Imidazoline-derived amphoterics

These imidazoline compounds have proved very useful as intermediates to amphoteric surfactants. Products made from them, alkylated with sodium chloroacetate or methyl acrylate were patented by Hans Mannheimer who founded Miranol Company in the USA during the 1950s [2]. Miranol Company became the major vendor of imidazoline derived amphoteric surfactants in the world. Other imidazolines are used to produce amphoteric surfactants, such as alkyl aminoethyl imidazoline, but those products are of less economic significance. 

As mentioned above, most commercial products are based on either a lauric (mainly C-12) or a whole coconut distribution (C-8 to C-18, with approximately 50% C-12) since these alkyl distributions give the best detergency. Early on, the imidazoline derived amphoterics were characterized as exceptionally mild to the skin and eyes relative to most surfactants available at the time. This made them excellent candidates for use in baby shampoos, geriatric cleansing products, hand wash for medical facilities and so on. 

The other major class of fatty imidazoline derived amphoteric surfactants is the amphopropionates. Again, the ampho portion of the name indicates that they are derived from imidazolines but, rather than being alkylated with sodium chloroacetate, they are carboxy-lated with an acrylate via the Michael reaction. A primary or secondary amine is added across the double bond of the acrylate to yield the beta-alanine derivative. 

Table 1.7 Commercially prominent imidazoline-derived amphoterics [111]...

Characterization of an imidazoline-derived amphoteric requires considering the reaction pathway used to prepare the compound. For example, an amidobetaine may be made by sodium chloroacetate treatment of the imidizoline/linear amide mixture obtained by reacting a fatty acid or ester with iV-hydroxyethylethylenediamine. Possible compo-... 

Derian, P. J., J. M. Ricca, F. Marcenac, R. Vukov, D. Tracy, M. Dahanayake, Imidazoline-derived amphoteric surfactants, SOFW Journal, 1995,121, 399-410. 

Most commercially important imidazoline-derived amphoteric surfactants can be described as fatty acid/aminoethylethanolamine condensates of the general structure... 

Imidazolinium Derivatives. Amphoteric imidazolinium derivatives are prepared from the 2-alkyl-l-(2-hydroxyethyl)-2-imidazolines and from sodium chloroacetate. The most likely structure of the reaction product is as follows (109) ... 

Two major classes of amphoteric surfactants are derived from fatty alkyl hydroxyethyl imidazolines which, in turn, are produced from fatty acids and low molecular weight amines. Because fatty acids are fairly economic, the imidazoline derived amphoacetates tend to be less expensive than the iminodipropionates discussed above. Most imidazoline derived... 

Amphoteric Surfactants. Steiner (13) reported the nature of the interactions between a water-insoluble HMHEC and a commercial amphoteric surfactant (Miranol HS, a sulfonated amphoteric imidazoline derivative) at various pH levels. She found that the HMHEC was solubilized in the presence of a large excess (between 10 and 20%) of the surfactant. (More... 

A secondary surfactants group with increasing economical importance are the A -(2-aminoethyl)-2-aminoethanol (aminoethylethanolamine)-derived amphoterics. Because the intermediate in the synthesis of these surfactants is a substituted imidazoline, they are also classified as being imidazoline-derived. Historically, these mild surfactants have been the first to offer the possibility for the production of non-eye-stinging shampoos. Still today, aminoethylethanolamine-derived amphoterics are mainly used in personal care formulations where mild properties are desired, whereas industrial applications play only a minor role. 

The intermediate in the synthesis of aminoethylethanolamine-derived amphoterics is a heterocyclic imidazoline with an unsaturated five-membered ring system containing an amine and an imine group (Figure 15.13). 

Figure 15.13. The imidazoline intermediate for aminoethylethanolamine-derived amphoterics...

The amount of residual dimethylaminopropylamine (DMAPA) is usually determined directly after the first reaction step of the betaine synthesis, i.e. the preparation of amidoamine. After this has been reacted with phenyl isothiocyanate, it can be analysed by HPLC using a reversed-phase column. The quantitative determination of aminoethylethanolamine (AEEA) in aminoethylethanolamine-derived amphoterics cannot currently be accomplished in the final product. Residual amounts of this compound have to be measured in the imidazoline intermediate of the reaction sequence. 

Owing to their compatibility with cationic biocides, amphoteric and amine oxide surfactants continue to be used widely in the development and formulation of disinfectants and sanitizers for personal care, household, industrial, and institutional markets. For instance, substituted imidazoline amphoteric surfactants, in combination with didecyl dimethyl ammonium chloride, have been found to display unexpected synergistic irritation reduction compared to formulas with alkyl dimethyl benzyl ammonium chlorides [57]. Also, imidazoline derivatives and betaines are known to impart moderate cleansing without causing skin roughness, stickiness, or irritating reactions with cationic disinfectants [58], Amphoteric surfactants are also suitable for use in antimicrobial medications requiring subcutaneous, cutaneous, or mucosal membrane administration [36]. 

MIRANOL Amphoteric Surfactants - Carboxylated Imidazoline Derivatives ... 

Chem. Descrip. Coconut monocarboxylic propionate, imidazoline-derived, salt-free Ionic Nature Amphoteric... 

Kawase, J., K. Tsuji, Y. Yasuda, K. Yashima, Amphoteric surfactants by LC with post-column detection. II Imidazoline-type amphoteric surfactants derived from sodium chloroacetate, J. 

As mentioned above, the increased importance of the imidazoline-derived surfactants stems primarily from their mildness and low toxicity. The extent of their use in shampoos and body care products has followed closely the overall increase in the use of such products worldwide. Their amphoteric nature also makes them useful in a wide range of water types, ranging from hard to soft water and high to low pH. Such flexibility makes them useful in cleaning formulations that will see a variety of conditions. 

Amphoteric Detergents. These surfactants, also known as ampholytics, have both cationic and anionic charged groups ki thek composition. The cationic groups are usually amino or quaternary forms while the anionic sites consist of carboxylates, sulfates, or sulfonates. Amphoterics have compatibihty with anionics, nonionics, and cationics. The pH of the surfactant solution determines the charge exhibited by the amphoteric under alkaline conditions it behaves anionically while ki an acidic condition it has a cationic behavior. Most amphoterics are derivatives of imidazoline or betaine. Sodium lauroamphoacetate [68647-44-9] has been recommended for use ki non-eye stinging shampoos (12). Combkiations of amphoterics with cationics have provided the basis for conditioning shampoos (13). 

Many of the surfactants made from ethyleneamines contain the imidazoline stmcture or are prepared through an imidazoline intermediate. Various 2-alkyl-imidazolines and their salts prepared mainly from EDA or monoethoxylated EDA are reported to have good foaming properties (292—295). Ethyleneamine-based imida zolines are also important intermediates for surfactants used in shampoos by virtue of their mildness and good foaming characteristics. 2- Alkyl imidazolines made from DETA or monoethoxylated EDA and fatty acids or their methyl esters are the principal commercial intermediates (296—298). They are converted into shampoo surfactants commonly by reaction with one or two moles of sodium chloroacetate to yield amphoteric surfactants (299—301). The ease with which the imidazoline intermediates are hydrolyzed leads to arnidoamine-type stmctures when these derivatives are prepared under aqueous alkaline conditions. However, reaction of the imidazoline under anhydrous conditions with acryflc acid [79-10-7] to make salt-free, amphoteric products, leaves the imidazoline stmcture essentially intact. Certain polyamine derivatives also function as water-in-oil or od-in-water emulsifiers. These include the products of a reaction between DETA, TETA, or TEPA and fatty acids (302) or oxidized hydrocarbon wax (303). The amidoamine made from lauric acid [143-07-7] and DETA mono- and bis(2-ethylhexyl) phosphate is a very effective water-in-od emulsifier (304). 

Most of the amphopropionate surfactants produced are of the amphodipropionate type, 2 mol of methyl acrylate or sodium acrylate added per mole of imidazoline. Depending on the reaction conditions, 1 mol of acrylate can add to the fatty R group at the alpha carbon. Upon hydrolysis of the imidazoline, the second reacts with the liberated secondary amine to produce the beta alanine derivative. If methyl acrylate is used, the methyl ester of the amphoteric surfactant is formed. An equimolar amount of sodium hydroxide is added to effect saponification to the sodium salt of the surfactant. Methanol is formed as a by-product and it is generally left in the final product as part of the solvent system. 

Other amphoteric surfactants include the betaines derived from imidazolines, which absorb UV light and the lecithins or phosphati-dicholines, which are naturally occurring phospholipids [7]. Multifunctional surfactants associating a nonionic moiety with a charged one are considered ionic surfactants. 

The amphoteric compounds in this group originally were viewed as heterocyclic derivatives of imidazolines. 

Rieger, M. M. The structure of amphoterics derived from imidazoline. Cosmet. Toil. 99 61-67, 1984. 

Isoelectric point. Trne amphoteric snrfactants are characterized by their ability to vary their net charge, according to pH conditions. Compared to betaines, which have a permanent positive charge on the qnaternized nitrogen atom, trne amphoterics have both a carboxyl- and an amine gronp that can be protonated. Amphoterics derived from imidazoline can exist in anionic (alkaline conditions), cationic (acidic conditions), or zwitterionic form (aronnd the isoelectric point at pH 5.3). 

The most important shampoo hair conditioners are the alkylamido alkylamines. As a rule, they are complex mixtures derived from the reaction of alkyl-substituted imidazolines with chlo-roacetic acid or ethyl acrylate [8]. Similar to the acylated protein derivatives, these amphoteric surfactants exhibit detergency, are compatible with anionic detergents, and reportedly form complex salts with anionics. These complexes reportedly do not sting the eyes and are employed in baby shampoos. These amphoterics in combination with anionic detergents leave the hair conditioned after rinsing. 

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