| dc.description.abstract | Polyoxometalate metal-organic fragments are molecular complexes that combine metal ions with organic ligands within the same structure. These complexes integrate the properties of both polyoxometalates, which are inorganic clusters of transition metal ions and oxide ions, and organic molecules, which provide additional functionality and structural diversity. In this study, cobalt based polyoxometalate metal organic frameworks (POM-MOFs) were synthesized using the hydrothermal process by mixing appropriate amounts of selenium as the heteroatom, tungstate, cobalt (II) and glutaric acid and phthalic acid as the organic ligands. The cobalt based POM-MOFs were characterized using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDX), transmission electron microscopy (TEM), and powdered X-ray diffraction (PXRD). The POM-MOFs were utilized in the synthesis of carbamate from alcohols and amines in the presence of carbon dioxide as the carbonyl source. The catalyzed reaction was carried out in a high pressure stainless steel autoclave in one-pot set up without need for isolation of the reaction intermediates. Determination of the optimal reaction parameters such as temperature, reaction time, CO2 pressure and catalyst load was done using the central composite design (CCD) of response surface methodology (RSM). The optimal reaction conditions were found to be temperature (140oC), catalyst load (0.05 g), CO2 pressure (20 bars) and reaction time (16 h). The carbamates from the reaction of CO2, alcohol and amines were identified using gas chromatography mass spectrometry (GC-MS) and quantified using gas chromatography flame ionization detector (GC-FID). Under reaction conditions, several carbamates were synthesized using a combination of amines like butylamine, cyclohexylamine and aniline, with alcohols such as methanol, butanol, propan-2-ol and hexanol in the presence of CO2 and a co-catalyst tetrabutylammonium bromide (0.01 g). In this respect, hexyl-N-cyclohexylcarbamate was formed from hexanol and cyclohexylamine with 85.2% yield and 97.2% selectivity and amine conversion of 87.6%. While butyl-N-butylcarbamate was obtained in 76.4% yield and 97.8% selectivity at amine conversion of 79.8%. Other carbamates were also produced in good yields in the range 57.6 – 76.4% and excellent selectivity (81.4-95.7%). The cobalt based POM-MOF catalysts could be recovered at the end of the reaction and reused without significant loss in activity up to three cycles. | en_US |
