Acyl sarcosinates

These surfactants are interrupted soaps, in that they have additional functionality added to the carboxylate. In this case an amide function is created and the surfactant head group is a carboxylate salt, as in soap. The additional function produces a surfactant which shares some properties of soap but with generally enhanced performance. 

Salt is a by-product. Due to the stability of the amide group, the free acid can be formed and separated from the reaction mixture to give a salt-free product. The stability of the amide group also allows sarcosinates to be used in a wider range of chemical environments than isethionates (see below). Sarcosinates are stable under moderately acidic conditions but will degrade at low pH or with elevated temperature. The surfactants are moderately soluble at high pH and the sodium salts are supplied as a 30% solution. 

Sarcosine is a naturally occurring amino acid but is made industrially by reacting methy-lamine with monochloroacetic acid (MCA), a common reagent also used in the manufacture of betaines. 

Structure vs. properties. Few data exist on variants of sarcosinates, with the cocoyl variant being dominant. The lauryl (C12) variant has been prepared and shows a higher CMC and higher surface tension at the CMC than the cocoyl and the surface tension also shows some dependency on pH. 

Applications. Sarcosinates show low irritation potential and are good foamers. Due to these properties they find applications in personal care products where synergistic effects with other surfactants may also be exploited. In combination with other anionics, sarcosinates will often detoxify the formulation and give improved foaming and skin feel. Sarcosinates are also used for their hydrotropic properties - the addition of sarcosinate to other anionics often gives a reduced Kraft point or a raised cloud point if combined with non-ionic surfactants. Lauroyl sarcosinate is used to formulate SLS-free toothpastes which are claimed to have improved taste profile. 

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Sarcosinate specialty surfactants are currently made by acylation of naturally occurring amino acids with an acyl chloride. The use of a secondary amide for amidocarbonylation has been reported to give poor yields of amido acid since the corresponding oxazolone intermediate cannot be formed. Lin has demonstrated, however, that the amidocarbonylation of A-methylamine gives excellent yields of A-acyl sarcosinates (eq. (11)) when conducted in the presence of dicobalt octacarbonyl at 120°C with CO/H2 = 3 1. Sarcosinate selectivity is typically 95 %, at 92 % A-methylamine conversion. 

N-acyl methyltaurates, N-acyl sarcosinates, acyl isethionates, IV-acyl polypeptide condensates, polyalkoxylated ether glycolates, monoglyceride sulfates, and fatty glyceryl ether sulfonates [1,23]. 

R = CH3 —> Af-methyl tauride N-acyl amino acids Example acyl sarcosinates... 

Sarcosinate surfactants are derived from natural fatty acids and an amino acid, sarcosine (A -methyl glycine). Typically the sarcosinate is used in the form of its sodium, potassium, or ammonium salt solution. A -Acyl sarcosinates are produced commercially by the Schotten-Baumann reaction of the sodium salt of sarcosine with the appropriate fatty acid chloride under carefully controlled conditions. The commercially available sarcosinate surfactants are cocoyl sarcosine, lauroyl sarcosine, myristoyl sarcosine, oleoyl sarcosine, stearoyl sarcosine, sodium cocoyl sarcosinate, sodium lauroyl sarcosinate, sodium myristoyl sarcosinate, ammonium lauroyl sarcosinate, TEA lauroyl sarcosinate, ammonium cocoyl sarcosinate, monoethanolamine cocoyl sarcosinate, and TEA oleoyl cocoyl sarcosinate. 

Alternatively, the free carboxylic acid can react with methylamine to form the corresponding N-methylamide (a secondary amide moiety), followed by amidocarbonylation with paraformaldehyde and syngas (CO/H2) in the presence of dicobalt octacarbonyl (C02(C0)8) at 120 °C to give N-acyl sarcosinate in excellent yields. The product selectivity is typically 95% at 92% N-methylamide conversion. This synthesis approach avoids use of acid chloride, and allows the introduction of both the carboxylic acid and secondary amide functionalities in a single step. 

Fatty acids and acyl sarcosines may be extracted with petroleum or diethyl ether from an acidified aqueous solution if no other surfactants are present, or with petroleum ether from acidified 50% ethanol if they are. The extract is evaporated and the residue weighed. Alkylether carboxylic acids cannot be quantitatively extracted with petroleum ether. They can be extracted from aqueous solution with chloroform, but they are best determined by two-phase titration with benzethonium chloride in akaline solution (bromophenol blue method) or direct potentiometric acid-base titration. 

Fatty acids can be separated from acyl sarcosines by extraction from 70% propanol with petroleum ether. The fatty acids are extracted. It is necessary to do at least four extractions and three washes with 70% propanol. 

Soaps and sarcosinates can be determined in aqueous solution by titrating to bromocresol green or bromophenol blue with hydrochloric or sulphuric acid in the presence of petroleum ether or diethyl ether. The solution is shaken after each addition of titrant to extract the liberated fatty acid or acyl sarcosine. Alkylether acids can probably be determined in the same way if chloroform is used as extracting solvent. 

Any carboxylate can be determined in any mixture of anionics by extraction of the acid form from acidified 50% ethanol, using petroleum ether for fatty acids and acyl sarcosines and chloroform for alkylether carboxylic acids. 

Dialkoxylated alkylpolyoxy alkylamine Product of 4,4 -thiodiphenol, formaldehyde and cocoamines Reaction products of hydroxyl-methyl imidazoline and acyl sarcosine Salts of imidazolines... 

Most published information deals with the analysis of sarcosine derivatives. Sarcosine is often made by reaction of chloroacetic acid with methylamine. M-acylated sarcosine is made by reaction of the acyl chloride with sarcosine in the presence of alkali. Possible impurities in the final product thus include glycolic acid and Ai-methylalkylamide. Fatty acid and chloride salts are expected as byproducts of the acylation reaction, and ethyl esters of fatty acids and acylsarcosine may be formed during workup of the synthesis product with ethanol (137). 

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