Atmospheric degradation of biofuel cyclic esters initiated by chlorine atom: Product yields and ring-retaining oxidation vs. ring opening mechanisms

A product study was carried out for the reaction of γ-caprolactone and γ-heptalactone with Cl atoms at (298 ± 2) K and atmospheric pressure. The experiments were performed in a 480L glass multipass reactor with in situ FT-IR detection. The main products identified and quantified includes (in molar yield %): succinic anhydride (68 ± 2), propanoic acid (25 ± 1), acetaldehyde (59 ± 1), formaldehyde (10 ± 1) and acetic anhydride (26 ± 2) in the Cl atoms with γ-caprolactone reaction. Meanwhile, butanoic acid (26 ± 1), succinic anhydride (70 ± 2), propanaldehyde (63 ± 1) and propanoic acid (11 ± 1) were identified and quantified for Cl atoms with γ-heptalactone reaction. In addition, a chemical mechanism has been proposed taking into account the identified and quantified products. The mechanistic provided by the identified products, reveals that the degradation mechanisms can proceed either through ring opening or oxidation pathways. In these sense, the opening path leads to the carboxylic acids formation and the oxidation forms succinic anhydride. The succinic anhydride quantification, as the major product in both reactions, suggests that the oxidation ring is the most relevant channel in the reactions studied. Considering that the identified acids and anhydrides are of atmospheric importance, due to their potential for acidification of the troposphere and the atmospheric implications have been discussed.