Division of Chemistry, California Institute of Technology, MC 127-72, 1200 East California Boulevard, Pasadena, California 91125, USA.
J Phys Chem A. 2010 Aug 12;114(31):8106-13. doi: 10.1021/jp103907c.
Epoxydiols are produced in the gas phase from the photo-oxidation of isoprene in the absence of significant mixing ratios of nitrogen oxides (NO(x)). The reactive uptake of these compounds onto acidic aerosols has been shown to produce secondary organic aerosol (SOA). To better characterize the fate of isoprene epoxydiols in the aerosol phase, the kinetics and products of the acid-catalyzed ring-opening reactions of four hydroxy-substituted epoxides were studied by nuclear magnetic resonance (NMR) techniques. Polyols and sulfate esters are observed from the ring-opening of the epoxides in solutions of H(2)SO(4)/Na(2)SO(4). Likewise, polyols and nitrate esters are produced in solutions of HNO(3)/NaNO(3). In sulfuric acid, the rate of acid-catalyzed ring-opening is dependent on hydronium ion activity, sulfate ion, and bisulfate. The rates are much slower than the nonhydroxylated equivalent epoxides; however, the hydroxyl groups make them much more water-soluble. A model was constructed with the major channels for epoxydiol loss (i.e., aerosol-phase ring-opening, gas-phase oxidation, and deposition). In the atmosphere, SOA formation from epoxydiols will depend on a number of variables (e.g., pH and aerosol water content) with the yield of ring-opening products varying from less than 1% to greater than 50%.
环氧二氢在不存在显著氮氧化物（NO(x)）混合比的情况下，由异戊二烯的光氧化作用在气相中产生。这些化合物对酸性气溶胶的反应性吸收已被证明会产生二次有机气溶胶（SOA）。为了更好地描述气溶胶相中的异戊二烯环氧化物的命运，通过核磁共振（NMR）技术研究了四种羟基取代的环氧化物的酸催化开环反应的动力学和产物。在 H(2)SO(4)/Na(2)SO(4)溶液中，观察到从环氧化物开环生成多元醇和硫酸盐酯。同样，在 HNO(3)/NaNO(3)溶液中生成多元醇和硝酸盐酯。在硫酸中，酸催化开环的速率取决于氢离子活度、硫酸根离子和亚硫酸氢根离子。其速率比非羟基化的等效环氧化物慢得多；然而，羟基使其水溶性大大提高。构建了一个模型，其中包括环氧二氢损失的主要途径（即气溶胶相开环、气相氧化和沉积）。在大气中，SOA 的形成将取决于许多变量（例如 pH 和气溶胶含水量），开环产物的产率从不到 1%到大于 50%不等。
