Fenton’s reagent, hydrogen peroxide

Oxidation. Oxidation is one of the main chemical methods to treat and decompose dyes in wastewater. The oxidation agents used ate chlorine, bleach, ozone, hydrogen peroxide, Fenton s reagent, and potassium permanganate. 

One method of generating hydroxyl radicals is by a dding a soluble iron salt to an acid solution of hydrogen peroxide (Fenton s reagent) (176—180), ie ... 

The uv—hydrogen peroxide system has advantages over the iron—hydrogen peroxide (Fenton s reagent) procedures, eg, the reaction is not limited to an acid pH range and the iron catalyst and resulting sludges are eliminated. However, the system to date is not effective for dye wastewaters because of absorption of uv by colored effluent. 

Venkatadri, R. and Peters, R.W., Chemical oxidation technologies ultraviolet light/ hydrogen peroxide, Fenton s reagent, and titanium dioxide-assisted photocatalysis, Hazardous Waste Hazardous Mater., 10, 107-149, 1993. 

The first example of the direct hydroxylation of arenes to phenols was reported in 1900 and described oxidation of benzene with a mixture of iron(II) sulfate and hydrogen peroxide (Fenton s reagent) [1], Low yields of phenol (21% yield based on H202) are typically obtained in such cases, in addition to significant amounts of biphenyl (24% yield based on H202) [1-3]. Both selectivity to phenol and overall... 

Mechanisms have been proposed for the model system, but before discussing them it will be useful briefly to review current ideas about the related but simpler system, ferrous ion-hydrogen peroxide (Fenton s reagent) (see 27,30,31,266,651,771,790,798). 

Fenton s reagent. To a solution of tartaric acid or a tartrate add 1 drop of freshly prepared ferrous sulphate solution, i drop of hydrogen peroxide solution and then excess of NaOH solution an intense violet coloration is produced, due to the ferric salt of dihydroxyfumaric acid, HOOC C(OH) C(OH)COOH. 

Hydrogen peroxide may react directiy or after it has first ionized or dissociated into free radicals. Often, the reaction mechanism is extremely complex and may involve catalysis or be dependent on the environment. Enhancement of the relatively mild oxidizing action of hydrogen peroxide is accompHshed in the presence of certain metal catalysts (4). The redox system Fe(II)—Fe(III) is the most widely used catalyst, which, in combination with hydrogen peroxide, is known as Fenton s reagent (5). 

The Tf- CF system is preferred over Fenton s reagent because Ti4 is a less powerful oxidizing agent than Fc5+ and the above mentioned pathway and other side reactions are therefore of less consequence.252 Much of the discussion on redox initiation in Section 3.3.2.6.1 is also relevant to hydrogen peroxide. 

The use of hydrogen peroxide in conjunction with Fe(II) (Fenton s reagent) or ozone has already been noted. It has been nsed alone to examine the products from o - and m-phenylenediamines in the context of their mntagenicity (Watanabe et al. 1989). Successive reactions produced 3,4-diaminophenazine from o-phenylenediamine, and 3,7-diaminophenazine from m-phenylenediamine. 

Contaminated soil from a manufactured coal gas plant that had been exposed to crude oil was spiked with acenaphthene (400 mg/kg soil) to which Fenton s reagent (5 mL 2.8 M hydrogen peroxide 5 mL 0.1 M ferrous sulfate) was added. The treated and nontreated soil samples were incubated at 20 °C for 56 d. Fenton s reagent did not promote the mineralization of acenaphthene by indigenous microorganisms to any appreciable extent. The mineralization of acenaphthene was enhanced only 1.2-fold when compared with the nontreated control sample. The amounts of acenaphthene recovered as carbon dioxide after treatment with and without Fenton s reagent were 20 and 17%, respectively (Martens and Frankenberger, 1995). 

August et al. (1998) conducted kinetic studies for the reaction of benzene (0.2 mM) and other monocyclic aromatics with Fenton s reagent (8 mM hydrogen peroxide [Fe ] = 0.1 mM) at 25 °C. They reported a reaction rate constant of 0.0530/min. 

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