scholarly journals The photochemical Beckmann rearrangement

1969 ◽  
Vol 47 (1) ◽  
pp. 51-62 ◽  
Author(s):  
H. Izawa ◽  
P. De Mayo ◽  
T. Tabata
Keyword(s):  
Quantum Yield ◽  
Stationary State ◽  
Irradiation Time ◽  
Hydrogen Abstraction ◽  
High Energy ◽  
Beckmann Rearrangement ◽  
Direct Irradiation ◽  
Temperature Irradiation ◽  
Oxygen Migration ◽  
Favorable Conditions

The direct irradiation of aryl aldoximes gives the amide (the photochemical Beckmann rearrangement) by intramolecular oxygen migration. This has been shown by the rearrangement of 18O-labelled benzaldoxime in the presence of p-tolualdoxime: no exchange of label was observed.The rearrangement usually gives the amide, but in the case of the anisyl derivative the anilide was also obtained. The highest quantum yield for benzamide formation noted (in acetic acid) was 0.034, but the figure is dependent on irradiation time. The results of low-temperature irradiation suggest that an oxazirane is an intermediate. Phenyl-N-methyl oxazirane is converted into the amide on irradiation (though not thermally) and it seems likely that the reaction is induced, under the conditions of the reaction, by benzylic hydrogen abstraction by thermally produced small amounts of benzaldehyde; a fact which may explain the variation in quantum yield of amide formation with extent of irradiation. An additional route from oxazirane to amide may also be available.The activation of the oxime by high energy sensitizers under the most favorable conditions gives Φamide = 0.002, and so a singlet pathway for oxazirane formation is preferred. The main route for energy degradation appears to be by syn–anti isomerism. This can be induced by a variety of sensitizers and so can be a triplet process. The direct irradiation of benzaldoxime leads to isomerism with Φαβ = 0.40 and Φβα = 0.38. From these figures, together with the composition of the stationary state found, the composition of the sensitized stationary state can be calculated in fair agreement with the experimentally found value. This suggests that the isomerization following direct irradiation is also a triplet process.In a single example of an aralkyl ketoxime (p-anisylmethyl ketoxime) irradiation products of both aryl and alkyl migration, were found.

scholarly journals Monte Carlo Modeling and Design of Photon Energy Attenuation Layers for >10× Quantum Yield Enhancement in Si-Based Hard X-ray Detectors

Instruments ◽  
2021 ◽  
Vol 5 (2) ◽  
pp. 17
Author(s):  
Eldred Lee ◽  
Kaitlin M. Anagnost ◽  
Zhehui Wang ◽  
Michael R. James ◽  
Eric R. Fossum ◽  
...  
Keyword(s):  
Monte Carlo Simulation ◽  
Monte Carlo ◽  
Quantum Yield ◽  
Photon Energy ◽  
High Efficiency ◽  
High Energy ◽  
Yield Enhancement ◽  
X Ray ◽  
Simulation Results ◽  
Conversion Efficiencies

High-energy (>20 keV) X-ray photon detection at high quantum yield, high spatial resolution, and short response time has long been an important area of study in physics. Scintillation is a prevalent method but limited in various ways. Directly detecting high-energy X-ray photons has been a challenge to this day, mainly due to low photon-to-photoelectron conversion efficiencies. Commercially available state-of-the-art Si direct detection products such as the Si charge-coupled device (CCD) are inefficient for >10 keV photons. Here, we present Monte Carlo simulation results and analyses to introduce a highly effective yet simple high-energy X-ray detection concept with significantly enhanced photon-to-electron conversion efficiencies composed of two layers: a top high-Z photon energy attenuation layer (PAL) and a bottom Si detector. We use the principle of photon energy down conversion, where high-energy X-ray photon energies are attenuated down to ≤10 keV via inelastic scattering suitable for efficient photoelectric absorption by Si. Our Monte Carlo simulation results demonstrate that a 10–30× increase in quantum yield can be achieved using PbTe PAL on Si, potentially advancing high-resolution, high-efficiency X-ray detection using PAL-enhanced Si CMOS image sensors.

scholarly journals Optimization of Waste Cooking Oil’s FFA as Biodiesel Feedstock

Teknomekanik ◽  
2021 ◽  
Vol 4 (1) ◽  
pp. 14-21
Author(s):  
Sri Rizki Putri Primandari ◽  
Andril Arafat ◽  
Harumi Veny
Keyword(s):  
Irradiation Time ◽  
Control Variable ◽  
Waste Cooking Oil ◽  
Biodiesel Production ◽  
Molar Ratio ◽  
Cooking Oil ◽  
Biodiesel Feedstock ◽  
Temperature Irradiation ◽  
Acid Esterification ◽  
Central Composite

Waste cooking oil has high Free Fatty Acid (FFA). It affected on decreasing a biodiesel production. FFA reduction is one of important processes in biodiesel production from waste cooking oil. Thus, this study aimed to examine the optimum condition in FFA reduction. The process is assisted by using ultrasonic irradiation on acid esterification. Variables of the process are acid concentration, molar ratio of methanol and oil, and irradiation time. Meanwhile temperature irradiation on 45oC is a control variable. Process optimization is conducted by Response Surface Methodology (RSM) with Central Composite Design (CCD). The optimum conditions of response were 7.22:1 (methanol to oil molar ratio), 0.92% wt H2SO4, 26.04 minutes (irradiation time), and 45oC (irradiation temperature). Ultrasonic system reduced FFA significantly compared to conventional method.

Evidence Against a Hydrogen Abstraction Mechanism in the Photorearrangement of Azoxybenzene to 2-Hydroxyazobenzene

1973 ◽  
Vol 51 (23) ◽  
pp. 3827-3841 ◽  
Author(s):  
David J. W. Goon ◽  
N. G. Murray ◽  
Jean-Pierre Schoch ◽  
N. J. Bunce
Keyword(s):  
Free Radical ◽  
Quantum Yield ◽  
Isotope Effect ◽  
Polar Solvent ◽  
Hydrogen Abstraction ◽  
Fold Increase ◽  
Transfer Mechanism ◽  
Deuterium Isotope Effect ◽  
Ring Carbon

In an attempt to distinguish between ionic and free radical mechanisms for the photorearrangement of azoxybenzene to 2-hydroxyazobenzene, aromatic azoxycompounds carrying C—H functions ortho to the azoxy linkage have been prepared and irradiated. The failure of these weaker C—H bonds to divert the reaction from its normal course argues against a hydrogen abstraction–hydroxyl transfer mechanism. This conclusion is supported by the observation of a 30-fold increase in quantum yield for 2-hydroxyazobenzene formation on changing from a non-polar to a polar solvent and by the kinetic deuterium isotope effect, which is too small for the primary isotope effect required by the abstraction mechanism. It is concluded that the experimental observations to date may most easily be accommodated in the route originally proposed by Badger and Buttery, where the rearrangement is seen as a substitution by oxygen at the ortho ring carbon.

Coulomb Interactions between Cosmic Rays and Charged Dust Grains

1993 ◽  
Vol 10 (3) ◽  
pp. 218-221 ◽  
Author(s):  
S.E. Byleveld ◽  
D.B. Melrose ◽  
LE. Cram
Keyword(s):  
Cosmic Rays ◽  
High Energy ◽  
Heating Time ◽  
Low Energy ◽  
High Energy Density ◽  
Charged Dust ◽  
Dust Grains ◽  
Coulomb Interactions ◽  
Time Required ◽  
Favorable Conditions

AbstractThe transfer of kinetic energy between cosmic rays and charged dust grains is investigated. The time required for heating of the dust grains due to Coulomb interactions is estimated and compared with the heating time due to ionisation losses by the cosmic rays. Heating of dust grains by cosmic rays is examined in connection with the FIR–radio correlation in galaxies: even for the most favorable conditions, including a high energy density in low-energy, ≲ 100 keV, cosmic rays, the conclusions are equivocal.

Enhancement of luminescence quantum yield of 1.5 µm emission from Er-doped SiO2 sensitized with Si nanocrystals

2014 ◽  
Vol 1592 ◽  
Author(s):  
S. Saeed ◽  
T. Gregorkiewicz
Keyword(s):  
Quantum Yield ◽  
Threshold Energy ◽  
Threshold Value ◽  
High Energy ◽  
Excitation Energies ◽  
Si Nanocrystals ◽  
Incoming Photon ◽  
Photon Conversion ◽  
Sample Characteristics ◽  
Er Doped

ABSTRACTExcitation of multiple Er3+ ions upon absorption of a single high-energy photon increases Er-related emission at 1.5 μm, and therefore enhances UV/visible-to-IR photon conversion efficiency. Here we investigate this effect for layers of Er-doped SiO2 sensitized with silicon nanocrystals by measuring the quantum yield of 1.5 µm Er-related emission. We demonstrate dramatic increase of the emission commencing for excitation energies above a certain threshold value, as the number of Er3+ ions excited upon absorption of a single incoming photon increases. By comparing differently prepared materials, we show that the actual value of this threshold energy and the rate of the observed increase of the quantum yield depend on sample characteristics – the size of Si nanocrystals and the ratio of Er3+ ions and nanocrystals concentrations.

Quantitative Determination of Photokinetic Parameters for Reversible Photoisomerizations in Light Scattering Adsorbent-Adsorbates

2000 ◽  
Vol 214 (2) ◽  
Author(s):  
R. Gade ◽  
Th. Porada
Keyword(s):  
Approximate Solution ◽  
Light Scattering ◽  
Quantum Yield ◽  
Present Method ◽  
Irradiation Time ◽  
Initial Slope ◽  
Quantum Yields ◽  
Absorption Coefficients ◽  
Actinic Light

Based on an approximate solution of the differential equations describing the rate of a reversible photoisomerization and the attenuation of the actinic light in a powdered adsorbent-adsorbate a method is presented permitting us to predict the irradiation time dependence of the sample reflectance and to determine both the quantum yields of the partial reactions and the absorption coefficients of the reactant and the product from the reflectance-time-curves measured at two different wavelengths. The present method, thus, is an improved version of the peviously reported procedure [1] which enables the quantum yield of a simple photoreaction to be calculated from the initial slope of the R(

The Mercury-Sensitized Photolysis of Pentamethyldisilane

1996 ◽  
Vol 51 (1-2) ◽  
pp. 105-115 ◽  
Author(s):  
C. Kerst ◽  
P. Potzinger ◽  
H. Gg. Wagner
Keyword(s):  
Quantum Yield ◽  
Rate Constants ◽  
Hydrogen Abstraction ◽  
Branching Ratios ◽  
Bond Breaking ◽  
Hydrogen Atoms ◽  
Substitution Reactions ◽  
Abstraction Reaction

Abstract Two primary processes were observed in the Hg-sensitized photolysis of Me 5 Si 2 H: (I) hydrogen abstraction from the Si-H bond with a quantum yield of 0(1) = 0.85, (V) Si-Si bond breaking with 0(V) = 0.04. The hydrogen atoms formed in (/) undergo an H atom abstraction reaction (k(3)), as well as substitution reactions at the Si centers resulting in the formation of dimethylsilane and trimethylsilyl radical (k(4)) or trimethylsilane and dimethylsilyl radical (k(5)). The following branching ratios have been determined:[xxx]The ratio of disproportionation (k(2)) to combination (k(1)) for the pentamethyldisilyl radical has been determined with MeOH as the scavenger for 1-methyl-l-trimethylsilylsilene, 0.046 < k(2)/A: C1) < 0.071. A mechanism with pertinent rate constants has been proposed which accounts for theresults.

Photolysis of 4-Methyl 3-Hexanone and 2-Methoxy 3-Pentanone in Hydrocarbon Solution

1971 ◽  
Vol 49 (8) ◽  
pp. 1310-1314 ◽  
Author(s):  
L. P-Y. Lee ◽  
B. McAneney ◽  
J. E. Guillet
Keyword(s):  
Quantum Yield ◽  
Hydrogen Abstraction ◽  
Type I ◽  
Type Ii ◽  
Cage Effect ◽  
Predominant Type ◽  
Norrish Type ◽  
Hydrocarbon Solution ◽  
Membered Transition State ◽  
Made In

Studies of the photolysis of 4-methyl 3-hexanone and the iso-electronic 2-methoxy 3-pentanone have been made in hydrocarbon solution using light of wavelength 313 nm. The latter compound gives only Norrish type II products with a quantum yield of 0.19 ±.01. The former gives a predominance of type I products with a total quantum yield of 0.23 ±.01 and the quantum yield for type II is reduced to 0.10 ±.01. The predominant type I reaction appears to involve α-scission to give an ethyl and a 2-methyl butyryl radical, which suggests a "cage effect". It is suggested that the reason for the suppression of the type I reaction in 2-methoxy 3-pentanone is the greater ease of γ-hydrogen abstraction due to the presence of the oxygen atom in a six-membered transition state.

THE LOSS OF FREE ELECTRONS IN IRRADIATED AIR

1963 ◽  
Vol 41 (4) ◽  
pp. 625-631 ◽  
Author(s):  
B. G. Young ◽  
A. W. Johnson ◽  
J. A. Carruthers
Keyword(s):  
High Pressures ◽  
Irradiation Time ◽  
High Energy ◽  
Free Electrons ◽  
Loss Mechanism ◽  
High Energy Electrons ◽  
Ion Recombination ◽  
Three Body ◽  
Microwave Probe ◽  
Low Pressures

The loss of free electrons in air, nitrogen, and oxygen is studied as a function of pressure by continuously irradiating the gases with high-energy electrons and measuring the equilibrium electron densities with a microwave probe. At low pressures (1–10 mm Hg) electrons are lost by free diffusion to the chamber walls before cooling. At intermediate pressures (10–100 mm Hg) electrons cool rapidly without loss to thermal energy and then disappear by three-body attachment in air and oxygen, and by electron–ion recombination in nitrogen. At high pressures (100–1000 mm Hg) the electron density increases with irradiation time and the controlling loss mechanism is uncertain.

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