Véronique Nardello

Singlet oxygen generation from H2O2/MoO42-: peroxidation of hydrophobic substrates in pure organic solvents

Abstract Seventeen organic solvents are screened as reaction media to conduct the molybdate-catalyzed disproportionation of hydrogen peroxide into singlet molecular oxygen, 1 O 2 ( 1 Δ g ). The solvents are investigated by resorting to the detection of the infra-red luminescence of 1 O 2 at 1270 nm. Preparative peroxidations of representative substrates are carried out in the most efficient ones. The latter are protic and polar and constitute a simpler alternative to the well suited but more intricate microemulsion systems for the peroxidation of hydrophobic substrates with chemically generated 1 O 2 .

Measurement of photogenerated singlet oxygen (1O2(1Δg)) in aqueous solution by specific chemical trapping with sodium 1,3-cyclohexadiene-1,4-diethanoate

Abstract A new method for the determination of the quantum yields of singlet oxygen ( 1 O 2 ( 1 Δ g ) ) formation in aqueous media is described. It is based on the chemical trapping of 1 O 2 with sodium 1,3-cyclohexadiene-1,4-diethanoate (CHDDE), a specific, water-soluble trap which exhibits transparency to visible and near-UV light. The advantages and limits of this method are illustrated with various photosensitizers: nalidixic acid, rose bengal and sodium tetraphenylporphine tetrasulphonate.

Synthesis and properties of a new cationic water-soluble trap of singlet molecular oxygen

Abstract A new cationic water-soluble trap of singlet oxygen ( 1 O 2 , 1 Δ g ), the bis -9,10-anthracene-(4-trimethylphenylammonium) dichloride (BPAA), gives a specific endoperoxide BPAAO 2 as the sole product and allows the detection and the quantification of 1 O 2 generated from cationic chemical or photochemical sources.

SYNTHESIS AND PHOTOOXIDATION OF SODIUM 1,3-CYCLOHEXADIENE-1,4-DIETHANOATE : A NEW COLORLESS AND WATER-SOLUBLE TRAP OF SINGLET OXYGEN

Abstract The sodium 1,3-cyclohexadiene-1,4-diethanoate has been designed as a new colorless trap for the measurement of photogenerated singlet oxygen in aqueous solution. Kinetic studies carried out by flash and steady-state photolysis have shown that this compound interacts with singlet oxygen via a pure chemical quenching with a rate constant kr equal to (2.6 × 107 ± 0.3) M−1.s−1. The two products obtained by photooxidation have been identified. The major one (88%) is a stable endoperoxide whereas the minor one (12%) is an hydroperoxide which decomposes into a phenolic derivative by prolongated warming at 37 °C.

Olefin oxidation by the system H2O2MoO2−4: competition between epoxidation and peroxidation

Abstract The oxidation of tiglic acid by the catalytic system hydrogen peroxide/molybdate ions is investigated in water under varying conditions of pH. Using similar conditions of temperature and concentrations, we show that two different reaction pathways compete leading either to an epoxide in acidic medium or to an allylic hydroperoxide in alkaline medium. These results are interpreted in terms of the involvement of two peroxomolybdates. Epoxidation probably proceeds via the tetraperoxodimolybdate Mo 2 O 3 (O 2 ) 2− 4 whereas peroxidation involves singlet oxygen, 1 O 2 , ( 1 Δ g ), formed as a result of the decomposition of the triperoxomolybdate MoO(O 2 ) 2− 3 . Finally, experimental conditions are given to obtain selectively the epoxide or the hydroperoxide.

[5] Measurement of photogenerated singlet oxygen in aqueous media

Publisher Summary For many years, much work has been devoted to the involvement of singlet molecular oxygen, O 2 ( 1 Δ g ), in many processes occurring in aqueous environments (biological systems, natural waters, reaction media). Chemical trapping is the most widely used and sensitive method to detect and quantify this excited species. Accordingly, a large number of water-soluble traps have been developed to measure the cumulative amount of 1 O 2 in an aqueous environment. The most selective ones belong to the series of polycyclic aromatic compounds, which react with 1 O 2 according to a [4 + 2] cycloaddition, affording a stable endoperoxide highly specific for 1 O 2 . Popular examples of this type of trap are tetrapotassium rubrene-2,3,8,9-tetracarboxylate (RTC) and disodium 9,10-anthracenedipropanoate (ADP) (Scheme 1). However, these compounds absorb light in the visible range and, accordingly, may themselves act as photosensitizers. Hence, they are unsuitable for the measurement of photogenerated 1 O 2 . Naphthalene derivatives such as disodium 4-methyl-1,3-naphthalenedipropanoate (MNDP) (Scheme 1) or disodium 1,4-naphthalenedipropanoate (NDP) overcome this problem, but these compounds react slowly with 1 O 2 and the endoperoxides thus obtained are unstable. To overcome these problems, a new colorless trap, the disodium 1,3-cyclohexadiene-1,4-diethanoate (CHDDE) 4, has been designed on the basis of a 1,3-cyclohexadienic core. This trap has several advantages: it is readily water soluble, it does not absorb visible light, and it is highly reactive toward 1 O 2 by giving mainly a specific and stable endoperoxide (Scheme 2).

“Dark” Singlet Oxygenation of Hydrophobic Substrates in Environmentally Friendly Microemulsions

The molybdate-catalyzed “dark” singlet oxygenation of hydrophobic compounds with hydrogen peroxide proceeds efficiently with low catalyst loadings (10 –3 mol %) in chlorine-free w/o microemulsions. These micro-heterogeneous systems are composed of sodium dodecyl sulfate (SDS)/n-butanol/water/organic phase, the latter being either a ”green” solvent such as ethyl acetate or a liquid substrate, such as α-terpinene or β-citronellol. Very high reactor yields with improved product/SDS ratio can be obtained for the ”dark” singlet oxygenation of such liquid substrates.

Lanthanum-exchanged zeolites as active and selective catalysts for the generation of singlet oxygen from hydrogen peroxide.

Lanthanum(III)-exchanged zeolites Beta and USY are active and selective catalysts for the generation of singlet oxygen from H2O2 showing superior activity and oxidant efficiency compared to unsupported La-catalysts, e.g. La(OH)3.

Identification of the precursor of singlet oxygen (1O2, 1Δg) involved in the disproportionation of hydrogen peroxide catalyzed by calcium hydroxide

Catalytic disproportionation of hydrogen peroxide by calcium hydroxide generates singlet molecular oxygen 1O2 (1Δg) through the diperoxohydrate peroxide CaO2·2H2O2 with a 50% yield based on the calcium peroxide.