Gas-phase ozonolysis of furans, methylfurans, and dimethylfurans in the atmosphere
Gas-phase ozonolysis of furans, methylfurans, and dimethylfurans in the atmosphere
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大气中呋喃、甲基呋喃和二甲基呋喃的气相臭氧分解
DOI：
10.1039/c8cp04947e
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发表时间：
2018
影响因子：
3.3
通讯作者：
Wang Liming
中科院分区：
文献类型：
--
作者：
Li Mengke;Liu Yuhong;Wang Liming
呋喃及其甲基取代物在化学工业中是很有前途的替代可再生燃料和原料，它们可以大规模排放到大气中，并通过它们与OH、O_3、NO_3、Cl等的反应在大气中被降解。预测的速率系数与呋喃、3-甲基呋喃(3-MF)和2，5-二甲基呋喃(2，5-DMF)的实验值吻合较好，表明臭氧氧化对它们的去除可以与大气中OH自由基的去除相媲美，特别是对甲基呋喃。计算了呋喃甲醛臭氧化反应的速率系数。呋喃的臭氧化反应遵循Criegee机理，生成初级臭氧化合物(POZ)。RRKM-ME计算表明，POZ的分解以β不饱和中间体(Ccr-CHO或Ccr-C(OO)CH_3，R=H或CH_3)的形成为主。这些顺式化合物在高激发度下形成，可迅速异构化为二氧六环和二恶烯产物，或迅速解离为乙氧基型自由基和羟基自由基。二恶烯将进一步异构化为含有另外两个羰基或一个羰基和一个环氧化物的乙醚产物，例如呋喃中的HC(O)OC(O)CH2CHO和HC(O)O-[CHOCH]-CHO。对于3-/4-位取代的呋喃，如3-MF和2，3-DMF，可能会形成OH自由基。3-MF臭氧化反应中羟基自由基产率的预测值为0.31，与之前的实验值0.59(不确定度系数约为1.5)符合得很好。
Furan and its methyl substituents, as promising alternative and renewable fuels and feedstock in the chemical industry, could be emitted to the atmosphere in a large scale and be degraded there by their reactions with OH, O3, NO3, Cl, etc. In this study, we investigate the mechanism of gas-phase ozonolysis of furans using quantum chemistry and kinetic calculations. The predicted rate coefficients agree well with the available experimental values for furan, 3-methylfuran (3-MF), and 2,5-dimethylfuran (2,5-DMF), suggesting that their removal by ozonolysis could be comparable to their removal by OH radicals in the atmosphere, particularly for methylfurans. Rate coefficients for the ozonolysis of furaldehydes were also calculated. The ozonolysis of furans follows the Criegee mechanism by forming primary ozonides (POZs). RRKM-ME calculations show that the decomposition of the POZs is dominated by the formation of β-unsaturated Criegee intermediates (CIs as CCR–CHOO or CCR–C(OO)CH3, R = H or CH3). These CIs, formed with high excitation up to 250–280 kJ mol−1, would isomerize promptly to dioxirane and dioxolene products or dissociate promptly to a vinoxy-type radical and an OH radical. The dioxolenes would further isomerize to ether products containing another two carbonyl groups or one carbonyl group and one epoxide group, e.g., HC(O)OC(O)CH2CHO and HC(O)O–[CHOCH]–CHO in furan. Formation of OH radicals is expected for furans with alkyl substitution at 3-/4-positions such as 3-MF and 2,3-DMF. The predicted fractional yield of 0.31 for OH radicals in the ozonolysis of 3-MF agrees well with the previous experimental values of 0.59 (with an uncertainty factor of ca. 1.5).