Selective synthesis of a valuable unsaturated fatty alcohol via catalytic and non-catalytic liquid-phase methyl oleate reduction

The upgrading of oleyl alcohol synthesis via methyl oleate reduction using NaBH4 without H2 supply was investigated. It was possible to synthesize selectively the valuable unsaturated fatty alcohol with high yields. Non-catalytic and catalytic experiments were developed trying to improve the low final oleyl alcohol yield previously obtained. The effect of reaction temperature, methyl oleate/NaBH4 molar ratio and properties of different catalysts on final oleyl alcohol yield was analyzed. Thus, alumina-supported metal (M) catalysts (M = Fe, Ce, Mo) were synthesized by impregnation at incipient wetness. The M/Al2O3 catalysts were characterized in their chemical, textural, structural and acid-base properties using ICP, N2 physisorption, XRD and NH3 and CO2 TPD. During non-catalytic methyl oleate reduction final methyl oleate conversion and oleyl alcohol yield of 94% were obtained using a methyl oleate/NaBH4 molar ratio of 0.11 at 333 K. Catalytic activity of M/Al2O3 solids did not correlate with basic site number but increased as acid site number and ionic potential of M cations increase. This suggests that cations with high acid site number and polarizing power are the ones that promote the polarization of the ester C=O and anion [BH4]- bonds favoring de methyl oleate conversion. In addition, the reaction mechanism for fatty acid methyl ester reduction was investigated from a theoretical approach using Density Functional Theory method at B3LYP/6-31++G(d,p) computational level. Results obtained during theoretical calculations confirmed that the formation of reducing alcoxyborohydride species is energetically favored and allowed to understand the events at microscopic level involved in the reaction mechanism.