Abstract
Surfactants in commercial products commonly contain catanionic mixtures thus many studies of aqueous surfactant mixtures have been carried out. However, hardly any studies have been dedicated to pure catanionic surfactants often termed salt-free catanionic surfactants. One of the difficulties is in acquirement of samples with required purity due to difficult separation of these compounds from inorganic salts. In this work we present an alternative method of synthesis using dimethyl carbonate as the alkylating agent in order to obtain alkyl trimethylammonium alkanecarboxylates with medium alkyl chain lengths (6-10).
Highlights
Along the studies of non-ionic and ionic surfactants in their pure form as well as in binary aqueous solutions, significant focus has been dedicated to aqueous mixtures of cationic and anionic surfactants – catanionic mixtures
An interesting group of catanionic surfactants are salt-free catanionics, where often the challenge of preparing these surfactants in their pure form is the removal of all inorganic salts upon mixing the parent cation and anion salts
In this work we present two synthetic procedures to prepare alkyltrimethylammonium alkanecarboxylate catanionic surfactants (Figure 1)
Summary
Commercial surfactants are commonly a mixture of cationic, anionic and non-ionic surfactants due to their enhanced performance as mixtures.[1,2] along the studies of non-ionic and ionic surfactants in their pure form as well as in binary aqueous solutions, significant focus has been dedicated to aqueous mixtures of cationic and anionic surfactants – catanionic mixtures. Many surfactants, especially those interesting for application, are soluble in both, organic and aqueous media This limits the separation techniques to ion-exchange columns or the precipitation of silver halides from water solutions. Jiang et al presented a synthetic procedure for the preparation of salt-free quaternary ammonium carboxylates using dimethyl carbonate (DMC) as alkylating agent of appropriate tertiary amines, with one or two alkyl chains exceeding 12 carbon atoms and a short-chain carboxylate anion (acetate, propionate, lactate).[8] They expanded the scope to long-chain catanionic surfactants in the follow-up papers, namely tetradecyltrimethylammonium alkanecarboxylates (hexanoate, octanoate, decanoate, dodecanoate, tetradecanoate)[9] and alkyl (decyl, dodecyl, tetradecyl, hexadecyl, octadecyl) trimethylammonium decanoates.[10] DMC represents an attractive eco-friendly alternative to methyl halides.[11]. We compare the thermal properties of products obtained by both procedures
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