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

Abstract

In 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.

Synthesis and Monolayer Behaviors of Succinic Acid-Type Gemini Surfactants Containing Semifluoroalkyl Groups

“…In the case of the hydrocarbon geminis dl-and meso-C11 , although the values of A L were same for both isomers, dl-and meso-C11 exhibited completely different π-A isotherms 16 . That is, as shown in Fig.…”

“…In our previous work on dl-and meso-C11 16 , it was concluded that the two hydrophobic alkyl groups were in an almost upright orientation, with the hydrophobic and hydrophilic groups set in an eclipsed conformation across the carbon-carbon bond of the gemini spacer. In the meso-isomer, the two hydrophobic alkyl chains were parallel to each other across the carbon-carbon bond of the gemini spacer, while those of the dl-isomer were set in a skewed position.…”

“…In this work, 2,3-bis semifluoroalkyl succinic acids were the synthetic targets. In our previous work 16 , we referred to Quermann et al 22 , and dl-and meso-2,3-bis undecyl succinic acid geminis were successfully synthesized by the oxidative coupling of enolates of tridecanoic acid methyl and tert-butyl esters using copper II bromide. Interestingly, in the case of tert-butyl ester, Claisen condensation did not occur due to steric hindrance, and tert-butyl diesters were smoothly converted to their carboxylic acids by treatment with CF 3 COOH.…”

“…Concurrently, we also developed all-hydrocarbon geminis having COOH as hydrophilic head groups, including succinic acid-type 15,16 , adipic acid-type, and suberic acid-type gemini surfactants 17 . Succinic acid-type geminis were synthesized by the oxidative coupling of enolates of fatty acid tert-butyl esters using copper II bromide and subsequent treatment with CF 3 COOH, and the influence of the stereochemistry dl-and meso-of the succinic acid geminis on their monolayer behaviors at the air-water interface was explored by investigating the surface pressure-area π-A isotherms, the compression modulus of monolayers E G , and by Brewster angle microscopy BAM 16 .…”

Novel Synthesis of Anionic Gemini Surfactants from 1, 4-Diol as a Key Block Material

“…Previously, we have reported the synthesis of 2,3-bis undecyl succinic acid, an all-hydrocarbon gemini. This gemini is formed by having two vicinal COOH head groups attached directly to the gemini platform by the interconversion of an OH group of corynomicolic acid to a COOH group 27,31 . Moreover, the effect of stereochemistry mesoand dl-of the two COOH groups of the succinic acid gemini surfactant on its properties was studied.…”