Pivalic acid as combined buffer and scavenger for studies of cloud water chemistry with pulse radiolysis
作者:Thomas Nauser、Rolf E. Bühler
DOI:10.1039/ft9949003651
日期:——
The reactions of cloud water with transition-metal ions may be studies using pivalic acid as buffer and ˙OH scavenger. Commonly used phosphate buffers form strong complexes that may have an important effect on reaction kinetics. Low solubility products limit transition-metal ion concentrations to very low levels (micromolar). With pivalic acid as buffer, we can increase the CuII concentration typically by a factor of 340. At the same time better buffer characteristics and less complex formation is achieved. The scavenger efficiency equals that of tert-butyl alcohol.The rate data and the spectra of pivalic acid radicals have been measured in N2O-saturated solutions of pivalic acid. The acid constant was found to be 4.9 ± 0.1. The rate constants for the reaction of ˙OH with pivalic acid have been re-evaluated: k[(CH3)3CCO2–+˙OH]=(7 ± 2)× 108 dm3 mol–1 s–1 and k[(CH3)3CCO2H +˙OH]= 6.5 × 108 dm3 mol–1 s–1. The importance of including reactions like H˙+˙CH2(CH3)2CCO2H in the reaction model is shown. The rate constants for the recombination of pivalic acid radicals are: k[2˙CH2(CH3)2CCO2H]=(7 ± 1)× 108 dm3 mol–1 s–1, k[˙CH2(CH3)2CCO2H +˙CH2(CH3)2CCO2–]=(7 ± 3)× 108 dm3 mol–1 s–1 and k[2˙CH2(CH3)2CCO2–]=(3.7 ± 0.4)× 108 dm3 mol–1 s–1.
云水与过渡金属离子的反应可以使用庚酸作为缓冲剂和·OH清 scavenger进行研究。常用的磷酸盐缓冲剂形成强的络合物,这可能对反应动力学产生重要影响。低溶解度的产物将过渡金属离子的浓度限制在非常低的水平(微摩尔级)。使用庚酸作为缓冲剂,我们可以将CuII的浓度通常提高340倍。同时,获得了更好的缓冲特性和较少的络合物形成。清 scavenger的效率等于叔丁醇的效率。在N2O饱和的庚酸溶液中测量了速率数据和庚酸自由基的光谱。发现酸常数为4.9 ± 0.1。对·OH与庚酸反应的速率常数进行了重新评估:k[(CH3)3CCO2–+·OH]=(7 ± 2)× 10^8 dm³ mol⁻¹ s⁻¹ 和 k[(CH3)3CCO2H +·OH]= 6.5 × 10^8 dm³ mol⁻¹ s⁻¹。显示了在反应模型中包括像H·+·CH2(CH3)2CCO2H这样的反应的重要性。庚酸自由基重合的速率常数为:k[2·CH2(CH3)2CCO2H]=(7 ± 1)× 10^8 dm³ mol⁻¹ s⁻¹,k[·CH2(CH3)2CCO2H +·CH2(CH3)2CCO2–]=(7 ± 3)× 10^8 dm³ mol⁻¹ s⁻¹ 和 k[2·CH2(CH3)2CCO2–]=(3.7 ± 0.4)× 10^8 dm³ mol⁻¹ s⁻¹。