Kinetic study of the gas phase reactions of a series of alcohols with the NO3 radical.

The rate coefficients for the reaction of NO(3) radical with 2-butanol, 3-methyl-2-butanol, and 2,3-dimethyl-2-butanol were determined using relative rate technique in a 50 L glass pyrex photoreactor using in situ FT-IR spectroscopy at room temperature and a pressure of 350-670 Torr. The rate coefficient for the reaction of 2-methyl-2-butanol with NO(3) radical was also determined using, in this case, GC/MS. The rate coefficients calculated (in units of cm(3) molecule(-1) s(-1)) were (2.51 ± 0.42) × 10(-15), (3.06 ± 0.52) × 10(-15), (2.67 ± 0.3) × 10(-15), and (1.57 ± 0.16) × 10(-15), respectively. Results indicate that the reaction occurs by an initial H-abstraction of the alcohols by the NO(3) radical and that NO(3) is more reactive toward a H atom attached to a tertiary carbon than that attached to a secondary or primary carbon. Results are also discussed as related to their homologous structural alkanes and in comparison with the reactivity of other atmospheric oxidants. Atmospheric relevance of the considered reactions is evaluated, concluding that they are potential ozone generators, they have no significant influence on global warming, and the dominant atmospheric loss process for these alcohols is their daytime reaction with OH radicals.

Night-time atmospheric chemistry of methacrylates.

BACKGROUND, AIM, AND SCOPE: Methacrylates are α, ß-unsaturated esters that are widely used in the polymer plastics and resins production. Kinetic information of NO(3) radical reactions is especially scarce and a good understanding of all the atmospheric oxidation processes of these compounds is necessary in order to determine lifetimes in the atmosphere and to evaluate the impact of these reactions on the formation of ozone and other photooxidants. MATERIALS AND METHODS: The experiments have been carried out using the relative technique in a static Teflon reactor at room temperature and atmospheric pressure (N(2) as bath gas) using gas chromatography (GC)-flame ionization detection (FID) as detection system. Products were analyzed using solid phase microextraction (SPME)-GC-mass spectrometry (MS) technique and Fourier transform infrared spectroscopy (FTIR) using air as bath gas. RESULTS: The following rate coefficients were obtained (in cm(3) molecule(-1) s(-1)): methyl methacrylate + NO(3) = (3.55 ± 0.62) × 10(-15), ethyl methacrylate + NO(3) = (5.42 ± 1.90) × 10(-15), butyl methacrylate + NO(3) = (7.87 ± 3.86) × 10(-15). Methylpyruvate, ethylpyruvate, and butylpyruvate/butanol were identified as main degradation products respectively in the GC-MS analysis. Nitrates compounds were also identified in the FTIR study. DISCUSSION: The reactivity increases with the substitution and with the chain of the alkyl group in -C(O)OR. An electrophilic addition mechanism is proposed as dominant degradation process. Estimations of the atmospheric lifetimes clearly indicate that the dominant atmospheric loss process for methacrylate esters is their daytime reaction with the hydroxyl radical. NO(3) and ozone are the main oxidants at night time. RECOMMENDATIONS AND PERSPECTIVES: A detailed products analysis including quantification could elucidate the mechanism for butanol generation for butyl methacrylate reaction.