Selective photochemical reduction of carbon-chlorine bond in fluoropropanoates and its quantum yields

1983 ◽  
Vol 48 (3) ◽  
pp. 766-771 ◽  
Author(s):  
Oldřich Paleta ◽  
Rudolf Ježek ◽  
Václav Dědek
Keyword(s):  
Ultraviolet Light ◽  
Quantum Yields ◽  
Reduction Mechanism ◽  
Photochemical Reduction ◽  
A Chain ◽  
Chlorine Bond

Ultraviolet light initiated reduction of methyl 2,2,3-trichlorodifluoropropanoate (I), methyl 2,3-dichlorotrifluoropropanoate (II) and methyl 2-chlorotetrafluoropropanoate (III) in 2-propanol afforded methyl 2,3-dichloro-3,3-difluoropropanoate (IV), methyl 3-chloro-2,3,3-trifluoropropanoate (V) and methyl 2,3,3,3-tetrafluoropropanoate (VI) in the respective yields 81%, 86% and 75%. Maximum quantum yields, φmax, of the reduction at 254 nm for the ester IV, V and VI are 225, 240 and 270, respectively, indicating thus a chain reduction mechanism.

Photocatalytic Effect of Fe(III) on Oxidation of Two-Carbon Substrates Related to Natural Waters

1994 ◽  
Vol 59 (5) ◽  
pp. 1066-1076 ◽  
Author(s):  
Šárka Klementová ◽  
Dana M. Wagnerová
Keyword(s):  
Mathematical Model ◽  
Natural Waters ◽  
Substrate Oxidation ◽  
Quantum Yields ◽  
Ferric Ions ◽  
Photochemical Reduction ◽  
Photocatalytic Effect ◽  
Carbon Substrates ◽  
Glyoxalic Acid ◽  
The Common

The influence of ferric ions on photoinitiated reaction of dioxygen with two carbon organic acids, aldehydes and alcohols related to natural waters was demonstrated. Photocatalytic effect of ferric ions, i.e. photochemical reduction of Fe(III) as the catalyst generating step, has been found to be the common principal of these reactions. The overall quantum yields of the reactions are in the range from 0.3 to 1.2. A mathematical model designed for the mechanism of cyclic generation of catalyst in the singlet substrate oxidation by O2 was applied to the system glyoxalic acid + Fe(III); a fair agreement between the simulated and experimental kinetic curves was obtained. The experimental rate constant is 4.4 .10-4 s -1.

Reactions of Thiyl Radicals. XI. Further Investigations of Thiol–Disulfide Photolyses in the Liquid Phase

1973 ◽  
Vol 51 (9) ◽  
pp. 1410-1415 ◽  
Author(s):  
Donna D. Carlson ◽  
Arthur R. Knight
Keyword(s):  
Liquid Phase ◽  
Room Temperature ◽  
Liquid Mixtures ◽  
Quantum Yields ◽  
Chain Reaction ◽  
Photochemical Process ◽  
High Quantum Efficiency ◽  
Thiyl Radicals ◽  
Exchange Processes ◽  
A Chain

The photolysis of C2H5SH liquid at 2537 Å has been shown to give H2 and C2H5SSC2H5 at equal rates with a quantum yield of 0.25. The photolysis of ethanethiol – methyl disulfide liquid mixtures leads, via a chain reaction involving propagation by attack of thiyl radicals on the disulfide S—S bond, to the formation with high quantum efficiency of CH3SH, C2H5SSC2H5 and, as an intermediate that is consumed after long exposures, CH3SSC2H5. The net result of the sequence of exchange processes is the essentially irreversible conversion of the methyl disulfide into methanethiol. The same overall reaction occurs thermally at room temperature, but the rate is appreciably less than that of the photochemical process. The quantum yields of formation of the unsymmetrical disulfides arising from the photochemically initiated exchange reaction in equimolar mixtures of CH3SSCH3 + n-C3H7SSC3H7 and C2H5SSC2H5 + n-C3H7SSC3H7 have been shown to be 6.9 and 4.4, compared to 355 for CH3-SSCH3 + C2H5SSC2H5 mixtures. In all three types of system examined in this investigation all thiyl radicals can be accounted for stoichiometrically on the basis of exchange and combination reactions alone, indicating negligible disproportionation of these species in condensed phase.

Un exemple d'isomérisation radicalaire en chaînes: la photoinduction de l'isomérisation cis–trans de la pentène-3 one-2

1977 ◽  
Vol 55 (22) ◽  
pp. 3915-3926 ◽  
Author(s):  
Armel Rioual ◽  
André Deflandre ◽  
Jacques Lemaire
Keyword(s):  
Energy Transfer ◽  
Quantum Yields ◽  
Unsaturated Ketone ◽  
Chain Process ◽  
Triplet Energy ◽  
Low Concentrations ◽  
Energy Transfers ◽  
Donor And Acceptor ◽  
A Chain ◽  
Triplet Energy Transfer

Mechanisms of the photosensitized cis–trans photoisomerization of 3-penten-2-one which do not imply only classical triplet–triplet energy transfer are proposed; they are based upon measurements of the variations of initial quantum yields of isomerization with the initial donor and acceptor concentrations, the wavelength of excitation, and the nature of the donor and of the solvent. Carbonyl donors (acetophenone, benzophenone, acetone) induce a radical isomerization by a chain process in reducing solvents; the example of acetophenone is specially interesting. In solvents in which the donor is not photoreduced (as benzene or CCl4) classical triplet–triplet energy transfers occur. Sensitization with aromatic donors (benzene, mesitylene) proceeds through triplet–triplet energy transfer at low concentrations of the acceptor. At higher concentrations of acceptor, an exciplex is formed between the ketone and the aromatic in its singlet excited state; this exciplex is deactivated by dissociation and by causing the isomerization of the α,β-unsaturated ketone.

The Quantum Yield of Oxidation of Hevea Rubber and GR-S

1948 ◽  
Vol 21 (3) ◽  
pp. 639-653 ◽  
Author(s):  
E. J. Hart ◽  
M. S. Matheson
Keyword(s):  
Quantum Yield ◽  
Room Temperature ◽  
Wave Length ◽  
Radical Reaction ◽  
Quantum Yields ◽  
Initial Reaction ◽  
Free Radical Reaction ◽  
Stable Intermediate ◽  
A Chain ◽  
Reaction Chain

Abstract The initial quantum yields of photoöxidation for purified Hevea rubber have been measured for various mercury arc lines in the wave length region 2537– 17,400 A˚. All experiments were carried out at room temperature and at an oxygen pressure of one atmosphere. At the outset of irradiation all quantum yields of combined oxygen are less than unity, although the quantum efficiency rises above 1.0 at 2537 and 3130 A˚. as photoöxidation proceeds. The low quantum yield suggests that in its initial stages (less than 0.1 per cent oxygen combined on the rubber) photoöxidation is not a chain reaction. It is postulated as the first step in rubber photoöxidation that the light activated rubber group reacts with oxygen to give a relatively stable intermediate which does not immediately dissociate to give a free radical reaction chain. The quantum yields of photoöxidation of purified GR-S were also measured under the same conditions as used for rubber. At each wave length the quantum yield was lower than for rubber, indicating formation of a stable intermediate in the initial reaction also.

scholarly journals Generation of Ketene With High Quantum Yield by a KrF Laser

1985 ◽  
Vol 5 (5) ◽  
pp. 257-273 ◽  
Author(s):  
Zhang Yunwu ◽  
W. Fuss ◽  
K. L. Kompa ◽  
F. Rebentrost
Keyword(s):  
Thermal Decomposition ◽  
Single Step ◽  
Quantum Yields ◽  
Methyl Radicals ◽  
High Quantum ◽  
Photochemical Formation ◽  
A Chain ◽  
Technical Interest ◽  
Approximate Rate ◽  
Pulsed Laser Irradiation

Acetone was photolyzed around 770 K by pulsed laser irradiation at 248 nm. The methyl radicals, generated in the primary step, trigger a chain reaction, producing ketene (CH2CO) and methane. Long chains (high quantum yields) result from low radical concentrations. Using a collimated laser beam of low intensity, quantum yields up to 300 have been demonstrated. Approximate rate constants have been derived and used for extrapolation to higher temperatures and different densities. Compared to the thermal process, the photochemical formation of ketene is faster. Therefore its thermal decomposition can be avoided to some extent. But the improvement is probably too small to be of technical interest. We also found indications that the thermal decomposition of acetone above about 500 to 600 K yields three fragments in a single step.

Far ultraviolet induced decomposition of thymine in deaerated and aerated aqueous solutions

1986 ◽  
Vol 64 (12) ◽  
pp. 2297-2300 ◽  
Author(s):  
Bunsho Ohtani ◽  
Hiroshi Nagasaki ◽  
Sei-Ichi Nishimoto ◽  
Koichi Sakano ◽  
Tsutomu Kagiya
Keyword(s):  
Aqueous Solution ◽  
Aqueous Solutions ◽  
Ultraviolet Light ◽  
Quantum Yields ◽  
Near Ultraviolet ◽  
Induced Decomposition ◽  
Far Ultraviolet ◽  
Cis And Trans

Thymine in aqueous solution was decomposed with quantum yields of 0.3 and 0.4 under N2-saturated and aerated conditions by far-ultraviolet light (> 180 nm, far-uv), and quantum yields of 2 × 10−4 and 3 × 10−4 by near-ultraviolet light (> 220 nm, near-uv), respectively. The main photolytic products by far-uv were 5,6-dihydrothymine (DHT) (selectivity: S (DHT) = 0.2) and 5-hydroxymethyluracil (HMU) (S(HMU) = 0.1) under N2-saturated conditions, cis- and trans-5,6-Dihydroxy-5,6-dihydrothymine (TG), 6(5)-hydroperoxy-5(6)-hydroxy-5,6-dihydrothymine (HTP) (S(TG) + S (HTP) = 0.2), and N1 -formyl-N2-pyruvylurea (FPU) (S(FPU) = 0.4) were obtained under aerated conditions. These products were attributed to the reactions of thymine with the H and OH produced by photolysis of water.

High efficiency photoresist-free lithography of UO3 patterns from amorphous films of uranyl complexes

1998 ◽  
Vol 13 (5) ◽  
pp. 1379-1389 ◽  
Author(s):  
M. Gao ◽  
Ross H. Hill
Keyword(s):  
Uranium Oxide ◽  
High Efficiency ◽  
Optical Lithography ◽  
Silicon Surfaces ◽  
Quantum Yields ◽  
Chain Reaction ◽  
Amorphous Films ◽  
Chain Reactions ◽  
A Chain ◽  
Primary Photochemical Reaction

The solid state photochemistry of uranyl carboxylate complexes is presented with the purpose of developing methods for optical lithography of uranium oxide films. These complexes of the general formula, UO2(OOCR)2 (R = i-C3H7, C5H11, CH2C6H5, CH2OC2H5, C2H4OC2H5), were all photosensitive as thin amorphous films. The primary photochemical reaction for each of these complexes was the extrusion of a CO2 from the ligand and the production of radicals which initiated a chain reaction. The nature of this chain reaction was dependent upon the identity of the organic substituents, R. In some cases the chain reaction required a photochemical step while others were entirely thermal in nature. Of importance are the potentially high quantum yields which can be associated with thermal chain reactions. Some of the systems presented here exhibit quantum yields in excess of 1. This process was shown to be compatible with optical lithography by the patterning of the uranium oxide product on silicon surfaces.

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