Reactivity of 3-hydroxy-3-methyl-2-butanone: Photolysis and OH reaction kinetics

Abstract

h i g h l i g h t s 3H3M2B photolysis is the major oxidation channel in the atmosphere. Slight positive temperature dependence in the OH þ 3H3M2B reaction kinetics. Need for a better understanding of the atmospheric chemistry of oxygenated VOC. a b s t r a c t Hydroxycarbonyl compounds are important secondary reaction products in the oxidation of Volatile Organic Compounds (VOCs) in the atmosphere. The atmospheric fate of these oxygenated VOCs is however poorly understood, especially the relevance of the photolytic pathway. In this work, a combined investigation of the photolysis and temperature-dependent OH radical reaction of 3-hydroxy-3-methyl-2-butanone (3H3M2B) is presented. A photolysis lifetime of about 4e5 days was estimated with a global quantum yield of 0.10. The OH reaction rate coefficient follows the Arrhenius trend (298e356 K) and could be modelled through the following expression: k 3H3M2B (T) ¼ (5.12 ± 0.07) Â 10 À12 exp(À563 ± 119/ T) in cm 3 molecule À1 s À1 . A 3H3M2B atmospheric lifetime of 15 days towards the OH radical was evaluated. Our results showed that the photolysis pathway is the major degradation channel for 3H3M2B. Photolysis products were identified and quantified in the present work with a carbon balance of around 80% enabling a reaction mechanism to be proposed. The present work underlines the need for further studies on the atmospheric chemistry of oxygenated VOCs.

Kinetics of the photolysis and OH reaction of 4-hydroxy-4-methyl-2-pentanone: Atmospheric implications

“…An overall QY of 0.15 was obtained for the atmospheric windows, in good agreement with the estimation of Magneron et al (2003) of <0.20. This QY is somewhat larger than those determined previously for 3H3M2B (0.10) (Bouzidi et al, 2014) and 4H2B (0.08) (Bouzidi et al, 2015).…”

“…Then the substitution of hydrogen atoms adjacent to the hydroxyl group by methyl groups deactivates this reaction and confirms that OH radicals proceed preferentially via H-abstraction of the weakest CeH bond on the eCH 2 OH group activated by the presence of the eOH group. In addition, the rate coefficients obtained in this work at 298 K for reactions with OH is higher by a factor of 6 than the one obtained for 3-hydroxy-3-methyl-2-butanone (Bouzidi et al, 2014). As expected this comparison shows that b-hydroxyketones are more reactive than a-hydroxyketones toward OH radicals.…”

“…Both setups were described in details in previous publications (Bouzidi et al, 2014;Szabo et al, 2011) and thus, only essential features are recalled in the next paragraphs.…”

“…Therefore, 4H4M2P photolysis may represent up to 20% of the gasphase degradation of this compound in the atmosphere. Comparing with 4H2B (4-hydroxy-2-butanone) and 3H3M2B (3-hydroxy-3- methyl-2-butanone) for which lifetimes of 26 and 4e5 days towards photolysis were calculated (Bouzidi et al, 2014(Bouzidi et al, , 2015, respectively, emphasizes the role of the molecular structure and absorption properties on the atmospheric fate of hydroxyketones. Hence, the present results underline the need for a precise knowledge of hydroxyketone photolysis under real conditions to better constrain atmospheric chemistry models.…”

“…In their study of 3-hydroxy-3-methyl-2-butanone (3H3M2B), Bouzidi et al (2014) compared the kinetics of OH reaction and photolysis and concluded that photolysis may be the major gasphase degradation loss of 3H3M2B in the atmosphere, producing acetone and formaldehyde as main products. Conversely, for 4-hydroxy-2-butanone (4H2B), photolysis is negligible and OH initiated oxidation represents the main fate (Bouzidi et al, 2015), due to both a higher OH reactivity and a lower photo-activity compared to 3H3M2B.…”