scholarly journals 1,3-Dipolar Cycloadditions ofN-(p-Substituted benzylidene)p-Substituted BenzylamineN-Oxides withtrans-Bis(p-substituted benzoyl)ethylenes and the Substituent Effects on the Reaction Rates

1978 ◽  
Vol 51 (6) ◽  
pp. 1839-1843 ◽  
Author(s):  
Keishi Tada ◽  
Tomoharu Yamada ◽  
Fujio Toda
Keyword(s):  
Substituent Effects ◽  
Reaction Rates ◽  
Dipolar Cycloadditions

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 Additive-assisted regioselective 1,3-dipolar cycloaddition of azomethine ylides with benzylideneacetone

2014 ◽  
Vol 10 ◽  
pp. 352-360 ◽  
Author(s):  
Chuqin Peng ◽  
Jiwei Ren ◽  
Jun-An Xiao ◽  
Honggang Zhang ◽  
Hua Yang ◽  
...  
Keyword(s):  
Substituent Effects ◽  
Azomethine Ylides ◽  
Dipolar Cycloaddition ◽  
Dipolar Cycloadditions ◽  
Nitrobenzoic Acid

1,3-Dipolar cycloadditions of isatins, benzylamine and benzylideneacetones were studied to prepare a series of novel spiropyrrolidine-oxindoles – 4′-acetyl-3′,5′-diarylspiro[indoline-3,2′-pyrrolidin]-2-ones and 3′-acetyl-4′,5′-diarylspiro[indoline-3,2′-pyrrolidine]-2-ones in good yields of up to 94% and with good regioselectivities. Regioselectivities are reversible by the addition of water or 4-nitrobenzoic acid, respectively. The substituent effects on the regioselectivity were also investigated.

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.

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