Preparation And Transesterification Characterization Of Feruloyl Glycerols

Feruloyl glycerols (FGs), the water-soluble glycerol derivatives of Ferulic acid (FA), canbe used as natural organic ultraviolet filters and antioxidants in the fine chemical, food,pharmaceuticals and drug industry. In the paper, selective synthesis, preparation, andtransesterification characteristics of FGs were studied.In [BMIM]PF6, the enzymatic transesterification of ethyl ferulate (EF) and glycerol toprepare FGs was investigated. FGs are a water-soluble mixture of feruloyl glycerol (FG) anddiferuloyl glycerol (DFG). The effect of various reaction parameters on the performance andthe selectivity of the biocatalytic process in [BMIM]PF6was also studied. Response surfacemethodology (RSM) was also used to establish the models of EF conversion and yields of FGand DFG, and the RSM models were verified by the good agreement between theexperimental and the predicted values. The maximum EF conversion (98.26±1.05％) and FGyield (63.72±1.26％) or maximum EF conversion (99.24±0.61％) and DFG yield (78.80±2.09％) were obtained. The activation energies (Ea) of the transesterification to form FG and DFGand the hydrolysis to form FA were calculated as40.16,31.43and85.38kJ/mol, respectively,based on Arrhenius law. The reaction kinetics agreed with the Ping-Pong Bi-Bi mechanismwith the inhibition of EF and glycerol, and Vmax, KMA, KMB, KiA, and KiBwere12.01mol/(L·min),0.23mol/L,0.42mol/L,1.20mol/L and0.48mol/L, respectively. Theactivation of immobilized Novozym435can be maintained in the [BMIM]PF6, and[BMIM]PF6can be used for four times without obvious loss of activity and structure change.Selective separation of FG from [BMIM]PF6solution of transesterification products ofEF with glycerol was investigated. The effect of different extractants (water, acetic acid,ethanol,20%ethanol,40%ethanol, isopropanol and chloroform) and extraction conditions onthe selective separation of FG were also studied. Results showed that high extraction yield(98.23±1.09%) and relative content (94.50±1.59%) of FG in the extracts were achieved from[BMIM]PF6solution under following conditions: extraction time6min, centrifugation time6min, relative centrifugation force1795g, neutral deionized water as extractant, volume ratio 0.5, and extraction8times. The extraction thermodynamics showed that the extraction of FGwas an exothermic process, and the hydrophilic interaction is the main driving force for theselective separation of FG. Notably, the isolated FG exhibited good UV adsorbing propertiesat280–360nm with a λmax325nm.Novozym435catalyzed the transesterification of FG with gyceryl monooleate (GMO)and glyceryl distearate(GDS) were studied, respectively. Results showed that, the effect ofkinds and the structures of ionic liquids on the transesterification and reaction selectivity wereobvious, and hydropholic ionic liquids with long carbon chain favor the transesterification.Raising temperature and high enzyme load favored FG conversion and FAGs formation. TheEa of the enzymatic transesterification of FG with GMO for FG conversion, transesterificationto form FAGs, and hydrolysis to form DFG were calculated as30.87,37.16and21.45kJ/mol,respectively. The Ea of the enzymatic transesterification of FG with GDS for FG conversion,transesterification to form FAGs, and hydrolysis to form DFG were calculated as74.93,92.87and61.85kJ/mol, respectively, based on Arrhenius law. The effect of feruloyl acceptors on thetransesterification was significant. And the transesterification of FG agreed with thePing-Pong Bi-Bi mechanism, and the reaction steps of FG with different feruloyl acceptorswere also given.Transesterifications of EF with glycerol to synthesize FG were also performed using[BSO3HMIM]TS,[PSO3HMIM]TS,[BSO3HMIM]OTF,[BSO3HMIM]HSO4,[HMIM]HSO4,[BMIM]OH,[BMIM]FeCl4,[BMIM]FeCl4, H2SO4, and p-toluene sulfonic acid as catalysts,respectively. High EF conversion (98.01±1.52%) and reaction selectivity for FG(90.47±2.11%) were obtained using [BSO3HMIM]TS as catalyst under optimized condition:[BSO3HMIM]TS load13.92%(relative to all substrates), glycerol/EF molar ratio12.88:1,reaction temperature79.4°C, reaction time11.19h. The Ea of the transesterification was65.91kJ/mol. And the hydrogen protons nucleophilic catalysis mechanism was speculated.