Ozone reactions with phenols

The chemistry of ozone is different from chlorine since ozone is a powerful oxidant. For example, hydroxylation is the characteristic reaction with phenol. Ozone is of course free of any complications from formation of chlorinated derivatives. It decomposes quite rapidly in water, the kinetics of the reaction (10) being pH dependent... 

Additionally in the case of ozone reaction with electron-rich compounds, such as phenols (phenolates) and akoxylated aromatics in aqueous phase again OH radicals are formed, most probably via the mechanism of formation of the respective ozone adduct [88,89]. For example it has been established that as a result of the electron transfer from phenol to ozone (reaction 11) at neutral pH the radical anion O3 " is obtained with an 5deld of 22% [90]. 

It has been established that the main products are again OZ, DMPC and AcP but higher amounts of phenol are identified. In addition, the ozone reaction with CHCl yields inorganic chlorocontaining acids and the pH of the medium approaches values of 1-2. These acids (probably HCl and HOCl) are efficient catalysts for the CHP decomposition to phenol. The ratios of the rates are W .,p W. = 2.5 1 and W . W =1 14. 

TS-1 is a material that perfectly fits the definition of single-site catalyst discussed in the previous Section. It is an active and selective catalyst in a number of low-temperature oxidation reactions with aqueous H2O2 as the oxidant. Such reactions include phenol hydroxylation [9,17], olefin epoxida-tion [9,10,14,17,40], alkane oxidation [11,17,20], oxidation of ammonia to hydroxylamine [14,17,18], cyclohexanone ammoximation [8,17,18,41], conversion of secondary amines to dialkylhydroxylamines [8,17], and conversion of secondary alcohols to ketones [9,17], (see Fig. 1). Few oxidation reactions with ozone and oxygen as oxidants have been investigated. 

The dissociation energy of the O—H bond of H03 is 350.4 kJ mol-1 [112]. It can be anticipated that, like peroxyl radicals, ozone reacts with inhibitors (phenols) by the reaction [113] ... 

Kinetic Parameters of Phenols and Amines Reactions with Hydroperoxides, Dioxygen, Ozone, and Nitrogen Dioxide in IPM Model [4,110-114]... 

In this study, synthetic aqueous solutions of phenol were treated with ozone. The reaction of ozone with phenol was investigated at several conditions, such as different phenol and ozone concentrations, and contact times. Total Organic Carbon (TOC) and UV analysis of the aromatic by-products formed during and after the ozonation reaction were employed. The reaction rates calculated from TOC analysis were investigated. 

Seventy-five milliliters of samples were collected from reaction column upper end at different time intervals during the ozonation reaction for the determination of the by products. Ozonation of phenol was carried out at four different initial concentrations, 25, 50, 75 and 100 mg/L, with three different ozone concentrations 2, 4 and 6 g/L h. 

The UV absoibance is used for the preliminary control of the degree of decomposition. The GC/MS and HPLC analysis are used to identily intermediate and final products formed during ozonation. It was found that reaction of ozone with phenol at pH 9, in addition to catechol (C) and hydroquinone (HQ) are likely primary oxidation products, p-benzoquinone (PBQ) and o-benzoquinone (OBQ), the others are more oxidized species, and CO and water the final oxidation products. The detected degradation products are shown in Scheme 24.1. 

Anticipated products from the reaction of phenol with ozone or OH radicals in the atmosphere are dihydroxybenzenes, nitrophenols, and ring cleavage products (Cupitt, 1980). Reported rate constants for the reaction of phenol and OH radicals in the atmosphere 2.8 x 10 " cmVmolecule-sec at room temperature (Atkinson, 1985) and with NO3 in the atmosphere 2.1 x lO" cmVmolecule-sec at 296 K (Atkinson et al., 1984). 

Phenol and aniline quick reaction with ozone. (From Langlais, B. et at., Ozone in Water Treatment Application and Engineering, Lewis Publishers, Boca Raton, FL, 1991. With permission.)... 

Correlation between rate constant for reaction with ozone and Hammett s a constant for substituted phenols. (From Gurol, M.D. and Nekoulnalni, S., Indust. Eng. Chem. Fundam., 23, 1-54, 1984. With permission.)... 

For GC analysis, the salts of the lowest molecular weight acids present in ozonation products subjected to base-promoted hydrolysis have been converted to their benzyl esters by reaction with benzyl bromide (Bonnet et al. 1989). The salts of all acids produced have commonly been converted to the free acids, usually with the aid of a cation exchange resin. The acids have then been converted to methyl esters by reaction with diazomethane (Bonnet et al. 1989) or, more often, have been converted to trimethylsilyl (TMS) esters (Matsumoto et al. 1986, Taneda et al. 1989, Habu et al. 1990). Trimethylsilylation has the major advantage that alcoholic and phenolic hydroxyl groups are simultaneously converted to TMS ethers, thus greatly facilitating GC analysis. 

Surface water photooxidation t,/j = 66-3480 h in water, based on reaction rate constants for OH and ROj radicals with the phenol class (Gtiesten et al. 1981 Mill Mabey 1985 quoted, Howard et al. 1991) rate constant k = (1.2 0.3) x 10 M- s- for the reaction with ozone at pH 1.5/2.0 (Hoign6 Bader 1983) Vj(aerobic) = 2 d, t,//anaerobic) = 15 d in natural waters (Capel Larson 1995)... 

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