Direct Synthesis of Amides from Amines and Carboxylic Acids under Hydrothermal Conditions
Direct Synthesis of Amides from Amines and Carboxylic Acids under Hydrothermal Conditions
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DOI：
10.1021/acsearthspacechem.0c00009
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发表时间：
2020-05-21
影响因子：
3.4
通讯作者：
Yang, Ziming
中科院分区：
文献类型：
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作者：
Fu, Xuan;Liao, Yiju;Yang, Ziming
热液系统为地下生物圈提供了一个独特的栖息地，并可能为生命的起源。酰胺是热液有机地球化学和深层地下生物学研究的基础，这在很大程度上是因为它们参与新陈代谢，例如以肽和蛋白质的形式，还因为它们参与深层氮循环及其在生命起源中的潜在作用。酰胺的水热化学也是天体生物学研究的重要内容，因为它可能揭示地球外太空中肽和生物分子的潜在形成途径。在这里，我们描述了在水热条件下（250摄氏度和40巴，P-sat）酰胺合成的非矿物催化合成途径。我们发现，一套酰胺（12个例子）很容易通过胺和羧酸之间的直接缩合合成，酰胺产率高达90%以上的时间尺度小时。进行时间序列水热实验，以获得酰胺合成的表观速率常数。对于某些胺（例如，0.2对于苄胺为h-1）比对于其它（例如，0.05 h（-1）表示环己胺），这表明对酰胺形成的强取代作用。提出了一种胺酰化反应机理，与前人的研究结果一致。此外，发现酰胺形成在高或低pH溶液（例如，pH 12），这进一步支持缩合反应应该发生在中性胺和酸之间。我们发现一个可行的和选择性的酰胺键形成的水热途径可能会提供新的见解，了解肽和生物分子的合成在相关的水热环境。
Hydrothermal systems provide a unique habitat for the subsurface biosphere, and possibly, for the origin of life. Amides are fundamental to hydrothermal organic geochemistry and deep subsurface biology research, in large part because of their involvement in metabolism, such as in the forms of peptides and proteins, and also because of their participation in the deep nitrogen cycle and their potential role in the origin of life. Hydrothermal chemistry of amides is also of great interest to astrobiology research because it may reveal potential formation pathways of peptides and biomolecules in the space outside Earth. Here, we describe a nonmineral-catalyzed synthetic pathway for amide synthesis under hydrothermal conditions (250 degrees C and 40 bar, P-sat). We find that a suite of amides (12 examples) are readily synthesized through a direct condensation between amines and carboxylic acids, with an amide yield of up to 90% over a timescale of hours. Time-series hydrothermal experiments were performed to obtain apparent rate constants for amide synthesis. The observed hydrothermal rate constants were significantly larger for certain amines (e.g., 0.2 h-1 for benzylamine) than for others (e.g., 0.05 h(-1) for cyclohexylamine), which suggests a strong substitution effect on amide formation. An amine acylation mechanism is proposed, and also consistent with previous studies. Furthermore, amide formation is found to be strongly inhibited in high or low pH solutions (e.g., pH 12), which further supports that the condensation reaction should occur between the neutral amine and acid. Our finding of a feasible and selective hydrothermal pathway for amide bond formation may provide new insights into understanding peptides and biomolecule synthesis in relevant hydrothermal environments.