铱（III）离子催化铈（IV）离子氧化异丁醇的反应动力学及机理

在酸性介质中用氧化还原滴定法研究了铈（IV）离子在痕量铱（III）离子催化作用下,于25～40 ℃区间氧化异丁醇（BA）的反应动力学.结果表明反应对铈（IV）离子为一级,对异丁醇的表观反应级数为正分数.准一级速率常数kobs随H＋]及催化剂Ir(Ⅲ)]增加而增大,随HSO4-]增加而减小.在氮气保护下,反应不能引发丙烯酰胺聚合,说明在反应中没有自由基产生.提出了催化剂、底物和氧化剂间生成双核加合物的反应机理,通过kobs与HSO4-的依赖关系,找到本反应体系的动力学活性物种是Ce(SO4)2＋,并计算出平衡常数、速控步骤的速率常数及相应的活化参数.

Kinetics and Mechanism of Iridium(Ⅲ) Catalyzed Oxidation of Isobutyl Alcohol by Cerium(Ⅳ) in Aqueous Sulphuric Acid Medium

The kinetics of iridium(III) catalyzed oxidation of isobutyl alcohol by cerium(III) in aqueous sulphuric acid medium has been investigated by titrimetric technique in the temperature range of 25～40 ℃.The reaction order of Ce(IV)] was found to be unity and that in isobutyl alcohol to be positive fractional. It was found that the pseudo first order ((CH3)2CHCH2OH] >> Ce(IV)]) rate constants kobs increases with the increase of Ir(III)] and H＋],but decreases with the increase of HSO4-].Under the protection of nitrogen the reaction system does not induce polymerization of acrylamide indicating no generation of free radicals. Formatoin of a dinuclear complex involving the oxidant, catalyst and the substrate before the rate-determining step has been proposed in the reaction mechanism, and the rate equation derived from the mechanism can explain all experimental observations. From the hydrogensulphate dependence, Ce(SO4)2＋ has been found as the kinetically active species. The pre-equilibrium constants, rate constants of the rate-determining step together with the parameters were evaluated.