Spontaneous Generation of -CH2CN from Acetonitrile at the Air-Water Interface.

Acetonitrile (CH₃CN) is considered a very stable molecule in aqueous solutions, and its deprotonation to produce strongly basic ^-CH₂CN requires harsh conditions. CH₃CN is also present in the atmosphere, but its chemical transformation pathway at the air-water interface is unknown. In this study, we discovered and verified the unprecedented spontaneous generation of ^-CH₂CN from the CH₃CN-H₂O solution at the air-water interface of microdroplets, and revealed the indirect deprotonation mechanism of CH₃CN by synergistic redox of ^•OH and electrons in the microdroplets through the capture of key intermediates and computational chemistry. In addition, the dynamic process of indirect deprotonation-protonation was also observed. The high reactivity of ^-CH₂CN in the droplets was revealed via nucleophilic addition to acetone, benzaldehyde, and the parent CH₃CN molecule. Furthermore, the ^-CH₂CN generated in the microdroplets underwent a barrier-free nucleophilic addition reaction with CO₂ to produce 2-cyanoacetic acid for CO₂ fixation. The synergistic redox reaction process revealed in this study provides new insights into microdroplet chemistry, and the distinctive CH₃CN reactions identified may provide new clues to unravel the mystery of the CH₃CN transformation in the atmospheric environment.