Institute for Green Science, Department of Chemistry, Carnegie Mellon University , 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, United States.
Institute for the Environment, Brunel University , Halsbury Building (130), Kingston Lane, Uxbridge, Middlesex, UB8 3PH, United Kingdom.
J Am Chem Soc. 2017 Jan 18;139(2):879-887. doi: 10.1021/jacs.6b11145. Epub 2017 Jan 3.
TAML activators enable homogeneous oxidation catalysis where the catalyst and substrate (S) are ultradilute (pM-low μM) and the oxidant is very dilute (high nM-low mM). Water contamination by exceptionally persistent micropollutants (MPs), including metaldehyde (Met), provides an ideal space for determining the characteristics and utilitarian limits of this ultradilute catalysis. The low MP concentrations decrease throughout catalysis with S oxidation (k) and catalyst inactivation (k) competing for the active catalyst. The percentage of substrate converted (%Cvn) can be increased by discovering methods to increase k/k. Here we show that NaClO extends catalyst lifetime to increase the Met turnover number (TON) 3-fold compared with HO, highlighting the importance of oxidant choice as a design tool in TAML systems. Met oxidation studies (pH 7, DO, 0.01 M phosphate, 25 °C) monitored by H NMR spectroscopy show benign acetic acid as the only significant product. Analysis of TAML/NaClO treated Met solutions employing successive identical catalyst doses revealed that the processes can be modeled by the recently published relationship between the initial and final [S] (S and S, respectively), the initial [catalyst] (Fe) and k/k. Consequently, this study establishes that ΔS is proportional to S and that the %Cvn is conserved across all catalyst doses in multicatalyst-dose processes because the rate of the k process depends on [S] while that of the k process does not. A general tool for determining the Fe required to effect a desired %Cvn is presented. Examination of the dependence of TON on k/k and Fe at a fixed S indicates that for any TAML process employing Fe < 1 × 10 M, small catalyst doses are not more efficient than one large dose.
TAML 激活剂能够实现均相氧化催化，其中催化剂和底物 (S) 的浓度非常低（pM-低 μM），氧化剂的浓度也非常低（高 nM-低 mM）。水受到持久性微量污染物（MPs）的污染，包括甲缩醛（Met），这为确定这种超稀释催化的特性和实用限制提供了理想的条件。随着 S 的氧化（k）和催化剂失活（k）与活性催化剂竞争，MP 浓度在整个催化过程中逐渐降低。通过发现提高 k/k 的方法，可以提高底物的转化率（%Cvn）。在这里，我们表明 NaClO 可以延长催化剂的寿命，使 Met 的转化率（TON）相对于 HO 提高 3 倍，这突出了氧化剂选择作为 TAML 系统设计工具的重要性。通过 1 H NMR 光谱监测的 Met 氧化研究（pH 7、DO、0.01 M 磷酸盐、25°C）表明，只有温和的乙酸是唯一重要的产物。对采用 TAML/NaClO 处理的 Met 溶液进行分析，采用连续相同的催化剂剂量，结果表明可以采用最近发表的关于初始和最终[S]（分别为 S 和 S）、初始[催化剂]（Fe）和 k/k 之间的关系来对该过程进行建模。因此，本研究表明，ΔS 与 S 成正比，并且在多催化剂剂量过程中，所有催化剂剂量下的 %Cvn 都是守恒的，因为 k 过程的速率取决于[S]，而 k 过程的速率则不取决于[S]。提出了一种用于确定实现所需 %Cvn 所需的 Fe 的通用工具。在固定 S 的情况下，考察 TON 对 k/k 和 Fe 的依赖性表明，对于任何使用 Fe < 1 × 10 M 的 TAML 过程，小剂量的催化剂并不比大剂量的催化剂更有效。
