Carbon isotopic composition of acetic acid generated by hydrous pyrolysis of macromolecular organic matter from the Murchison meteorite
Carbon isotopic composition of acetic acid generated by hydrous pyrolysis of macromolecular organic matter from the Murchison meteorite
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DOI：
10.1111/j.1945-5100.2006.tb00514.x
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发表时间：
2006-08
影响因子：
2.2
通讯作者：
Y. Oba;H. Naraoka
中科院分区：
文献类型：
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作者：
Y. Oba;H. Naraoka
摘要-低分子量的一元羧酸，包括乙酸，是碳质碳酸盐中最丰富的有机化合物。到目前为止，水可提取羧酸的13 C和D富集特征暗示了它们起源的星际贡献。然而，也有人提出，一元羧酸可以通过陨石母体上的水反应形成。在这项研究中，我们进行了大分子有机物的纯化从默奇森陨石（CM 2）的水合热解，以检查其稳定的碳同位素测量的单羧酸的产生。在270-330 °C的大分子有机物的水合热解过程中，检测到碳数为2（C2）至5（C5）的一元羧酸，乙酸（CH 3COOH; C2）是最丰富的。生成的乙酸的浓度随着反应温度的升高而增加;在330 °C下高达0.48 mmol乙酸/g大分子有机物。这一结果表明，Murchison大分子有可能产生至少0.4mg乙酸/g陨石，这比Murchison报告的水可提取乙酸的量高约4倍。大分子有机物水合热解生成的乙酸的碳同位素组成为13 C-27‰（相对于PDB），比Murchison报道的水可提取乙酸的13 C含量低得多。分子内碳同位素分布表明，甲基（CH 3-）-C相对于羧基（-COOH）-C更富集13 C，表明这种形成的动力学过程。虽然本研究的实验条件（即，270-330 °C持续72小时）可能无法模拟碳质球粒陨石母体上的反应条件，但可能在较低温度下持续较长时间生成单羧酸。
Abstract— Low molecular weight monocarboxylic acids, including acetic acid, are some of the most abundant organic compounds in carbonaceous chondrites. So far, the 13C‐ and D‐enriched signature of water‐extractable carboxylic acids has implied an interstellar contribution to their origin. However, it also has been proposed that monocarboxylic acids could be formed by aqueous reaction on the meteorite parent body. In this study, we conducted hydrous pyrolysis of macromolecular organic matter purified from the Murchison meteorite (CM2) to examine the generation of monocarboxylic acids with their stable carbon isotope measurement. During hydrous pyrolysis of macromolecular organic matter at 270–330 °C, monocarboxylic acids with carbon numbers ranging from 2 (C2) to 5 (C5) were detected, acetic acid (CH3COOH; C2) being the most abundant. The concentration of the generated acetic acid increased with increasing reaction temperature; up to 0.48 mmol acetic acid/g macromolecular organic matter at 330 °C. This result indicates that the Murchison macromolecule has a potential to generate at least ˜0.4 mg acetic acid/g meteorite, which is about four times higher than the amount of water‐extractable acetic acid reported from Murchison. The carbon isotopic composition of acetic acid generated by hydrous pyrolysis of macromolecular organic matter is ˜‐27‰ (versus PDB), which is much more depleted in 13C than the water‐extractable acetic acid reported from Murchison. Intramolecular carbon isotope distribution shows that methyl (CH3‐)‐C is more enriched in 13C relative to carboxyl (‐COOH)‐C, indicating a kinetic process for this formation. Although the experimental condition of this study (i.e., 270–330 °C for 72 h) may not simulate a reaction condition on parent bodies of carbonaceous chondrite, it may be possible to generate monocarboxylic acids at lower temperatures for a longer period of time.