CI~-+CH_3I反应的溶剂效应机理研究

本研究用集团结构适应性理论探讨了Cl~-+CH_3I反应在十一种质子溶剂和极性非质子溶剂中的溶剂效应机理。实验表明,亲核试剂Cl~-越游离,反应速率就越大。按集团结构适应性理论,一个良好的溶剂应同时具备下述两种集团结构:(1)强负电集团,以便栓住正离子M~+,使Cl~-游离;(2)带有一定量的正电荷的正电集团,而且电荷又较分散,这有助于Cl~-从M~+的束缚中解脱出来,使Cl~-更游离。如DMF和DMSO等极性非质子溶剂就是具有上述两种集团结构的优良溶剂。若溶剂正电集团过强或正电荷高度集中,则正电集团又抑制了Cl~-的进攻能力。因此能与Cl~-形成氢键的质子溶剂是不良溶剂。

A Study on Solvent Effect Mechanism for Reaction Between Cl- and CH_3I

The solvent effects of the reaction CH3I+Cl- on 11 solvents have been investigated with the help of the adaptability theory of group structure. It has been shown that a good solvent for this reaction should possess the following required group structures : (1) strong negative group to attract cation M+,to make Cl- freely ionized, (2) positive group with moderate positive and dispersed charge to accelerate the separation of Cl- ion from M+.DMF and DMSO are good solvents with the above group structures. If the positive charge of group is too strong or highly centred,the positive charged group will hinder the attacking ability of Cl- ion toward CH3I. Those solvents with proton capable of forming hydrgen bond are not adaptable to this reaction.