Synthesis, Surface Properties, and Hydrolysis of Chemodegradable Anionic Surfactants: Diastereomeric Sodium Carboxylates Derived from 1,3-Dioxane

Abstract

Mixtures of cis- and trans-2-n-alkyl-5-carboxy-5-methyl-1,3-dioxanes, 3a–3e, were obtained in the reaction of aliphatic aldehydes 1a–1e (from n-octanal to n-dodecanal) with 2,2-bis(hydro-xymethyl)propionic acid (DMPA), 2, carried out in boiling n-hexane or in the isomerization reaction of an appropriate cis-3a–3e. Pure trans-3a–3e were isolated from the above mixtures by selective crystallization and then converted into surface-active sodium salts, trans-4a–4e, by neutralization with sodium hydroxide or sodium methoxide. Surface properties of these surfactants, i.e., critical micelle concentration (CMC), surface excess concentration (ΓCMC), surface area demand per molecule (ACMC), effectiveness of surface tension reduction (γCMC), and standard free energy of micellization (ΔG°mic) were determined and compared with the appropriate surface properties of isomeric cis-4a–4e. It was shown that the properties of surfactants under study are dependent both on the length of a hydrophobic n-alkyl substituent at the C2 carbon atom of the 1,3-dioxane ring and on the configuration of a polar sodium carboxylate group at C5. The acids 3 undergo hydrolysis/isomerization reactions in acidic D2/d6-DMSO media. The cis isomers are hydrolyzed faster than trans isomers probably due to the steric hindrance of the axial methyl group at C5 of the latter ones.