Toward Rational Design of Amine Solutions for PCC Applications: The Kinetics of the Reaction of CO2(aq) with Cyclic and Secondary Amines in Aqueous Solution

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• 作者：William Conway ; Xiaoguang Wang ; Debra Fernandes ; Robert Burns ; Geoffrey Lawrance ; Graeme Puxty ; Marcel Maeder
• 刊名：Environmental Science & Technology (ES&T)
• 出版年：2012
• 出版时间：July 3, 2012
• 年：2012
• 卷：46
• 期：13
• 页码：7422-7429
• 全文大小：398K
• 年卷期：v.46,no.13(July 3, 2012)
• ISSN：1520-5851

文摘

The kinetics of the fast reversible carbamate formation reaction of CO₂(aq) with a series of substituted cyclic secondary amines as well as the noncyclic secondary amine diethanolamine (DEA) has been investigated using the stopped-flow spectrophotometric technique at 25.0 掳C. The kinetics of the slow parallel reversible reaction between HCO₃^{鈥?/sup> and amine has also been determined for a number of the amines by 1H NMR spectroscopy at 25.0 掳C. The rate of the reversible reactions and the equilibrium constants for the formation of carbamic acid/carbamate from the reactions of CO₂ and HCO₃鈥?/sup> with the amines are reported. In terms of the forward reaction of CO₂(aq) with amine, the order with increasing rate constants is as follows: diethanolamine (DEA) < morpholine (MORP) thiomorpholine (TMORP) < N-methylpiperazine (N-MPIPZ) < 4-piperidinemethanol (4-PIPDM) piperidine (PIPD) < pyrrolidine (PYR). Both 2-piperidinemethanol (2-PIPDM) and 2-piperidineethanol (2-PIPDE) do not form carbamates. For the carbamate forming amines a Br酶nsted correlation relating the protonation constant of the amine to the carbamic acid formation rate and equilibrium constants at 25.0 掳C has been established. The overall suitability of an amine for PCC in terms of kinetics and energy is discussed.}