Mechanisms of isomerization and hydration reactions of typical β-diketone at the air-droplet interface.

• A good accumulation and accommodation of interface is towards acetylacetone (AcAc). • AcAc isomerization is favorable on acidic interface as "water-bridge" is destroyed. • Carbonyl/hydroxyl O-atom of AcAc displays an energetical preference to hydration. • Unfeasible hydration on acidic interface leads to the accumulation of product. Acetylacetone (AcAc) is a typical class of β-diketones with broad industrial applications due to the property of the keto-enol isomers, but its isomerization and chemical reactions at the air-droplet interface are still unclear. Hence, using combined molecular dynamics and quantum chemistry methods, the heterogeneous chemistry of AcAc at the air-droplet interface was investigated, including the attraction of AcAc isomers by the droplets, the distribution of isomers at the air-droplet interface, and the hydration reactions of isomers at the air-droplet interface. The results reveal that the preferential orientation of two AcAc isomers (keto - and enol -AcAc) to accumulate and accommodate at the acidic air-droplet interface. The isomerization of two AcAc isomers at the acidic air-droplet interface is more favorable than that at the neutral air-droplet interface because the "water bridge" structure is destroyed by H 3 O+, especially for the isomerization from keto -AcAc to enol -AcAc. At the acidic air-droplet interface, the carbonyl or hydroxyl O-atoms of two AcAc isomers display an energetical preference to hydration. Keto -diol is the dominant products to accumulate at the air-droplet interface, and excessive keto -diol can enter the droplet interior to engage in the oligomerization. The photooxidation reaction of AcAc will increase the acidity of the air-droplet interface, which indirectly facilitate the uptake and formation of more keto -diol. Our results provide an insight into the heterogeneous chemistry of β-diketones and their influence on the environment. [Display omitted] [ABSTRACT FROM AUTHOR]