Red gypsum catalyzed alcoholysis of urea with α-D-mannopyranose to carbonate compound (2,3-O-carbonyl-α-D- mannopyranose) / Anisah Sajidah Haji Saud

Faculty of Industrial Sciences and Technology

Thesis (Master of Science in Industrial Chemistry) -- Universiti Malaysia Pahang – 2017

Bibliography : p. 78-90

Sugar carbonate has been in an ever-increasing demand from researchers since it has high potential to be used in various applications either direct or indirect uses. For instance, it is used as polar aprotic solvent due to their polarity, viscosity, low toxicity and high degradability. The only existing method to synthesize sugar carbonate that involved hazardous and toxic route through phosgenation process and excess pyridine has to be neutralized. Besides, the yield of sugar carbonate was found to be low, i.e. 5%. Therefore, a safer and environmentally friendly route through utilization of urea as carbonyl source was used for the first time to produce analogue sugar carbonate. The reaction was carried out under solvent–free condition in the presence of red gypsum catalyst originated from TiO2 manufacturing plant. The characteristic of red gypsum is tuned by pretreatment at different calcination temperature. Then, catalysts were characterized by using X-ray diffraction (XRD), Thermogravimetric analysis (TGA), N2 physisorption, Field Emission Scanning Microscopy/Energy Dispersive X-ray Analysis (FESEM-EDX), FTIR, and Hammett test to obtain the catalyst structure-activity relationship. Tunable physicochemical properties of red gypsum after calcination pretreatment contributed to the variation of catalytic activity toward 2,3-O-Carbonyl-α-D-mannopyranose formation from α-D-mannopyranose. The best catalytic activity obtained for calcined red gypsum consisting β-CaSO4 (RG150) phase where it produced 62.7% conversion of D-mannose, 74.3% selectivity and 46.6% yield of 2,3-O-Carbonyl-α-D-mannopyranose, respectively. However, γ-CaSO4 (RG800) was proven to be stable, easily recoverable and reusable for subsequent cycles of reaction. The effect of the element contained in red gypsum to the yield of 2,3-O-Carbonyl-α-D-mannopyranose production is reported to be high for CaSO4 and CaO since the elements are dominantly present in red gypsum while calcium ion acts as a weak Lewis acid in the catalytic reaction. Besides, the physico-chemical properties of spent catalyst were similarly characterized through XRD, FTIR and Hammett test analysis. The presence of 2,3-O-Carbonyl-α-D-mannopyranose was confirmed by GC-FID, 13C NMR and FTIR analysis. Then, the general mechanistic pathway is proposed. Besides, the ability of sugar carbonate as a fuel additive has been confirmed through engine testing where it gave a good performance on exhaust gas temperature and lubricant oil temperature compared to the commercial gasoline. In concise, new catalytic system through alcoholysis of urea for the synthesis of sugar carbonate (2,3-O-Carbonyl-α-D-mannopyranose) was successfully developed using environmentally friendly approach. The knowledge gained will open up the possibility of utilizing abundantly available carbohydrate feedstock for wealth creation.