationic or nonionic surface-active compounds ( detergents ).
Most often, these compounds are used in the form of their sodium salts , which have a high foaming power and cause only minor skin and eye irritation.
Manufacturing
The synthesis of amphoacetates takes place in two reaction stages. In the first stage, a long-chain fatty acid (> C 8 chain length) or a fatty acid mixture (e.g. by hydrolysis of coconut oil , palm oil or soybean oil ) reacts when heated with 2- (2-aminoethylamino) ethanol under reduced pressure to temperatures above 200 ° C. The corresponding 2-alkyl-1-hydroxyethylimidazoline is formed with elimination of water, which is usually obtained as a low-melting white wax in yields of> 95%.
In the second stage, the imidazoline is hydrolyzed to the linear amidoamine with sodium hydroxide solution and carboxymethylated with a small molar excess of the sodium salt of monochloroacetic acid in an optimal pH range of 8.5 to 9.5 at 75 ° C. Earlier assumptions that carboxymethylation occurs on the imidazoline ring have now been refuted. The reaction yield is practically quantitative. At the end of the reaction, the product is adjusted to a solids content of approx. 45% with water.
The aim of the reaction is to generate the lowest possible total amounts of the by-product sodium chloride and the toxic reactant sodium monochloroacetate (<115 ppm) with as complete a conversion of the amidoamine as possible , as well as the formation of the sodium salt of glycolic acid - by alkaline hydrolysis from monochloroacetic acid - to the lowest possible values ( <2.5%). Contamination by glycolic acid is disadvantageous because of the skin-irritating properties and the lack of surface-active properties.
When the substituted hydroxyethylimidazoline is reacted with higher molar amounts of monochloroacetic acid salt, the so-called amphodiacetates are formed. Up to four different structures for amphodiacetates are discussed, of which the O -carboxymethylated derivative C is most often given as the target product.
Larger proportions of amphodiacetates mixed with amphoacetates are undesirable since they reduce the foam height of amphoacetates, especially in hard water.
use
Amphoacetates are particularly mild surfactants with little irritation to the skin, mucous membranes and eyes and are therefore often used in shampoos , liquid soaps and shower gels . They ensure rapid surface wetting and reduction of surface tension and are good foaming agents . The aggressive fat solution of anionic fatty alcohol sulfates or alkyl ether sulfates , such as, for. B. SLES is moderated by adding amphoacetates. As co-surfactants, they act as solubilizers for more hydrophobic surfactants and hydrotropically on sparingly soluble additives in emulsions . Amphoacetates are compatible with anionic, cationic and non-ionic surfactants as well as with electrolytes . They are biodegradable and hydrolytically stable over a wide pH range.
Typical compositions of commercial cocoamphodiacetates and cocoamphodiacetates are shown in the following table:
| Components | Cocoamphoacetate | Cocoampho di acetate |
|---|---|---|
| Active substance [%] | 45 | 50 |
| Sodium chloride [%] | 7.5 | 13 |
| Coconut fatty acids [%] | <0.7 | <0.7 |
| Glycolate [%] | <4 | <8 |
| Na chloroacetate [ppm] | variable | 100 - 2000 |
Amphodiacetates are themselves good foaming agents and improve the skin compatibility of surfactant mixtures, but play only a marginal role because of their mostly significantly higher glycolate and monochloroacetic acid contents.
Because of their pronounced skin-friendliness and tendency to foam, amphoacetates are mainly found in baby shampoos and soaps, and in liquid dishwashing detergents. In many technical applications, however, the foam formation of the amphoacetates is undesirable and the comparatively high price is unfavorable.
Amphoacetates made from coconut fatty acids ( INCI name: Sodium Cocoamphoacetate) and amphodiacetate (INCI name: Disodium Amphodiacetate), which are sold by a large number of specialty chemical companies under the respective brand names, are most widespread in the market . a. BASF as Dehyton R , Colonial Chemical as Cola R Teric, Croda International as Crodateric TM CY, Evonik Industries as Rewoteric AM C, Kaō as Betadet R THC, Rhodia as Miranol R Ultra C32 or Mackam R 1C or 2C and Stepan Company as Amphosol R 1C and 2C, respectively.
literature
- Drew Myers: Surfactants Science and Technology, 3rd Edition . John Wiley & Sons, Hoboken, NJ, USA 2005, ISBN 978-0-471-68024-6 , doi : 10.1002 / 047174607X .
- Amphoteric Surfactants, 2nd Edition . In: Eric G. Lomax (Ed.): Surfactant Science Series, Volume 59 . Marcel Dekker, Inc., New York, NY, USA 1996, ISBN 0-8247-9392-7 .
Individual evidence
- ↑ a b Patent US2528378 : Metal salts of substituted quaternary hydroxy cycloimidinic acid metal alcoholates and process for preparation of the same. Registered on September 20, 1947 , published October 31, 1950 , applicant: JJ McCabe, HS Mannheimer, inventor: HS Mannheimer.
- ↑ a b Patent US4269730B : Substituted imidazoline reactions with chloroacetate salts. Applied on August 28, 1979 , published May 26, 1981 , Applicant: Stepan Chemical Co., Inventors: JR Wechsler, TG Baker, GT Battaglini, FL Skradski.
- ↑ a b c Patent US6057282 : High purity imidazoline-based amphoacetate surfactants. Applied on August 23, 1999 , published May 2, 2000 , Applicant: Rhodia Inc., Inventors: B. Desai, P. Lees, J.-M. Ricca, DJ Tracy.
- ↑ External identifiers or database links for disodium lauroamphodiacetate: CAS number: 68298-20-4, EC number: 269-546-7, ECHA InfoCard: 100.063.205 , PubChem : 109973 , ChemSpider : 98782 , Wikidata : Q27287787 .
- ↑ Amphosol R 2C. (PDF; 48 kB) Product Bulletin. Stepan, 2012, accessed June 22, 2018 .
- ↑ Mackam 2C. (PDF; 31 kB) Technical Data Sheet. Rhodia , March 2012, accessed June 22, 2018 .
- ↑ Cola R Teric 2C. (PDF; 99 kB) Technical Data Sheet. Colonial Chemical, 2015, accessed June 22, 2018 .
- ↑ U. Zoller, P. Sosis (Ed.): Handbook of Detergents, Part F: Production . CRC Press, Boca Raton, FL, USA 2009, ISBN 978-0-8247-0349-3 , pp. 223-227 .