By photochemical oxidation

Phosgene may be formed when chlorinated hydrocarbons are exposed to ultraviolet radiation in the presence of air [627]. Dichloromethane was found to contain trace quantities of phosgene after storage for a few days in clear glass flasks, despite being protected from exposure to direct sunlight [855]. Trichloromethane decomposes photooxidatively in a similar way to that described for its thermal oxidation (Section 3.3.3), the process differing in the 

Although stable in the absence of u.v. radiation [1836], tetrachloroethene can be decomposed photooxidatively into COCIj. In the chlorine-sensitized oxidation of CCljCClj, approximately 20% of the starting material is converted into COClj (the remaining 80% of the tetrachloroethene is transformed into CCI3COCI, trichloroethanoyl chloride). The following scheme was proposed to account for the products [1813]  

Solvents containing CCl2=CCl2 as the major chemical constituent have been shown to be responsible for causing eye and throat irritations in the employees of a publishing company [228], following the introduction of a mercury-vapour lamp into the factory, which was shown to induce breakdown of the tetrachloroethene into COCI2 and HCl [228]. 

Phosgene was detected, by g.c.-m.s. and n.m.r. spectroscopy, in a commercial solvent mixture of trichloroethene and tetrachloroethene (80 20) [1254]. Such contamination is likely to arise as a result of photochemical decomposition. The primary product of the oxidation of trichloroethene under ultraviolet radiation is trichloroepoxyethane cf. the thermal decomposition product, structure (3.4), which rearranges to dichloroethanoyl chloride and chloral. Secondary decomposition of one of these compounds occurs to give CO, COj, HCl and COCI2 [ICI55]. 

Phosgene in ambient air, derived from the photooxidation of C2CI4 and C2HCI3 [1886], is discussed in Section 3.7. 

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With the addition of CO caused by photochemical oxidation of methane, a significant flux enters the atmosphere annually, but the principal global contributions are terrestrial, anthropogenic and from atmospheric photolysis of methane. 

Guderian, R. Tingey, D.T. Rabe, R. In Air Pollution by Photochemical Oxidants Formation, Transport, Control, and Effects on Plants] Guderian, R. Ed Ecological Studies, Vol 52 Springer Verlag New York, NY, 1985 pp 129-169. 

Also, nitrones can be formed by photochemical oxidation (X350 nm) of aldimines in acetonitrile, in the presence of O2 over a TiC>2 suspension (20, 21). Air oxidation of imines into oxaziridines with their subsequent transformation into nitrones, using cobalt catalysts, provides good yields. Utilization of molecular oxygen in the oxidation process seems highly promising due to its cost-effectiveness, availability, and the possibility of industrial application (22). 

Increased understanding of reaction mechanisms in the 1940s and 1950s pinpointed general acid or base catalysis as likely to be of importance in many hydrolytic reactions. The imidazole nucleus in histidine was the obvious center in proteins to donate or accept protons at physiological pH. The involvement of histidine was shown by photochemical oxidation in the presence of methylene blue (Weil and Buchert, 1951) which destroyed histidine and tryptophan and inactivated chymotrypsin and trypsin. 

Some effort is needed to explore the feasibility of using plants to monitor the overall biologic activity (or biomass reductions) caused by photochemical oxidants in specific air basins or regions. The response of sensitive plants should be correlated with the response of plants of economic and aesthetic importance. Additional monitoring of multiple pollutants is needed in rural areas. 

A further chiral auxiliary-based tactic exploited tricarbonyl( 76-arene)chromium complexes of aromatic imines 71, which reacted under ultrasound (US) irradiation with a-bromoesters in a predictable stereochemical course to give comparable amounts of /S-aminoesters and / -lactams, as outlined in equation 44127. Chromium decomplexation is eventually achieved by photochemical oxidation under air. 

For a long time, transport from the stratosphere to the troposphere was thought to be the dominant source of ozone in the troposphere. Early in the 1970s, it was first suggested that tropospheric ozone originated mainly from production within the troposphere by photochemical oxidation of CO and hydrocarbons catalysed by HO and NO c- These sources are balanced by in-situ photochemical destruction of ozone and by dry deposition at the earth s surface. Many studies, both experimental- and model-based have set about determining the... 

Reaction with thiocarbonyl compounds. The thiocarbonyl compounds obtained by photochemical oxidation of phenacyl sulfides can be trapped efficiently by a 1,3-dipolar cycloaddition with 1 to give 2. This heterocycle can be cleaved to carbonyl compounds by Bu4N F or (CjH5)3N HF. This process is more efficient and more general than photolysis of phenacyl sulfides in the presence of oxygen. 

The preparation of the perchlorosUoxanes CI3 Si(OSiCl2 ) -SiCb (n = 0-5) has been discussed above in the halosilanes section. The highly reactive CbSiOH may, however, be generated by photochemical oxidation of SiHCb by O2 or O3 at low temperature in either an argon matrix or... 

Decomplexation of ArCr CO)3. The chromium carbonyl complexes of arenes are useful for activation of the aryl group to nucleophilic attack (6, 28, 125-126 7, 71-72). Decomplexation has been effected with iodine or by photochemical oxidation with destruction of the expensive Cr(CO)3 unit. A more recent method involves reflux with pyridine to form Py3-Cr(CO)3 in yields of 70-100%. The pyridine complex in the presence of BF3 can be reused for preparation of ArCr(CO)3. Isomerization of 1,3-dienes. Ergosteryl acetate (1) is isomerized by chromium carbonyl to ergosteryl 83 acetate (2) in 81% yield. Under the same conditions ergosteryl 83 acetate (3) is isomerized to ergosteryl 81 acetate (4). 80th reactions involve isomerization of a cisoid diene to a transpid diene. In contrast iron carbonyl isomerizes steroidal transoid 3,5- and 4,6-dienes to 2,4-dienes. ... 

Because of the high selectivity often observed and the mild reaction conditions required, PET provides a powerful tool for carrying out single electron transfer reactions . By photochemical oxidation excitation of either the electron donor or the acceptor, the redox properties of the respective species change. For example, 9,10-dicyanoanthracene in its singlet state (dca ) is a powerful oxidant = +1.28 V vs. Ag/AgNOs with an... 

Conjugated dienes (and compounds that behave like conjugated dienes in the Diels-Alder reaction) react with singlet oxygen to form cyclic peroxides as if molecular oxygen acted as a dienophile. The yields of the peroxides, prepared by photochemical oxidation [13, 55] or by chemical oxidations with hydrogen peroxide and sodium hypochlorite, alkaline hydrogen peroxide and bromine, alkaline salts of peroxy acids [14, 26], or the ozonide of triphenyl phosphite [29], are comparable. 

ODNs containing the oxidatively damaged guanosine oxazolone (117) were prepared by photochemical oxidation, and the mutagenic behaviour of the analogue studied. The analogue induced misincorporation of dAMP and to a lesser extent dGMP. 

R = H, Me, Ph, 4-O2NC6H4, 2-pyridinyl, benzothiazol-2-yl) gives methanols (21 R = OH, R same) and ketones,213 and oxothiochrome (22) is formed by photochemical oxidation of aqueous solutions of thiochrome, using 02(1 Ag) generated from Rose Bengal adsorbed on Sephadex G-25.214 Dialkyl phosphite inhibition of the photooxidation of 4-(p-tolylazo)-l-naphthol with 02(1 Ag) has been employed as an indicator of reaction in the kinetic determination of dialkyl phosphites and some aromatic aldehydes.2l5... 

The products obtained by the action of peracids upon 3-alkoxy-3,5-dienes are dependent upon the reaction conditions. Aqueous organic solvents and the gradual addition of peracid favour the formation of 6 -hydroxy-4-en-3-one, but when an excess of peracid is added in one portion the product, obtainable in high yield, is the unsaturated aldehyde-ester (393) which has also been obtained (as ethyl ester) by photochemical oxidation of the oxathian (394) followed by a reductive desulphuration. In non-polar solvents a 1 1 adduct (395) is formed between m-chloroperbenzoic acid and 3-acetoxy-3,5-dienes which is sufficiently stable (in the presence of a 17-ketone function) to be isolated and acetylated to the 6 -acetate or oxidised by chromium trioxide in pyridine to the b-ketone. ... 

BECKER, K.H., W.FRICKE, J. LOBEL and U. SCHURATH. 1985 Formation, transport and control of photochemical oxidants in air pollution by photochemical oxidants, Ed. R. GUDERIAN, Ecological studies vol. 52. Springer Verlag, Heidelberg 1985. 

Examination of the reactions outlined above shows that alkoxy radicals (RCH2O) should be produced by photochemical oxidation of alcohols and a necessary corollary of these processes is that tertiary alkoxy radicals, generated in the presence of paraquat cation... 

COS is produced in the ocean by photochemical oxidation of organic sulfur compounds whereby dissolved organic matter acts as a photosensitizer. The aqueous concentration of COS manifests a strong diel cycle, with the highest concentrations in daytime (concentration range on the order of 0.03-0.1 nmol U ). COS hydrolyzes in water to H2S at rates dependent on water temperature and pH. The flux of oceanic COS to the atmosphere may represent about one-third of the global COS flux. 

The absolute stereochemistry of loliolide (71) and dihydroactinidiolide (72) has been determined by their synthesis from zeaxanthin (12) by photochemical oxidation. Dihydroactinidiolide and theaspirone (73) have been synthesized by another variation on previous routes (Scheme 4). In Crocus sativus a large... 

C 5H2203, Mr 250.34, cryst., mp. 85 - 86 °C, [alp - 56° (CHCI3), a cyclofamesane sesquiterpene formed by photochemical oxidation of violaxanthin. It has been detected in several marine and higher plants. Naturally occurring X. exists as a mixture of -isomers of the 2,3-double bond of the 2,4-pentadienal side chain. It is an inhibitor of plant growth and is involved in the winter rest phase of plants (senescence), in some cases it is also involved in the damage to trees X. is closely related structurally and in its biological activity to abscisic acid and presumably functions as an intermediate in the biosynthesis of it. 

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