Wolfson Atmospheric Chemistry Laboratories, Department of Chemistry, University of York, UK.
Phys Chem Chem Phys. 2019 Jan 21;21(3):1160-1171. doi: 10.1039/c8cp06437g. Epub 2019 Jan 8.
Unsaturated 1,4-dicarbonyl compounds, such as 2-butenedial and 4-oxo-2-pentenal are produced in the atmospheric boundary layer from the oxidation of aromatic compounds and furans. These species are expected to undergo rapid photochemical processing, affecting atmospheric composition. In this study, the photochemistry of (E)-2-butenedial and both E and Z isomers of 4-oxo-2-pentenal was investigated under natural sunlight conditions at the large outdoor atmospheric simulation chamber EUPHORE. Photochemical loss rates, relative to j(NO), are determined to be j((E)-2-butenedial)/j(NO) = 0.14 (±0.02), j((E)-4-oxo-2-pentenal)/j(NO) = 0.18 (±0.01), and j((Z)-4-oxo-2-pentenal)/j(NO) = 0.20 (±0.03). The major products detected for both species are a furanone (30-42%) and, for (E)-2-butenedial, maleic anhydride (2,5-furandione) (12-14%). The mechanism appears to proceed predominantly via photoisomerization to a ketene-enol species following γ-H abstraction. The lifetimes of the ketene-enol species in the dark from 2-butenedial and 4-oxo-2-pentenal are determined to be 465 s and 235 s, respectively. The ketene-enol can undergo ring closure to yield the corresponding furanone, or further unimolecular rearrangement which can subsequently form maleic anhydride. A minor channel (10-15%) also appears to form CO directly. This is presumed to be via a molecular elimination route of an initial biradical intermediate formed in photolysis, with an unsaturated carbonyl (detected here but not quantified) as co-product. α-Dicarbonyl and radical yields are very low, which has implications for ozone production from the photo-oxidation of unsaturated 1,4-dicarbonyls in the boundary layer. Photochemical removal is determined to be the major loss process for these species in the boundary layer with lifetimes of the order of 10-15 minutes, compared to >3 hours for reaction with OH.
不饱和 1,4-二羰基化合物，如 2-丁烯二醛和 4-氧代-2-戊烯醛，是由芳香族化合物和呋喃的氧化作用在大气边界层中生成的。这些物质预计会经历快速的光化学处理，从而影响大气成分。在本研究中，在大型户外大气模拟室 EUPHORE 中，在自然光条件下研究了（E）-2-丁烯二醛以及 4-氧代-2-戊烯醛的 E 和 Z 异构体的光化学。相对于 j(NO)，光化学损失率被确定为 j((E)-2-丁烯二醛)/j(NO) = 0.14（±0.02），j((E)-4-氧代-2-戊烯醛)/j(NO) = 0.18（±0.01），和 j((Z)-4-氧代-2-戊烯醛)/j(NO) = 0.20（±0.03）。两种物质检测到的主要产物是呋喃酮（30-42%），对于（E）-2-丁烯二醛，还有马来酸酐（2,5-呋喃二酮）（12-14%）。该机制似乎主要通过γ-H 抽提后异构化为烯酮-烯醇物种进行。从 2-丁烯二醛和 4-氧代-2-戊烯醛在暗处的烯酮-烯醇物种的寿命分别确定为 465 s 和 235 s。烯酮-烯醇可以进行环化以生成相应的呋喃酮，或者进一步进行单分子重排，随后可以形成马来酸酐。一个较小的通道（10-15%）似乎也可以直接形成 CO。这被认为是通过在光解中形成的初始双自由基中间体的分子消除途径，其副产物是不饱和羰基（此处检测到但未定量）。α-二羰基和自由基的产率非常低，这对边界层中不饱和 1,4-二羰基化合物的光氧化产生臭氧有影响。光化学去除被确定为这些物质在边界层中的主要损失过程，其寿命约为 10-15 分钟，而与 OH 反应的寿命则超过 3 小时。
