A kinetic study on singlet molecular oxygen (O₂(¹Δ_g)) generation and quenching by dihydroxynaphthalenes

Abstract

Abstract:A kinetic study on the aerobic (02('Ag)-mediated) photooxidation of a series of dihydroxynaphthalenes was carried out. Members of this family of compounds include important environmental contaminants. The interaction with 0 2 ( l~g ) , determined by both time-resolved phosphorescence and static methods, yields a quenching rate constant in the range of 10'-lo9 M-I s-l, depending on the solvent polarity, pH, and substitution pattern of the dihydroxynaphthalene. According to experimental evidence, the mechanism of the interaction seems to be mediated by an encounter complex with a considerable charge transfer component. From a mechanistic point of view this characteristic of DHN indicates a behaviour very similar to that of simple substituted phenols and dihydroxybenzenes. Quantum yields for DHN photooxidation (@,) indicate that these substrates are excellent candidates for Oz(l~g)-mediated degradation under environment conditions. Furthermore, these compounds proved to be good self-sensitizers upon irradiation at 337 nm. Quantum yields (QA) for the production of Oz('Ag) were determined to be on the order of 0.25 in benzene.Key words: dihydroxynaphthalenes, photooxidation, quenching, sensitization.RksumC : On a rCalisi une Ctude cinetique de la photooxydation aCrobique (avec midiation par le OZ('Ag)) d'une sCrie de dihydroxynaphtalttnes. Les membres de cette famille sont des contaminants environnementaux importants. L'interaction avec le O2('Ag) a CtC diterminie par des mCthodes statiques ainsi que par phosphorescence rCsolue en fonction du temps et elle conduit h une constante de vitesse de desactivation de I'ordre de lo5 a lo9 M-I s-I, suivant la polarit6 du solvant, le pH et le patron de substitution du dihydroxynaphtalkne. Sur la base des donnCes expCrimentales obtenues, il semble que le mecanisme de I'interaction soit I'objet d'une mediation de la part d'un complexe de rencontre qui implique une composante importante de transfert de charge. D'un point de vue mecanistique, cette caractbristique du DHN indique un comportement trks semblable a celui des phCnols et des dihydroxybenzenes simples, substituks. Les rendements quantiques pour la photooxydation du DHN (@, ) indiquent que ces substrats sont d'excellents candidats pour des digradations avec midiation du Ol(lAg) dans des conditions environnementales naturelles. De plus, lorsqu'on les a irradiCs i 337 nm, ces composts ont montrk d'excellentes propriCtCs comme autosensibilisateurs. On a ditermint que les rendements quantiques (OA) pour la production du Oz('Ag) sont de l'ordre de 0,25, dans le benzene.

Singlet oxygen (1Δg) production by pterin derivatives in aqueous solutions

“…However, it may be assumed that k t Sens values either do not change drastically at lower pH, or might be even lower as observed for other compounds. 42, 43 Then, reported Φ ∆ app values may be considered as Φ ∆ values. There are significant differences between the Φ ∆ values shown in Table 1, revealing that the nature of the substituent at position 6 on the pterin moiety and the pH considerably affect the capacity of pterins to produce 1 O 2 .…”

Photooxygenations in a bubble column reactor

“…21 Previous studies have shown that 1,5-dihydroxynaphthalene 1 can self-sensitize the photooxidation to 2. 13,22 Irradiation in the absence of any sensitizer, however, resulted in a low conversion to 2 of just 8% (entry 4). The influence of the irradiation time and the air flow rate was furthermore investigated in aqueous tert-amyl alcohol with rose bengal as sensitizer and a 500 μm aeration capillary under slug flow conditions (Table 4).…”

Photochemical Behavior of 6‐Methylpterin in Aqueous Solutions: Generation of Reactive Oxygen Species¶

“…K Sens t was not measured in acidic medium; therefore, the determined value of quantum yields of 1 O 2 production for the acid form (pD = 5.4), 0.10 ± 0.02, is a φ app Δ value. However, it may be assumed that the k Sens t value obtained in alkaline medium ( vide supra ) either does not change drastically at lower pH or might be even lower, as observed for other compounds (50,51). Then, the reported φ app Δ value may be considered as the φ Δ value.…”