Eco-conception of Highly Salt-Tolerant Alkyl Ether Carboxylate Hydrotropes with a Glyceryl Spacer.

New alkyl ether carboxylates with a glyceryl spacer instead of ethylene glycol units have been synthesised using environmentally friendly methodology. A cascade synthesis of acetalisation and hydrogenolysis was developed to obtain products containing an alkyl chain linked to a glycerol unit bearing a polar carboxylate head. These products were methylated by using trimethyl phosphate to observe the influence of a free or methoxylated alcohol on the physicochemical properties. Finally, saponification gave the carboxylate anionic group of the new hydrotropes. Studying the amphiphilicity, the tolerance to sodium and calcium ions, and the solubilising power of these bio-based ionic/nonionic hydrotropes has shown that they exhibit significantly improved application properties compared to similar petro-based hydrotropes.

Salt-tolerance of alkyl-glyceryl ether carboxylates hydrotropes and surfactants. Dramatic effect of the methylation of the glyceryl spacer.

HYPOTHESIS: The insertion of polyether spacers between the anionic head and the alkyl chain of ionic surfactants significantly improves their salt-tolerance. The aim of this work is to study whether the petro-based polyethoxy spacer can be replaced by a glyceryl ether group for high salinity applications. EXPERIMENTS: A series of amphiphilic sodium salts of alkyl glyceryl ether carboxylates are synthesized with different alkyl chain lengths from 4 to 12 and various spacers between the glyceryl and the carboxylate groups. Their aggregation behavior is studied by tensiometry and their amphiphilicities are assessed by the PIT-slope method. The dramatic effect of the methylation of the glyceryl spacer on the salt-tolerance is highlighted, and rationalized by DFT calculations and molecular dynamics. FINDINGS: In contrast to the corresponding sodium soap, n-C6H13-CO2Na, and to the non-methylated counterpart, the sodium salt of 1-pentyl-3-methyl glyceryl ether methylene carboxylate ([5.0.1]-CH2CO2Na) exhibits an excellent salt-tolerance since it remains water-soluble with NaCl or CaCl2 concentrations greater than 20 wt% at 25 °C. Amphiphiles with short alkyl chains (