Transesterification catalyst strength as observed by solution-based oxygen-17 nuclear magnetic resonance spectroscopy

Natural abundance oxygen-17 nuclear magnetic resonance spectroscopy ( 17 O-NMR) was applied to study homogeneous transesterification catalysts for fatty acid methyl ester production. Alkoxide catalysts were made with selected permutations of lithium, sodium, magnesium, and potassium hydroxides with ethanol, methanol, isopropanol, and glycerol. Pilot scale transesterification reactions of Canola oil were completed and the 17 O-NMR spectra were collected from the reaction products. The alkoxide solutions showed the downfield shifts relative to the reagent alcohol, in a linear relationship with the concentration of catalyst ion. The electron deshielding of the oxygen of the alkoxide catalyst is observed directly by 17 O-NMR, and the fastest catalyst has the largest downfield (high frequency) shift. This effect is most pronounced in potassium methoxide and less pronounced for less polar solvents such as isopropanol.