Molecular Iodine As Catalyst For Organic Reactions

In this dissertation, the catalysis efficiency of molecular iodine for several classic organic reactions was investigated in datails.These model reactions include Knoevenagel condensation, Henry reaction, condensation of aldehyde with amine, cyanation, Michael reaction, synthesis of acetal, esterification and transesterification reaction. Meanwhile, one-pot synthesis of highly substituted imidazoles,5-unsubstituted-3,4-dihydropyrimidin-2(1H)-ones,2-amino-2-chromenes and 2,4,6-triarylpyridines was also explored. The reaction conditions such as reaction temperature,reaction time, addition of I₂, solvents were optimized.The results show that the above-mentioned reactions can be effectively promoted by using molecular iodine as catalyst. Generally, the introduction of molecular iodine can offer the model reactions with milder reaction conditions, simpler experimental procedure while higher yields.For instance, Knoevenagel condensation, Henry reaction and Micheal reaction could be catalyzed by molecular iodine with high yields at room temperature.The highest yield of 98% could be achieved for Knoevenagel condensation within 1.5 h; and 99% yield for the Henry reaction within 5 h and; while 95% yield for Micheal reaction within 5 h.In this dissertation, the catalysis efficiency of molecular iodine was further explored in some model reactions in environmentally benign medium like water or even solvent-free reaction systems. In aqueous medium, Knoevenagel condensation, Henry reaction, cyanation and synthesis of 2-amino-2-chromenes were studied as model reactions. In solvent-free system, the synthesis of highly substituted imidazoles,5-unsubstituted-3,4-dihydropyrimidin-2(1H)-ones and 2,4,6-triarylpyridines was explored.In addition, the direct oxidative conversion of aldehydes and alcohols into nitriles was achieved by using aqueous NH4OAc as a nontoxic cyanide source.NH4OAc is found to be more eco-friendly than s ammonia solution as no gaseous ammonia produces in the reaction.The recovery of molecular iodine catalyst was investigated by using PEG derived ionic liquids (PEG₂₀₀-IL, PEG₄₀₀-IL, PEG₁₀₀₀-IL, PEG₂₀₀₀-IL) and toluene co-solvent system. This co-solvent system shows interesting properties at varying temperature, i.e., heterogeneous at low temperatures and homogeneous at high temperatures (ca 80℃).By using PEG-derived ionic liquids,the molecular iodine can be effectively recovered in the model reaction such as the synthesis of acetal,esterification and transesterification reaction. The molecular iodine recovered by simple liquid-liquid extraction can be recycled several times (ca 4 times) with consistent reactivity.Finally, the immobilization of molecular iodine was explored by using modified polystyrene resins.The preliminary results indicate that these polymer-supported catalyst was not very stable for Michael reaction and difficult to recover and reuse without losing their catalysis efficiency.