Petr Sedlák

Photoinitiated reactions of hydrogen peroxide in the liquid phase

Abstract This review introduces the most commonly known types of photoinitiated reactions of hydrogen peroxide. In the first part the photolysis of hydrogen peroxide is discussed. Particular attention is paid to the photocatalytic effects of transition metals and a mechanism of their photocatalytic action is proposed. In the second part the photoinitiated reactions of hydrogen peroxide with inorganic and organic compounds are discussed. Attention is also devoted to the exploitation of these reactions in environmental protection.

Methylene-blue-sensitized photochemical hydroxylation of 2-hydroxybenzoic acid by hydrogen peroxide: photocatalytic effect of ferric chloride

Abstract The methylene-blue-sensitized hydroxylation of 2-hydroxybenzoic acid by hydrogen peroxide initiated by visible radiation and catalysed by ferric chloride has been investigated. The major reaction product is 2,3-dihydroxy-benzoic acid. In the absence of iron(III), the reaction occurs extremely slowly. Iron(III) is observed to have an appreciable catalytic effect on the photosensitized reaction at concentrations as low as 10 −8 M. The first step of the reaction is the photochemical reduction of iron(III) to iron(II), i.e. the generation of Fentons reagent.

Photocatalytic effects of Fe(III) compounds on the hydroxylation of benzoic acid by hydrogen peroxide initiated by UV-radiation

The addition of FeCl3 and Na2[Fe(CN)5NO] increases the quantum yields of photochemical hydroxylation of benzoic acid by hydrogen peroxide. The photocatalytic effects operate especially when the radiation is absorbed by benzoic acid. When hydrogen peroxide is excited, the catalytic effects in the hydroxylation are small.AbstractДобавки FeCl3 и Na2[Fe(CN)5NO] повышают квантовые выходы фотохимического гидроксилирования бензойной, кислоты перекисью водорода. Фотокаталитические эффекты проявляются особенно тогда, когда радиация абсорбируется бензойной кислотой. Нри возбуждении перекисн водорода каталитический эффект гидроксииирования мал.

Photocatalytic effects of Fe(III) compounds on the hydroxylation of benzoic acid by hydrogen peroxide initiated by 589 nm radiation and sensitized by methylene blue

Abstract The hydroxylation of benzoic acid by hydrogen peroxide initiated by 589 nm radiation is catalyzed by the following Fe(III) compounds: FeCl3, K3[Fe(C2O4)3], Na2[Fe(CN)5NO], and K3[Fe(CN)6]. This photochemical reaction can be effectively sensitized by methylene blue.

Photochemical hydroxylation of salicylic acid by hydrogen peroxide. Photocatalytic effect of Fe(III)

The rate and quantum yields of photoinitiated hydroxylation of salicylic acid by hydrogen peroxide can be increased substantially by adding Fe(III) compounds to the reaction mixture. The UV radiation reduces the catalytically inactive Fe(III) to catalytically active Fe(II) during the reaction, thereby continuously producing the Fenton reagent.AbstractСкорость и квантовые выходы фотоинициированного гидроксилирования салициловой кислоты с помощью перекиси водорода могут быть значительно повышены добавлением соединений Fe(III) к реакционной смеси. У Ф облучение восстанавливает каталитически неактивное Fe(III) до каталитически активного Fe(II) в ходе реакции, тем самым неапрерывно вырабатывая раегент фентона.

Photocatalytic effects of halogenpentaamminecobalt(III) complexes on hydrogen peroxide photolysis

Abstract The effects of [Co III (NH 3 ) 5 L]A n compounds (LNH 3 , H 2 O, F − , Cl − , Br − , I − , CO 3 2− ; ACl − , Br − , I − , NO 3 − ; n = 1–3) on the thermal decomposition and photolysis of hydrogen peroxide (λ irr =365 nm) were studied. Complexes containing the fluoride anion are almost inactive in terms of their catalytic/photocatalytic effects, whereas those containing the iodide anion catalyse the thermal reaction effectively. The [Co(NH 3 ) 5 Cl]Cl 2 and [Co(NH 3 ) 5 Br]Br 2 complexes show significant photocatalytic effects including an autocatalytic reaction and a marked post-irradiation effect. The photocatalytic activity is explained by the photochemical reduction of the central ion and the subsequent formation of the peroxo complexes of the [Co II (NH 3 ) 5 O 2 Co II (NH 3 ) 5 ] 4+ type.

Photochemical degradation of pesticides: photocatalytic effect of Fe(III) ions on methylene blue sensitized interaction of 4-chlorophenoxyacetic acid with H2O2.

In our previous papers (Lun~k et al 1987, 1989a) we have described marked photosensitizing effects of methylene blue, as well as the photocatalytic effects of Fe(III) ions, on hydroxylation of some aromatic substrates (i.e., benzoic acid and 2-hydroxybenzoic acid) using hydrogen peroxide. The two effects have been evidenced (Lun~k et al 1987) even at very low additions of both the photocatalyst and the photosensitizing agent, of the order of 0.01 ~M.

Photolysis of Hydrogen Peroxide. Photocatalytic Effects of Bromopentaamminecobalt(III) Bromide

Since 1957, when BAXENDALE and WILSON [1] discovered the strong catalytic effect of Cu + on the photolysis of hydrogen peroxide, there have been several studies examining catalytic action of various transition metals on this reaction [2-6]. With the exception of ALEXANDER and ROUNDHILL [7], who investigated the catalytic effects of dichenium decacarbonyl, most workers have reported on photocatalytic effects of Cu(II) and Fe(IIl). Our study [8] of the catalytic activity of 3d transition metal ions in the form of sulphates on hydrogen peroxide photolysis has also demonstrated appreciable catalytic effects for Cu(II) and Fe(III) only. However, VARFOLOMEYEV and co-workers [9] have detected photocatalytic effects of bromopentaamminecobalt(III) bromide in photoinitiated oxidations of dyes (Alizarin S) by hydrogen peroxide. Bromopentaamminecobalt(III) bromide serves as a model compound in studies of photochemical reactions of coordination compounds [10, 11], When the complex is irradiated in the region of charge transfer (Ama, = 275 nm), the predominant reaction is photoreduction of Co(III),