Synthesis of bifunctional monomers via homometathesis of fatty acid derivatives

Thermoplastic elastomers consist of two molecular regions, an amorphous region for elastic and a harder crystalline section for thermoplastic properties. Long-chained bifunctional compounds, products of the conversion of fatty acids, can serve as “soft”, amorphous monomer. The synthesis of bifunctional monomers from oleic acid and their derivatives for the production of polymers based on renewable resources is thus useful in the field of thermoplastic elastomers.
Organo-metal-catalyzed metathesis [1] of C18-compounds, based on oleic acid [2], oleic acid esters [3, 4] and other readily available educts from the tenside industry such as oleyl alcohol [5], oleic amide and amines as feedstock can supply the necessary bifunctional monomers for polycondensation. The metathesis of oleic acid provides two olefins, octadec-9-ene and octadec-9-ene-1,18-dicarboxylic acid, both C18 compounds. The homometathesis of oleic acid and derivatives therefore is an interesting way to synthesize ,-functionalized fatty acid compounds.
To be applied later in industry, the production of these monomers must be scaled up now. Ruthenium compounds for metathesis belong to a class of extremely efficient catalysts, tolerant to many functional groups. Technical grade educts may provide catalyst poisoning effects. Especially nitrogen-containing compounds present many problems due to their basicity. We report the metathetic synthesis of bifunctional products, based on nitrogen based derivatives. Ruthenium-based homometathesis of oleic acid esters, oleyl alcohol, oleic acid amides and oleyl amines have been conducted. For esters and oleyl alcohol, maximum conversion could be achieved, even with technical grade educts without further pretreatment. Even solvent-free synthesis at low catalyst loadings was possible. The C18-diester was obtained via thin film evaporation, the diol was obtained via precipitation and recrystallization.
Oleyl amine itself could not be converted, but protected amines, like oleyl amides or oleyl n-alkyl-amines can be converted. The metathetical conversion of amides provide a lower yield in bifunctional compounds compared to diester and diol, but is nevertheless interesting, because the diamide precipitates during reaction and is easily isolized via centrifugation and recrystallization.

References:
1. Grubbs, R.H., Handbook of Metathesis, ed. R.H. Grubbs. Vol. 1-3. 2003, Weinheim: Wiley-CH. 204.
2. Foglia, T.A., H.L. Ngo, and K. Jones, Metathesis of unsaturated fatty acids: Synthesis of long-chain unsaturated-alpha,omega-dicarboxylic acids. Journal of the American Oil Chemists Society, 2006. 83(7): p. 629-634.
3. Boelhouwer, C. and J.C. Mol, Metathesis Reactions of Fatty-Acid Esters. Progress in Lipid Research, 1985. 24(3): p. 243-267.
4. Van Dam, P.B., C. Boelhouwer, and M.C. Mittelmeijer, Metathesis of Unsaturated Fatty-Acid Esters by a Homogeneous Tungsten Hexachloride-Tetramethyltin Catalyst. Journal of the Chemical Society-Chemical Communications, 1972(22): p. 1221-1222.
5. Brändli, C. and T.R. Ward, Libraries via Metathesis of Internal Olefins. Helvetica Chimica Acta, 1998. 81(9): p. 1616-1621.