Ozonation of aromatics

Ozonation of Aromatics. Aromatic ring unsaturation is attacked much slower than olefinic double bonds, but behaves as if the double bonds in the classical Kekule stmctures really do exist. Thus, benzene yields three moles of glyoxal, which can be oxidized further to glyoxyUc acid and then to oxahc acid. Substituted aromatics give mixtures of aUphatic acids. Ring substituents such as amino, nitro, and sulfonate are cleaved during ozonation. 

Ozonization of aromatic hydrocarbons is possible. Benzene itself gives ethanedial (glyoxal) ... 

Advanced Chemical Oxidation (ACO) treatment of dye wastewater, a. Ozonation of Aromatic Dyes... 

CHAPTER 4 RESULTS DISCUSSION ADVANCED CHEMICAL OXIDATION (ACO) TREATMENT OF DYE WASTEWATER - OZONATION OF AROMATIC DYES... 

The ozonization of aromatic compounds is more interesting and complex in that each bond in the aromatic system has a certain degree of double bond character and this is reflected in the amounts of ozonization products since this reaction is specific for do >le bonds. Benzene, for example, has six bonds of equal double bond character. This can be represented by its two Kekul resonance structures which we must realize do not denote independent, existing forms but they do approximate the relative amount of double bond character for each bond. 

Recent papers reporting on oxidation reactions of dithio-esters deal with ozonization of aromatic dithio-esters to give the corresponding sulphines, " permanganate oxidation of dithio-esters to give the corresponding thiolo-esters, and iodine oxidation of 2-phenyl-3-anilinopropenedithioates to isothiazolium tri-iodides. ... 

Environmental Impact of Ambient Ozone. Ozone can be toxic to plants, animals, and fish. The lethal dose, LD q, for albino mice is 3.8 ppmv for a 4-h exposure (156) the 96-h LC q for striped bass, channel catfish, and rainbow trout is 80, 30, and 9.3 ppb, respectively. Small, natural, and anthropogenic atmospheric ozone concentrations can increase the weathering and aging of materials such as plastics, paint, textiles, and mbber. For example, mbber is degraded by reaction of ozone with carbon—carbon double bonds of the mbber polymer, requiring the addition of aromatic amines as ozone scavengers (see Antioxidants Antiozonants). An ozone decomposing polymer (noXon) has been developed that destroys ozone in air or water (157). 

In addition to reactions with HO, tropospheric organic compounds may be oxidized by ozone (via ozonation of non-aromatic carbon/carbon double bonds, Atkinson 1990) and in some cases by reaction with nitrate radical, described below. Table I gives representative trace-gas removal rates for these three processes. In spite of these competing reactions, HO largely serves as... 

Ozone-Mediated Nitration of Aromatic Compounds with Lower Oxides of Nitrogen," Mori, T. Srnm Synlett, 1995, 383... 

The Effect of Mineral Matters on the Decomposition Ethers. Recently, the effect of mineral matters of coal on the coal liquefaction has received much attention. It was shown that small amounts of FeS or pyrite are responsible for the hydro-genative liquefaction of coal. Therefore, it is interesting to elucidate the effect of mineral matters of coal on the decomposition rate and products of aromatic ethers, and so three diaryl ethers were thermally treated in the presence of coal ash obtained by low temperature combustion of Illinois No.6 coal at about 200°C with ozone containing oxygen. 

As the reaction temperature is increased, chemiluminescence is observed in the reactions of ozone with aromatic hydrocarbons and even alkanes. Variation of temperature has been used to control the selectivity in a gas chromatography (GC) detector [35], At room temperature, only olefins are detected at a temperature of 150°C, aromatic compounds begin to exhibit a chemiluminescent response and at 250°C alkanes respond, giving the detector a nearly universal response similar to a flame ionization detector (FID). The mechanisms of these reactions are complex and unknown. However, it seems likely that oxygen atoms produced in the thermal decomposition of ozone may play a significant role, as may surface reactions with 03 and O atoms. 

Ozone vigorously reacts with the double bonds of alkenes and quite rapidly with the iT-bonds of aromatic rings. Its reaction with the C—H bonds of hydrocarbons occurs relatively slowly and is accompanied by the formation of free R and HCV radicals followed by the decomposition of the unstable radical H03 (see Chapter 3). 

Cyanoacetaldehyde, freshly prepared by the ozonization of allyl cyanide or ( )-l,4-dicyanobut-2-ene, reacts with primary aromatic amines to give the fi-cyanoenamines 279307. 

Turhan, K., 2001, Investigation of Decomposition Kinetics of Aromatic Compounds with Ozone in Aqueous Solutions, Ph.D. dissertation, Yildiz Technical University, Istanbul, Turkey. 

Parabens are widely used as preservatives in the cosmetic and pharmaceutical industries and also as food additives, due mainly to their bactericidal and fungicidal properties. Terasaki and Makino identified 14 monochloro- and dichloro-parabens formed by chlorination of parabens [117]. Ozonation of parabens in aqueous solutions produced paraben DBPs mainly through hydroxylation of their aromatic ring and/or their ester chain [118]. 

Preliminary chemical oxidation of aromatic hydrocarbons by H2O2 or ozone will improve the biodegradability of these hazardous substances because of the cleavage of aromatic rings. 

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