IFISUR   23398
INSTITUTO DE FISICA DEL SUR
Unidad Ejecutora - UE
artículos
Título:
Glycerolysis of methyl oleate on MgO: experimental and theoretical study of the reaction selectivity
Autor/es:
BELELLI, PATRICIA GABRIELA; FERRETI, CRISTIÁN; APESTEGUÍA, CARLOS; FERULLO, RICARDO MARIO; DI COSIMO, ISABEL
Revista:
JOURNAL OF CATALYSIS
Editorial:
ACADEMIC PRESS INC ELSEVIER SCIENCE
Referencias:
Lugar: Amsterdam; Año: 2015 vol. 323 p. 132 - 144
ISSN:
0021-9517
Resumen:
The liquid-phase MgO-promoted glycerolysis of methyl oleate, a fatty acid methyl ester (FAME), to give acylglycerol products was studied both, experimentally and by density functional theory (DFT). Catalytic results showed that strongly basic low coordination O2 surface sites participate in kinetically relevant steps of the glycerolysis reaction. Changes in the selectivity toward the different mono- and diglyceride isomers were investigated by varying the reaction conditions. The main product was always a-glyceryl monooleate (a-MG), a monoglyceride with the ester fragment at one of the terminal positions of the glycerol molecule; the b-MG isomer, with the ester substituted at position 2 was obtained in much lower amounts.The molecular modeling of glycerol (Gly) and FAME adsorptions as well as of the glycerolysis reaction was carried out using periodic DFT calculations and a Model of stepped MgO surface. Results indicated that FAME was more weakly adsorbed than Gly; the latter adsorbs on a coordinatively unsaturated surfaceO2 site with OAH bond breaking at position 2 of the Gly molecule, giving therefore a surface b-glyceroxide species. Calculations explained the apparent contradiction between the preferential formation of the a-MG isomer and the energetically favored dissociation of the secondary OH group of Gly that leadsto the b-glyceroxide species. They predict that the b-glyceroxide species participates in the pathways conducting to both, a- and b-MG isomers. Synthesis of a-MG occurs by CAO coupling of b-glyceroxide with FAME at one of the two primary OH groups of the b-glyceroxide species. Two transition states (TS) and a tetrahedral intermediate (TI) are involved in both, a-MG and b-MG isomer formation. However, the pathway toward b-MG is limited by the large sterical effects associated to the TI formation. Contrarily, the TI leading to a-MG is relatively easy to form.