Acyl Migration Kinetics of 2‐Monoacylglycerols from Soybean Oil via ¹H NMR

Abstract

The acyl migration kinetics of neat 2-monoacylglycerol (2-MAG) to form 1-MAG was determined using 1 H NMR spectroscopy to monitor the b-proton integration ratios of the two species over time. 2-MAG was synthesized by the Novozym 435-catalyzed alcoholysis of soybean oil and isolated by solvent extraction or molecular distillation at a mole fraction (X 2-MAG ) of 0.94 relative to total MAG. The kinetics parameters of the neat 2-MAG acyl migration were investigated over the temperature range of 23-80°C. The 2-MAG mol fraction remained unchanged at 23°C over the course of 168 h and reached an equilibrium of X 2-MAG = 0.09 at only 80°C. Modeling of the kinetics data revealed a 2-MAG half life (t 1/2 ) of 3,500 and 22.8 h at 23 and 80°C, respectively, with an activation energy of 79.0 ± 6.5 kJ mol -1 . The use of 1 H NMR spectroscopy proved an expedient method for monitoring the acyl migration in 2-MAG compared to other reported methods (e.g. GC, HPLC, and 13 C-NMR spectroscopy), requiring no sample manipulation and minimizing the deleterious effects of high temperatures and solvent exposure.

Continuous lipase-catalyzed production of esters from crude high-oleic sunflower oil

“…MAGs reach an equilibrium resulting in a sn2-MAG:sn1-MAG ratio of $1:9, while long-chain DAGs typically display a $1:2 ratio of sn1(3),2-DAG to sn1,3-DAG at equilibrium (Compton et al, 2007;Laszlo et al, 2008). It has been demonstrated that acid and base impurities, and enzymatic support carrying charges catalyze acyl-migration (Fureby et al, 1996).…”

“…In our work, the sn2-MAG produced are not converted by this mechanism, suggesting that the reaction media and enzymatic supports do not offer ideal conditions for acyl migration (dry medium, non-water-miscible alcohols). Compton et al (2007) and Laszlo et al (2008) demonstrated that at 40°C and in the absence of catalyzing agent, the acyl-migration is relatively slow: only 20% conversion of sn2-MAG into sn1(3)-MAG and sn1 (3),2-DAG into sn1,3-DAG were reached in $120 and 200 h respectively. Acyl migration was accelerated at 60°C, and 20% conversion was attained in 24 h for MAG and $30 h for DAG.…”

“…Novozym 435 was demonstrated by many authors (Criado et al, 2007;Hernandez-Martin and Otero, 2008) to be a non-regiospecific lipase even if there is some exceptions especially at high ethanol/ TAG molar ratios (Irimescu et al, 2002;Compton et al, 2007). This biocatalyst was able to catalyze the transesterification of fatty acid both on sn1(3) and sn2 glycerol positions.…”

Application of Taguchi design to produce polyols based on castor oil derivatives with diethylene glycol

“…The other CH2 groups from the DEG structure generate a group of poorly resolved signals in the range of 3.5-3.75 ppm, restricting their use in quantitative analysis. Compton showed that the 1H NMR spectrum is a useful tool to quantify MAG and DAG 23 . The remaining acylglycerols in the DEG ester products, such as MAG and DAG, showed signals near 3.9, 4.05 and 4.09 ppm, while TAG showed a signal near 5.23 ppm.…”

A novel method for the synthesis of symmetrical triacylglycerols by enzymatic transesterification

“…In this study, the low acyl migration rate was contributed to the low reaction temperature. It has been reported that rate constants of 2-MAGs in a solventfree system at 23 and 60°C are 0.00018 and 0.00752 h À1 , respectively (Compton et al, 2007). Thus, the reaction temperature dramatically affects the acyl migration rate.…”