N-Heterocyclic Carbene Functionalized Covalent Organic Framework for Transesterification of Glycerol with Dialkyl Carbonates

The development of a heterogeneous catalyst through the combination of novel carrier and powerful catalytic active sites is of particular interest. Herein, the successful integration of an N-Heterocyclic carbene (NHC) moiety into a covalent organic framework (COF) was achieved by coupling 4,4′,4′′,4′′′-(pyrene-1,3,6,8-tetrayl) tetraaniline (PyTTA) and equimolar 5,6-bis(4-formylphenyl)-1-methyl-1H-benzimidazole (IM) and 2′3′5′6′-tetrafluoro-[1,1′:4′,1′′-terphenyl]-4,4′-dicarbaldehyde (4F) followed by ionization with 1-bromobutane (C4H9Br) and then deprotonation upon addition of a base. The resulting material exhibited promising heterogeneous catalytic activity towards transesterification reaction of glycerol with dialkyl carbonate. Moreover, good recyclability granted no substantial loss of activity upon five cycles. Combination of COFs and NHCs might synergize their characteristics, thus providing more possibilities for creating new patterns of catalytic reactivity.

Benzo-Fused 1,4-Heterocycles via Dialkyl Carbonate Chemistry

A novel halogen-free synthesis of benzo-fused six-membered 1,4-heterocycles through the chemistry of dialkyl carbonates is reported. Commercially available catechol, 2-aminophenol, and 2-amino­thiophenol were reacted first with ethylene carbonate in an autoclave to give O-hydroxyethyl, N-hydroxyethyl, and S-hydroxyethyl derivatives respectively, through a BAl2 mechanism. Then 2-(2-hydroxyethoxy)phenol and 2-(2-hydroxyethylamino)phenol were cyclized in excellent yields by reaction with dimethyl carbonate (DMC) and DABCO as a bi­cyclic organic base to give the corresponding benzodioxine and benzoxazine derivative, respectively. Moreover, 2-(2-aminophenylthio)ethanol afforded the benzothiazine derivative in good yield by reaction with DMC with an excess of a strong base such as NaH. The investigation on the cyclization reaction has highlighted that several equilibria are involved leading to the formation of carbonate and carbamate intermediates through BAc2 mechanisms. Depending on the reaction conditions employed, these intermediates may undergo either kinetic-controlled ring closure by a BAl2 mechanism or by-product formation.

OPTIMASI PROSES PEMBUATAN BIODIESEL DARI ASAM LEMAK SAWIT DISTILAT (ALSD) DAN DIMETHYL CARBONATE (DMC) MENGGUNAKAN KATALIS NOVOZYM®435

Biodiesel production has rapidly grown over the last decades, and it has attracted much attention in the market as fuel that promising substitute for petroleum diesel, because its physical and chemical properties and energy content are similar to those of petroleum diesel. The main problem in producing biodiesel is its high cost which could be reduced by use of less expensive feedstock. Therefore, in this work biodiesel is synthesized by enzymatic esterification from low quality feedstock which is unrefined and much cheaper than the refined oil, such as palm fatty acid distillate (PFAD) with dialkyl carbonate using immobilized lipase (Novozym®435). Enzymatic process has certain advantages over the chemical process, as it is less energy intensive, allowing the esterification of glycerides with high free fatty acid contents (PFAD, 85-95% FFA) and no enzymatic activity loss. Methanol replaced by dialkyl carbonate, especially DMC due to esterification (methanolysis) is close to equilibrium reaction whereas using DMC the intermediate compound immediately decomposes to carbon dioxide and an alcohol, which have been investigated. Moreover, DMC are cheap, eco-friendly chemical, non-toxic properties and widely available. Factors affecting the reaction such as DMC to PFAD molar ratio, reaction temperature, reaction time and catalyst concentration were systematically analyzed by response surface methodology (RSM) with central composite design (CCD). The optimal condition is using 6:1 molar ratio of DMC to PFAD at 60 oC, for a reaction time 3h in the presence 10wt% of catalyst (based on oil weight). The results showed that synthesis of biodiesel through enzymatic esterification using PFAD suitable for biodiesel production.