Carbon dioxide, photolysis

Photochemical elimination of carbon dioxide from suitable precursors has given a variety of reactive intermediates at low temperatures where they are often stable and can be studied further. This approach has been utilized in attempts to generate new 1,3-dipolar species, and photolysis of (515) gave an azomethine nitrene intermediate (516) (see Section 4.03.6)... 

Carbon dioxide is readily extruded from five-membered rings, by thermolysis or photolysis (Scheme 28). 

All the O atoms evolved as Og come from water none comes from carbon dioxide. But 12 O atoms are evolved as 6 Og, and only 6 O atoms appear as 6 HgO in the equation. Also, 6 COg have 12 O atoms, yet there are only 6 O atoms in CgHigOg. How can yon account for these discrepancies Hint Consider the partial reactions of photosynthesis ATP synthesis, NADP reduction, photolysis of water, and the overall reaction for hexose synthesis in the Calvin-Benson cycle.)... 

Phenyl radical, side by side with methyl radical, carbon dioxide and methyl benzoate, was also stabilized in an inert matrix as a product of UV photolysis of acetyl(benzoyl)peroxide [112] (Pacansky and Brown, 1983). Of nine IR bands of the radical C6H5, intense absorption at 710 cmwhich was shifted to 519 cm for the deuterium-labelled radical C Ds, has been assigned to out-of-plane CH deformation. The bands of the phenyl radical... 

Note that the same sensor technique was used in rather intriguing experiments on photolysis of acetone [12], ammonia [13], nitrogen [14], oxygen [15], and carbon dioxide [16]. 

No information was found on the transformation of diisopropyl methylphosphonate in the atmosphere. Based on the results of environmental fate studies of diisopropyl methylphosphonate in distilled water and natural water, photolysis (either direct or indirect) is not important in the transformation of diisopropyl methylphosphonate in aquatic systems (Spanggord et al. 1979). The ultraviolet and infrared laser-induced photodegradation of diisopropyl methylphosphonate in both the vapor or liquid phase has been demonstrated (Radziemski 1981). Light hydrocarbon gases were the principal decomposition products. Hydrogen, carbon monoxide (CO), carbon dioxide (C02), and water were also detected. 

This new and novel method to study the photochemical degradation of Kevlar-29 fabric in air divides into four steps (1) fabric cleaning, (2) photolysis at specified temperature and time in 0.2 atm - 02, (3) preparation of the degraded (DMAc-soluble) sample surface for decarboxylation at 25° and 196°C in the concentrated sulfuric acid, and (4) the total carbon dioxide analyses by gas chromatography and the isotopic carbon dioxide ( °C02 and 48co2) ratios by GC-mass spectrometer. 

Recently, results of careful experiments were reported by Ito et a/.101 They claimed that formic acid, formaldehyde, and methanol, which had been previously reported as photoelectrochemical reduction products of carbon dioxide, were observed also by photolysis of cell materials, such as electrolytes, including 15-crown-5 ether, and epoxy resin, which has often been used as the molding material of semiconductor electrodes in aqueous solutions. Previously reported reduction products were obtained also under nitrogen with (Table 4) and without (Table 5) a p-GaP photocathode under illumination. These precise experiments under improved conditions, where no photolytic products were observed, gave the result that the main reduction product of carbon dioxide at a p-GaP photocathode in aqueous electrolytes was formic acid. Thus, many kinds of products reported in previous papers83,97,100 were suggested to be due to photolysis of cell materials. 

Photolysis of the triazepine products produces 2,2-dimethylpropanenitrile and the corresponding pyrazole in quantitative yield <1997BSF927>. Reaction of sydnone 89 with fulvene 91 proceeds by [ji4s + jt6s]-cycloaddition followed by spontaneous loss of carbon dioxide and a molecule of dimethylamine or acetic acid from the pseudo-azulene , cyclopentaMpyridazine 92 (Equation 9) <1996CC1011, 1997T9921>. 

Nalidixic acid is stable up to five years under reasonable conditions of temperature and humidity. Pawelczyk and Plotkowiakowa(17) subjected sodium nalidixate solutions to accelerated aging, but were unable to identify decomposition products. Detzer and Huber(lS) studied the photolysis and thermolysis of nalidixic acid in the presence of oxygen. Photolysis produced de-carboxylated nalidixic acid, structure A, and a diketone product, structure B, as well as carbon dioxide and ethylamine. 

Photolysis of hexachloroethane in water has been reported, but degradation to carbon dioxide occurred at a temperature of 90-95 C (Knoevenagel and Himmelreich 1976). The relevance of these results to ambient conditions are uncertain. 

Much interest has recently been shown in artificial photosynthesis. Photosynthesis is a system for conversion or accumulation of energy. It is also interesting that some reactions occur simultaneously and continuously. Fujishima et al. [338] pointed out that a photocatalytic system resembles the process of photosynthesis in green plants. They described that there are three important parts of the overall process of photosynthesis (1) oxygen generation by the photolysis of water, (2) photophosphorylation, which accumulates energy, and (3) the Calvin cycle, which takes in and reduces carbon dioxide. The two reactions, reduction of C02 and generation of 02 from water, can occur simultaneously and continuously by a sonophotocatalytic reaction. 

The decompositions of C302, CO, C02, CS2, COS, CSe2 and COSe are dealt with in this section. Apart from carbon suboxide, this is a group of stable, un-reactive compounds. Considerable emphasis has been placed on the investigation of the photolytic decompositions of some of these compounds which are thought to provide useful sources of atoms (C, O, S and Se) and free radicals (C20). The photochemistry of carbon dioxide has particular relevance to the chemistry of planetary atmospheres, although to date the mechanism of C02 photolysis remains obscure. 

Oxidation, hydrolysis, and photolysis are the three predominant chemical processes that may cause loss of simple cyanides in aquatic media are. Cyanides are oxidized to isocyanates by strong oxidizing agents the isocyanates may be further hydrolyzed to ammonia and carbon dioxide (Towill et al. 1978). However, it has not yet been determined whether such oxidation and subsequent hydrolysis of isocyanate is a significant fate process in natural waters known to contain peroxy radicals (EPA 1992f). 

Photolysis of chlordecone in the atmosphere does not appear to be an important degradation pathway for this compound. While nonvolatile products of photolysis were not monitored, only 1.8% of the chlordecone adsorbed on silica gel and exposed to ultraviolet light (wavelength >290 nm) was photolyzed to carbon dioxide or other volatile compounds (Freitag et al. 1985). 

The photodecarboxylation of p-(nitrophenyl) glyoxylic acid 156, which was studied by time-resolved and steady-state methods at room temperature93, leads to p-nitrosobenzoic acid and carbon dioxide in good yields with = 0.28 in aqueous solution at pH 2-12 and excitation at 313, 280 or 254 nm (equation 76). An intermediate (Xmax = 350, r 2 xs) observed by nanosecond laser flash photolysis is assigned to the aci-form of the nitroketene... 

Photolytic. Photolysis products include carbon monoxide, ethylene, free radicals, and a polymer (Calvert and Pitts, 1966). Anticipated products from the reaction of acrolein with ozone or OH radicals in the atmosphere are glyoxal, formaldehyde, formic acid, and carbon dioxide (Cupitt,... 

Titanium dioxide suspended in an aqueous solution and irradiated with UV light X = 365 nm) converted benzene to carbon dioxide at a significant rate (Matthews, 1986). Irradiation of benzene in an aqueous solution yields mucondialdehyde. Photolysis of benzene vapor at 1849-2000 A yields ethylene, hydrogen, methane, ethane, toluene, and a polymer resembling cuprene. Other photolysis products reported under different conditions include fulvene, acetylene, substituted trienes (Howard, 1990), phenol, 2-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol, 2,6-dinitro-phenol, nitrobenzene, formic acid, and peroxyacetyl nitrate (Calvert and Pitts, 1966). Under atmospheric conditions, the gas-phase reaction with OH radicals and nitrogen oxides resulted in the formation of phenol and nitrobenzene (Atkinson, 1990). Schwarz and Wasik (1976) reported a fluorescence quantum yield of 5.3 x 10" for benzene in water. 

In a solution containing oxygen, photolysis yields a mixture of 6,12-, 1,6-, and 3,6-diones. Nitration by nitrogen dioxide forms 6-nitro-, 1-nitro-, and 3-nitrobenzo[a]pyrene. When benzo [a] pyrene in methanol (1 g/L) was irradiated at 254 nm in a quartz flask for 1 h, the solution turned pale yellow. After 2 h, the solution turned yellow and back to clear after 4 h of irradiation. After 4 h, 99.67% of benzo[a]pyrene was converted to polar compounds. One of these compounds was identified as a methoxylated benzo[a]pyrene (Lu et al, 1977). A carbon dioxide yield of 26.5% was achieved when benzo [a] pyrene adsorbed on silica gel was irradiated with light (A, >290 nm) for 17 h (Freitag et al, 1985). 

Hydrolysis and photolysis of carbaryl forms 1-naphthol (Wauchope and Haque, 1973 Rajagopal et al., 1984, 1986 Miles et al., 1988 MacRae, 1989 Ramanand et al., 1988a Lewis, 1989 Somasundaram et al, 1991) and 2-hydroxy-l,4-naphthoquinone (Wauchope and Haque, 1973), respectively. In aqueous solutions, carbaryl hydrolyzes to 1-naphthol (Boethling and Alexander, 1979 Vontor et al., 1972), methylamine, and carbon dioxide (Vontor et al., 1972), especially under alkaline conditions (Wolfe et al., 1978). At pH values of 5, 7, and 9, the hydrolysis half-lives at 27 °C were 1,500,15, and 0.15 d, respectively (Wolfe et al., 1978). 

Photolysis of an aqueous solution containing chloroform (314 pmol) and the catalyst [Pt(cohoid)/Ru(bpy) /MV/EDTA] yielded the following products after 15 h (mol detected) chloride ions (852), methane (265), ethylene (0.05), ethane (0.52), and unreacted chloroform (10.5) (Tan and Wang, 1987). In the troposphere, photolysis of chloroform via OH radicals may yield formyl chloride, carbon monoxide, hydrogen chloride, and phosgene as the principal products (Spence et al., 1976). Phosgene is hydrolyzed readily to hydrogen chloride and carbon dioxide (Morrison and Boyd, 1971). 

Photolytic. Photodegrades under simulated atmospheric conditions to phosgene and nitrosyl chloride. Photolysis of nitrosyl chloride yields chlorine and nitrous oxide (Moilanen et al., 1978 Woodrow et ah, 1983). When aqueous solution of chloropicrin (10 M) is exposed to artificial UV light (X <300 nm), protons, carbon dioxide, hydrochloric and nitric acids are formed (Castro and Belser, 1981). 

Surface Water In an estuary, the half-life of chlorpyrifos was 24 d (Schimmel et al., 1983). Photolytic. 3,5,6-Trichloro-2-pyridinol formed by the photolysis of chlorpyrifos in water. Continued photolysis yielded chloride ions, carbon dioxide, ammonia, and possibly poly-hydroxychloropyridines. The following photolytic half-lives in water at north 40° latitude were reported 31 d during midsummer at a depth of 10 cm 345 d during midwinter at a depth of 10 ... 

Photolytic. Photolysis of lindane in aqueous solutions gives p BHC (U.S. Department of Health and Human Services, 1989). When an aqueous solution containing lindane was photooxidized by UV light at 90-95 °C, 25, 50, and 75% degraded to carbon dioxide after 3.0, 17.4, and 45.8 h, respectively (Knoevenagel and Himmelreich, 1976). 

Photolytic. Under smog conditions, indirect photolysis via OH radicals yielded phosgene, di-chloroacetyl chloride, and formyl chloride (Howard, 1990). These compounds are readily hydrolyzed to HCl, carbon monoxide, carbon dioxide, and dichloroacetic acid (Morrison and Boyd, 1971). Dichloroacetic acid and hydrogen chloride were reported to be aqueous photodecomposition products (Dilling et al., 1975). Reported rate constants for the reaction of trichloroethylene and OH radicals in the atmosphere 1.2 x 10 cm /molecule-sec at 300 K... 

Photolytic. Dalapon (free acid) is subject to photodegradation. When an aqueous solution (0.25 M) was irradiated with UV light at 253.7 nm at 49 °C, 70% degraded in 7 h. Pyruvic acid is formed which is subsequently decarboxylated to acetaldehyde, carbon dioxide, and small quantities of 1,1-dichloroethane (2-4%) and a water-insoluble polymer (Kenaga, 1974). The photolysis of an aqueous solution of dalapon (free acid) by UV light (X = 2537 A) yielded chloride ions, carbon dioxide, carbon monoxide, and methyl chloride at quantum yields of 0.29, 0.10, 0.02, and 0.02, respectively (Baxter and Johnston, 1968). 

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