Irradiation, ultraviolet

Ultraviolet (UV) irradiation is used to destroy bacteria and reduce organic compounds (measured as TOC) as well as destruction of chlorine and chloramines. This technique involves passing water over a UV lamp that is operating at a specific wavelength of energy. 

Bacteria require a dosage of radiation equivalent to about 10,000 -30,000 microwatt-seconds/square centimeter. This can achieved by using a 254-nanometer wavelength. This wavelength alters the DNA of microbes, causing them to be unable to reproduce, leading to their death. 

A significant advantage of UV over use of chemical oxidizers for microbial control is that no trihalomethane (THM) compounds are generated (see Chapter 8.2.1). Additionally, the need to store and feed a hazardous chemical oxidizer is avoided. 

Maximum contact between the water and the quartz sleeve is achieved by using plug flow with a tangential flow pattern for the water. Retention time of water in a UV unit is designed to be at least 15 minutes. 

For UV to be effective, certain water conditions must be met. The water must be free of suspended solids, which can foul quartz sleeves, thereby reducing the amount of radiation reaching the water. Some UV systems include cleaning mechanisms for quartz sleeves. The water should also be free of taste, odor, iron, and manganese. Furthermore, chloride, bicarbonate, and sulfates should be reduced, as these affect the absorption of UV radiation.(9) Thus, some pretreatment is required prior to sending water to a UV system. 

Visible light is capable of decomposing starch, especially when air is concurrently passed through it and sensitizers are present. Zinc oxide is an effective 

In addition to zinc oxide, other sensitizers of photoxidation may be employed. The addition of sodium nitrite in the presence of moisture turns starch into lower dextrins when the material is irradiated with 355-nm light.256 Ruthenium(IV) and titanium(IV) oxides as well as platinum oxide, all in conjunction with aqueous solutions of starch, eventually produce (in the presence of alkali) hydrogen, carbon dioxide, and photoxidation products.257 The use of Methylene Blue has also been reported. These studies provide evidence that only the sensitizer, and not the starch, is sensitized.258 

Water plays an essential role in this photoxidation. Its presence is necessary for, among other effects, the photodecomposition taking place in the natural environment, in conjunction with microbial and enzymic degradation of organic matter.259 

The character and properties of free radicals produced by ultraviolet radiation appear to be identical to those produced thermally they are stable and their EPR patterns are the same. Their concentration increases with duration of irradiation within the first 5 h of irradiation. Irradiation during an initial 5 h is slightly more effective268 than irradiation over the next 20 h. At a given temperature, the yield of radicals generated thermally is much less time-dependent. A comparison of the generation of free radicals by temperature and by ultraviolet irradiation in solid starch is shown in Table XVII. 

Free radicals originating from starch, amylose, and amylopectin form well-distinguished 1 3 1 or 1 4 1 triplets showing hyperfine splitting of 30 gauss. These triplets are attributed to the derivatives of alkyl radicals produced by abstraction of hydrogen atoms from the 2-, 3-, and/or 4-positions of glucose residues.269 

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Again with platinized Ti02, ultraviolet irradiation can lead to oxidation of aqueous CN [323] and to the water-gas shift reaction, CO + H2O = H2 + CO2 [324]. Some mechanistic aspects of the photooxidation of water (to O2) at the Ti02-aqueous interface are discussed by Bocarsly et al. [325]. 

Oxidation. Acetaldehyde is readily oxidised with oxygen or air to acetic acid, acetic anhydride, and peracetic acid (see Acetic acid and derivatives). The principal product depends on the reaction conditions. Acetic acid [64-19-7] may be produced commercially by the Hquid-phase oxidation of acetaldehyde at 65°C using cobalt or manganese acetate dissolved in acetic acid as a catalyst (34). Liquid-phase oxidation in the presence of mixed acetates of copper and cobalt yields acetic anhydride [108-24-7] (35). Peroxyacetic acid or a perester is beheved to be the precursor in both syntheses. There are two commercial processes for the production of peracetic acid [79-21 -0]. Low temperature oxidation of acetaldehyde in the presence of metal salts, ultraviolet irradiation, or osone yields acetaldehyde monoperacetate, which can be decomposed to peracetic acid and acetaldehyde (36). Peracetic acid can also be formed directiy by Hquid-phase oxidation at 5—50°C with a cobalt salt catalyst (37) (see Peroxides and peroxy compounds). Nitric acid oxidation of acetaldehyde yields glyoxal [107-22-2] (38,39). Oxidations of /)-xylene to terephthaHc acid [100-21-0] and of ethanol to acetic acid are activated by acetaldehyde (40,41). 

Water-soluble sdanols such as (1) were found to undergo successive oxidative demethylations with tropospheric ultraviolet irradiation in the presence of suitable chromophores, such as nitrogen oxides (516). The water-soluble methylated sdicones did not promote diatom (Nap cu/apelliculosd) growth but the demethylated photo products did. The sequence of sod-induced degradation of sdicones to water-soluble species such as (1), followed by light-induced conversion to sdicate, suggests a pathway, conceptually at least, for the mineralization of sdicones. 

The first, and to this writing still only case of a ketone a-cleavage-recombi-nation sequence in the steroid field was reported by Butenandt, who found that 17-ketones epimerize at C-13. Ultraviolet irradiation of either stereoisomer produces an equilibrium mixture in which the thermodynamically more favored 13a-compound cf. (15)] with cw-fusion of rings C and D predominates at room temperature. As ultraviolet absorption energies and intensities of the two isomeric ketones are practically identical, the equilibrium composition depends largely on the rate of the competing recombination process from (14). For further examples of the photoisomerization at C-13 of 17-ketosteroids, see ref. 8, 12, 15 and 43. 

Dehydrotestosterone acetate (174) in nonprotic solvents (dioxane, benzene) undergoes a rearrangement to the isomer (175). This product is photolabile and isomerizes readily to new cross-conjugated dienones. Thus, ultraviolet irradiation of (174), its 1-, 2- and 4-methyl homologs, and its lOa-stereoisomer (188) in dioxane solution causes, in each case, a series of rearrangements as summarized on page 331 for (174) and (188). ... 

Simple a-fluorosulfides are reduced to the fluoroalkanes by sodium-ethanol [9J (equation 75). Clean conversion of bis(trifluoromethyl) diiulfide to trifluoromethyl mercaptan is accomplished with hydrogen sulfide and ultraviolet irradiation (941 (equation 76). Perfluoroalkanesulfonyl fluondes are converted to the sulfmate salts by hydrazine [95] (equauon 77)... 

Reaction times can be shonened and yields improved through the use of high pressure [40] (equation 28) Reactions may also be conducted in aqueous medium under ultraviolet irradiation [41] (equation 29)... 

When position 4 of perfluoropyridine is blocked with a poor leaving group, ammonia replaces the fluonne in position 2 in good yield. Oxidation of the products obtained with hypochlorite, followed by lodme-catalyzed rearrangement, yields interesting fluorodienes [78] (equation 41) Ultraviolet irradiation can be used to assist reactions m which substitution is difficult [79]... 

TFifluorothiolacetic acid adds to a senes of olefins under ultraviolet irradiation The addition appears to start by a CFjCOS radical attack, giving the more stable radical intermediate [14] (Table 2)... 

Table 2. Addition of Trifluorothiolacetic Acid to Alkenes under Ultraviolet Irradiation [/4]...

There are two general routes to complexes. The first involves direct addition of molecular Ht either to an unoccupied coordination site in a 16-electron complex (as above) or by displacement of a ligand such as CO, Cl, H2O in the coordination sphere of an 18-electron complex in this latter case ultraviolet irradiation may be required to assist in the... 

Until fairly recently only the pentafluorides and SbCE were known, but the exceedingly elusive AsCE was finally prepared in 1976 by ultraviolet irradiation of AsCE in liquid CE at — 105°C. Some properties of the 5 pentahalides are given in Table 13.9. 

F3CIO tends to react slowly at room temperature but rapidly on heating or under ultraviolet irradiation. Typical of its fluorinating reactions are ... 

Figure 7 Light resistance of low-density polyethylene upon ultraviolet irradiation. 1-normal 2-quenched.

On exposure to ultraviolet irradiation over a period of 25 hours, specific elongation of normal polyethylene decreases by half, and complete decomposition is observed after a 50-hour exposure. At the same time, specific elongation of quenched polyethylene, when exposed to irradiation not greater than 50 hours, is little affected, but when exposed over a period of 100 hours, its specific elongation amounts to 100%. 

Ultraviolet (UV) spectroscopy (Section 14.7) An optical spectroscopy employing ultraviolet irradiation. UV spectroscopy provides structural information about the extent of 7r electron conjugation in organic molecules. 

Essential for induction ofthe/Z-5 gene in inflammatory reactions is the binding site for nuclear factor kappa B (NF-kB). NF-kB responds to cytokines, stress, free radicals, ultraviolet irradiation, and bacterial, viral, or even parasitic antigens [2]. NF-kB stands for a family of subunits, which form homo-, and heterodimers. All NF-kB proteins share a highly conserved DNA-binding/dimerization domain called the Rel homology domain (RHD) consisting of two (3-strand core domains... 

The photochemical behavior of a number of substituted derivatives of thiochroman-4-one 1-oxides has been examined by Still and coworkers192-194. These authors also report that rearrangement to cyclic sulfenates, with subsequent reaction by homolysis of the S—O bond, appears to be a particularly favorable process. For example, ultraviolet irradiation of a solution of 8-methylthiochroman-4-one 1-oxide (133) in benzene for 24h afforded a single crystalline product which was assigned the disulfide structure 134 (equation 54). More recently, Kobayashi and Mutai195 have also suggested a sulfoxide-sulfenate rearrangement for the photochemical conversion of 2,5-diphenyl-l,4-dithiin 1-oxide (135) to the 1,3-dithiole derivatives 136 and 137 (equation 55). 

Steindler and coworkers found that PuF6 could be synthesized using ultraviolet irradiation of PuFi (s) and F2(g)... 

A variety of more complicated compounds having a CH2CH2 linkage to the POSS core have been prepared using methods outlined in Table 29. Thus, epoxides have been made from cyclohexene-terminated POSS (Table 29, entries 1 and 2) and are precursors for the preparation of nanocomposite polymers under ultraviolet irradiation (Figure 43). ... 

Usually, a-bromo-substituted arenes have been prepared through the reaction of arenes with bromine under ultraviolet irradiation. In the presence of benzoyl peroxide, N-bromosuccinimide can also be used for this purpose. 

El Beit lOD, Cotton DE, Wheelock V. 1983. Persistence of pesticides in soil leachates Effect of pH, ultraviolet irradiation and temperature. Int J Environ Stud 21 251 -259. 

The biological activity of several halogenated herbicides in water is destroyed by ultraviolet irradiation (18). Irradiation seems to be a promising method for decontaminating small quantities of pesticides. The chemical similarity between the chlorinated dioxins and other chlo-rinted aromatic compounds suggested that if there were parallels in their photochemical behavior, sunlight might destroy dioxins in the environment. 

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