Heterogeneous catalysis for valorization of vegetable oils via metathesis reactions

ANDRÉS F. TRASARTI; DARÍO J. SEGOBIA; CARLOS R. APESTEGUÍA

Beijing

Congreso; The 16th International Congress on Catalysis; 2016

International Asociation of Catalysis Societies

The metathesis of unsaturated fatty acid methyl esters (FAME) to obtain value-added chemical and polymer intermediates is a field of increasing interest in green chemistry and oleochemistry industry. Homogeneous catalysts have been successfully employed for converting unsaturated fatty acids and oils via metathesis reactions especially using Grubbs? Ru complexes and second generation ruthenium Hoveyda-Grubbs (HG) catalysts that are remarkably tolerant to the presence of moisture and oxygen. However, the industrial application of homogeneous olefin metathesis catalysts is hampered by the expensive catalyst separation processes needed to obtain high-purity chemicals and the Contamination of products by Ru catalyst residues that are difficult to eliminate. This situation turns clearly attractive the development of active and stable immobilized supported complexes that would allow straightforward catalyst separation. However, very few papers deal with the use of supported H-G catalysts for the metathesis of functionalized substrates1,2. The cross- metathesis of FAME with simple non-functionalized alkenes like ethylene and 2-butene has been traditionally studied to produce less abundant medium-chain fatty acid esters that are valuable intermediates in fine chemistry. Here, we investigate the cross-metathesis of methyl oleate (MO) with 1-hexene (C6) on silica-supported Hoveyda-Grubbs complexes (Figure 1). The reaction produces1-decene (1-DC), methyl 9-tetradecenoate (9-TDE), 5-tetradecene (5-TDC) and methyl 9-decenoate (9-DCE). 9-DCE is used in the synthesis of fragrances and prostaglandins while 9-TDE is a valuable pheromone precursor. The selective synthesis of MO/C6 cross-metathesis products on HG/SiO2 catalysts is improved by using high 1-hexene/methyl oleate ratios. The increase of 1-hexene concentration shifts the reaction equilibrium to high MO conversion equilibrium values and concomitantly suppresses the MO self-metathesis competitive reaction. Thus, the yield and selectivity to MO/C6 cross-metathesis products reported here on HG(3.36%)/SiO2 for a RC6/MO ratio of seven are 87% and 93%, respectively. The product distribution also depends on RC6/MO ratio; in fact, the yield to terminal olefins (9-decenoate, 1-decene) increases from 28% (RC6/MO = 1) to 62% (RC6/MO = 7) while that of internal olefins (9-tetradecenoate, 5-tetradecene) does not change significantly.