Ozone degradation

Ozone degradation Ozone Check Gibitre, Italy available from Negretti Automation ... 

One of the chief uses of chloromethane is as a starting material from which sili cone polymers are made Dichloromethane is widely used as a paint stripper Trichloromethane was once used as an inhalation anesthetic but its toxicity caused it to be replaced by safer materials many years ago Tetrachloromethane is the starting mate rial for the preparation of several chlorofluorocarbons (CFCs) at one time widely used as refrigerant gases Most of the world s industrialized nations have agreed to phase out all uses of CFCs because these compounds have been implicated m atmospheric processes that degrade the Earth s ozone layer... 

A technique based on ozonation, in contrast, provides information on the stmcture of the lignin side chain by degrading the aromatic rings (33). Thus the side chain of the dominant stmcture ia all native lignins, the arylglycerol—P-aryl ether moiety, can be obtained ia the form of erythronic and threonic acids. Ozonation proves to be an elegant method for determination of the stereospecificity ia lignin. 

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). 

Antiozonants (qv) prevent or reduce polymer degradation by the active ozone molecule. Some antioxidant compounds, such as the /)i7n7-phenylenediamines, are excellent as antiozonants (36). The protection by these compounds is thought to be either a reaction with the ozone before it can react with the surface of the mbber or an aid in reuniting chains severed by ozone (37). 

Ozone can be used to completely oxidize low concentrations of organics in aqueous streams or partially degrade compounds that are refractory or difficult to treat by other methods. Compounds that can be treated with ozone include alkanes, alcohols, ketones, aldehydes, phenols, benzene and its derivatives, and cyanide. Ozone readHy oxidizes cyanide to cyanate, however, further oxidation of the cyanate by ozone proceeds rather slowly and may require other oxidation treatment like alkaline chlorination to complete the degradation process. 

Ozonation can be enhanced by the addition of ultraviolet (uv) radiation. This combination can be effective in degrading chlorinated organic compounds and pesticides. In addition, metal ions such as iron, nickel, chromium, and titanium [7440-32-6] can act as catalysts, as can ultrasonic mixing. 

The common oxidants are ozone, hydrogen peroxide, H2O, catalyzed usually with ferrous iron, Fe , and ia some cases chlorine dioxide and uv light. Advanced oxidation systems iaclude H2O2 + uv ozone + uv and H2O2, ozone, and uv. Depending on the appHcation, the oxidation can be complete to end products as in a contaminated groundwater or partial to degradable intermediate products as in a process wastewater. 

Ai,Af-Disubstituted- -phenylenediamines, such as A/-phenyl-Af -(l,3-dimethylbutyl)-/)-phenylenediamine [793-24-8] (10), are used in greater quantities than other classes of antioxidants. These products protect unsaturated elastomers against oxidation as well as ozone degradation (see Antiozonants). 

Polyisobutylene has the chemical properties of a saturated hydrocarbon. The unsaturated end groups undergo reactions typical of a hindered olefin and are used, particularly in the case of low mol wt materials, as a route to modification eg, the introduction of amine groups to produce dispersants for lubricating oils. The in-chain unsaturation in butyl mbber is attacked by atmospheric ozone, and unless protected can lead to cracking of strained vulcanizates. Oxidative degradation, which leads to chain cleavage, is slow, and the polymers are protected by antioxidants (75). 

O-rings, especially Buna-N (Nitrile compound), should be stored away from fluorescent lighting and electric motors. These are sources of ozone. Ozone causes a general degradation of these elastomers. 

This method for the preparation of cyclobutanone via oxaspiropentane is an adaptation of that described by Salaiin and Conia. The previously known large-scale preparations of cyclobutanone consist of the reaction of the hazardous diazomethane with ketene, the oxidative degradation or the ozonization in presence of pjrridine of methylenecyclobutane prepared from pentaerythritol, or the recently reported dithiane method of Corey and Seebach, which has the disadvantage of producing an aqueous solution of the highly water-soluble cyclobutanone. A procedure involving the solvolytic cyclization of 3-butyn-l-yl trifluoro-methanesulfonate is described in Org. Syn., 54, 84 (1974). 

Since the mid-1950s several materials have been found effective in combating ozone-initiated degradation, in particular certain p-phenylenediamine derivatives. The actual choice of such antiozonants depends on the type of polymer and on whether or not the polymer is to be subject to dynamic stressing in service. Since antiozonants are not known to have any use in plastics materials, even those which may have certain rubber particles for toughening, they will not be dealt with further here. Anyone interested further should consult references 3-5. 

MURRAY, R. w.. Chapter entitled Prevention of Degradation by Ozone in Polymer Stabilization (Ed. HAWKINS, w. L.), Wiley, New York (1972)... 

As with c -polyisoprene, the gutta molecule may be hydrogenated, hydro-chlorinated and vulcanised with sulphur. Ozone will cause rapid degradation. It is also seriously affected by both air (oxygen) and light and is therefore stored under water. Antioxidants such as those used in natural rubber retard oxidative deterioration. If the material is subjected to heat and mechanical working when dry, there is additional deterioration so that it is important to maintain a minimum moisture content of 1%. (It is not usual to vulcanise the polymer.)... 

With rubber base adhesives, it is necessary to prevent their properties from changing during service life. Oxidative changes induced by thermal, ozone exposure and UV light can dramatically affect service life of rubber base adhesives. More precisely, the rubber and the resin are quite susceptible to oxidative degradation. Environmental and physical factors exert detrimental effects on rubber base adhesive performance. These effects can be mitigated by the incorporation of low levels of stabilizers during the fabrication process of the adhesive. 

Degradation of rubbers and resins can also be produced by ozone attack. Ozone directly reacts with, and cleaves, the carbon-carbon double bonds of rubbers and resins. Thus only polymers with backbone unsaturation will be cracked by ozone. Unlike oxidation, ozone attack cannot be accelerated by increasing the... 

Brittleness with age. Degradative oxidation can be produced, even after vulcanization, due to oxygen and ozone attack to the carbon-carbon double bonds. Adequate antioxidants must be added if ageing is a key factor in performance. 

Environmental Fate. A portion of releases of toluene to land and water will evaporate. Toluene may also be degraded by microorganisms. Once volatilized, toluene in the lower atmosphere will react with other atmospheric components contributing to the formation of ground-level ozone and other air pollutants. 

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