Chemistry Review 2: OH-Initiated Oxidation of Acetylacetone: Implications for Ozone and Secondary Organic Aerosol Formation

Chemistry Review 2:  OH-Initiated Oxidation of Acetylacetone: Implications for Ozone and Secondary Organic Aerosol Formation
                                                                                                  

Good Day, Evolution Through the Ages followers!

   To further explain how this sub-channel of the blog will be run, I will be alternating every week between our two chemistry subfield topics of biochemistry and environmental chemistry. For this week’s review I am now on the topic of environmental science. The article’s title is OH-Initiated Oxidation of Acetylacetone: Implications for Ozone and Secondary Organic Aerosol Formation.



Acetylacetone is the compound the researchers want to know more about pertaining environmental impacts. Acetylacetone is used in industrial applications across the world. With this organic compound being used so  readily among consumers and industry, the compound is now commonly being found in the atmosphere. Once the compound is incorporated within the atmosphere, it becomes a common atmospheric oxygenated volatile organic compound which can be a form of acid rain. Prior to this articles composition, there was not much known about the atmospheric oxidation mechanism. To better elucidate more about these concepts, the authors researched into the potential mechanism, kinetics, and the atmospheric fate of the compound.


   With regards to Acetylacetone, there are two isomers which form when the OH-initiated oxidation process occurs. These two isoforms are known as enolic (enol-) and ketonic (keto-). The primary distinction between these two isoforms occurs when the overall molecule undergoes a conformation shift to better stabilize the overall structure of the compound. This strengthening of the structure's stability occurs when the central carbon (green circle – C) atom loses a hydrogen atom (White circle) to form a double bond between adjacent carbon atoms. Due to rules of how bond reconfiguration affects the overall conformation of a molecule, this additional double bond causes the -Enol form of the molecule to have the two double-bonded oxygen molecules to be closer to each other; in regards to space within the compound structure.

While performing the experiments, the authors found that the enol-acetylacetone is more favorable with regards to the additional -OH being added to the compound; in comparison to the addition to form the keto-acetylacetone. The oxidation of this compound is predicted to yield high amounts of acetic acid and methylglyoxal. This predicted yield discussed from the authors’ findings is larger than the currently recognized statistic.

   So here is a little background, ketones as a class are an important organic molecule. They are oxygenated volatile organic compounds which means they have a high vapor pressure in an oxygen enriched environment at typical room temperature. These compounds can be either emitted by natural causes and anthropogenic causes (ex. Industrial activities). When ketones are oxidized in the atmosphere, they have been identified as an important source of HOradical species and secondary organic aerosols (SOA).

   What this all means is that these HOx radical species and secondary organic aerosols highly impact air quality, our health and overall climate. Since acetylacetone is so widely used within the consuming world, here is a list of some of its common uses: reagent in preparation of chelate compounds for a wide range of transition metals and a building block for the synthesis of heterocyclic compounds. What is meant by this phrasing is that the acetylacetone compound is used in a wide range of industrial plants; as well as a raw material for Sulfonamidedrugs. Sulfonamide drugs are a class of antibiotic medication. 

   The mechanism for acetylacetone compound is complex and can take multiple pathways with a myriad of steps to successfully form the ending compound. When the oxidation occurs, it is normally started by the hydroxyl radical (HOx. There has been little previous work on this topic of interest before these authors findings; this lack of research performed hinders possessing a more accurate assessment of what the roles acetylacetone and its two isoforms may play in the formation and effects on the ozone. So what are the atmospheric implications that this research showed?


   It was found that the enolic form of this isomers is more favorable then the ketonic form. The authors estimated that acetylacetone has a lifetime of less than a few hours in the tropospheric level of the atmosphere; due to the oxidation that happens. With acetylacetone short lifespan, as well as its isomers reacting so highly and violently with -OH radicals, it is very important to further study this topic of interest.  Acetylacetonedoes produce a tropospheric ozone and secondary organic aerosols. These byproducts of acetylacetone haveimplications such as poor air quality, human health, and changes to the overall climate. This research article is just another step in further elucidating the overall mechanism of this process. Additional studies are needed to further assess the impacts acetylacetone and secondary organic aerosols on the ozone. 


   Until next time, thank you for taking the time to learn about acetylacetone and secondary organic at Evolution Through the Ages.

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Reviewed  by Sydney Edwards

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Reference:
OH-Initiated Oxidation of Acetylacetone: Implications for Ozone and Secondary Organic Aerosol FormationYuemeng Ji, Jun Zheng, Dandan Qin, Yixin Li, Yanpeng Gao, Meijing Yao, Xingyu Chen, Guiying Li, Taicheng An, and Renyi Zhang, Environmental Science & TechnologyArticle ASAP
DOI: 10.1021/acs.est.8b03972

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