Phenolics Photooxidation

Martianov, I.N., Savinov, E.N., and Parmon, V.N., A comparative study of efficiency of photooxidation of organic contaminants in water solutions in various photochemical and photocatalytic systems. 1. Phenol photooxidation promoted by hydrogen peroxide in a flow reactor, /. Photochem. Photobiol. A Chem., 107, 227-231, 1997,... 

De AK, Bhattacharjee S, Dutta BK. Kinetics of phenol photooxidation by hydrogen peroxide and ultraviolet radiation. Ind Eng Chem Res 1997 36 3607-3612. 

Martyanov IN, Savinov EN, Parmon VN (1997) A Comparative Study of Efficiency of Photooxidation of Organic Contaminants in Water Solutions in Various Photochemical and Photocatalytic Systems. 1. Phenol Photooxidation Promoted by Hydrogen Peroxide in a Flow Reactor, J. Photochem. Photobiol. A Chem. 107 227-231. 

Figure 9.1 reports the photoreduction of silver cations at different initial concentrations. A continuous decrease of silver cations is consistently observed. These rates of photoreduction are much faster than the rates of phenol photooxidation, as it will be described later. 

Both thermooxidation and photooxidation of polyolefins can be prevented by using the same antioxidants as those employed for the stabilization of polypropylene, ie, alkylated phenols, polyphenols, thioesters, and organic phosphites in the amount of 0.2—0.5% (22,25). 

Chen, J., Eberlein, L., and Langford, C.H. (2002) Pathways of phenol and benzene photooxidation using Ti02 supported on a zeolite. Journal of Photochemistry and Photobiology A Chemistry, 148 (1-3), 183-189. 

As a beginning toward understanding and preventing this phenomenon, the effect of selected amines and phenol stabilizers on the pigment-sensitized photooxidation of the leuco triphenylmethane dye I to the blue dye II was determined (Scheme 2). 

Inhibition of T102 - Sensitized Photooxidation of a Leuco Dye by Amines and Phenols... 

Tetrahydrofuran has been reported to exhibit an absorption maximum at 280 nm (52,56), but several workers have shown that this band is not produced by the purified solvent (30,41,57). Oxidation products from THF have been invoked in order to account for the appearance of the 280-nm band in PVC films that are solvent-cast from THF in air (57. 581. However, in some reported cases (56,59), this band was undoubtedly produced, at least in part, by a phenolic antioxidant (2.6-di-tert-butyl-p-cresol)(59) in the solvent. Since certain -alkylphenols have now been shown to be powerful photosensitizers for the dehydrochlorination of PVC (60), it is clear that antioxidant photosensitization might well have been responsible for some of the effects attributed previously (56) to THF alone. On the other hand, enhanced rates of photodegradation under air have also been observed for PVC films cast from purified THF (57), a result which has been ascribed to radical formation during the photooxidation of residual solvent (57,61). Rabek et al. (61) have shown that this photooxidation produces a-HOO-THF, a-HO-THF, and y-butyro-lactone, and they have found that the hydroperoxide product is an effective sensitizer for the photodehydrochlorination of PVC at X = 254 nm (61). 

Photolytic. A photooxidation rate constant of 6 x 10 " cm /molecule-sec at room temperature was reported for the vapor-phase reaction of benzene with OH radicals in air (Atkinson, 1985). The reported rate constant and half-life for the reaction of benzene and OH radicals in the atmosphere are 8.2 x 10 M/sec and 6.8 d, respectively (Mill, 1982). Major photooxidation products in air include nitrobenzene, nitrophenol, phenol, glyoxal, butanedial, formaldehyde, carbon dioxide, and carbon monoxide (Nojima et al., 1975 Finlayson-Pitts and Pitts, 1986). 

Photolytic. Based on data for phenol, a structurally related compound, an aqueous solution containing 1-naphthoxide ion (3 x 10 M) in room light would be expected to photooxidize to give 2-hydroxy-1,4-naphthoquinone (Tomkiewicz et al., 1971). 1-Naphthol, methyl isocyanate, and other unidentified cholinesterase inhibitors were reported as products formed from the direct photolysis of carbaryl by sunlight (Wolfe et al., 1976). In an aqueous solution at 25 °C, the photolysis half-life of carbaryl by natural sunlight or UV light (X = 313 nm) is 6.6 d (Wolfe et al, 1978a). 

Photooxidation of chlorobenzene in air containing nitric oxide in a Pyrex glass vessel and a quartz vessel gave 3-chloronitrobenzene, 2-chloro-6-nitrophenol, 2-chloro-4-nitrophenol, 4-chloro-2-nitro-phenol, 4-nitrophenol, 3-chloro-4-nitrophenol, 3-chloro-6-nitrophenol, and 3-chloro-2-nitrophenol (Kanno and Nojima, 1979). A carbon dioxide yield of 18.5% was achieved when chlorobenzene adsorbed on silica gel was irradiated with light (A. >290 nm) for 17 h. The sunlight irradiation of chlorobenzene (20 g) in a 100-mL borosilicate glass-stoppered Erlenmeyer flask for 28 d yielded 1,060 ppm monochlorobiphenyl (Uyeta et al., 1976). 

Irradiation of toluene in the presence of chlorine yielded benzyl hydroperoxide, benzaldehyde, peroxybenzoic acid, carbon monoxide, carbon dioxide, and other unidentified products (Hanst and Gay, 1983). The photooxidation of toluene in the presence of nitrogen oxides (NO and NO2) yielded small amounts of formaldehyde and traces of acetaldehyde or other low molecular weight carbonyls (Altshuller et al, 1970). Other photooxidation products not previously mentioned include phenol, phthalaldehydes, and benzoyl alcohol (Altshuller, 1983). A carbon dioxide yield of 8.4% was achieved when toluene adsorbed on silica gel was irradiated with light X >290 nm) for 17 h (Freitag et ah, 1985). 

Tomkiewicz, M.A., Groen, A., and Cocivera, M. Electron paramagnetic resonance spectra of semiquinone intermediates observed during the photooxidation of phenol in water, J. Am. Chem. Soc., 93(25) 7102-7103,1971. 

MI1 55CRV9, p.99). It was later prepared by coupling of 4-isopropyl-p-tropoquinone with 5-hydroxyhinokitiol or by a biomimetic photooxidation of hinokitiol (161) sensitized by tetraphenylporphin (83CL1371). These reactions exemplify the phenol oxidation in troponoid chemistry. 

Faust BC, Holgne J. 1987. Sensitized photooxidation of phenols by fulvicacid in natural waters. Environ Sci Technol 21 957-964. 

In the photooxidation of phenol induced by excited titanium dioxide, the hydroxy radical was directly implicated as the reactive species, the observed organic products having incorporated oxygen, Eq. (16) On further photolysis, aldehydes, acids, and CO2 could be obtained. 

With the fO2]0 (24 h) value calculated above, the half-life of a phenol with respect to photooxidation by 02 in the epilimnion of Greifensee is then given by ... 

From the half-lives indicated in Fig. 16.5 it can be seen that for most pollutants, the assumption of a well-mixed epilimnion (typical mixing rates 1-10 d-1) with respect to indirect photolysis with 02 is a reasonable assumption. Furthermore, for compounds exhibiting iq2 values [or (1 - aia) k ptQ values for phenolate species] greater than 107 M l s-1, during the summer, photooxidation by 02 is equal to, or more important than, depletion of the concentration by dilution with inflowing water [f,/2(dilution) in the epilimnion of Greifensee on the order of 70 days]. We should recall, however, that only a few compound classes exhibit such large kplQ values, and that, therefore, 02 must be considered to be a rather selective photooxidant. 

O Shea, K. and Cardona, C., Hammett study on the Ti02-catalyzed photooxidation of para-substituted phenols a kinetic and mechanistic analysis, /. Org. Chem., 59, 5005, 1994. 

Thomas, J.J. and C.S. Foote. 1978. Chemistry of singlet oxygen. XXVI. photooxidation of phenols. Photochem. Photobiol. 27 683-687. 

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