Study On Photochemical Process Of Typical Carbonyl Compounds Based On Transient And Steady State Analysis

Carbonyl compounds are important constituents of atmospheric volatile organic compounds,which are ubiquitous in gas,liquid and particulate phases,and play an important role in atmospheric chemical reactions.On the one hand,carbonyl compounds in the atmospheric environment directly cause harm to air quality and human health,on the other hand,it is an important precursor to the formation of secondary organic aerosols,ozone and active substances such as free radicals,so it has received widespread attention.Although many studies have focused on the monitoring,environmental distribution and atmospheric polymers generating of carbonyl compounds,the photochemical properties of carbonyl compounds in the liquid environment and the changes in properties in complex environments need further exploration.In this thesis,taking carbonyl compound was excited by light to generate singlet oxygen as the starting point,and the transient intermediates generated in this process were observed by laser flash photolysis technology.Combined with other detection and characterization methods,the photochemical properties of carbonyl compounds in simple and complex environments were studied,and the relationship between transient and steady-state products and the formation of singlet oxygen was explained.The photosensitive ability of twelve carbonyl compounds to generate singlet oxygen and the relationship between their material structures were studied through photosensitive experiments.It was found that dicarbonyl compounds would generate more singlet oxygen than monocarbonyl compounds.Among dicarbonyl compounds,the photosensitivity also had the following order:α-keto acid>diacid>ketone aldehyde>aldehyde acid>dialdehyde>γ-keto acid;Whether the two carbonyl structures of a dicarbonyl compound are located in the ortho had a decisive influence on its photosensitivity:the photosensitivity of the ortho was much greater than that of the metastatic.Then,the transient spectra of these compounds were analyzed,and the transient absorption spectra of pyruvic acid was found.The quenching experiments were used to prove the existence of pyruvate-excited triplet substances,and the second-order decay rate constant was obtained as 2.78×10~7 M^-1s^-1.After further study of the photochemical reaction of pyruvic acid,its three main steady-state products were determined,with m/z of 175.06,177.04 and 219.05,respectively.It was proved by steady-state and transient quenching that pyruvate excited triplet species serving as a key role of intermediates in the generation of singlet oxygen and subsequent steady-state products in the photochemical process of pyruvic acid.The effects of inorganic salts and pH on transient and steady-state processes of pyruvic acid and methylglyoxal were also studied.The experimental results showed that ammonium sulfate,sodium chloride and sodium sulfate had little effect on the transient spectra of pyruvic acid and methylglyoxal,and their photosensitivity had the same trend with the change of inorganic salt concentration.Unlike methylglyoxal,which was less affected by pH,the changes of pH can significantly affect the transient spectrum and photosensitivity of pyruvic acid,and an increase in pH significantly reduced the production of singlet oxygen from pyruvic acid.Further by studying the effect of organic amines on the photochemical properties of pyruvic acid,methylglyoxal and glyoxal,it was ascertained that after the three carbonyl compounds reacted with dimethylamine:（i）the pyruvic acid system was most affected by pH,and the amount of singlet oxygen in the system under acidic conditions was at least one order of magnitude greater than that of all other systems;（ii）the methylglyoxal system can produce more singlet oxygen in acidic and alkaline environment,and the UV-vis absorption spectrum showed that a large amount of light-absorbing organics was produced in the system,while the absorption peaks of transient substances were also found in the transient spectra of the in acidic and neutral conditions,and the combined product identification showed that the most nitrogen-containing compounds produced in this system;（iii）the singlet oxygen produced by the glyoxal system was little affected by pH,and the concentration was also very low.The number of compounds obtained by product identification was also the least.The research in this thesis provided direct observation for the mechanism of singlet oxygen formation in organic matter,and provided a new perspective for the correct understanding of the photochemical process of carbonyl compounds in nature.