In an effort to advance the understanding of multiamine based CO₂ capture process absorbents, we report here the determination of the kinetic and equilibrium constants for a simple linear diamine N,N-dimethylethylenediamine (DMEDA) via stopped-flow spectrophotometric kinetic measurements and ¹H/¹³C NMR titrations at 25.0 °C. From the kinetic data, the formation of monocarbamic acid (DMEDACOOH) from the reaction of DMEDA with CO₂(aq) is the dominant reaction at high pH > 9.0 (k₇ = 6.99 × 10³ M^–1·s^–1). Below this pH, the formation of protonated monocarbamic acid (DMEDACOOH₂) via the pathway involving DMEDAH⁺ and CO₂(aq) becomes active and contributes to the kinetics despite the 107-fold decrease in the rate constant between the two pathways. ¹H and ¹³C NMR spectra as a function of decreasing pH (increasing HCl concentration) at 25.0 °C have been evaluated here to confirm the protonation events in DMEDA. Calculations of the respective DMEDA nitrogen partial charges have also been undertaken to support the NMR protonation study. A comparison of the DMEDA kinetic constants with the corresponding data for piperazine (PZ) reveals that despite the larger basicity of DMEDA, the enhanced and superior kinetic performance of PZ with CO₂(aq) above its predicted Bronsted reactivity is not observed in DMEDA.

中文翻译：

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二胺水溶液中CO ₂（aq）和H ⁺的化学机理的见解-N，N-_二甲基乙二胺水溶液燃烧后CO ₂捕集的实验停止流动力学和¹ H / ¹³ C NMR研究

为了增进对基于多胺的CO ₂捕集工艺吸收剂的理解，我们在此报告通过停止流分光光度法动力学测量和¹ H确定简单线性二胺N，N-二甲基乙二胺（DMEDA）的动力学和平衡常数。/ ¹³在25.0℃下C NMR滴定。根据动力学数据，在高pH> 9.0（k ₇ = 6.99×10 ³ M ^–1 ·s ^–1）时，DMEDA与CO ₂（aq）反应形成的单氨基甲酸（DMEDACOOH）是主要反应。低于此pH值，会形成质子化一氨基甲酸（DMEDACOOH ₂）通过包含DMEDAH ⁺和CO ₂（aq）的途径变得活跃，尽管在两条途径之间的速率常数降低了107倍，但仍有助于动力学。¹ H和¹³ C NMR光谱作为在25.0°C下pH值降低（HCl浓度增加）的函数进行了评估，以确认DMEDA中的质子化事件。还进行了相应DMEDA氮部分装料的计算，以支持NMR质子化研究。将DMEDA动力学常数与哌嗪（PZ）的相应数据进行比较后发现，尽管DMEDA的碱度较大，但CO _2可以增强PZ的动力学性能，使其具有优越的动力学性能。在DMEDA中未观察到（aq）高于其预期的布朗斯台德反应性。