Night-time atmospheric chemistry of methacrylates

Methacrylates are α, β-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.

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.

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.

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.

A detailed products analysis including quantification could elucidate the mechanism for butanol generation for butyl methacrylate reaction.