Oxidation, by Fenton s reagent

When lactose is oxidized by Fenton s reagent,23 no osone is formed. 

Chemical/Physical. Oxidation by Fenton s reagent (hydrogen peroxide and Fe " ) produced nitrohydroquinone and 3-nitrocatechol (Andersson et al, 1986). In an aqueous solution (initial pH 5.0), 2-nitrophenol (100 pM) reacted with Fenton s reagent (35 pM). After 60-min and 4-h, about 50 and 90% of the 2-nitrophenol was destroyed, respectively. The pH of the solution decreased due to the formation of nitric acid (Lipczynska-Kochany, 1991). 

Ingles, D.L., Studies of oxidations by Fenton s reagent using redox titration, Australian J. Chem., 25, 87-95, 1972. 

Fig. 2. Zoom into region B oiSiK XANES spectra of rice husk silicas obtained by different treatments, and of some reference compounds a, cristobalite b, fused silica c, precipitated silica d, calcined rice husks (600°C in air for 4 h) e, rice husks oxidized by Caro s acid f rice husks oxidized by Fenton s reagent.

In view of possible commercial applications of rice husk silicas, e.g. as catalyst supports, their surface areas and porosities are important properties. Nitrogen sorption measurements of the three differently treated rice husk silicas show that these are porous materials with moderately large surface areas. The surface areas are, in detail 73 m /g for the calcined material, 75 mVg in the case of the material oxidized by Fenton s reagent and 51 m /g for the rice husks treated with Caro s acid. As the shapes of the ad- and desorption isotherms reveal (Fig. 3), pores ranging from micro- up to macropores are present. 

When benzene is oxidized by Fenton s reagent in the presence of air or oxygen, the only detectable organic product is phenol (that is, equation 76) whereas in the absence of air both phenol and diphenyl are produced (31). This oxygen effect may be due to the interaction of free phenyl radicals with oxygen, forming free radical peroxides, and ultimately phenol, in the presence of ferrous ion. The reaction between free radical and oxygen therefore appears to be faster than the dimerization of the free radical (31). 

Xu X-R, Zhao Z-Y, Li X-Y, Gu J-D (2004) Chemical oxidative degradation of mehyl tert-butyl ether in aqueous solution by Fenton s reagent. Chemosphere 55 73-79... 

Yields of osones obtained by the oxidation of sugars by Fenton s reagent are low, and the osones are invariably contaminated both with starting material and with the products of further oxidation in consequence, the method has had only limited application.44... 

In water, carbofuran reacted with OH radicals at a first-order rate constant of 2.2 x 10 /M-sec (Mabury and Crosby, 1996a). Benitez et al. (2002) reported an apparent pseudo-first-order rate constant ranging from 5.1 x 10to 19.5 x lO Vsec for the reaction of carbofuran with ozone in water. When ozone and UV radiation was used to study the degradation kinetics, the pseudo-first-order rate constant was 22.8 x 10 Vsec. Similarly, the oxidation of carbofuran by Fenton s reagent and UV radiation ranged from 17.2 x 10 to >200 x lO Vsec. 

The feasibility of benzenic ring amines, benzenic ring structures and aliphatic acids oxidation by means of Fenton chemistiy was tested in synthetic, acidic wastewaters by Fenton s reagent electrogenerated at a reticulated vitreous carbon cathode using the flow-cell. The organic molecules considered were phenol (Ph), cresol (Cr), aniline (An) hydroquinone (HQ), catechol (Cat), parabenzoquinone (pBQ) and oxalic acid (OxAc). Their initial... 

Rate equations for the oxidation of aldehydes, RCHO (R = H, Me2CH, Ph, /j-MeOCgHzt), by Fenton s reagent (Fe2+-H2C>2-H+) have been determined.175 The reactions were first order in ferrous ion, peroxide, and aldehyde, except for aromatic aldehydes, where die order in peroxide was measured as 0.5. 

Merz and Waters (1949) showed that oxidation of organic compounds by Fenton s reagent could proceed by chain as well as non-chain mechanisms, which was later confirmed by Ingles (1972). Kremer (1962) studied the effect of ferric ions on hydrogen peroxide decomposition for Fenton s reagent. It was confirmed that once ferric ions are produced the ferric-ferric system is catalytic in nature, which accounts for relatively constant concentration of ferrous ion in solutions. 

It was also shown that the ratio of oxidized alcohol to oxidized Fe2+ could be greater then one. Baxendale and Wilson (1957) showed that hydroxyl radical initiating the chain polymerization of olefins by hydrogen peroxide was the same process as the rapid oxidation of glycolic acid. Merz and Waters (1947) confirmed that simple water-soluble alcohols are oxidized rapidly by Fenton s reagent. The primary alcohols are oxidized to aldehydes, which are further oxidized at comparable rates by exactly the same mechanism. Merz and Waters proposed a mechanism of chain oxidation of alcohols and aldehydes by sodium persulfate, hydrogen peroxide, and an excess of ferrous salt as follows ... 

The oxidation rates for bromoform were slower than the oxidation rates of unsaturated chlorinated aliphatic compounds, including the TCE. Because the hydroxylation rate constant of TCE is 109 Mr1 s 1 and the hydrogen abstraction of bromoform is 1.1 x 108 M 1 s aromatics and alkenes react more rapidly by hydroxyl addition to double bonds than does the more kinetically difficult hydrogen atom abstraction. No oxidative destruction of chloroform by Fenton s reagent was experimentally observed an explanation for this is that both H202 and Fe2+ have rate constants about one magnitude higher with respect to hydroxyl radicals than chloroform. 

Martin et al. (1989) studied the oxidation of HMSA by Fenton s reagent and investigated the decomposition of both hydrogen peroxide and HMSA. They determined an estimate of the absolute rate of reaction between HMSA and hydroxyl radicals. The decomposition of hydrogen peroxide follows the first-order kinetics and can be described as follows ... 

Martin, L.R., Easton, M.P, Foster, J.W., and Hill, M.W., Oxidation of hydroxymethane-sulfonic acid by Fenton s reagent, Atmospheric Environ., 23(3), 563, 1989. 

Tang, W.Z. and Huang, C.P, 2,4-Dichlorophenol oxidation kinetics by Fenton s reagent, Environ. Technol., 17, 1371-1378, 1996a. 

The degradation of 2-deoxyribose by Fenton s reagent has been conducted in acidic, neutral, and alkaline media, and in the presence and absence of hydroxyl-radical scavengers. It seems that both the substrate and the scavengers interact with the metal ions.110 Traces of Fe(II) accelerate the oxidation of carbohydrates by H202, but larger quantities of such a cation has a retarding elfect.111... 

For phenol hydroxylation it is shown that Fe2+ and Fe3+ ion activity increases in the presence of other ions, among which the highest activity is displayed by salts and complexes of the following metals Co, Mn, Mo, Cu, Fe, etc. In aqueous solution Fenton s reagent oxidizes substrates according to the radical mechanism in which reactions with 0H radicals play the central role. In aprotic solvents oxidation with Fenton s reagent suggests the participation of different intermediates—complexes with iron ions, Fe=0, for example. 

The rate constant for the reaction of Fe(II) with hydrogen peroxide is high and Fe(II) is oxidized to Fe(III) in a few seconds in the presence of excess hydrogen peroxide. For this reason, it is believed that the majority of the waste destruction catalysed by Fenton s reagent is simply a Fe(III)-H202-catalysed destruction processes. 

---