Synthesis and Surface Properties of a Novel Sodium 3-(3-Alkyloxy-3-oxopropoxy)-3-oxopropane-1-sulfonate at the Air–Water Interface

Abstract

The present paper describes the synthesis and evaluation of surface properties of a novel series of anionic surfactant, namely sodium 3-(3-alkyloxy-3-oxopropoxy)-3-oxopropane-1-sulfonate with varying alkyl chain length (C8–C16). Synthesis involves initial formation of the 3-alkyloxy-3-oxopropyl acrylate along with fatty acrylate during the direct esterification of fatty alcohol with acrylic acid in the presence of 0.5 % NaHSO₄ at 110 °C followed by sulfonation of the terminal double bond of the 3-alkyloxy-3-oxopropyl acrylate. Synthesized compounds were evaluated for surface and thermodynamic properties such as critical micelle concentration (CMC), surface tension at CMC (γ_cmc), efficiency of surface adsorption (pC₂₀), surface excess (Γ_max), minimum area per molecule at the air–water interface (A _min), free energy of adsorption (∆G°_ads), free energy of micellization (∆G°_mic), wetting time, emulsifying properties, foaming power and calcium tolerance. Effect of chain length on CMC follows the classic trend, i.e. decrease in CMC with the increase in alkyl chain length. High pC₂₀ (>3) value indicates higher hydrophobic character of the surfactant. These surfactants showed very poor wetting time and calcium tolerance, but exhibited good emulsion stability and excellent foamability. Foaming power and foam stability of C14-sulfonate were found to be the best among the studied compounds. Foam stability of C14-sulfonate was also studied at different concentrations over time and excellent foam stability was obtained at a concentration of 0.075 %. Thus this novel class of surfactant may find applications as foam boosters in combination with other suitable surfactants.