Application Of Modern Green Synthetic Technique In Some Condensation Reations

Green chemistry (also known as Environmentally Friendly Chemistry or Clean Chemistry), guided by the environmental awareness, is to decrease even avoid the negative influences on the environment during the research and design of chemical process and chemicals. The technology developed on the basis of green chemistry is called green chemical technology or cleaning technology in production. The chemical reaction and its product based on green chemistry research have the following characteristics:firstly, both the reaction conditions and the materials should be non-toxic; secondly, the reactions should be highly effective with higher chemical selectivity but fewer by-products, or we say these reactions should be atom-economical; thirdly, the products, the materials and the technique should be environmentally friendly. To sum up, green chemistry can be regarded as the chemistry with maturely high level.With the fast growth of organic chemistry, new organic synthetic techniques come to the fore. Studies related with green chemistry in organic chemistry mainly focus on the following aspects:(1) organic synthesis of non-conventional solvent (such as water, ionic liquid, supercritical fluid); (2) Phase Transfer Catalysis; (3) solvent free organic synthesis; (4)organic synthesis stimulated by microwave; (5) Multicomponent Reaction. To be specific, this thesis is a broader study about the feasibility of several kinds of condensation reaction with modern green organic synthetic methods. Main contents and results are as follows:1. We have developed an environmentally friendly, economic and efficient synthetic protocol for the preparation of bis(indolyl)methanes or dipyrromethanes using H2SO4·SiO2 under solvent-free conditions at room temperature. The short reaction procedure and reusability of the catalyst make this method one of the most efficient methods for the synthesis of these two classes of compounds.2. The Knoevenagel and Aldol condensations of aromatic aldehydes with unmodified acetone or acidic methylene compounds proceeded efficiently in pure water in the presence of L-lysine at room temperature. This green catalytic system could be reused, and it provides a green and mild synthetic method for the preparation of these two classes of compounds. We also find that with no addition of catalyst the condensation reaction between aldehydes and 5,5-dimethyl-1,3-cyclohexanedione proceeded efficiently in hot water, which is efficient for the synthesis of xanthenediones and their ring-opening derivatives. The main advantages of this method include high yields, simple experimental procedure, no addition of toxic organic solvents or metal ions, which in line with the tenets of green chemistry.3. A novel pyrazole synthesis approach has been developed by using Br(?)nsted acidic ionic liquid BMImHS04, which acts as dual solvent-catalyst in promoting the condensation of hydrazines with various 1,3-dicarbonyl compounds at room temperature. In addition, at room temperature the ionic liquid l-butyl-3-methylimidazonium tetrafluoroborate [bmim] BF4 was used as another green recyclable alternatives to volatile organic solvents for the condensation between aldehydes and 5,5-dimethy1-1,3-cyclohexanedione in the presence of L-histidine. This is an efficient and green approach for the synthesis of 2,2'-arylmethylene bis(3-hydroxy-5,5-dimethylcyclohex-2-enone).4. We developed a very clean, simple and efficient method for the one-pot multi-component reactions of aromatic aldehydes with indoles and dimedone to obtain the unsymmetrical indole-substituted methane derivatives which are a new class of compounds. The main advantages of this method include high yields, short reaction times, no addition of catalyst or solvent, as well as simple work-up.