Synthesis of Succinic Gemini Surfactants and the Effect of Stereochemistry on Their Monolayer Behaviors

Abstract

AbstractIn this work, succinic gemini surfactants, dl‐ and meso‐2,3‐bis(alkyl)succinic acids (alkyl: C6H13–C13H27), were successfully synthesized by oxidative coupling of enolates of fatty acid tert‐butyl esters with copper(II) bromide followed by treatment with CF3COOH. Focusing on the influence of stereochemistry (dl‐ and meso‐) of succinic geminis, their monolayer behaviors at the air–water interface were explored using surface pressure–area (Π–A) isotherms, the compression modulus of monolayers (εs), and Brewster angle microscope (BAM) analysis. meso‐2,3‐Bis(undecyl)succinic acid showed a unique isotherm where the surface pressure drastically decreased at A = ~0.56 nm2 (Π = 21.9 mN m−1) regardless of compression rates and subphase temperatures, while dl‐isomer showed the common isotherm of gas → liquid‐expanded → liquid‐condensed phase transitions. BAM analysis on meso‐2,3‐bis(undecyl)succinic acid films at the air–water interface showed that small islands of aggregates appear just after the maximum pressure (A = ~0.56 nm2), and on further compression needle‐shaped assemblies appear that can grow in size. It was reasonably concluded that hydrophobic interactions can operate more effectively in meso‐isomers than in dl‐isomers, and that meso‐molecules can “jump up” to cause a transition from monolayer to bilayer. This is the first finding of the “jumping‐up” phenomenon of gemini surfactants having meso‐stereochemistry.