| Researches of carbon dioxide utilization have received a great deal of attention since people have become aware of the increasingly serious problem of global warming. New research on carbon dioxide utilization not only expands the choices of products made from carbon dioxide but also adds new concepts of carbon dioxide utilization including using carbon dioxide as a renewable carbon source and as a more benign reagent. The progress of this research and these new concepts will be introduced and explained in this dissertation.; In the reactions using carbon dioxide to produce formic acid, we found that ligands on the catalysts, bases, solvents, and additives affect the reaction rate tremendously. For the ligand effects, we found that 6 out of 22 active phosphine ligands were very active when an in situ catalysts prepared from [RuCl2(C6H6)]2 after 44 different phosphines ligands were tested. We also found that there is no correlation between the basicity of monophosphines (PR3) and the activity of the catalysts formed from them. However, weakly basic diphosphines formed highly active catalysts only if their bite angles are small, while more strongly basic diphosphines show the opposite trend. We also discovered that a trace amount of alcohol cocatalyst and a stoichiometric amount of base are required. Acidic, nonbulky alcohols and triflic acid increase the rate of hydrogenation an order of magnitude above that which can be obtained with traditionally used methanol or water. Similarly, the use of DBU rather than NEt3 increases the rate of reaction by an order of magnitude. Turnover frequencies up to 95,000 h-1 have now been obtained.; In the study of tetraalkylureas made from dialkylamines with CO 2, we found the reaction can be performed at 60°C. This reaction, which requires CCl4, is weakly promoted by DMAN or PPh3 and is not promoted by a Pd catalyst. A two-step procedure, in which dialkylammonium dialkylcarbamate is produced in situ and then reacts with CCl4 and free dialkylamine, gives greater yields of urea than the yields gives by a simple single-stage procedure. In addition to our finding about the tetraalkylureas, we also found the reason why formanilide and carbanalide cannot be made from the catalytic hydrogenation of CO2 in the presence of aniline. Now, formanilide can be prepared from CO2, H 2 and aniline with the use of 1,8-diazabicyclo[5.4.0]undec-7-ene. Omission of the H2 reductant causes the selectivity to switch to the production of carbanilide. |
