羟基自由基与乳酸水相反应的阿累尼乌斯参数和热力学参数的测定

Determination of arrhenius and thermodynamic parameters for the aqueous reaction of the hydroxyl radical with lactic acid.

作者信息

Martin Leigh R, Mezyk Stephen P, Mincher Bruce J

机构信息

Aqueous Separations and Radiochemistry Department, Idaho National Laboratory, P.O. Box 1625, Idaho Falls, Idaho 83415-7113, USA.

出版信息

J Phys Chem A. 2009 Jan 8;113(1):141-5. doi: 10.1021/jp806290s.

DOI:10.1021/jp806290s

PMID:19067560

Abstract

Lactic acid is a major component of the TALSPEAK process planned for use in the separation of trivalent lanthanide and actinide elements. This acid acts both as a buffer and to protect the actinide complexant from radiolytic damage. However, there is little kinetic information on the reaction of water radiolysis species with lactic acid, particularly under the anticipated process conditions of aerated aqueous solution at pH approximately 3, where oxidizing reactions are expected to dominate. Here we have determined temperature-dependent reaction rate constants for the reactions of the hydroxyl radical with lactic acid and the lactate ion. For lactic acid this rate constant is given by the following equation: ln k(1) = (23.85 +/- 0.19) - (1120 +/- 54)/T, corresponding to an activation energy of 9.31 +/- 0.45 kJ mol(-1) and a room temperature reaction rate constant of (5.24 +/- 0.35) x 10(8) M(-1) s(-1) (24.0 degrees C). For the lactate ion, the temperature-dependent rate constant is given by ln k(2) = (24.83 +/- 0.14) - (1295 +/- 42)/T, for an activation energy of 10.76 +/- 0.35 kJ mol(-1) and a room temperature value of (7.77 +/- 0.50) x 10(8) M(-1) s(-1) (22.2 degrees C). These kinetic data have been combined with autotitration measurements to determine the temperature-dependent behavior of the lactic acid pK(a) value, allowing thermodynamic parameters for the acid dissociation to be calculated as DeltaH(o) = -10.75 +/- 1.77 kJ mol(-1), DeltaS(o) = -103.9 +/- 6.0 J K(-1) mol(-1) and DeltaG(o) = 20.24 +/- 2.52 kJ mol(-1) at low ionic strength.

摘要

乳酸是计划用于分离三价镧系和锕系元素的TALSPEAK流程的主要成分。这种酸既作为缓冲剂，又用于保护锕系络合剂免受辐射分解损伤。然而，关于水辐射分解产物与乳酸反应的动力学信息很少，特别是在预期的pH约为3的充气水溶液的工艺条件下，预计氧化反应占主导。在此，我们确定了羟基自由基与乳酸和乳酸根离子反应的温度依赖性反应速率常数。对于乳酸，该速率常数由以下方程给出：ln k(1) = (23.85 ± 0.19) - (1120 ± 54)/T，对应活化能为9.31 ± 0.45 kJ mol⁻¹，室温反应速率常数为(5.24 ± 0.35) × 10⁸ M⁻¹ s⁻¹(24.0℃)。对于乳酸根离子，温度依赖性速率常数由ln k(2) = (24.83 ± 0.14) - (1295 ± 42)/T给出，活化能为10.76 ± 0.35 kJ mol⁻¹，室温值为(7.77 ± 0.50) × 10⁸ M⁻¹ s⁻¹(22.2℃)。这些动力学数据已与自动滴定测量相结合，以确定乳酸pK(a)值的温度依赖性行为，从而能够计算出酸解离的热力学参数，在低离子强度下，ΔH⁰ = -10.75 ± 1.77 kJ mol⁻¹，ΔS⁰ = -103.9 ± 6.0 J K⁻¹ mol⁻¹，ΔG⁰ = 20.24 ± 2.52 kJ mol⁻¹。