Francisco J. Poblete

Salicylic acid (SA, C ₇ H ₆ O ₃ ) is an aromatic compound widely used in medicine and industry. Its low solubility and partial dissociation in water affect its environmental persistence and transport via atmospheric aerosols, leading to its increasing detection in seawater and sea spray aerosols. Recent European Union regulations have heightened interest in its chemical transformations in natural systems. This study investigated the degradation of SA initiated by ·OH radicals either (1) spontaneously generated at the air–water interface of SA aerosols at 25°C, or (2) in the bulk aqueous phase, where they were produced by UV photolysis ( λ > 300 nm) of H ₂ O ₂ or NO ₃ ⁻ at 25°C. Aerosols were generated by nebulization, stabilized through alkaline deprotonation (pH 8.2), oxidized in a flow tube, collected onto filters and analyzed via ultra‐high‐performance liquid chromatography coupled with high‐resolution mass spectrometry (UHPLC‐HRMS), and at the bulk‐phase products at pH 4.5 were identified also by UHPLC‐HRMS. At the air–water interface, spontaneous dark oxidation yielded maleic acid, catechol, and dihydroxybenzoic acids within a 90‐s timescale. The bulk‐phase chemistry under simulated solar irradiation produced a consistent suite of products; notably, H ₂ O ₂ /UV and NO ₃ ⁻ /UV systems also generated trihydroxylated derivatives, triggering a temporary toxic activation window flagged by REACH Annex III regulations. These results demonstrate that SA undergoes radical‐mediated oxidation in both phases through highly spatially decoupled mechanisms, highlighting its complex role in atmospheric multiphase chemistry.

Advances in science and technology have improved the quality of life but have also contributed to environmental pollution through additives like parabens, commonly used as preservatives in personal care products. This study investigates the degradation of a series of parabens (methylparaben, ethylparaben, propylparaben, and butylparaben) in aqueous-phase solution initiated by peroxynitrous acid (HOONO), an oxidant present in environmental waters. A stopped flow system was employed to follow this oxidation reaction. A reaction mechanism, considering experimental variables, such as pH, temperature, ionic strength, radical scavengers, and reaction products detected, was proposed. This mechanism involves two competitive pathways: a radical attack producing hydroquinone and quinone and a nucleophilic attack by HOONO yielding p-hydroxybenzoic acid, a less ecotoxic compound than parabens. The acidic equilibrium constants of the carbonyl group of parabens and the rate constants for the nucleophilic attack of HOONO on parabens were experimentally determined. Additionally, a structure–reactivity correlation analysis (QSAR) through the Taft equation was applied for the determined equilibrium and nucleophilic attack rate constants. The derived QSAR can be applied to other water-soluble parabens.

Benzaldehyde and its derivatives are used as food supplements. These substances can be used mainly as flavorings or as antioxidants. Besides, peroxynitrite, an oxidizing agent, could be formed in canned food. Both species could react between them. The present article has focused on the kinetic study of the oxidation of aldehydes by peroxynitrite. A reaction mechanism that justifies all the experimental results is proposed. This mechanism, in acidic media, passes through three competitive pathways: (a) a radical attack that produces benzoic acid. (b) peracid oxidation, and (c) a nucleophilic attack of peroxynitrous acid over aldehyde to form an intermediate, X, that produces benzoic acid, or, through a Cannizzaro-type reaction, benzoic acid and benzyl alcohol. All rate constants involved in the third pathway (c) have been calculated. These results have never been described in the literature in acid media. A pH effect was analyzed.

Benzaldehyde and its derivatives are used as food supplements, due to their properties as anti-oxidants and mainly as organoleptic substances. The degradation of these aldehydes produces benzoic acid and benzyl alcohol derivatives, both of which present high toxicity levels. On the other hand, peroxynitrite acts as an oxidizing agent, thus strategies for its production control during food processing could help to improve food quality parameters such as taste, colour and functional properties. Therefore, the control of these degradative oxidation processes is of great interest to the food industry. In order to know in depth this problem, the present article has fo-cused on the kinetic study of the oxidation of aldehydes by peroxynitrite. The proposed mecha-nism justifies all the experimental results, passing through three competitive pathways were per-oxynitrite acts as a radical, nucleophilic or oxidant species. The possible increase of toxic prod-ucts was analyzed.

The reaction of Orange II with peroxynitrous acid has been studied by a spectrophotometrical method. The reaction rate is complex because the order changes from zero to one in function of substrate and oxidant concentration. The influence of pH and ionic strength has been investigated, but their effect on the reaction rate appears to be negligible under the experimental conditions used. A reaction mechanism based on the experimental results is proposed, involving a radical cage solvent attack from peroxynitrous acid to Orange II. Copyright © 2009 John Wiley & Sons, Ltd.

The reactions of 2,3‐butanediol by hexacyanoferrate(III) in alkaline medium using ruthenium compounds as catalysts have been studied spectrophotometrically. The effect on the reaction rate of concentration of substrate, oxidant, catalyst and basicity of the medium leads to similar experimental rate equations for both catalysts, Ru(III) and Ru(VI). The reaction mechanism involves the formation of a catalyst–substrate complex that yields a carbocation for Ru(VI) or a radical for Ru(III) oxidation. Hexacyanoferrate(III)'s role is the catalyst regeneration. The rate constants of complex decomposition and catalyst regeneration have been determined. Copyright © 2006 John Wiley & Sons, Ltd.