Substituent effects on the photochemical reaction rates of the uranyl-alcohol system

1971 ◽  
Vol 93 (21) ◽  
pp. 5421-5423 ◽  
Author(s):  
Ryoka Matsushima ◽  
Shukichi Sakuraba
Keyword(s):  
Photochemical Reaction ◽  
Substituent Effects ◽  
Reaction Rates ◽  
Alcohol System

The Thermal Decomposition of N-Arylcarbamates of t-Alcohols. 2. Effects of Solvent, Temperature, and Substituents

1972 ◽  
Vol 50 (21) ◽  
pp. 3478-3487 ◽  
Author(s):  
S. J. Ashcroft ◽  
Melanie P. Thorne
Keyword(s):  
Diphenyl Ether ◽  
Substituent Effects ◽  
Reaction Rates ◽  
Specific Rate ◽  
Cyclic Transition ◽  
Tertiary Alcohols ◽  
Carbonium Ion ◽  
Tertiary Carbon ◽  
Cyclic Transition State ◽  
Influence Of Solvent

The influence of solvent, ring substituents, and tertiary carbon atom substituents on the decomposition at 423–473 K of some N-arylcarbamates of tertiary alcohols (p-XC6H4NHCO2C(CH3)2R, where X = CH3, H, Cl, NO2, R=C≡CH, C2H5, CH=CH2) has been investigated. In dodecane, diphenyl ether, acetophenone, nitrobenzene, and decanol, the reactions were first order yielding chiefly carbon dioxide, amine, and olefin. t-Pentyl carbamates yielded the olefins 2-methyl-1-butene and 2-methyl-2-butene in a 3:1 mixture. Solvent effects are reflected in variations in enthalpies and entropies of activation, but effects on the actual values of the specific rate constants are small. Substituent effects are also small, with changes in R from C≡CH to CH=CH2 producing only a tenfold rate increase. Variations in X yield Hammett σρ plots with slopes of about 0.50. These results are consistent with the charge separated cyclic transition state proposed before (1). In ethylene glycol, increased reaction rates and 1:1 yields of the olefins from the t-pentyl carbamates indicate a mechanism with greater carbonium ion character.

scholarly journals Determination of photochemical reaction rates using thermal lens spectrometry

2010 ◽  
Vol 214 ◽  
pp. 012125 ◽  
Author(s):  
N G C Astrath ◽  
F B G Astrath ◽  
J Shen ◽  
J Zhou ◽  
K H Michaelian ◽  
...  
Keyword(s):  
Thermal Lens ◽  
Photochemical Reaction ◽  
Reaction Rates ◽  
Thermal Lens Spectrometry

Single-Phase Flow in a Micro-Structured Packed Bed Photo-Reactor: Effect of Packing Size on Flow Regime and on the Reactor Performance for Homogeneous Photocatalysis

2018 ◽  
Author(s):  
Bruno Ramos ◽  
Atieh Parisi Couri ◽  
Shinichi Ookawara ◽  
Antonio Carlos Silva Costa Teixeira
Keyword(s):  
Flow Regime ◽  
Aqueous Phase ◽  
Residence Time ◽  
Photochemical Reaction ◽  
Collection Efficiency ◽  
Structural Parameters ◽  
Packed Bed ◽  
Reaction Rates ◽  
Glass Spheres ◽  
Packing Size

Dedicated research on photochemical reactors is fundamental to the application of this technology to real-life problems. In line with this trend, we report a study of structural parameters of micro-structured packed bed reactors (μPBR) regarding their ability to promote intensification. We present an investigation on the effects of the size of spherical packings on the developed flow regime, and its implications for the performance of the reactor on a photochemical reaction in aqueous phase. Tubular reactors were built with combinations of borosilicate glass tubes of two diameters (20 and 30 mm) packed with soda-lime glass spheres of three average diameters (1.0, 3.0 and 6.0 mm), alumina spheres of 6.0 mm diameter, and polished iron spheres of 5.0 mm diameter. Residence Time Distributions (RTD) were measured for each combination of outer tube and glass sphere sizes. Results showed that as the packing size decreases, the observed flow regime becomes closer to an ideal PFR, suggesting that smaller packings are more suitable to applications that require precise control of residence time. The aqueous-phase oxidation of benzoic acid by oxygen radicals generated by UV-A irradiation of nitrite ions was used as model photochemical reaction. We also observed that increasing the D/d<sub>p</sub> ratio for narrower reactors faster specific reaction rates are achieved, suggesting that intensification is possible in these reactors; however, the overall yield decreases, probably due to increased photon loss. Lastly, we found that glass spheres can be replaced by alumina spheres with little loss in light-collection efficiency, indicating an attractive pathway for immobilized photocatalysis.

Arrhenius behavior of hydrocarbon fuel photochemical reaction rates by thermal lens spectroscopy

2009 ◽  
Vol 95 (19) ◽  
pp. 191902 ◽  
Author(s):  
N. G. C. Astrath ◽  
F. B. G. Astrath ◽  
J. Shen ◽  
J. Zhou ◽  
K. H. Michaelian ◽  
...  
Keyword(s):  
Thermal Lens ◽  
Photochemical Reaction ◽  
Hydrocarbon Fuel ◽  
Reaction Rates ◽  
Arrhenius Behavior ◽  
Thermal Lens Spectroscopy

Kinetics and mechanism of the oxidation of alcohols by ferrate ion

1993 ◽  
Vol 71 (9) ◽  
pp. 1394-1400 ◽  
Author(s):  
Donald G. Lee ◽  
Huifa Gai
Keyword(s):  
Transition Metal Oxides ◽  
Isotope Effects ◽  
Substituent Effects ◽  
Kinetic Isotope Effects ◽  
Reaction Rates ◽  
Radical Intermediates ◽  
Kinetic Isotope ◽  
Oxidation Of Alcohols ◽  
Aliphatic Ether ◽  
High Valent

A kinetic study of the reduction of ferrate ion under basic conditions has been completed. The observation that a typical aliphatic ether, tetrahydrofuran, is oxidized at a rate comparable to that of aliphatic alcohols, such as cyclopentanol, indicates that the reaction between ferrate and alcohols is likely initiated by attack of the oxidant at an α-C—H bond, a conclusion that is consistent with the occurrence of primary deuterium kinetic isotope effects (2.8–4.3 at 25 °C) when α-hydrogens are replaced by deuterium. Because only acyclic products are obtained from the oxidation of cyclobutanol by ferrate, it may be concluded that free radical intermediates are involved in the reaction. The insensitivity of the reaction rates to substituent effects during the oxidation of substituted mandelic acids indicates that substantial charges are not built up in the transition state. All of these observations are most readily accommodated by a mechanism in which the reaction is initiated by a 2 + 2 addition of an Fe=O bond to the α-C—H of an alcohol to give an organometallic intermediate that subsequently decomposes by homolytic cleavage of the resulting C—Fe bond. Comparisons are made with the reactions between alcohols and other high-valent transition metal oxides.

scholarly journals Chemical structure and biodegradability of halogenated aromatic compounds. Substituent effects on 1,2-dioxygenation of catechol

1978 ◽  
Vol 174 (1) ◽  
pp. 85-94 ◽  
Author(s):  
E Dorn ◽  
H J Knackmuss
Keyword(s):  
Chemical Structure ◽  
Substituent Effects ◽  
Alcaligenes Eutrophus ◽  
Reaction Rates ◽  
Pseudomonas Sp ◽  
Substituent Constant ◽  
Binding Studies ◽  
Km Value ◽  
Michaelis Constants ◽  
Halogenated Aromatic Compounds

1. The influence of halogen substituents on the 1,2-dioxygenation of catechols was investigated. The results obtained with the two isoenzymes pyrocatechase I and pyrocatechase II from the haloarene-utilizing Pseudomonas sp. B 13 and the pyrocatechase from benzoate-induced cells of Alcaligenes eutrophus B.9 were compared. 2. Substituents on catechol were found to interfere with O2 binding by the two isoenzymes from Pseudomonas sp. B 13, whereas the Km value for catechol kept constant at different O2 concentrations. 3. Electron-attracting substituents decreased the Km values for catechols. 4. Results from binding studies with substituted catechols demonstrated narrow stereospecificities of pyrocatechase I from pseudomonas sp. B 13 and the pyrocatechase from alcaligenes eutrophus B.9. In contrast, a low steric hindrance by substituents in the binding of catechols with pyrocatechase II was observed. 5. Low pK′1 values of substituted catechols resulted in low Michaelis constants. 6. Electron-attracting substituents such as halogen decreased the reaction rates of catechol 1,2-dioxygenation. The correlation of the Vmax. values observed with pyrocatechase II from Pseudomonas sp. B 13 with the substituent constant sigma+ (Okamoto–Brown equation) was distinctly greater than with Hammett's sigma values. The corresponding logVmax. against sigma+ correlation for pyrocatechase I was considerably disturbed by steric influences of the substituents.

Regioselectivity of glycoluril-directed Claisen condensations — A kinetic and mechanistic study of substituent effects in the nucleophilic acyl group

2006 ◽  
Vol 84 (9) ◽  
pp. 1188-1196 ◽  
Author(s):  
Mei Chen ◽  
Katie Won ◽  
Robert S McDonald ◽  
Paul H.M Harrison
Keyword(s):  
Kinetic Data ◽  
Uv Spectroscopy ◽  
Substituent Effects ◽  
Reaction Rates ◽  
Quantitative Yield ◽  
Mechanistic Study ◽  
Claisen Condensation ◽  
Bond Forming ◽  
Rate Limiting

The Claisen-like condensation of a series of 1-arylacetyl-6-acetyl-3,4,7,8-tetramethylglycolurils (Ar = Ph, p-OMeC6H4, and p-ClC6H4) was studied in preparative experiments and by analysis of kinetic data. The reactions proceeded in virtually quantitative yield and were highly regioselective: the corresponding N-(2′-aryl-3′-ketobutanoyl)-3,4,7,8-tetramethylglycolurils were obtained in all cases, with none of the 4′-aryl regioisomers being detected. Clean bimolecular kinetics were observed for each conversion using UV spectroscopy. Reaction rates followed the order Ar = p-OMeC6H4 < Ph < p-ClC6H4. The results are explained by a mechanism in which the deprotonation of the substrates is rate-limiting; thus, deprotonation of the arylacetyl groups is favoured. The ensuing enolate reacts rapidly in the C–C bond-forming step.Key words: glycoluril, biomimetic, Claisen condensation, regioselectivity, kinetics, mechanism, substituent effects.

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