Theoretical and Experimental Study on the Reaction of <i>tert</i>-Butylamine with OH Radicals in the Atmosphere

Abstract

The OH-initiated atmospheric degradation of tert-butylamine (tBA), (CH3)3CNH2, was investigated in a detailed quantum chemistry study and in laboratory experiments at the European Photoreactor (EUPHORE) in Spain. The reaction was found to mainly proceed via hydrogen abstraction from the amino group, which in the presence of nitrogen oxides (NOx), generates tert-butylnitramine, (CH3)3CNHNO2, and acetone as the main reaction products. Acetone is formed via the reaction of tert-butylnitrosamine, (CH3)3CNHNO, and/or its isomer tert-butylhydroxydiazene, (CH3)3CN═NOH, with OH radicals, which yield nitrous oxide (N2O) and the (CH3)3Ċ radical. The latter is converted to acetone and formaldehyde. Minor predicted and observed reaction products include formaldehyde, 2-methylpropene, acetamide and propan-2-imine. The reaction in the EUPHORE chamber was accompanied by strong particle formation which was induced by an acid–base reaction between photochemically formed nitric acid and the reagent amine. The tert-butylaminium nitrate salt was found to be of low volatility, with a vapor pressure of 5.1 × 10–6 Pa at 298 K. The rate of reaction between tert-butylamine and OH radicals was measured to be 8.4 (±1.7) × 10–12 cm3 molecule–1 s–1 at 305 ± 2 K and 1015 ± 1 hPa.