Degradation by Photooxidation

The photooxidative degradation of anhydride-cured epoxies was studied. The degradation was heterogeneous, the surface being much more affected than the bulk. The disappearance rate of aromatic groups was dependent only upon their initial concentration, while the formation kinetics of hydroxyl groups was determined by the diffusion of oxygen into the material. The formation of hydrophilic products. 

The photooxidation of a nonwoven PE fabric showed hydroperoxide, alcohol, aldehyde, ketone, carboxylic acid, and anhydride groups were formed as the products of the photooxidation of the PE fabric and the relative amount of carboxyl increased as the photooxidation progressed. Distribution of the photooxidation products was inhomogeneous between the two surfaces of the fabric. The UV radiation at 254 nm caused photooxidation of PE. No photooxidation was observed in the fabric exposed to the UV radiation at 350 nm under the same conditions (288). 

PEO and polymethyl vinyl ether were UV irradiated in hydrogen peroxide solutions. Hydroxy and hydroperoxy radicals accelerate the oxidative degradation of these polymers. Hydroxy and possibly hydroperoxy radicals can abstract hydrogen from methylene groups in both polymers. As a result of further oxidative reactions, different carbonyl, hydroxy and hydroperoxy groups are formed (297). 

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One of the first substances to be developed was permethrin. This substance differs from the natural pyrethroids in that two methyl groups have been replaced by chorine atoms, and an unstable side chain has been altered so that the substance is not so easily degraded by photooxidation or by enzymes in the insects. 

When several sources of energy are combined to cause degradation, their synergism can be sometimes spectacular. For instance, degradations by photooxidation and thermal oxidation are particularly effective—in particular, in the degradation of polyethylene films. 

Knoevenagel K, Himmelreich R. 1976. Degradation of compounds containing carbon atoms by photooxidation in the presence of water. Arch Environ Contain Toxicol 4 324-333. 

The major fate mechanism of atmospheric 2-hexanone is photooxidation. This ketone is also degraded by direct photolysis (Calvert and Pitts 1966), but the reaction is estimated to be slow relative to reaction with hydroxyl radicals (Laity et al. 1973). The rate constant for the photochemically- induced transformation of 2-hexanone by hydroxyl radicals in the troposphere has been measured at 8.97x10 cm / molecule-sec (Atkinson et al. 1985). Using an average concentration of tropospheric hydroxyl radicals of 6x10 molecules/cm (Atkinson et al. 1985), the calculated atmospheric half-life of 2-hexanone is about 36 hours. However, the half-life may be shorter in polluted atmospheres with higher OH radical concentrations (MacLeod et al. 1984). Consequently, it appears that vapor-phase 2-hexanone is labile in the atmosphere. 

Atmospheric formaldehyde is rapidly degraded by photolysis and photooxidation. It will undergo significant biodegradation in the soil or in water and shows no evidence of bioconcentration in several types of fish and shrimp. 

Oxygen and suitable catalysts can also be used for the conversion of phenol to ben-zoquinone. Thus, irradiation of phenol in the presence of [Cu(bpy)2] or [Cu(l,10-phenanthroline)] + brings about degradation by a path that shows both pH and solvent dependency . Thus in acetonitrile benzoquinone predominates, but in water carbon dioxide is the sole product. Benzoquinone can also be formed from phenol by continuous irradiation in the presence of the catalysts [Crfbpyfs] or less effectively with [Ru(bpz)3] + and [Ru(bpy)3] +. The reaction path involves 02( A ) as the oxidant . Porphyrins such as 5,10,15,20- tetrakis(2,6-dichlorophenyl)porphyrin and chlorins can also be used to convert naphthols and phenols to the corresponding quinones (Scheme 28) . Phthalocyanines immobilized on polymers have also been used as the catalyst system to effect photooxidation. ... 

PROBABLE FATE photolysis possible but actual significance is uncertain will also degrade by reactions with radicals oxidation oxidation by metal cations is very fast, reactions with oxygen and/or hyperoxy radicals are very important, photooxidation half-life in water 1.3-72.5 days, photooxidation half-life in air 0.312-3.12 hrs hydrolysis not an important process volatilization not an important process sorption very rapid adsorption by clay minerals, if spilled on soil, it will adsorb to it, especially if the soil is acidic biological processes no bioaccumulation, only slight biodegradation... 

PROBABLE FATE photolysis photolysis to quinones is rapid, but is greatly hindered by adsorption, atmospheric and aqueous photolytic half-life 1-3 hrs, in the unadsorbed state, will degrade by photolysis from hours to days oxidation oxidation by alkyl peroxy radicals could compete with photolysis dissolved benzo (a) anthracene, photooxidation half-life in water 3.2-160 days photooxidation oxidation half-life in air 0.801-8.01 hrs hydrolysis not an important process volatilization to slow to compete with sorption as a transport process sorption very strong adsorption by suspended solids is the principal transport process, when released to water, will quickly adsorb to sediment or particulate matter biological processes short-term bioaccumulation is accompanied by metabolization, biodegradation is the principal fate, but occurs slowly... 

PROBABLE FATE photolysis-, direct photolysis is probably not important, if released to atmosphere, will degrade by reaction with photochemically produced hydroxyl radicals (estimated half-life 1.15 days) oxidation photooxidation in atmosphere can occur, photooxidation half-life in air 4.61-46.1 hrs hydrolysis slow hydrolysis of carbon-chlorine bond, may be important fate mechanism volatilization if released to water, volatilization is expected to be the principle removal process, but may be slow, volatilization half-lives for a model river (1 m deep) and a model environmental pond 13.9 hr, and 6.6 days respectively sorption adsorption on organic matter is possible biological processes no data on bioaccumulation or biodegradation... 

PROBABLE FATE photolysis-, direct photolysis is not significant, photodissociation in stratosphere to chloroacetyl chloride oxidation photooxidation in water expected to be slow primarily removed in air by photooxidation degraded in atmosphere by reaction with hydroxyl radicals, half-life of 1 month and 1.9% loss/12 hr sunlit day products of photooxidation CO and HCl oxidation half-life 1.5 weeks-4 months hydrolysis not significant first-order hydrolytic half-life 1.1 yr volatilization high vapor pressure causes rapid volatilization, major transport process, half-life 30 min 25°C evaporation primary removal from water half-life from 1 ppm solution 25°C, still air, and an avg. depth of 6.5 cm 28 min., evaporation from water 25 °C of 1 ppm solution 50% after 29 min. and 90% after 96 min. 

PROBABLE FATE photolysis insufficient data, but photolysis may be very important, atmospheric and aqueous photolytic half-lives 21 hrs-2.6 days, in the unadsorbed state, it will degrade by photolysis with a half-life of a few days to a week oxidation chlorine and/or ozone in sufficient quantities may oxidize fluoranthene, photooxidation half-life in air 2.02-20.2 hrs hydrolysis not an important process volatilization not an important transport process sorption adsorption onto suspended solids and sediments is probably the dominant transport process, when released to water, it will quickly adsorb to sediment and particulate matter in the water... 

Photodecomposition, especially photooxidation, destabilizes pesticides in terms of further metabolic degradation by microorganisms. Many photolysis products are identical to the metabolites produced by living organisms. Does the DDD [l,l-dichloro-2,2-bis(p-chlorophenyl)ethane] detected in surface waters (59) represent the photoreduction of DDT or metabolism ... 

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