Kinetic investigation on carbamate formation from the reaction of carbon dioxide with amino acids in homogeneous aqueous solution
Kinetic investigation on carbamate formation from the reaction of carbon dioxide with amino acids in homogeneous aqueous solution
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均相水溶液中二氧化碳与氨基酸反应形成氨基甲酸酯的动力学研究
DOI：
10.1002/poc.1900
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发表时间：
2012
期刊：
影响因子：
--
通讯作者：
and Y. Ito
中科院分区：
文献类型：
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作者：
Y. Yamamoto;J. Hasegawa;and Y. Ito
首先通过核磁共振光谱研究了二氧化碳与α-氨基酸在D2 O中反应形成氨基甲酸酯的动力学。碳酸钾被用作CO2源。对于每种氨基酸，估计了最大氨基甲酸酯产率、氨基甲酸酯形成的表观速率常数kapp以及氨基甲酸酯形成的速率常数k1和分解的速率常数k-1。logk 1或logk− 1与氨基酸pKa的关系曲线表明，生成速率k1随氨基酸的碱度（pKa）增加而增加，而分解速率tek − 1则随氨基酸的碱度（pKa）增加而减少。由前一曲线得到的Br nstedβ值为0.39，与以前报道的值（0.26-0.43）一致。观察到的logk−1的负pKa依赖性（Br nstedα= 0.34）是合理的，因为氨基甲酸酯分解是酸催化的，并且对于较弱的碱性胺，H+的稳态浓度应该更高。计算氨基的氮原子处的电荷（σ）和孤对能量（EN）。虽然logk 1与σ和EN相关，但logk− 1与这两个参数无关。考虑到氨基甲酸酯的形成（k1）不仅是碱催化的，而且还应该受到氨基氮的亲核性的促进，因此它与σ和EN以及pKa 1的相关性是合理的。logk− 1与σ和EN无关并不奇怪，因为σ和EN不是解的[H+]的直接度量。版权所有© 2011约翰威利父子有限公司.
The kinetics of carbamate formation from the reaction of carbon dioxide with α‐amino acids in D2O was first investigated by means of nuclear magnetic resonance spectroscopy. Potassium carbonate was used as the CO2source. For each amino acid, the maximum carbamate yield, the apparent rate constant for the carbamate formationkapp, and the rate constants for the formationk1and the breakdownk−1of the carbamate were estimated. Plots of logk1or logk−1versus pKaof amino acids indicated that the formation ratek1increased with the basicity (pKa) of amino acid, while the decomposition ratek−1decreased. A Brϕnstedβvalue of 0.39 was obtained from the former plot, being in good agreement with the previously reported ones (0.26–0.43). The observed negative pKadependence of logk−1(Brϕnstedα= 0.34) is reasonable, because the carbamate decomposition is acid‐catalyzed and the steady‐state concentration of H+should be higher for weaker basic amines. The charge (σ) and the lone‐pair energy (EN) at the nitrogen atom of the amino group were calculated. Although logk1correlated with σ andEN, logk−1was unrelated with both of these parameters. Considering that the carbamate formation (k1) is not only base‐catalyzed but should also be promoted by the nucleophilicity of the amino nitrogen, its correlation with σ andENin addition to pKais rational. The irrelevance of logk−1to σ andENis not surprising, because σ andENare not a direct measure of [H+] of the solution. Copyright © 2011 John Wiley & Sons, Ltd.