1,721,033 research outputs found
Kinetic study of the reactions of some 5-nitro-2-(4-nitrophenoxy)-3-x-thiophenes with aniline and 4-methoxyaniline in methanol
No full textThe rate constants of the title reactions have been measured at various amine concentrations. The second-order kinetic constant for the amino substitution increases in a hyperbolic way as a function of the nucleophile concentration. The k3Am/k-1 ratio for each catalysed system is not a monotonic function of the X substituent. This result has been rationalized in the framework of the SB-GA (Specific Base-General Acid) mechanism of base catalysis
Mononuclear Heterocyclic Rearrangements. Part 16. Kinetic Study of the Rearrangement of Some ortho-Substituted Z-Phenylhydrazones of 3-Benzoyl-5-phenyl-1,2,4-oxadiazole into 2-Aryl-4-benzoylamino-5-phenyl-1,2,3-triazoles in Dioxane-Water and in Benzene.
No full textAnalysis of substituent effects in the reactions of some2-L-3-nitro-5-X-thiophenes with aniline in benzene. A new interpretation ofthe`element effect`
No full textThe kinetic constants for the title reactions have been measured in benzene, at 25 °C, at various aniline concentrations. In spite of the low kB/k0 ratios, the reactions are inferred to be genuinely base-catalyzed. The susceptibility constants estimated for the various steps of the reaction mechanism(s) have allowed to make clear the limits of the so-called "element effect" criterion
Mononuclear Heterocyclic Rearrangements. Part 16. Kinetic Study of the Rearrangement of Some ortho-Substituted Z-Phenylhydrazones of 3-Benzoyl-5-phenyl-1,2,4-oxadiazole into 2-Aryl-4-benzoylamino-5-phenyl-1,2,3-triazoles in Dioxane-Water and in Benzene.
No full textAromatic nucleophilic substitution reactions of some 3-nitro-2-p-nitro-phenoxy-5-X-thiophenes with substituted anilines in methanol
No full textA series of optimised 'thiophene' sigma constant values has been calculated by using the reactions of some 3-nitro-2-p-nitrophenoxy-5-X-thiophenes with some substituted anilines. The susceptibility constants obtained are discussed in the framework of the reactivity-selectivity principle
Analysis of substituent effects: The reactions of some 2-L-5-nitro-3-X-thiophenes with primary and secondary amines in methanol
No full textThe kinetics of the reactions of some 2-L-5-nitro-3-X-thiophenes with primary and secondary amines in methanol at various temperatures have been studied with the aim of obtaining information about the proximity effects of 3-X ortho-like substituents. The results obtained have shown that for all the substituents considered, except for X = Br, the proximity effects of steric nature are of little relevance with respect to the electronic ones. Thus, it has been possible to establish a set of ortho sigma constants which account well for the electronic effects of 3-X substituents and to obtain excellent linear free energy ortho-correlations
Linear free energy ortho-correlations in the reactions of some 2-bromo-5-nitro-3-x-thiophenes with primary and secondary amines in benzene
No full textlinear free energy ortho-correlationsThe kinetics of SNAr reactions of some 2-bromo-3-X-5-nitrothiophenes (X = Me, H, Br, CONH2, CO2Me, COMe, SO2Me, CN and NO2) with some primary (n-butylamine and benzylamine) and secondary (pyrrolidine, piperidine, morpholine and N-benzylamine) amines have been measured in benzene as a function of nucleophile concentration. Most of the reactions studied show apparent kinetic constants little affected or not affected by an increase in amine concentration, indicating that the overall reaction rate is controlled by the formation of the reaction intermediate. The reactions of the substrates where X = Br and CN with the two primary amines proved to be base-catalysed. The k3B/k-1values calculated for these substituents are inconsistent with the hypothesis of a base catalysis for the intermediate decomposition and strongly suggest a catalysis of the first step of the reaction pathway
The First Kinetic Evidence for Acid Catalysis in a Monocyclic Rearrangement of Heterocycles: Conversion of the Z-Phenylhydrazone of 5-Amino-3-benzoyl-1,2,4-oxadiazole into N,5-Diphenyl-2H-1,2,3-triazol-4-ylurea
No full textThe title reaction has been studied in dioxane/water in a large (0.1-14.9) pS+ range, evidencing, together with an uncatalyzed process at intermediate (3.5-8.0) pS+ values, the occurrence of a catalyzed pathway both in the acidic (pS+ 0.1-3.5) and in the basic region (pS+ 8.0-14.9): specificacid catalysis and general-base catalysis, respectively, have been found to take place by means of kinetic investigations at different buffer concentrations. Mechanisms for the three pathways have been advanced on the grounds of structural features. In a comparison with previous data particular attention has been paid to the acid-catalyzed pathway, herein observed for the first time in an azole-to-azole interconversion. The mechanistic hypotheses seem well supported by ab initio calculations
Studies on Azole-to-Azole Interconversion. An Interesting Case of Absence of “Primary Steric Effect” in the Ring-degenerate Equilibration between ortho-Substituted 3-Aroylamino-5-methyl-1,2,4-oxadiazoles and 3-Acetylamino-5-aryl-1,2,4-oxadiazoles in Methanol.
No full textNMR study of the (Z)-phenylhydrazones of 5-alkyl- and 5-aryl-3-benzoyl-1,2,4-oxadiazoles: Support for the interpretation of kinetic results on the rearrangement of 1,2,4-oxadiazoles to 1,2,3-triazoles.
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