Kinetics and Mechanism of Peroxymonocarbonate Formation
Kinetics and Mechanism of Peroxymonocarbonate Formation
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DOI：
10.1021/ic1007389
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发表时间：
2010-12-20
影响因子：
4.6
通讯作者：
Richardson, David E.
中科院分区：
文献类型：
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作者：
Bakhmutova-Albert, Ekaterina V.;Yao, Huirong;Richardson, David E.
在pH 6~9范围内，研究了过氧化氢与碳酸氢盐反应生成过氧单碳酸盐(HCO4-)的动力学和机理。采用双pH跳跃法，首先将C-13标记的碳酸氢盐溶液酸化，生成(CO2)-C-13，然后在过氧化氢存在下加入碱，使其达到较高的pH值。利用~(13)C核磁共振谱的时间演化来确定重碳酸盐和过氧单碳酸盐在第二次pH跃变后的竞争形成和随后的平衡。动力学模拟符合碳酸氢盐与过氧化氢反应的机理，在该反应机理中，碳酸氢盐脱水生成二氧化碳，然后二氧化碳与过氧化氢(过水化)及其共轭碱HOO-(碱催化过水化)反应。由于二氧化碳作为中间体的有效性增加，重碳酸盐生成过氧单碳酸盐的速率随着pH的降低而增加。由于HOO途径和较慢的总平衡速率，生成HCO4的选择性随着pH的增加而增加，这是一个较慢的总平衡速度的结果，并且这种pH倒数可以估计在25℃下CO2与过氧化氢和HOO-反应的速率常数(分别为2×10(-2)M-1 S(-1)和280M-1 S(-1))。与许多其他常见的无机酸和有机酸的过水化反应不同，CO2/HCO3-平衡的简便性和酸酐(CO2)在中性pH下相对较高的平衡利用率允许在没有强酸催化的情况下快速形成过氧单碳酸盐离子。碳酸酐酶和模型络合物[Zn(II)L(H2O)](2+)(L=1，4，7，10-四氮杂环十二烷)显著促进了HCO3-与H2O2反应生成过氧一碳酸酯。
The kinetics and mechanism of peroxymonocarbonate (HCO4-) formation in the reaction of hydrogen peroxide with bicarbonate have been investigated for the pH 6-9 range. A double pH jump method was used in which C-13-labeled bicarbonate solutions are first acidified to produce (CO2)-C-13 and then brought to higher pH values by addition of base in the presence of hydrogen peroxide. The time evolution of the C-13 NMR spectrum was used to establish the competitive formation and subsequent equilibration of bicarbonate and peroxymonocarbonate following the second pH jump. Kinetic simulations are consistent with a mechanism for the bicarbonate reaction with peroxide in which the initial formation of CO2 via dehydration of bicarbonate is followed by reaction of CO2 with H2O2 (perhydration) and its conjugate base HOO- (base-catalyzed perhydration). The rate of peroxymonocarbonate formation from bicarbonate increases with decreasing pH because of the increased availability of CO2 as an intermediate. The selectivity for formation of HCO4- relative to the hydration product HCO3- increases with increasing pH as a consequence of the HOO- pathway and the slower overall equilibration rate, and this pH cependence allows estimation of rate constants for the reaction of CO2 with H2O2 and HOO- at 25 degrees C (2 x 10(-2) M-1 s(-1) and 280 M-1 s(-1), respectively). The contributions of the HOO- and H2O2 pathways are comparable at pH 8. In contrast to the perhydration of many other common inorganic and organic acids, the facile nature of the CO2/HCO3- equilibrium and relatively high equilibrium availability of the acid anhydride (CO2) at neutral pH allows for rapid formation of the peroxymonocarbonate ion without strong acid catalysis. Formation of peroxymonocarbonate by the reaction of HCO3- with H2O2 is significantly accelerated by carbonic anhydrase and the model complex [Zn(II)L(H2O)](2+) (L = 1,4,7,10-tetraazacyclododecane).