Renewable branched-chain sulfonate surfactants by addition of sodium hydrogensulfite to alkyl oleate

Branched-chain surfactants, with unique properties that make them amenable to exclusive applications, are currently typically synthesized from petrochemically derived Guerbet alcohols. Natural oleic acid, as one of the renewable platform molecules, is attracting increasing interest for the synthesis of surfactants due to its C=C double bond and terminal hydrophilic carboxyl group. Herein, we report the synthesis of oleic acid-based branched-chain anionic surfactants with a sulfonate head group through terminal esterification of oleic acid with various alcohols (methanol, ethanol, and butanol) and subsequent sulfonation of the C=C double bond using sodium hydrogensulfite. The three resulting alkyl oleate sulfonates have been characterized by FTIR, HPLC, LC-MS, HR-MS, and NMR techniques. Their surfactant properties, including equilibrium surface tension, dynamic surface tension, foaming property, and wetting ability, have been thoroughly investigated and compared with those of methyl ester sulfonate (MES), a linear chain analogue of alkyl oleate sulfonates. The results showed that the synthesized surfactants exhibited superior defoaming capacities (foam height after 1200 s is approximately 5% of initial foam height) and wettabilities (8 s, measured by the canvas descending method), in line with expectation for branched-chain surfactants, indicating their potential as primary surfactants for industrial cleaning products.