【摘要】 用硫酸钴催化反式-二水·二草酸根络铬（Ⅲ）的顺反异构化反应,当离子强度为1.5mol·L^-1、pH为3及温度分别为25、35和45℃时,发现Co²⁺浓度不大时和反应速度成直线关系。Co²⁺浓度大于0.15mol·L^-1时,25℃的反应速度大于直线关系。表明Co²⁺和CoSO₄离子对,同时具有催化作用。测得25℃时k_Co²⁺=2.13×10^-2(mol·L^-1·s)^-1,k_CoSO4=5.77×10^-3(mol·L^-1·s)^-1,并测得Co²⁺和COSO₄的活化参数分别为 △S?=-26.4和-96.2J·K^-1·mol^-1,△H?=74.9和 56.9kJ·mol^-1。△E?₂₉₈=77.4和59.4kJ·mol^-1。根据活化参数推论该反应为开环机理。更多还原

【Abstract】 The catalysis of trans-cis isomerizationof trans-diaquobis （oxalato） -chromate（Ⅲ） byCoSO₄ was investigated at ionic strength 1.5mol·L^-1, pH 3 and 25, 35 and 45℃, respe-ctively.Linear behavior is observed betweenthe rate and the concentration of Co²⁺ ionuntil ca. 0. 15 mol·L^-1, after the ratebecomes much faster. If no CoSO₄ ion pair catalysis exists,the rate constant of isomerization k_obs willhave the formk_obs=k_H2O+k_Na⁺[Na⁺] + k_H⁺ [H⁺] ++ k₍Co²⁺[Co²⁺]= k₁+ k₍Co²⁺[Co²⁺]and a linear relation between(k_obs- k₁)and[Co²⁺] should be observed over the entirerange of Co²⁺ ion concentration. Failure ofthis observation indicates that a term k_CoSO4[CoSO₄] should be added to the k_obsequation, thus the following equation shouldhold(k_ObS-k₁)/ [Co²⁺] = k₍Co²⁺ + k_CoSO4k_AI [SO₄^2-]in which k_IA stands for the constant of ionassociation of CoSO₄. By our experimentaldata,a plot of (k_obs-k₁/ [Co²⁺] vs. [SO₄^2-]is indeed linear except for the highest[SO₄^2-]values where large errors arisebecause of small values of (k_obs-k₁) and[Co²⁺]. From the intercept and slope ofthe line, the catalytic rate constants can becalculated. The catalytic rate constants thus obtainedat 25℃ are k_Co²⁺=2.13×10^-2 (mol·L^-1·s)^-1,k_CoSO4=5.77×10^-3 (mol·L^-1·s)^-1 and theactivation paramaters obtained for Co²⁺ andCoSO₄ are ΔS≠=-26.4 and -96, 2 J·K^-1.mol^-1, ΔH≠= 74. 9 and 56. 9 kJ·mol^-l, ΔE≠₂₉₃=77.4 and 59.0 kJ mol^-1, respectively,from which the ring-opening mechanism ofthe reaction is reconfirmed.更多还原