T. I. Gubina

Mechanism of recyclization of furans to thiophenes and selenophenes under acid-catalysis conditions. 2. Kinetic investigations of the reaction of 2,5-dialkylfurans with hydrogen sulfide and hydrogen selenide in an anhydrous medium

The effect of the concentration of the acidic component on the rates of recyclization of 2,5-dialkylfurans to thiophenes and selenophenes was studied. On the basis of the direct correlation of log k on (Ho)I and the isotope effect of the solvent it was established that the reaction proceeds via a mechanism of specific acid catalysis. It was shown that the rates of the reactions with the participation of hydrogen sulfide and hydrogen selenide coincide at equal acidities and temperatures. A scheme for the mechanism of the reaction that includes a step involving the formation of the doubly protonated form of the substrate is proposed.

Study of the mechanism of recyclization of furans into thiophenes and selenophenes in conditions of acid catalysis. 5. Direction of protonation of furans

Abstract2,5-Dimethyl-3-D-furan was prepared for the first time. Its recyclization into the corresponding thiophene and selenophene was investigated. The possibility of β-C-protonation of the furan ring was confirmed by experimental and quantum chemical data.

Study of the mechanism of recyclization of furans into thiophenes and selenophenes in conditions of acid catalysis. 6. Experiments with labeled atoms. Quantum chemical calculations of intermediates of recyclization and hydrolysis

The reaction of 2-methyl-5-R-furans (R=Me, Bu, 2,2-pentyl-2-methylpentyl) with H218O was investigated. Furans and the corresponding 2,5-alkanediones containing the18O isotope were obtained. The general characteristics of the recyclization and isotope exchange reactions were established. A kinetic study of recyclization of 2,5-dimethylfuran with16O and18O into 2,5-dimethylthiophene was conducted. A reverse kinetic isotope effect was found. The schemes of the mechanisms of these processes were refined based on the experimental data and quantum-chemical calculations of the recyclization and hydrolysis intermediates.

Study of the mechanism of recyclization of furans into thiophenes and selenophenes in conditions of acid catalysis. 4. study of the effect of the solvent and direction of reactions of hydrolysis and recyclization of 2,5-dimethylfuran

The kinetics of hydrolysis of 2,5-dimethylfuran and its recyclization into the corresponding thiophene were investigated in water-alcohol medium W R I and 50% ethyl alcohol in the presence of HCl. It was found that the rates of these reactions are a function of both the initial concentration of the acid component and the concentration of water in the alcohol. The rate of hydrolysis is a function of the dilution of the alcohol to a greater degree than the rate of recyclization.

Mechanism of recyclization of furans to thiophenes and selenophenes under acid catalysis. 1. Kinetic studies of the reaction of 2,5-dialkylfurans with hydrogen sulfide in the presence of hydrochloric acid

The transformation of 2,5-dialkylfurans to thiophenes by reaction with hydrogen sulfide in the presence of hydrochloric acid was studied. The reaction was found to be first order with respect to the furan; the rate of consumption of the furan did not change with increasing length of one of the alkyl substituents. Recyclization in the presence of acid proceeds in two independent directions: through the formation of an intermediate dicarbonyl compound, and by direct conversion of the furan to a thiophene. Kinetic data showed that the reaction occurs mainly by the second route.

Conversion of di(furyl-2)alkyl and di(furyl-2)arylmethanes to the thiophene analogs

On reaction with hydrogen sulfide in strongly acidic media, difurylalkyl-(aryl)methanes are converted to furylthienylalkyl(aryl)- or dithienylalkyl-(aryl)methanes, depending on the conditions.

Reaction of furan compounds with hydrogen sulfide and aspects of its application

The conversion of α-methylfuran, di- and polyalkylfurans, and ethers, esters, ketones, and other derivatives of the furan series to the corresponding substituted thiophenes was realized under acid-catalysis conditions.

New method for synthesis of 2,5-disubstituted thiophenes

The use of hydrogen sulfide at the moment of formation is proposed for the recyclization of furans into thiophenes in acidic media. The advantages of this method are shown.

Study of the mechanism of recyclization of furans to thiophenes and selenophenes under theconditions of acid catalysis. 7. The effect of the nature of the nucleophile. The competition constant

Kinetic investigations into the reactions of, 2,5-dimethylfuran with mixtures of hydrogen sulfide and selenide in various quantitative ratios were undertaken, and the competition constant was determined. This made it possible to correlated numerically the nucleophilicity of hydrogen sulfide an selenide in the reaction.

Investigation of the mechanism of the recyclization of furans to thiophenes and selenophenes under acid-catalysis conditions. 3. Investigation of the recyclization of homologs and functional derivatives of furan. Quantum-chemical calculations of the objects of the recyclization

The kinetics of the conversion of di-, tri-, and tetraalkylfurans to the corresponding thiophenes were investigated. A correlation between the reactivities and structures of the investigated furans was established. Quantum-chemical calculations of the objects of the recyclization were made. The calculated and experimental data on the reactivities of the investigated compounds were compared. The most likely pathway of the protonation of furans in their recyclization was determined on the basis of calculations of the total energies of the protonated forms.