Structure of intermediates in the Hantzsch reaction of phenylchloropyruvic acid derivatives with N,N′-diphenylthiourea

The intermediates in the Hantzsch reaction of the methyl ester and diethylamide of phenylchloropyruvic acid with N,N-diphenylthiourea are derivatives of 2-phenylimino-3,5-diphenyl-4-hydroxythiazoline-4-carboxylic acid. They exist as an equilibrium mixture of two diastereomers in solution.A. E. Arbuzov Institute of Organic and Physical Chemistry of the Kazan Scientific Center, Russian Academy of Sciences, Kazan' 420088; Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 975–980, July, 1999.     

Ab initio study of the reaction path of the reaction HNCO+CN

HNCO is a convenient photolytic source of NCO and NH radicals for laboratory kinetics studies of elementary reaction[1] and plays an important role in the combustion and atmosphere chemistry. It can re- move deleterious compounds rapidly from exhausted ga…     

Electron transfer reaction of 4,4′-bipyridine with triethylamine in acetonitrile: effect of water addition on the reaction dynamics

The photo-induced electron-transfer reaction of 4,4-bipyridine (BPY) with triethylamine (TEA) in acetonitrile is studied by laser flash photolysis. The reaction mechanism and kinetics are found very sensitive to the presence of a small amount of water. At low water concentrations (i.e. <0.003 M), an extremely fast-rising metastable product is detected for the first time. A triplet charge transfer complex (³ECT) is found to be the primary intermediate preceding the electron transfer process. Up to about 0.1 M, water facilitates the electron transfer rate, whereas higher water concentrations retard the rate of electron transfer. The Stern-Volmer plot of the triplet decay rate versus the TEA concentration is consistent with the presence of ³ECT in equilibrium with the free excited triplet state of BPY.     

Mechanism of the reaction of 1,1′-diethylferrocene and decamethylferrocene with peroxides in organic solvents

Kinetic relationships of oxidation of 1,1′-diethylferrocene and decamethylferrocene with peroxides ROOR (R = H, t-C₄H₉) in organic solvents were studied and the composition of oxidation products was established. It is shown that reactivity of (C₅H₄C₂H₅)₂Fe is significantly lower than that of Cp*₂Fe [Cp* = η⁵-C₅(CH₃)₅] which is seen from the ability of the first metal complex to undergo oxidation with a notable rate only in the presence of Brønsted acids, whereas the second substance is oxidized both in the presence and in the absence of these acids. Two possible mechanisms of oxidation of metal complexes in the presence of strong acids are discussed. One of them is based on the ability of ferrocene to fast and equilibrium protonation with the formation of Cp₂Fe⁺—H structure. Another one considers the ability of metal complexes to coordinate peroxides with the formation of weakly bound charge transfer complexes of the composition Cp₂Fe^δ+·ROOR^δ-. The possibility of their formation is confirmed by the oxidation of Cp₂Fe with hydroperoxides in the absence of acids.     

Calorimetric study of the reaction between formic acid and N,N,N′,N′-tetramethylethylenediamine from the aspect of thermal energy storage

The attack by formic acid on the nitrogen electron pairs of N,N,N,N-tetramethylethylenediamine leads to the stoichiometric salt or to many other complexes with different molar fractions. Physical and thermodynamic parameters of two adducts, obtained by calorimetric study, are discussed in terms of their use as potential phase change materials in thermal energy storage because of their large heat of fusion between 288 and 333 K.

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Zusammenfassung Bei der Einwirkung von Ameisensäure auf die Elektronenpaare von N,N,N,N-Tetramethylethylendiamin entsteht ein stöchiometrisches Salz oder mehrere andere Komplexe mit unterschiedlichem Molenbruch. Es werden physikalische und thermodynamische Parameter zweier bei der kalorimetrischen Untersuchung erhaltenen Addukte hinsichtlich ihrer Verwendung als potentielle Phasenwechselsubstanzen bei der thermischen Energiespeicherung diskutiert, da sie im Bereich 288–333 K eine große Schmelz-wärme besitzen.

     

Investigation of regioselectivity in the synthesis of spiro [pyrrolidine-2,3′-oxindoles] by use of the Huisgen reaction

The Huisgen reaction has been used to synthesize five-membered heterocyclic compounds in high yield and with high regio and stereoselectivity. In the synthesis of spiro [pyrrolidine-2,3′-oxindole] derivatives from isatin, α-amino acids, and (E)-β-phenyl nitroolefins, two regioisomers were obtained in each reaction. The regioselectivity of the major product was found to be different from that in reported work, and was investigated at the B3LYP/6-311G* level of theory. On the basis of this new finding, several conditions, for example molar ratio, solvent, and temperature, which affect the regioselectivity of this reaction were investigated; the results obtained are discussed. It was found that the regioselectivity of this reaction was affected by solvent and temperature, irrespective of the ratio of the reactants. Low temperature and high solvent polarity leads to high regioselectivity, and protic solvents result in higher yield and regioselectivity. These results are of benefit for regioselective synthesis of some compounds.     

Synthesis of the diazepanone-nucleoside portion of liposidomycins by aldol reaction of the enolate of diazepanone with a nucleoside 5′-aldehyde

The diazepanone-nucleoside part of liposidomycins has been synthesized by the aldol reaction between the enolate of a stereochemically defined diazepanone and a uridine 5′-aldehyde. The configurations of two new stereocenters in the aldol product have been assigned on the basis of the ¹H NMR coupling constants and NOE of its derivative.     

Theoretical study of mechanism and kinetics for the reaction of hydroxyl radical with 2′-deoxycytidine

The reaction mechanism and kinetics for the abstraction of hydrogen and addition of hydroxyl radical (OH) to 2′-deoxycytidine have been studied using density functional theory at MX06-2X/6-311+G(d,p) level in aqueous solution. The optimized geometries, energies, and thermodynamic properties of all stationary points along the hydrogen abstraction reaction and the addition reaction pathways are calculated. The single-point energy calculations of the main pathways at CCSD(T)/6-31+G(d,p)//MX06-2X/6-311+G(d,p) level are performed. The rate constants and the branching ratios of different channels are evaluated using the canonical variational transition (CVT) state theory with small-curvature tunneling (SCT) correction in aqueous solution to simulate the biological system. The branching ratios of hydrogen abstraction from the C1′ site and the C5′ site and OH radical addition to the C5 site and the C6 site are 57.27% and 12.26% and 23.85% and 5.69%, respectively. The overall calculated rate constant is 4.47?×?10⁹ dm³ mol^?1 s^?1 at 298 K which is in good agreement with experiments. The study could help better understand reactive oxygen species causing DNA oxidative damage.     

2,2′-Dialkoxy, 2,2′-dihydroxy,and 2,2′-diamino derivatives of 1,1′-azobenzimidazole. The first synthesis of heterocyclic tetrazenes by means of a nucleophilic substitution reaction

2,2-Dimethanesulfonyl-1,1-azobenzimidazole is prepared by the oxidation of 1-amino-2-methanesulfonylbenzimidazole with lead tetraacetate. The reaction of this tetrazene with alkali in DMSO, with sodium alkoxides in the corresponding alcohol or ammonia, or with primary or secondary amines leads to the formation of 2,2-dihydroxy, 2,2-dialkoxy, or 2,2-diamino derivatives of 1,1-azobenzimidazole.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 190–193, February, 1992.     

Structure of compounds of chromium with 2,2′-bipyridyl that participate in the Belousov-Zhabotinskii oscillating reaction

It was shown that a binuclear complex of composition [Cr₂(OH)₂(bpy)₄]³⁺ acts as a reaction catalyst in the oscillating chemical system bromate-malonic acid-compound of chromium with 2,2 bipyridyl. The catalytically active compound was investigated by fast-atom-bombardment mass spectrometry, electron and EPR spectroscopies, and cerimetric analysis. The formal redox potential of such a complex E⁰ was obtained by cyclic voltammetry as +0.72 V.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 3, pp. 266–270, May–June, 1992.     

Kinetic study of the reaction between protonatedtrans-dioxotetracyanomolybdate(IV) and 2,2′-bipyridyl

Summary The kinetics of the reaction between the protonated forms of [MoO₂(CN)₄]^4– and 2,2-bipyridyl (bpy) have been studied in the 8.5–11.7 pH range. This study showed that the diprotonated form, [MoO(OH₂)(CN)₄]^2– is the only reactive species. The rate-limiting step is the substitution of the aqua ligand. This is followed by fast closure of the chelate ring, accompanied by the substitution of a cyanide ligand. With excess bpy the relatively slow formation of an adduct occurs. The nature of this adduct is discussed.     

Application of the Thorpe—Ziegler reaction for the synthesis of functionalized thiophenes,thienopyrimidines, and thienotriazines

Approaches to the synthesis of 3-aminothiophene-2,4-dicarboxylic acid derivatives and to their conversions into thieno[3,4-d]pyrimidines, thieno[3,4-d]-1,2,3-triazines, and thieno[3,2-d]pyrimidines are developed.     

Thermodynamical characteristics of the reaction of pyridoxal-5′-phosphate with L-amino acids in aqueous buffer solution

The reaction of pyridoxal-5′-phosphate with L-isomers of alanine, lysine, arginine, aspartic acid, glutamic acid, and glycine in phosphate buffer solution was studied by absorption spectroscopy and the calorimetry of dissolution at physiological acidity of the medium (pH 7.35). The formation constants of Schiff bases during reactions and changes in Gibbs energy, enthalpy, and entropy were determined. It was shown that the formation constant of the Schiff base and its spectral properties depend on the nature of the bound amino acid. The progress of the reaction with a majority of amino acids is governed by the entropy factor due to the predominant role of the dehydration effect of the reaction center of amino acids during chemical reactions. The intramolecular electrostatic interaction of an ionized phosphate group with the positively charged amino group on the end of the chain of amino acid residue stabilizes the Schiff bases formed by lysine and arginine. The extinction coefficient of the base, equilibrium constant, and the exothermic effect of the reaction then increase. The excess negative charge on the end of the chain of amino acid residues of aspartic and glutamic acids destabilizes the molecule of the Schiff base. In this case, the equilibrium constant decreases and the endothermic effect of the reaction increases.     

Kinetics and mechanism of the reaction of benzoyl chloride with 4-(4′-N,N-dimethylaminostyryl)pyridine-N-oxide in toluene

The reaction of benzoyl chloride with 4-(4-N,N-dimethylaminostyryl)pyridine-N-oxide in toluene proceeds according to an addition—elimination mechanism. The rate and equilibrium constants of the individual steps were determined. An inhibiting effect of the substrate was detected.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 31, No. 5, pp. 316–318, September–October, 1995.     

Crosslinking reaction in the cationic polymerization of 1, 3-pentadiene

The cationic polymerization of 1,3-pentadiene (PD) initiated by AlCl_3 in n-hexane was carried out. Effects of arenes, alkyl halides and ethers on the gel formation resulting from crosslinking reaction were investigated. The erosslinking was reduced by various arenes through a chain transfer mechanism. Alkyl halides such as tert-butyl chloride and allyl chloride could complex with AlCl_3 to generate an initiating system giving rise to a gel-free polymerization, while benzyl chloride reduced the formation of gel by chain transfer. Ethers exerted two effects on the polymerization system: giving a complex initiating system with AlCl_3 to produce a relatively high molecular weight polymer, or reducing crosslinking by lowering activity of carbocations.     

Electrochemically initiated fragmentation reaction of 9,9′-dinitro-9,9′,10,10′-tetrahydro-10,10′-bianthryl

A mechanism for the electroreduction of 9,9-dinitro-9,9,10,10tetrahydro-10,10-bianthryl in DMF, which results in the formation of anthracene and 9-nitroanthracene has been proposed on the basis of data from polarography, cyclic voltammetry, and electrolysis at a controlled potential.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1321–1325, June, 1991.     

A feature of reaction of 1,1′-diacetylferrocene with dimethylformamide dimethyl acetal leading to a new strategy of the synthesis of asymmetrical 1,1′-disubstituted ferrocene

The reaction of 1,1′-diacetylferrocene with the dimethylformamide dimethyl acetal proceeds regioselectively to afford [1-acetyl-1′-(1-dimethylamino-3-oxoprop-1-en-3-yl)]ferrocene, based on which new approaches to the synthesis of 1,1′-disubstituted unsymmetrical ferrocene derivatives via the reaction with nucleophilic reagents hydrazine hydrate, hydroxylamine, and amidines were developed.     

Formation of asymmetric N-hydroxyaryl-N′-aryl(hetaryl)diazenes in the reaction of N-aryl(hetaryl)-N′-phosphoryldiazene-N-oxides with bases

Aromatic and heterocyclic N-phenoxyphosphoryldiazene N-oxides react with bases to give asymmetric N-hydroxyaryl-N-aryl- and N-hydroxyaryl-N-hetaryldiazenes.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 609–610, March, 1993.