Wang Lina, Wu Zhuang, Lu Bo, Zeng Xiaoqing
Department of Chemistry, Shanghai Key Laboratory of Molecular Catalysts and Innovative Materials, Fudan University, Shanghai 200433, China.
Department of Chemistry, Shanghai Key Laboratory of Molecular Catalysts and Innovative Materials, Fudan University, Shanghai 200433, China.
J Environ Sci (China). 2022 Apr;114:160-169. doi: 10.1016/j.jes.2021.08.018. Epub 2022 Jan 14.
Criegee intermediates (CIs), also known as carbonyl oxide, are reactive intermediates that play an important role in the atmospheric chemistry. Investigation on the structures and reactivity of CIs is of fundamental importance in understanding the underlying mechanism of their atmospheric reactions. In sharp contrast to the intensively studied parent molecule (CHOO) and the alkyl-substituted derivatives, the knowledge about the fluorinated analogue CFC(H)OO is scarce. By carefully heating the triplet carbene CFCH in an O-doped Ar-matrix to 35 K, the elusive carbonyl oxide CFC(H)OO in syn- and anti-conformations has been generated and characterized with infrared (IR) and ultraviolet-visible (UV-vis) spectroscopy. The spectroscopic identification is supported by O-labeling experiments and quantum chemical calculations at the B3LYP/6-311++G(3df,3pd) and MP2/6-311++G(2d,2p) levels. Upon the long-wavelength irradiation (λ > 680 nm), both conformers of CFC(H)OO decompose to give trifluoroacetaldehyde CFC(H)O and simultaneously rearrange to the isomeric dioxirane, cyclic-CFCH(OO), which undergoes isomerization to the lowest-energy carboxylic acid CFC(O)OH upon UV-light excitation at 365 nm. The O-oxidation of CFCH via the intermediacy of CFC(H)OO and cyclic-CFCH(OO) might provide new insight into the mechanism for the degradation of hydro-chlorofluorocarbon CFCHCl (HCFC-123) in the atmosphere.
克里吉中间体（CIs），也被称为羰基氧化物，是在大气化学中起重要作用的反应性中间体。对CIs的结构和反应性进行研究对于理解其大气反应的潜在机制至关重要。与被深入研究的母体分子（CHOO）和烷基取代衍生物形成鲜明对比的是，关于氟化类似物CFC(H)OO的知识却很匮乏。通过在掺氧的氩气基质中将三线态卡宾CFCH小心加热至35 K，已生成了具有顺式和反式构象的难以捉摸的羰基氧化物CFC(H)OO，并通过红外（IR）和紫外可见（UV-vis）光谱对其进行了表征。光谱鉴定得到了O标记实验以及在B3LYP/6-311++G(3df,3pd)和MP2/6-311++G(2d,2p)水平的量子化学计算的支持。在长波长照射（λ > 680 nm）下，CFC(H)OO的两种构象都会分解生成三氟乙醛CFC(H)O，同时重排为异构的二氧杂环丙烷，即环状-CFCH(OO)，后者在365 nm的紫外光激发下会异构化为能量最低的羧酸CFC(O)OH。通过CFC(H)OO和环状-CFCH(OO)中间体对CFCH进行的O氧化可能为大气中氢氯氟烃CFCHCl（HCFC-123）的降解机制提供新的见解。
