Photodegradation products

The process by which a solubility differential between exposed and unexposed areas occurs is well known (74). Photodegradation products of the naphthoquinone diazide sensitizer, eg, a l,2-naphthoquinonediazide-5-sulfonic acid ester (11), where Ar is an aryl group, to an indene carboxylic acid confers much increased solubility in aqueous alkaline developer solutions. 

Irradiation of a solid film prepared from the polymer 11 in air afforded photodegradation products which are soluble in 2-ethoxy-ethanol. IR spectra of the products show strong absorption bands attributed to Si-OH and Si-O-Si stretching frequencies. In contrast to the products from 10, these products show absorption due to the Si-H bond. This result indicates that some of the silenes would be formed in this system. The intense absorption at 254 nm in the UV spectrum again disappeared after UV-irradiation. 

In the present paper, we describe how photodegradation of low density polyethylene films was enhanced by uniaxial elongation. An explanation of the enhancement process is given based on the photooxidation and deformation mechanisms, and the photodegradation products. 

Ephedrine (17) was known to give coloured products on exposure to sunlight. When a 1 % solution was irradiated with UV light from a 30 W tube the solution became coloured and colourless needle-shaped crystals separated. With prolonged exposure, the crystals redissolved as the solution darkened to an intense brown. On analysis, the crystalline compound was identified as the oxazolidine (18). This compound was known to be formed by reaction between ephedrine and benzaldehyde, so it was assumed that the primary photodegradation product of the drug was benzaldehyde [27]. 

The widely used diuretic frusemide (165a) is a good photosensitizer in vitro. Its phototoxicity may arise from ready free-radical formation [ 104] or could be a consequence of the production of toxic photodegradation products [105]. In burette administration sets, frusemide was shown to be decomposed by direct sunlight, but not by diffuse daylight or fluorescent light [ 106]. 

When Tonnesen et al. used an immersion lamp giving emission wavelengths between 240 and 600 nm, the same four photodegradation products were obtained from solutions of hydroxychloroquine (313) in water or isopropanol. Compounds (314) to (317) all derived from A-dealkylations. It was particularly noted that no photodechlorinated products were obtained in this work [181]. 

The antibacterial, nalidixic acid (337), is associated with a high incidence of photosensitivity reactions. Detzer and Huber irradiated a solution in 0.1 M sodium hydroxide with a high-pressure mercury lamp and identified four photodegradation products the decarboxylated derivative (338), carbon dioxide, ethylamine, and the new dione (339) [188]. 

Nemutlu, E., Ozaltin, N., and Altinoz, S. (2004). Determination of rofecoxib, in the presence of its photodegradation product, in pharmaceutical preparations by micellar electrokinetic capillary chromatography. Anal. Bioanal. Chem. 378, 504—509. 

Source Benzidine can enter the environment by transport, use, and disposal, or by dyes and pigments containing the compound. A photodegradation product of 3,3 -dichlorobenzidine. 

Bell (1956) reported that the composition of photodegradation products formed were dependent upon the initial 2,4-D concentration and pH of the solutions. 2,4-D undergoes reductive dechlorination when various polar solvents (methanol, butanol, isobutyl alcohol, ferf-butyl alcohol, octanol, ethylene glycol) are irradiated at wavelengths between 254 to 420 nm. Photoproducts formed included 2,4-dichlorophenol, 2,4-dichloroanisole, 4-chlorophenol, 2- and 4-chlorophenoxy-acetic acid (Que Hee and Sutherland, 1981). 

Photolytic. The major photolysis and hydrolysis products identified in distilled water were pentachlorocyclopentenone and hexachlorocyclopentenone. In mineralized water, the products identified include cis- and /ra/3s-pentachlorobutadiene, tetrachlorobutenyne, and pentachloro-pentadienoic acid (Chou and Griffin, 1983). In a similar experiment, irradiation of hexachlorocyclopentadiene in water by mercury-vapor lamps resulted in the formation of 2,3,4,4,5-pentachloro-2-cyclopentenone. This compound hydrolyzed partially to hexachloroindenone (Butz et ah, 1982). Other photodegradation products identified include hexachloro-2-cyclopentenone and hexachloro-3-cyclopentenone as major products. Secondary photodegradation products reported include pentachloro-as-2,4-pentadienoic acid, Z- and A-pentachlorobutadiene, and tetrachloro-butyne (Chou et ah, 1987). In natural surface waters, direct photolysis of hexachlorobutadiene via sunlight results in a half-life of 10.7 min (Wolfe et al, 1982). 

Photolytic. Kepone-contaminated soils obtained from a site in Hopewell, VA were analyzed by GC/MS. 8-Chloro and 9-chloro homologs identified suggested these were photodegradation products of kepone (Borsetti and Roach, 1978). 

Photolytic. Photodegradation products identified in aqueous hexazinone solutions following exposure to UV light (X = 300-400 nm) were 3-(4-hydroxycyclohexyl)-6-(dimethylamino)-l-meth-yl-s-triazine-2,4(l//,3//)-dione, 3-cyclohexyl-6-(methylamino)-l-methyl-s-triazine-2,4(1//,3/ di-one, and 3-cyclo-hexyl-6-(dimethylamino)-s-triazine-2,4(l//,3//)dione (Rhodes, 1980a). 

Sullivan. R.G., Knoche, H.W., and Markle, J.C. Photolysis of trifluralin characterization of azobenzene and azoxybenzene photodegradation products, J. Agric. Food Chem., 28(4) 746-755, 1980. 

---