Abstract Measured abundances of organic compounds can reveal information about the environments in which they formed. Since organic compounds can be mobilized and released from geologic and planetary settings, they have the potential to provide insights into environments that are difficult to observe directly. To advance our understanding of these environments, this study identifies organic reactions that approach metastable equilibrium in experiments, so that future studies can predict geochemical conditions in remote settings (e.g., deep Earth, extraterrestrial bodies) by monitoring reaction ratios of compounds involved in similar organic reactions. At high temperatures organic redox reactions can equilibrate, which allows comparisons with thermodynamic properties to yield estimates of reaction conditions. However, redox reactions may equilibrate too slowly to be applicable to lower temperature systems. To explore metastable equilibria at lower temperatures, we studied substitution reactions that tend to be faster than redox reactions. In this study, we demonstrate that oxygen- and nitrogen-bearing organic compounds at hydrothermal conditions undergo a series of simultaneous substitution reactions that rapidly approach steady-state ratios indicative of metastable equilibrium. Four sets of aqueous experiments were performed at 250 °C and 40 bar, each beginning with a single organic reactant: benzyl alcohol, benzylamine, dibenzylamine, or tribenzylamine. All reactant solutions were prepared with identical bulk elemental compositions by adjusting the concentrations of the starting organic compounds and adding ammonia as needed. After 2 h at hydrothermal reaction conditions, all of the model compounds were detectable in all four sets of experiments, evidence for reversibility of reactions among the compounds. After 72 h, reaction ratios between the model compounds converged in all four sets of experiments, consistent with approaches toward metastable equilibrium. Reaction ratios for ether and aldehyde formation reactions were also observed to group within a relatively small range, but without a clear convergence pattern, suggesting other non-redox reactions may approach metastable equilibrium. The approach to metastable equilibrium among the initial organic reactants could be observed and quantified even in the presence of competing redox reactions whose mechanisms are less understood, including dibenzylimine and toluene formation, which did not appear to reach steady-states. These findings identify classes of organic compounds and reactions that can reflect the conditions at which they last equilibrated and should be targeted for analysis in natural systems.

中文翻译：

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水热条件下含氧和含氮有机化合物之间取代反应的亚稳态平衡

摘要 测量的有机化合物丰度可以揭示有关它们形成环境的信息。由于有机化合物可以从地质和行星环境中移动和释放，它们有可能提供对难以直接观察的环境的洞察力。为了加深我们对这些环境的理解，本研究确定了在实验中接近亚稳态平衡的有机反应，以便未来的研究可以通过监测类似有机化合物中涉及的化合物的反应比率来预测遥远环境（例如地球深处、地外天体）的地球化学条件。反应。在高温下，有机氧化还原反应可以平衡，这允许与热力学性质进行比较以产生反应条件的估计值。然而，氧化还原反应可能平衡太慢而不适用于较低温度的系统。为了探索较低温度下的亚稳态平衡，我们研究了往往比氧化还原反应更快的取代反应。在这项研究中，我们证明了在水热条件下含氧和含氮的有机化合物会经历一系列同时发生的取代反应，这些反应迅速接近表明亚稳态平衡的稳态比率。在 250 °C 和 40 bar 下进行了四组水性实验，每组都从单一有机反应物开始：苄醇、苄胺、二苄胺或三苄胺。通过调节起始有机化合物的浓度并根据需要添加氨来制备具有相同本体元素组成的所有反应物溶液。在水热反应条件下 2 小时后，在所有四组实验中均可检测到所有模型化合物，这证明了化合物之间反应的可逆性。72 小时后，模型化合物之间的反应比率在所有四组实验中都收敛，与亚稳态平衡的方法一致。还观察到醚和醛形成反应的反应比率在相对较小的范围内分组，但没有明显的收敛模式，表明其他非氧化还原反应可能接近亚稳态平衡。即使存在机制尚不清楚的竞争氧化还原反应，包括二苄亚胺和甲苯的形成，也可以观察和量化初始有机反应物之间达到亚稳态平衡的方法，似乎没有达到稳态。这些发现确定了有机化合物和反应的类别，它们可以反映它们最后平衡的条件，并且应该作为在自然系统中分析的目标。