Photo-decomposition

Photo- decomposition High intensity sources may cause sample decomposition, which depends on the residence time of the sa le in the detector cell. 

Texas Red hydrazide is soluble in DMF and may be dissolved as a concentrated stock solution in this solvent prior to the addition of a small aliquot to an aqueous reaction medium. The solid and all solutions made from it must be protected from light to avoid photo-decomposition. Prepare the stock solution fresh immediately before use. A suggested protocol on the use of this fluorescent probe may be obtained by following the method outlined for fluorescein-5-thi-osemicarbazide in Section 1 of this chapter. Optimization may be necessary to achieve the best level of fluorescent modification (F/P ratio) for a particular application. 

It is also possible to make similar arguments for other cases, say photo-decomposition of phenyldiazonium salts 17 ) or phenyl halides. 

Although the photolysis of C302 has been used extensively as a source of C20 radicals and C atoms, little is known about the photochemistry of this molecule. Absorption and photo-decomposition commence2,4 at 3300 A and result in the production of CO and a polymer5. C02 is a minor product at short wavelengths6. The careful work of Bayes et alf has produced compelling, although indirect evidence for the importance of... 

Photodecomposition of pentachlorophenol was observed when an aqueous solution was exposed to sunlight for 10 d. The violet-colored solution contained 3,4,5-trichloro-6-(2 -hydroxy-3, 4, 5, 6 -tetrachlorophenoxy)-o-benzoquinone as the major product. Minor photo-decomposition products (% yield) included tetrachlororesorcinol (0.10%), 2,5-dichloro-3-hydroxy-6-pentachloro-phenoxy-p-benzoquinone (0.16%), and 3,5-dichloro-2-hydroxy-5-2, 4, 5, 6 -tetrachloro-3-hy-droxyphenoxy-p-benzoquinone (0.08%) (Plimmer, 1970). 

In this example, the volatile precursor compounds were heated to obtain the product. Other energy sources are also used, notably electromagnetic radiation. An example of vapour phase deposition involving photo-decomposition is given in the next section on vapour phase epitaxy. 

Eriksson J, Jakobsson E, Marsh G, et al. 2001. Photo decomposition of brominated diphenylethers in methanol/water. BFR 203-206. 

According to C. F. Barwald and A. Monheim (1835), the decomposition is accelerated by the presence of organic substances. J. Milbauer tried the effect of thirty-two metal chlorides of sodium tungstate and molybdate of uranyl sulphate and of sulphuric, selenic, arsenic, and boric acids on the photo-decomposition of chlorine water, and found. that none accelerated but that most retarded the action. Chlorine catalyzes the decomposition of bromine water and bromine, chlorine water while iodine does not accelerate, but rather retards the reaction, probably by forming relatively stable iodine compounds. A. Bcnrath and H. Tuchel found the temp, coeff. of the velocity of the reaction with chlorine water between 5° and 30° increases in the ratio 1 1 395 per 10°. 

Dissolve the required amount of BrdU in 1 mL of sterile saline immediately prior to use and protect the solution from light to prevent photo-decomposition. 

A carbene intermediate (28) was proposed in the photo-decomposition of the antibiotic agent lomefloxacin.39 Treatment of isoxazole-containing tetrachlorocyclo-propanes such as (29) with MeLi gave rise to 1-aza fulvenes via postulated vinylcarbene intermediates (30).40... 

Time-resolved CIDEP and optical emission studies provide further definitive characterization of the triplet and excited singlet states followed by their primary photochemical reactions producing transient radicals in individual mechanistic steps in the photolysis of a-guaiacoxylacetoveratrone. Both fluorescence and phosphorescence are observed and CIDEP measurements confirm the mainly n,n character of the lowest triplet state. The results indicate a photo triplet mechanism involving the formation of the ketyl radical prior to the P-ether cleavage to form phenacyl radicals and phenols. Indirect evidence of excited singlet photo decomposition mechanism is observed in the photolysis at 77 K. 

Jaeger CD, Bard AJ (1979) Spin trapping and electron-spin resonance detection of radical intermediates in the photo-decomposition of water at TO2 particulate systems. J Phys Chem 83 3146-3152... 

Holmstead, R.L., Casida, J.E., Luzo, L.O., Fullmer, D.G. (1978) Pyrethroid photo-decomposition Permethrin. J. Agric. Food Chem. 26, 590-595. 

Table 2 Photo-decomposition of thieno[3,2-c][lA4,2] thiazines (84) and related species <86JCS(P1)497>.

Effect of Foreign Gas on the Photo-Decomposition of Nitrogen Dioxide at 0°... 

The photo decomposition of carbofuran (2,3-dihydro-2,2-dimethyl-7-ben-zofuranyl-AT-methylcarbamate) (III) was investigated in pure water and in the presence of various samples of organic matter (soil-extracted humic and fulvic acids) [66]. Irradiation of carbofuran (1.3 x 10 5 M) in pure water at 254 nm yielded several photoproducts however, only Ilia and Illb could be firmly identified. A step reaction was proposed first, formation of Ilia by cleavage of the O - CO bond, and second, formation of Illb by photohydrolysis of the furan ring (see Scheme 3). 

Analogous to the cleavage reactions of radical cations, a number of synthetically useful reactions from radical anions are also derived. Photo-decomposition of benzylesters and benzylsulfones are some of the simpler examples of this series [119]. Photoreduction of carboxylic esters (e.g. 122) to corresponding... 

In the water-ln-oll mlcroemulslon the separation of photoproducts is achieved by means of the hydrophilic-hydrophobic nature of the products. A two compartment model system to accomplish the photo-decomposition of water is described. Photosensitized electron transfer reactions analogous to those occurring in the two half-cells are presented. In these systems the phase transfer of one of the photoproducts into the contlnuotis oil phase is essential to stabilize the photoproducts. 

Figure 7-14A). The base peak at m/z 305 might arise from the neutral loss of a 2-vinylamino-ethanol. The product ions formed by the neutral loss of 73 (2-methyleneamino-ethanol) and 44 (Ethenol) Da from the precursor ion of m/z 392 were also consistent with the proposed structure (Figure 7-15A). The production spectra of impurities D and E were similar in two ways. Both have a base peak at m/z 88 which was produced when an A-(2-hydroxyethyl) aminoethyl group was cleaved from the molecule. Both produce a less intense product ion that was 61 Da less than the precursor ion (Figure 7-15 m/z 278 in D, and m/z 263 in E). This 61-Da loss was found to be the loss of a 2-aminoethanol neutral. Further studies suggested that impurities D and E are photo-decomposition products of DuP 941[87]. Based on the LC/MS/MS data,... 

Below about 200 °C, the photo-decomposition of acetaldehyde becomes involved as a result of the increased stability of the formyl and acetyl radicals. The occurrence of new elementary steps, in addition to those already mentioned, renders the kinetics of the reaction rather complex. 

Arts JHE, Spoor SM, Mtrijser H (2000) Short-term inhalation exposure of healthy and compromised rats and mice to fine andrrltrafine carbon particles. Inhal Toxicol 12 (Suppl l) 261-266 Ausloos P, Rebbert RE, Glasgow L (1977) Photo-decomposition of chloromethanes adsorbed on silica surfaces. J Res Nat Bm Stand 82 1-8... 

Diketones.- Rubin has reviewed the recent photochemistry of 1,2-diketones. Studies of the gas phase photo-decomposition of glyoxylic acid and of pyruvic acid have been carried out. ... 

In water the photo-decomposition of APS-ER occurred very rapidly. For this it was not easy to obtain a very accurate fluorescence decay curve but the short-lived component is... 

The authors conclude that a combination of both explanations is responsible for the abnormal CH, radical. A comparable study (52) on Al.,0, was consistant with the results obtained with silica gel (50). The abnormal CD radical and C2HJ radicals were obtained (51) by the sensitized photo-decomposition of CD and 2 tL VG(y 0 ) at 77 K respectively. For the... 

One of the most important and fundamental questions in relation to the topochemical classification of Fig.1 is which contributes more to the a-Si nucleation, the gaseous phase photo decomposition or the decomposition of adsorbed molecules. The unambiguous answer to the question can be derived if we could eliminate illumination to the substrate surface without affecting excitation of gaseous phase molecules. Though it is hard to realize such a situation with the diffuse light, a similar... 

The Photo-Decomposition of Water Vapour (Cf A Coehn, Per d Deutsch Chem Gesell, 33, 880, 1910)... 

Photobinding of flunitrazepam and its major photo-decomposition product /V-dcsmcthy111 unitraz.cpam, Int. J. Pharm., 36, 113-120. 

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