Kinetics of Acid-Catalyzed Dehydration of Cyclic Hemiacetals in Organic Aerosol Particles in Equilibrium with Nitric Acid Vapor.
Kinetics of Acid-Catalyzed Dehydration of Cyclic Hemiacetals in Organic Aerosol Particles in Equilibrium with Nitric Acid Vapor.
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与硝酸蒸汽平衡的有机气溶胶颗粒中环状半缩醛的酸催化脱水动力学。
DOI：
10.1021/acs.jpca.6b01402
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发表时间：
2016
期刊：
影响因子：
--
通讯作者：
P. Ziemann
中科院分区：
文献类型：
--
作者：
A. Ranney;P. Ziemann
以往的研究表明，1，4-羟基羰基通常是碳氢化合物大气氧化的主要产物，它可以在气溶胶颗粒中经酸催化环化和脱水生成高活性的不饱和二氢呋喃。在这项研究中，环状半缩醛的脱水动力学是在一系列的环境室实验中进行的，其中含有环状半缩醛的二次有机气溶胶(SOA)是由正十五烷与羟基自由基在HNO3存在下在干燥空气中反应生成的。利用粒子束质谱仪实时监测环状半缩醛的生成和脱水过程，并通过重量分析和离子色谱对过滤样品中的SOA值和HNO3值进行了定量。实验测得的脱水速率常数随硝酸浓度的增加而线性增加，对应的催化速率常数分别为0.27h(-1)ppmv(-1)和7.0h(-1)M(-1)。测得硝酸在水中分配的亨利定律常数为3.7×10(4)M atm(-1)，∼为溶解在水中的2 5%，酸解离常数为-lt；8×10(-4)，至少比硝酸在水中的离解常数小10(4)倍。结果表明，HNO_3在SO_3中只有微弱的解离作用，环状半缩醛的脱水反应是由分子HNO_3而不是H(+)催化的。这里测量的亨利定律常数和动力学关系可以用来改进干燥空气中碳氢化合物在NOx存在下氧化生成SOA的机理和模型，这是实验室研究中常用的条件。讨论了环状半缩醛在大气中的去向，其中较高的相对湿度、有机/水相分离以及分子H_2SO_4和/或H(+)的酸催化的影响可能是重要的。
Previous studies have shown that 1,4-hydroxycarbonyls, which are often major products of the atmospheric oxidation of hydrocarbons, can undergo acid-catalyzed cyclization and dehydration in aerosol particles to form highly reactive unsaturated dihydrofurans. In this study the kinetics of dehydration of cyclic hemiacetals, the rate-limiting step in this process, was investigated in a series of environmental chamber experiments in which secondary organic aerosol (SOA) containing cyclic hemiacetals was formed from the reaction of n-pentadecane with OH radicals in dry air in the presence of HNO3. A particle beam mass spectrometer was used to monitor the formation and dehydration of cyclic hemiacetals in real time, and SOA and HNO3 were quantified in filter samples by gravimetric analysis and ion chromatography. Measured dehydration rate constants increased linearly with increasing concentration of HNO3 in the gas phase and in SOA, corresponding to catalytic rate constants of 0.27 h(-1) ppmv(-1) and 7.0 h(-1) M(-1), respectively. The measured Henry's law constant for partitioning of HNO3 into SOA was 3.7 × 10(4) M atm(-1), ∼25% of the value for dissolution into water, and the acid dissociation constant was estimated to be <8 × 10(-4), at least a factor of 10(4) less than that for HNO3 in water. The results indicate that HNO3 was only weakly dissociated in the SOA and that dehydration of cyclic hemiacetals was catalyzed by molecular HNO3 rather than by H(+). The Henry's law constant and kinetics relationships measured here can be used to improve mechanisms and models of SOA formation from the oxidation of hydrocarbons in dry air in the presence of NOx, which are conditions commonly used in laboratory studies. The fate of cyclic hemiacetals in the atmosphere, where the effects of higher relative humidity, organic/aqueous phase separation, and acid catalysis by molecular H2SO4 and/or H(+) are likely to be important, is discussed.
DOI：
10.1021/jp506562r
发表时间：
2014-09
期刊：
The journal of physical chemistry. A
影响因子：
--
作者：
A. Carrasquillo;J. F. Hunter;K. E. Daumit;J. Kroll
通讯作者：
A. Carrasquillo;J. F. Hunter;K. E. Daumit;J. Kroll