Ozone, oxidative degradation

The unsaturated structure of the diene hydrocarbon rubbers makes them susceptible to attack by both oxygen and ozone. Oxidative degradation of all rubbers, irrespective of their structures, is inevitable as the energy associated with incident natural light is approximately three times that of a typical carbon-carbon or carbon-hydrogen bond. 

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). 

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). 

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. 

Oxidative degradations of aldehyde derived enamines with ozone (4) or sodium dichromate (485-487) have been applied to the formation of progesterone from 3-ketobisnor-4-cholenaldehyde. 

The double bond present in the diene part of the elastomer is generally more susceptible to thermal and oxidative degradation. The selective hydrogenation of olefmic unsaturation in NBR imparts significant improvements in resistance to degradation and other properties, such as permeability, resistance to ozone and chemicals, and property retention at high temperature. 

Lang PS, W-K Ching, DM Willberg, MR Hoffmann (1998) Oxidative degradation of 2,4,6-trinitrotoluene by ozone in an electrohydraulic discharge reactor. Environ Sci Technol 32 3142-3148. 

Oxidant Removal The presence of oxidizers such as chlorine or ozone can degrade polyamide RO membranes, causing a drop in salt retention. Cellulosic membranes are less sensitive to attack. Addition of 1.5 to 6 mg sodium bisulfite/ppm chlorine or contacting with activated carbon will remove oxidizers. Vacuum degassing with a hydrophobic filter module is also used. 

Ermawati R, Morimura S, Tang YQ, Liu K, Kida K (2007) Degradation and behavior of natural steroid hormones in cow manure waste during biological treatments and ozone oxidation. J Biosci Bioeng 103 27-31... 

As discussed above, ufa, which are present primarily in cellular membranes, appear to be particularly susceptible to oxidative degradation by ozone. Various studies of membrane lipid peroxidation have implicated this process in damage to organelles, including mitochondria, micro-somes, and lysosomes, as well as to the cell membrane itself. By analogy, it is conceivable that many of the findings in cells and subcellular components described in other sections of this chapter are secondary to ozone-induced lipid peroxidation. However, this remains conjectural. 

While polymers that contain sites of unsaturation, such as polyisoprene and the polybutadienes, are most susceptible to oxygen and ozone oxidation, most other polymers also show some susceptibility to such degradation including NR, PS, PP, nylons, PEs, and most natural and naturally derived polymers. 

Another factor in oxidative degradation is ultraviolet radiation, of which sunlight is a rich source. The oxidation of parylene appears to be enhanced by ultraviolet radiation. Ozone may play a mechanistic role in the ambient temperature exposure of parylenes to ultraviolet radiation in the presence of oxygen. For the best physical endurance, exposure of the parylenes to ultraviolet light must be minimized. 

Beltran et al. (1995) concluded that (1) the UV/ozone oxidation process can achieve high removal rates of fluorene, phenanthrene, and acenaph-thene, with total efficiencies being near 100% in some cases (2) neutral pH of 7 yields the highest removal rate of fluorene in solution and (3) the greater the bicarbonate concentration added to fluorene, the lower the removal efficiency becomes. When an excess of ozone is present in the reaction mixture, the degradation rate of anthracene, phenanthrene, and pyrene can be given as ... 

Oxidation is, of course, the dominant reaction. For example, vaporized trifluralin ( a, a, < -trifluoro-2,6-dinitro-ll,ll-dipropyl-p-toluidine) was demethylated (Figure 7) (26), and its atmospheric half-life was found to be 8 minutes (27). However, the reaction occurred to a small extent even at night, and oxidation by ozone was implicated. In fact, there is evidence (28) that parathion photooxidation actually required the presence of ozone or other highly reactive oxidants. Degradation not requiring external reagents also may proceed rapidly trifluralin was cyclized to a substituted benzimidazole (11, 26), and dieldrin again formed photodieldrin (29). 

Oxidation rate constant k, for gas-phase second order rate constants, k0H for reaction with OH radical, kNQ3 with N03 radical and kG3 with 03 or as indicated, data at other temperatures see reference k (oxidative degradation rate of water dissolved PCDD by ozone) is 1.27 x 106 L g 1 min-1 under alkaline conditions at pH 10 and 20°C (Palauschek Scholz 1987) kOH(calc) = (21-22) 10 12 cm3 molecule-1 s 1 at room temp. (Atkinson 1991)... 

Groundwater oxidative degradation rate of water dissolved PCDD by ozone k = 1.27 x io6 L g-1 min-1 under alkaline conditions at pH 10 and 20°C (Palauschek Scholz 1987). 

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