Fatty acid control mechanism, scheme

Dimerisation of monounsaturated fatty acids has been exploited to prepare monomers bearing two carboxylic functions and, after reduction, the corresponding diols [2], i.e., potential monomers for the synthesis of polyesters, polyamides, polyethers and polyurethanes incorporating long aliphatic motifs. Scheme 2.7 shows two possible mechanisms associated with this reaction (i.e., ene- or carbonation coupling), which is inevitably accompanied by further additions to give trimers and oligomers, if not carried out under finely controlled conditions. 

Sulfur in oxidation state IV can be used to produce a variety of anionic snUbnates, as depicted in Scheme 1.5. Sodium bisulfite can be used to prepare sulfonates of a,b-unsaturated acids and esters, such as those prepared from maleic anhydride. The mechanism involves Michael addition to the activated double bond by the more nucleophilic sulfur atom, and is conducted in an aqueous two-phase system where, for example, a maleate half acid ester or diester is dispersed and heated under narrowly controlled pH conditions to minimize ester hydrolysis and avoid competitive hydroxide addition to the double bond. The resulting classes of surfactants include sulfosuccinates (which are in fact carboxylate sulfonate disalt surfactants) prepared from the maleic half acid esters of fatty alcohols or alcohol ethoxylates. Diesters of maleic are sulfonated by the same type of process to produce surfactants such as the ubiquitous dioctyl sulfosuccinate (DOSS) from the diester of 2-ethylhexyl alcohol and maleic anhydride. 

---