bluuebunny/crossref_metadata_2025 huggingface dataset:
Substitution effects in isomeric para and meta derivatives of benzonitrile revealed by UV photoelectron spectroscopy
Authors: Juška Tomáš
Published: September 2010

The UV photoelectron spectra of isomeric para and meta derivatives of benzonitrile with substituents NO2, COCH3, Cl, Br, CH2I and NH2 were measured. Their assignment was carried out with the aid of MNDO calculations. The splitting of the highest π orbitals e1gS, e1gA is in all para derivatives greater than in their meta isomers, the greatest difference of splittings 0.25 eV being caused by the amino group. The level ordering e1gS, A exists in all molecules except meta NO2, and COCH3 derivatives where it is believed to be reverse. The π'CN - πCN splitting keeps nearly constant and it is close to that in benzonitrile. The ionization potentials of σ orbitals e1uS, e1uA, b2u and b1u in meta NO2 derivative are, in agreement with our expectation, higher than in benzonitrile. It is not true for para isomer where on the contrary, they are lower and they differ from meta isomer by 0.71-1.8 eV.
Kinetics of reactions of 1,2,4-triazole-3-diazonium ions with phenol and with hydroxyl ion
Authors: Macháček Vladimír , Kořínek Josef , Kreuzigová Daniela , Štěrba Vojeslav
Published: September 2010

5-Methyl- and 5-phenyl-l,2,4-triazole-3-diazonium ions (IIIa, IIIb) react with undissociated phenol in diluted hydrochloric acid. At pH > 1 the reactions with phenolate ions become kinetically significant, their bimolecular rate constants approaching those of the diffusion-controlled reactions. At the same time, the diazonium ions are dissociated into the dipolar ions IIIb and IVb. At pH > 4 (for the phenyl derivative) and pH > 5 (for the methyl derivative), the reaction of the dipolar ions with phenolate ion becomes the main reaction path. The rate constant of the reaction of the dipolar ion IIIb with hydroxyl ion (3 . 103 l mol-1 s-1) is comparable with that of the analogous reaction of benzenediazonium ion, but the reverse reaction of the dipolar ion IIIb is slower by about 5 orders of magnitude, and the pKA value of the diazo hydroxide formed is higher by about 4 units than that of benzenediazo hydroxide. The high stability of the heterocyclic diazo hydroxide and its low acidity are explained by formation of a strong intramolecular hydrogen bond. In sodium hydroxide solutions, the (Z)-diazotate IIId initially formed is transformed into the (E)-isomer (the corresponding half-life being about 10 h) which, in contrast to the (Z)-isorner, does not practically react with aromatic hydroxy compounds in basic medium. The transformation of the (E)-isomer to the diazonium ion is general acid-catalyzed reaction. Transformation of nitrosamine into diazo hydroxide is suggested to be the rate-limiting step of this reaction in solutions of pH < 5.
Liquid-liquid equilibrium. Applicability of the Redlich-Kister, NRTL and LEMF equations to heterogeneous systems
Authors: Novák Josef P. , Matouš Jaroslav , Pick Jiří
Published: September 2010

The limits of applicability of the Redlich-Kister, NRTL and LEMF equations when applied to heterogeneous systems are specified. These limits follow from the requirement of solvability of relations of the equality of activities in coexisting phases on the one hand and of the monotonous dependence of activity coefficients on the other hand.
Activity and selectivity of non-uniform bifunctional catalysts
Authors: Ardiles Darío R. , Scelza Osvaldo A. , Castro Alberto A.
Published: September 2010

The activity and selectivity of non-uniform bifunctional catalysts are treated in this paper. For a bifunctional reacting network similar to pure hydrocarbons reforming, the effect to different radial distribution profiles of both catalytic functions in the catalytic particle on the activity and selectivity were theoretically predicted using an arbitrary set of kinetic parameters.
System of thermodynamic quantities in the McMillan-Mayer solution theory
Authors: Kodýtek Vilém
Published: September 2010

The McMillan-Mayer (MM) free energy per unit volume of solution AMM, is employed as a generating function of the MM system of thermodynamic quantities for solutions in the state of osmotic equilibrium with pure solvent. This system can be defined by replacing the quantities G, T, P, and m in the definition of the Lewis-Randall (LR) system by AMM, T, P0, and c (P0 being the pure solvent pressure). Following this way the LR to MM conversion relations for the first derivatives of the free energy are obtained in a simple form. New relations are derived for its second derivatives.
Convective diffusion to a slowly rotating spherical electrode; The effect of axial diffusion in the bulk liquid for Re 10
Authors: Mitschka Pavel , Wein Ondřej
Published: September 2010

A complete mathematical model has been solved of the steady axially symmetric convective diffusion toward the surface of a spherical electrode of radius R rotating at an angular velocity Ω under the creeping flow conditions Re ≡ ΩR2ρ/η < 10 and Pe ≡ Ω2R4ρ/(12Dη) > 10 by the method of singular perturbations. For Pe > 300 the effect of axial diffusion has been found entirely negligible; for 10 < Pe < 300 it causes an increase of local transfer coefficients by 1-10%. For Pe < 10 the applied asymptotic method of solution, assuming Pe >> 1 is no longer applicable.
Reactions of chromocene with diols and some their derivatives
Authors: Kalousová Jaroslava , Beneš Ludvík , Votinský Jiří , Nádvorník Milan
Published: September 2010

Chromocene reacts with diols having OH groups at 1,3 position or at a greater distance to give chromium(II) diolates. Only the chromium(II) diolates obtained from reactions with 1,2-diols give the chromium(III) diolates with excess of the reagent. Alkylation of one of these hydroxyl groups, however, prevents the oxidation-reduction course. The reaction of chromocene with 2-chloroethanol gives chromium(II) 2-chloroethanolate in the first step, chromium(III) 2-chloroethanolate being the final reaction product.
Preparation and absolute configuration at C(22) of 21,26,27-trinor-5α-cholestan-25→22-olide derivatives
Authors: Pouzar Vladimír , Drašar Pavel , Černý Ivan , Havel Miroslav
Published: September 2010

Epimeric 21,26,27-trinor-5α-cholestan-25→22-olides (X and XVII), 21,26,27-trinor-5α-cholest-23-en-25→22-olides (XV and XXII), and their 23-methyl derivatives XVI and XXIII were prepared by lengthening the side chain in 5α-pregnan-21-al (I). On the basis of CD spectra and chemical correlations with 21,26,27-trinor-5α-cholestane-22,25-diols, the configuration 22S was ascribed to lactones X, XXII and XXIII whereas lactones XV, XVI and XVII were assigned the 22R configuration.
Thermitase from Thermoactinomyces vulgaris; amino acid sequence of the large N-terminal cyanogen bromide peptide
Authors: Meloun Bedřich , Baudyš Miroslav , Pavlík Manfred , Kostka Vladimír , Hausdorf Gert , Höhne Wolfgang Ernst
Published: September 2010

The large cyanogen bromide fragment (CB1) represents the N-terminal part of the molecule of thermitase and contains 226 amino acid residues. Its molecular weight calculated from sequential data is 22 932 (the C-terminal residue is regarded as a methionine residue in the calculations). The amino acid sequence of fragment CB1 was determined by analysis of peptides obtained by tryptic hydrolysis of the fragment; these data were complemented by sequence analysis of the chymotryptic digest of fragment Mf (residues 75 through 226) and of chymotryptic fragment ET3 (residues 103 through 226) isolated from the limited tryptic digest of fragment CB1. The peptides were purified by high performance liquid chromatography and by thin layer techniques. The sequence analysis of the large peptides was effected in the sequenator, small peptides were sequenced manually by the DABITC/PITC double coupling technique. The results obtained in this study together with those of previous work5 permitted the complete amino acid sequence of fragment CB1 to be determined.
Synthesis of 19-nordeoxycorticosterone 3-(O-carboxymethyl)-oxime
Authors: Fajkoš Jan , Joska Jiří
Published: September 2010

Starting from the epoxide I a convenient synthesis of 19-nordeoxycorticosterone and its 3-(O-carboxymethyl)-oxime is described.
A feedback reactor for discontinuous feed of a reaction component with spectrophotometric indication
Authors: Skopal František
Published: September 2010

The absorbance-time dependence has been derived for a repeated arbitrary feed of one reaction component into solution of the other component controlled by the feedback. On the basis of the expressions derived, methods have been suggested for determination of the rate constant of irreversible reaction of the IInd order, and they have been experimentaly tested on two reactions.
Establishment of equilibrium between radioiodine
Authors: Beneš Jaroslav
Published: September 2010

The radioiodine retention effectiveness and its retention rates in different soils were determined. The effects of various factors on the retention dynamics preceding the equilibrium establishment, particularly the role or organic soil substances, jave been followed.
Partially acetylated sucrose. Preparation of 3-O-acetylsucrose and 3,6'-di-O-acetylsucrose and the analysis of mixtures of O-acetyl derivatives of sucrose of various degrees of acetylation by thin-layer chromatography with flame-ionization detection
Authors: Čapek Karel , Vydra Tomáš , Čapková Jindra , Ranný Mojmír , Bláhová Markéta , Sedmera Petr
Published: September 2010

Partial deacetylation of 3,3',4',6'-tetra-O-acetyl-l',2 : 4,6-di-O-isopropylidene sucrose (V) with aluminum oxide impregnated with potassium carbonate gave a mixture of 3,6'-di-O-acetyl-l',2 : 4,6-di-O-isopropylidenesucrose (VI) and 3-O-acetyl-l',2 : 4,6-di-O-isopropylidenesucrose (VII). 3,6'-di-O-acetylsucrose (IX) and 3-O-acetylsucrose (X) were prepared on deacetalation of compounds VI and VII, respectively. The structure of compounds IX and X was proved by 13C NMR and mass spectra of their deuterioacetyl derivatives XI and XII. Using procedures described in literature 3,3',4',6'-tetra-O-acetylsucrose (IV), 2,3,3',4',6-penta-O-acetylsucrose (III), l',2,3,3',4',6'-hexa-O-acetylsucrose (II) and 1',2,3,3',4,4',6-hepta-O-acetylsucrose (I) were prepared. These acetyl derivatives, sucrose and their octa-O-acetyl derivative were analysed by thin-layer chromatography with flame-ionization detection either separately or in mixtures. A chromatogram of the mixture was identical with a chromatogram of a mixture of O-acetyl derivatives of sucrose formed on deacetylation of octa-O-acetylsucrose with aluminum oxide impregnated with potassium carbonate; from this it follows that under the conditions of analysis O-acetyl derivatives of sucrose are separated on the basis of the degree of acetylation.
Cataleptic and noncataleptic neuroleptic agents: Synthesis and pharmacology of 4-(2-chloro and 8-chloro substituted 10,11-dihydrodibenzo[b,f]thiepin-10-yl)piperazine-1-ylalkyl ethers and sulfides
Authors: Valenta Vladimír , Prošek Zdeněk , Metyšová Jiřina , Valchář Martin , Dlabač Antonín , Protiva Miroslav
Published: September 2010

The title compounds Iab-Viab were prepared by substitution reactions of 2,11-dichloro- and 2,10-dichloro-10,11-dihydrodibenzo[b,f]thiepin with 1-(2-methoxyethyl)piperazine, 1-(3-methoxypropyl)piperazine, 1-(2-ethoxyethyl)piperazine, 1-(2-phenoxyethyl)piperazine, 1-(2-methylthioethyl)piperazine and 1-(2-phenylthioethyl)piperazine; they were transformed to hydrochlorides, maleates or methanesulfonates. Compounds of series a (8-chloro derivatives) are neuroleptics, with relatively strong cataleptic, antiapomorphine and central depressant activities (Ia, IIa, IIIa,Va) unless the volume and lipophilicity of the N-substituent exceeds certain limits (IVa and VIa are almost nontoxic and little active). Compounds of series b (2-chloro derivatives) are noncataleptic and devoid of the antiapomorphine potency; only two of them (IIb, Vb), however, showed a more pronounced effect in the test of influencing the turnover and metabolism of dopamine in the rat brain striatum.
Potential antidiarrheal agents: 1-(11-Cyano-6,11-dihydrodibenzo[b,e]thiepin-11-yl-alkyl)- and 1-(10-cyano-10,11-dihydrodibenzo[b,f]thiepin-10-yl-alkyl)-4-substituted piperidines
Authors: Šindelář Karel , Metyš Jan , Protiva Miroslav
Published: September 2010

Substitution reactions of 11-(2-bromoethyl)- and 11-(3-bromopropyl)-6,11-dihydrodibenzo[b,e]thiepin-11-carbonitrile and further of 10-(2-bromoethyl)- and 10-(3-bromopropyl)-10,11-dihydrodibenzo[b,f]thiepin-10-carbonitrile with ethyl 4-phenylpiperidine-4-carboxylate, 4-phenylpiperidin-4-ol, 4-(2-tolyl)piperidin-4-ol, 4-(4-fluorophenyl)piperidin-4-ol, 4-(2-oxobenzimidazolin-1-yl)-piperidine and 1-phenyl-1,3,8-triazaspiro[4,5]decan-4-one afforded the tricyclic piperidinoalkyl nitriles IV-XIII which are cyclic analogues of the antidiarrheal agents diphenoxylate (I) and loperamide (III). Out of the compounds prepared only IV and XI showed a significant inhibitory effect towards diarrhea elicited by intravenously administered serotonin in mice.
Chromatographic parameters, pKa, and surface activity of a series of hydrochlorides of perhydroazepinylethyl esters of alkoxyphenylcarbamic acids and their relation to anaesthetic activity
Authors: Blešová Marie , Čižmárik Jozef , Bachratá Mária , Bezáková Želmíra , Borovanský Alois
Published: September 2010

Hydrochlorides of perhydroazepinylethyl esters of alkoxyphenylcarbamic acids were separated by adsorption and partition TLC. The surface tensions, γ, of aqueous solutions of the compounds were measured and the values of pKa were determined. The relation between structure and physico-chemical properties has been confirmed by the dependences of RM and γ on the number of carbon atoms in the alkoxyl chain. Employing the method of regression analysis, the physico-chemical parameters of lipophilicity and the surface activity were correlated, and their effect on biological activity (relative local anaesthetic efficacy) has been assessed.
Determination of trace quantities of heavy metals in food by anodic voltammetry. Determination of cadmium, lead and copper in beer
Authors: Aliakbar Alireza , Popl Milan
Published: September 2010

The optimum conditions for the determination of Cd, Pb, and Cu in beer were sought by the factorial design and the simplex method approaches. Two methods of sample treatment were used, viz. mineralization and mineralization combined with ashing. The values obtained, 0.32 μg l-1 for Cd, 15.6 μg l-1 for Pb, and 64.7 μg l-1 for Cu, were compared with those obtained by atomic absorption spectrophotometry.
Glass transition temperatures and glass-forming region of the system lithium chloride-dimethyl sulphoxide-water
Authors: Malá Jarmila , Sláma Ivo
Published: September 2010

Glass transition temperatures (Tg) of the system LiCl-DMSO-H2O have been measured. A small addition of DMSO to the binary aqueous system removes its unusual variation of Tg with salt concentration. The concentration dependence of Tg of the ternary system at a constant composition of the mixed solvent can be described by a linear equation. The variation in Tg with the mixed solvent composition at constant LiCl concentration follows a complicated pattern which cannot be described by commonly used relations. The boundaries of glass-forming region are discussed in terms of the effect of a change in solution composition on the induction period of equilibrium solid phase nucleation.
Synthesis of 2,3,5-tri-O-benzoyl-D-pentofuranosyl cyanides and their CD spectra
Authors: Farkaš Jiří , Frič Ivo
Published: September 2010

The title compounds I-IV with the respective ribo-, arabino-, xylo- and lyxo-configuration were prepared by reaction of 1-O-acetyl-2,3,5-tri-O-benzoyl-D-pentofuranoses with trimethylsilyl cyanide in 1,2-dichloroethane, catalyzed with tin tetrachloride. The CD spectra of compounds I-IV and of the conformationally rigid 1,5-anhydro-2,3-di-O-benzoyl-β-D-pentofuranoses VI-VIII were measured and interpreted by the exciton chirality method.
Preparation and properties of three analogues of [5-leucine]enkephalin, substrates for enzyme conversion studies
Authors: Vičar Jaroslav , Servítová Linda , Flegel Martin , Hauzer Karel , Barth Tomislav
Published: September 2010

Analogues of [5-Leu]enkephalin, prolonged by methionine on the N-terminus or, by lysine or methionine on the C-terminus were prepared by fragment condensation, purified by ion exchange chromatography or high-pressure liquid chromatography. The substances were characterised by their opioid activity in a test on guinea-pig ileum in comparison with the activity of [5-Leu]enkephalin.
The shell progressive model of adsorption in a single particle
Authors: Brunovská Alena , Ilavský Ján , Kukurucová Helena
Published: September 2010

A model is formulated of nonisothermal adsorption in a single sorbent particle on the assumption that the adsorption takes place in terms of a so-called "shell-progressive" mechanism, external heat transfer only being considered. The model results are compared with experimental ones and with those of diffusion model formulated by us previously.
Preparation of 7-substituted 7-carba-nido-undecaboranes(12)
Authors: Jelínek Tomáš , Plešek Jaromír , Heřmánek Stanislav , Štíbr Bohumil
Published: September 2010

Reactivity of the ammine group in the 7-H3N-7-CB10H12 carbaborane was examined and a series of new 7-L-7-CB10H12 derivatives [L = (CH3)2C=NH, (CH2)5C=NH, C6H5CH=(C6H5CH2)N, HOOCCH2NH2, CH3CONH2, (CH2)6N4, and (CH3)2S] was characterized. Constitution of all compounds isolated was established on the basis of their mass, IR, 1H, and 11B NMR spectra.
Reaction mechanism graphs
Authors: Koča Jaroslav , Kratochvíl Milan , Kvasnička Vladimír
Published: September 2010

The concept of reaction mechanism graphs has been introduced. These graphs describe the decomposition of an arbitrary organic reaction into its most elementary mechanistic steps representing heterolytic or homolytic dissociation and association processes, etc.. A clustering method of reaction mechanism graphs with the same number of elementary steps is specified. The suggested formalism was successfully used in our preliminary computer analysis of reaction mechanism.
A study of mixed crystals in the InPO4-InVO4 system and their infrared spectra
Authors: Hájek Bohumil , Muck Alexander , Šantavá Eva
Published: September 2010

The crystal symmetry was studied for mixed crystals in the InPO4-InVO4 orthorhombic system. The infrared spectra were examined using the site group and factor group approach, and the Td → Cs → C2v correlation was found more appropriate than the Td → C2v → D2h correlation.
Evidence in favour of Exner isokinetic method to determine activation parameters
Authors: Segura Pascual
Published: September 2010

Exner method to ascertain the isokinetic relationship (IKR) and obtain isokinetic activation parameters in a reaction series, although well known, is relatively little applied; A great many chemists do not appear to be convinced of the superiority of isokinetic activation parameters over conventional ones, and the IKR itself is still a controversial matter. From our kinetic results on the decarboxylation of a series of 4-substituted-2,6-dinitrobenzoate ions in aqueous solution, activation parameters were calculated, both by Exner method and by a conventional one. The obtained isokinetic activation enthalpies correlate much better (r = 0.998, 5 points) than the conventional ones (r = 0.97, 5 points), with the energies (calculated at the STO-3G ab initio level) for the formation of substituted aryl anions, the latter being a process expected to be energetically related to the decarboxylation reaction. This is the first example of non-statistical evidence in favour of Exner method to determine activation parameters, a method that we strongly advocate.
Relation between reduction and sulphidation process during the activation of a Co-Mo/Al2O3 hydrodesulphurization catalyst
Authors: Zahradníková Hana , Kárník Václav , Beránek Ludvík
Published: September 2010

The course of activation at 673 and 773 K of an industrial hydrodesulphurization catalyst CHEROX 36-01 was followed gravimetrically. Reduction with hydrogen, reductive sulphidation with a H2S/H2 mixture, non-reductive sulphidation with a H2S/He mixture and sulphidation of prereduced catalysts were compared. All sulphidation procedures are much faster than the reduction alone, the latter has, however, a higher apparent activation energy. In the reductive sulphidation with H2S/H2, reduction and sulphidation take place simultaneously, sulphidation being a predominant process at the beginning of the activation, especially at 673 K. It has been shown how the two processes can be decoupled or superposed. The catalytic activity in ethylene hydrogenation develops much more slowly when the catalyst is activated only by reduction than when it is activated by reductive sulphidation, in accordance with the relative velocities of these two activation procedures. The hydrogenation activity of catalysts reduced to a different extent correlates with their oxygen chemisorption capacity at 195 K.
Kinetics of redox reaction of lactic acid with bromate ions, and Belousov-Zhabotinskii oscillator with lactic acid
Authors: Adamčíková Ľubica , Halinárová Irena
Published: September 2010

The kinetics and mechanism of the redox reaction of bromate ions with lactic acid was studied in the medium of sulphuric acid. The reaction is of first order with respect to both reactants. The dependence of the measured rate constant on the concentration of hydrogen ions was analysed and the activation parameters of the reaction were determined. Based on the experimental kinetic data, the probable mechanism is discussed. Oscillations of bromine and catalyst are observed in the system KBrO3-CH3CHOHCOOH-H2SO4-MnSO4 if the solution is bubbled with nitrogen. The dependence of the induction period and oscillation period on the concentration of the reactants was evaluated.
Stability of radical anions derived from substituted 5-nitrofurans investigated by ESR spectroscopy
Authors: Klíma Jiří , Baumane Larisa , Stradinš Janis , Volke Jiří , Gavars Romualds
Published: September 2010

It has been found that the decay in dimethylformamide and dimethylformamide-water mixtures of radical anions in five of the investigated 5-nitrofurans is governed by a second-order reaction. Only the decay of the radical anion generated from 5-nitro-2-furfural III may be described by an equation including parallel first- and second-order reactions; this behaviour is evidently caused by the relatively high stability of the corresponding dianion, this being an intermediate in the reaction path. The presence of a larger conjugated system in the substituent in position 2 results in a decrease of the unpaired electron density in the nitro group and, consequently, an increase in the stability of the corresponding radical anions.
Interphase distribution of 2-furylethylenes
Authors: Baláž Štefan , Kuchár Anton , Šturdík Ernest , Rosenberg Michal , Štibrányi Ladislav , Ilavský Dušan
Published: September 2010

The distribution kinetics of 35 2-furylethylene derivatives in two-phase system 1-octanol-water was investigated. The transport rate parameters in direction water-1-octanol (l1) and backwards (l2) are partition coefficient P = l1/l2 dependent according to equations l1 = logP - log(βP + 1) + const., l2 = -log(βP + 1) + const., const. = -5.600, β = 0.261. Importance of this finding for assesment of distribution of compounds under investigation in biosystems and also the suitability of the presented method for determination of partition coefficients are discussed.
Analysis of mixtures of 4-nitrotoluene-2-sulphonic acid and 4,4'-dinitrostilbene-2,2'-disulphonic acid by tast polarography, differential pulse polarography and thin layer chromatography
Authors: Barek Jiří , Daňhel Ivo
Published: September 2010

Conditions are sought for the determination of 4-nitrotoluene-2-sulphonic acid (I) and 4,4'-dinitrostilbene-2,2'-disulphonic acid (II) by TAST polarography within the concentration range of 10-2 - 10-6 mol l-1 and by differential pulse polarography (DPP) within the concentration range of 10-3 - 10-8 mol l-1. DPP is applied to the determination of these substances after the thin layer chromatographic separation of their mixtures. Methods are also worked out for their analysis without prior separation, based either on the combined DPP determination of I and the TAST polarographic determination of the sum of I and II in sulphuric acid solutions, or on the DPP determination of the C=C bond in II and the TAST polarographic determination of the sum of the two substances in tetramethylammonium bromide solutions.
Reaction of 3-chlorononafluoro-1,5-hexadiene with sodium cyanide
Authors: Linhart Igor , Dědek Václav
Published: September 2010

3-Chlorononafluoro-1,5-hexadiene (I) is isomerized into 6-chlorononafluoro-1,4-hexadiene (II) by action of basic catalysts as sodium cyanide in anhydrous dimethylformamide, lithium chloride in dimethylformamide, and triethylamine in dioxane or dimethylformamide. Sodium cyanide also catalyzes addition of methanol to the chlorodiene I. The reaction course is more complex than in the alkoxide-catalyzed addition of primary alkohols to I. 6-Methoxynonafluoro-1,4-hexadiene (III), methyl perfluoro-3,6-heptadienoate (VII), and 3,6-dimethoxy-1,1,2,3,4,4,5,6,6-nonafluoro-1-hexene (VIII) have been isolated besides the known products 1,6-dimethoxy-1,1,2,3,4,5,6,6-octafluoro-2,4-hexadiene (IV) and 1,6-dimethoxy-1,1,2,3,4,4,5,6,6-nonafluoro-2-hexene (V). The hexene VIII reacts with sodium methoxide in methanol to give the diether V and with lithium chloride in dimethylformamide it gives 1-chloro-6-methoxy-1,1,2,3,4,4,5,6,6-nonafluoro-2-hexene (IX). Stereospecificity and mechanism of the reaction are discussed.
A diffusion kinetic model for epitaxial growth of gallium arsenide layers from the gas phase
Authors: Erdös Emerich , Voňka Petr , Stejskal Josef , Klíma Přemysl
Published: September 2010

The growth model of gallium arsenide epitaxial layers has been further extended in two ways. First of all, the location of the substrate in experiments in the reactor has been taken into account, and a general relationship has been derived for dependence of the mean effective thickness of the boundary layer on the distance of the substrate from the leading edge and on the substrate size. Secondly, the effect of rate of the chemical heterogeneous reaction has been investigated in addition to the diffusion rate on the resulting growth velocity of epitaxial gallium arsenide layers. A quantitative model comprising the rates of the both partial processes has been formulated. The theoretical relationships obtained in this way have been confronted with experimental results.
Reversible adsorption of hydrogen in adsorption-saturated acetylene layers on palladium surfaces
Authors: Kopešťanský Josef
Published: September 2010

Palladium films with preadsorbed acetylene layers were interacted with molecular hydrogen. Reversibly adsorbed hydrogen in the molecular form was found on the surface. The molecule probably occurs in a more reactive state than the molecule of hydrogen gas; this state precedes the dissociative adsorption of hydrogen and it may be involved in catalytic reactions of hydrocarbons on metals.
Determination of carcinogenic azobenzene derivatives by constant-potential coulometry
Authors: Barek Jiří , Berka Antonín , Zima Jiří
Published: September 2010

The reduction of azobenzene, N,N-dimethyl-4-aminoazobenzene, N,N-dimethyl-4-amino-4'-hydroxyazobenzene, and N,N-dimethyl-4-amino-4'-aminoazobenzene was studied by constant-potential coulometry, and conditions were found for the determination of milligramme quantities of these substances in their aqueous -methanolic solutions.
Mechanism of the dehydration of 1-butanol over zeolites
Authors: Olaofe O. , Yue P. L.
Published: September 2010

The product distribution from the dehydration of 1-butanol over zeolites (13X, 4A, ZNa) has been investigated to gain insight of the reaction mechanism. The formation of 2-alkenes (cis-2-butene and trans-2-butene) in the absence of isomerization reactions during the catalytic dehydration of 1-butanol over zeolites is unambiguous evidence in favour of a positively charged intermediate, indicating that reaction proceeds via a E1 type of mechanism. Experimental data also showed the preferential formation of cis-2-butene over that of trans-2-butene. The predominance of E1 type mechanism increases with increasing temperature.
Chlorination of 2,4,6-trichlorophenol in acidic aqueous medium
Authors: Švec Petr
Published: September 2010

The course of chlorination of 2,4,6-trichlorophenol (I) in water and approximately 20% sulfuric and hydrochloric acids has been investigated. In all these media the reaction gives primarily 2,4,6,6-tetrachloro-2,4-cyclohexadienone (II) which is subsequently chlorinated under formation of polychlorinated alicyclic ketones or isomerized to give the more stable 2,4,6,6-tetrachloro-2,5-cyclohexadienone (III), the precursor of further arising chlorinated 1,4-benzoquinones. The ratio of the arising polychlorinated alicyclic ketones to chlorinated 1,4-benzoquinones is significantly influenced by concentration of hydrogen chloride in the reaction medium. On the basis of model experiments, the reaction mechanism of exhaustive chlorination of 2,4,6-trichlorophenol has been suggested.
Structure of laserolide and isolaserolide: Revision of constitution and determination of relative and absolute configuration
Authors: Holub Miroslav , Buděšínský Miloš , Smítalová Zdenka , Šaman David , Rychłewska Urszula
Published: September 2010

The position of the ester groups in sesquiterpenic lactones laserolide (I) and isolaserolide (II) has been revised and its relative and absolute configuration determined by chemical and physical methods (NMR and CD spectroscopy). The structure I was confirmed by X-ray diffraction analysis. Laserolide (I) is the first germacranolide found in the Umbelliferae family, isolaserolide (II) is the first representative of new stereostructural group of elemanolides - 5βH,6αH,7αH,10αCH3-elema-1,3-dien-6,12-olides.
Prediction of viscosity of organic liquids
Authors: Škubla Pavol
Published: September 2010

A method was proposed for predicting the viscosity of organic liquids which is based on known saturated vapour pressures and the chemical structure. For 199 compounds (4 144 measurements), the method gives the mean relative deviation of 3.35% and the maximum deviation of 59.0%. A lower mean value of the relative deviation than 2% was obtained for 44.3% compounds, 76% compounds possess a lower deviation than 5%.
Effect of mercury chlorides on the activity of complex titanium-based catalysts for the cyclotrimerization of butadiene
Authors: Poláček Jindřich , Mach Karel , Petrusová Lidmila
Published: September 2010

Mercury chlorides decompose arenetitanium(II) complexes by redox reactions, e.g. Ti2+ + Hg+ → Ti3+ + Hg0, and thus inhibit their catalytic activity in the cyclotrimerization of butadiene. The effect of mercury chlorides added to the TiCl4-Et3Al catalytic system depends on their ratio to organoaluminium compound. The cyclotrimerization activity is preserved when a sufficient excess of the latter is present, ensuring the reverse reduction of Ti(III) to Ti(II). A high cyclotrimerization activity and selectivity of the catalysts are achieved if Ti(II) is converted to trinuclear Al-Ti-Al complex under the effect of ethylaluminium dichloride.
Synthesis and biologic properties of an enkephalin analogue, a model substrate for enzymic conversion
Authors: Vičar Jaroslav , Flegel Martin , Hauzerová Linda , Dash Tzezengijn , Hauzer Karel , Barth Tomislav
Published: September 2010

An octapeptide analogue of Leu5-enkephalin, prolonged in the carboxyterminal part by the tripeptide Lys-Lys-Leu was prepared. Its action on guinea-pig ileum and splitting by trypsin and tissue cathepsin B was investigated.
Bonding and stability in the ordered alloys FeV and CoTi. Comparison with FeTi
Authors: Pick Štěpán , Tomášek Mojmír , Šob Mojmír
Published: September 2010

Partial wave analysis together with the qualitative examination of hybridization has been performed for two ordered intermetallic alloys with CsCl structure, FeV, and CoTi. The results resemble those obtained previously for FeTi, although important deviations are present as well. The stabilization of the ordered phase is again due to ionic effects. Qualitative arguments are suggested to explain the small stability of the CsCl phase of FeV and some differences in the FeTi and CoTi phase diagrams.
Photolytic reaction of iodide with di-μ-hydroxo-bis(diphenanthrolinoferric) chloride
Authors: Novák Josef , Vyhlídka Pavel , Flašarová Marie
Published: September 2010

The reaction of di-μ-hydroxo-bis(diphenanthrolinoferric) chloride with iodide in aqueous solutions at pH 3.0 to 6.5 under the action of light radiation at wavelenghts shorter than 590 nm was studied. A procedure is suggested for the quantitative determination of iodide in concentrations of 0.7-9.4 μmol l-1, based on the evaluation of the slope of the time dependence of absorbance at 530 nm.
Infrared spectra of the natural zeolite heulandite
Authors: Pechar František
Published: September 2010

The mid-infrared (4 000-200 cm-1) absorption spectra, far infrared (400-40 cm-1) absorption spectra, infrared (1 400-200 cm-1) reflection spectra, and Raman spectra (3 600-50 cm-1) were measured at room temperature for polycrystalline heulandite, a natural zeolite from Poonah, India.
Volume properties of dilute aqueous solutions of poly(oxyethylene) and its low molecular models
Authors: Sikora Antonín
Published: September 2010

The densities were measured of pure liquid mono-, di-, tri-, and poly(oxyethylene) up to the molar mass 20 000, of 3-oxa-1-butanol and 3,6-dioxa-1-heptanol, 3-oxa-1-pentanol and 3,6-dioxa-1-octanol, 3,6-dioxa-1-decanol, 2,5-dioxahexane, 2,5,8,11-tetraoxadodecane and 2,5,8,11,14-pentaoxapentadecane, 3,6-dioxaoctane and 3,6,9-trioxaundecane and their aqueous solutions at the mass concentrations smaller than 0.02 in the temperature range 15-50 °C. The experimental data thus obtained were used to calculate values of the apparent specific volume at infinite dilution, specific expansion at infinite dilution, excess limiting partial specific volume and excess limiting molar expansibility of the dissolved compound. The suitability of these values as criteria of hydrophobicity of the respective compounds was verified. The volume contributions of homologous and end groups were calculated.
Potential metabolites of the neuroleptic agents belonging to the 8-methylthio-10-piperazino-10,11-dihydrodibenzo[b,f]thiepin series; Synthesis of 2-hydroxy and 3-hydroxy derivatives
Authors: Jílek Jiří , Holubek Jiří , Svátek Emil , Metyšová Jiřina , Pomykáček Josef , Šedivý Zdeněk , Protiva Miroslav
Published: September 2010

The acid VI, prepared by reaction of potassium salts of (2-iodo-5-methoxyphenyl)acetic acid and 4-(methylthio)thiophenol in the presence of copper, was transformed via intermediates VII-IX to 2-methoxy-8-methylthio-10-piperazino-10,11-dihydrodibenzo[b,f]thiepins X and XI. Their demethylation with boron tribromide afforded 2-hydroxy derivatives of the neuroleptic agents methiothepin and oxyprothepin I and II. 11-Chloro-7-methoxy-2-methylthio-10,11-dihydrodibenzo[b,f]thiepin was subjected to substitution reactions with 1-methylpiperazine and 1-(ethoxycarbonyl)piperazine and gave piperazine derivatives XIII and XIV, out of which the latter gave the secondary amine XV by alkaline hydrolysis. The ethers XIII and XV were also cleaved with boron tribromide and gave 3-hydroxy derivatives of methiothepin (III) and its demethyl derivative IV. The phenols I, II, and IV are potential metabolites of the mentioned neuroleptic agents; compound III, which already was identified as a metabolite, disclosed properties of a strong and cataleptic neuroleptic agent with prolonged duration of the effects. The methoxy compounds X, XI, and XIII are practically devoid of the neuroleptic activity.
Modelling of fixed bed catalytic reactors catalyst poisoning
Authors: Markoš Jozef , Brunovská Alena , Ilavský Ján
Published: September 2010

The paper deals with modelling of catalytic reactors in which an irreversible catalyst deactivation takes place. The dimensionless model equations are derived for heterogeneous models of well-mixed regions in series, an algorithm for their solution is proposed. The obtained results are compared with experimental ones in the case of hydrogenation of benzene on a nickel catalyst with thiophene as a poison.
Kinetics and mechanism of base-catalysed aldolization of 1,3-dimethoxy-2-propanone
Authors: Fedoroňko Michal , Petrušová Mária , Kováčik Vladimír
Published: September 2010

1,3-Dimethoxy-2-propanone (HA) in an aqueous alkaline solution undergoes specifically base-catalysed aldolization with the formation of a dimer, 4-hydroxy-1,3,5-trimethoxy-4-methoxymethyl-2-pentanone (H2A2). The reaction is reversible and involves the formation or decomposition of an intermediate anion, HA2-, as the rate-determining step. The formation of a carbanion ion, A-, of the starting compound and of the HA2- anion are rapid, preceding, and generally base-catalysed reaction steps. The activation and thermodynamic parameters of the reversible reaction were determined from the dependences of the rate and equilibrium constants on the temperature.
Benzylidenemalonaldehydes: A redox reaction during the attempted cycloaddition on nitrosobenzene
Authors: Dvořák Dalimil , Buděšínský Miloš , Šaman David , Arnold Zdeněk
Published: September 2010

Reaction of p-chlorobenzylidenemalonaldehyde with nitrosobenzene represents a reduction-oxidation process leading to 2-formyl-3-anilino-3-(4-chlorophenyl)acrylic acid (III). The structure of the product, including two intramolecular hydrogen bonds, has been proved by analysis of the 1H and 13C NMR spectra of the acid III, its deuterated form and the methyl ester obtained by reaction with diazomethane.
Benzylidenemalonaldehydes: Synthesis of 4-aryl-2-dimethylamino-4H-1,3-oxazine-5-carboxaldehyde
Authors: Arnold Zdeněk , Dvořák Dalimil
Published: September 2010

Reaction of substituted benzylidenemalonaldehydes Ia-Ic and thienylmethylenemalonaldehyde (Id) with dimethylcyanamide in boiling benzene afforded the corresponding 4-aryl-2-dimethylamino-4H-1,3-oxazine-5-carboxaldehydes III. Electronic requirements for this cyclization reaction are discussed in relation with general rules and further applicability.
Hydroboration of 1,4-diallylpiperazine
Authors: Kafka Stanislav , Ferles Miloslav
Published: September 2010

Hydroboration of 1,4-diallylpiperazine (I) with triethylamine-borane afforded 5,8-diaza-1,9-diboradispiro[4,2,4,2]tetradecane (II). 1,4-Diallylpiperazine dihydrochloride reacted with sodium borohydride to give 1,4-diallylpiperazine-diborane (V). Ethanolysis of II furnished 1,4-bis(3-diethoxyborylpropyl)piperazine (IV). The products of hydroboration of I were subjected to hydrolysis with hydrochloric acid and subsequent oxidation with alkaline hydrogen peroxide and the obtained mixtures were analysed by gas-liquid chromatography and mass spectrometry.
4-(3-Alkylamino-2-hydroxypropoxy)-3-(alkoxymethyl)acetophenones
Authors: Čižmáriková Ružena , Borovanský Alois , Kozlovský Ján , Béderová Eva , Dingová Anna
Published: September 2010

A series of new beta-adrenolytics derived from p-hydroxyacetophenone was synthesized by four methods. The most advantageous was found to be the five-step synthesis via reaction of the intermediate oxirane with amines. The selected compounds reveal a beta-adrenolytic and antiarrhythmic activities.
Photochemical synthesis of C(5) alkyl and heteroaryl substituted pyrimidine nucleotides
Authors: Hassan Mohamed E.
Published: September 2010

A simple and direct method for the synthesis of C-5 modified nucleosides is described. Photoirradiation of 2'-deoxyuridine 5'-phosphate (I), in the presence of haloheteroarenes afforded the C-5 heteroaryl substituted nucleotides. 5-(2-Hydroxyethyl)nucleotide also obtained from photocoupling of I with 2-iodoethanol. Photoirradiation of 5-iodo-2-deoxyuridine 5'-phosphate (II), in the presence of methyl acrylate or acrylonitrile, gave 5-(2-methoxycarbonylethenyl) and 5-(2-cyanoethenyl) nucleotide, respectively.
1H NMR study of cation solvation in the mixed solvent dimethylformamide-water
Authors: Kyselka Petr , Sláma Ivo
Published: September 2010

Solvation effects of Li+, Na+, and Mg2+ on the mixed solvent dimethylformamide-water were investigated by the 1H NMR method. The dependence of the chemical shift of solvent protons on the mixed solvent composition was established for various concentrations of perchlorates. Isosolvation points were determined, and the dependences of charge transfer from solvent to cation on the chemical shift of solvent, as obtained by a quantum chemical calculation, were compared for the systems DMF-Mn+ and DMF-Mn+-H2O.
Ion solvation. Application of combined discrete and continuum models
Authors: Kyselka Petr , Sláma Ivo
Published: September 2010

Thermodynamic functions for the solvation systems ion-solvent (ion = Li+, Be2+, Na+, Mg2+, and Al3+; solvent = H2O, CH3CN, DMSO, and DMF) are calculated on the basis of combined continuum and discrete models. For the mixed systems water-ion-solvent, the mole fraction of solvent is included in the calculation.
Oxidation of Mn(II) ions with bromate
Authors: Adamčíková Ľubica , Ševčík Peter
Published: September 2010

Oxidation of Mn(II) with bromate ions was studied in the medium of aqueous sulphuric acid. The introduction period as well as the maximum rate of formation of Mn(III) ions depend on the concentration of reactants, Br2, Br-, H3O+, and Mn(III) ions. The results are compared with kinetic data on oxidation of Ce(III) with bromate ions.
Irreversible (rational) thermodynamics of fluid-solid mixtures
Authors: Samohýl Ivan , Nguyen X. Quang , Šípek Milan
Published: September 2010

Reversible and irreversible (transport) phenomena in fluid-solid mixtures were analysed by the method of rational thermodynamics (nonlinear continuum mechanics). After formulating the balances and the second law of thermodynamics, constitutive equations for the binary mixture were proposed involving diffusion, heat conduction, and long-term memory characterized by an internal parameter. Viscosity and chemical reactions were disregarded. The final form of the constitutive equations is based on the constitutive principles of determinism, local action, memory, equipresence, objectivity, and on the entropic principle of Coleman and Noll. The cases of an isotropic solid and a mixture of fluids are also discussed.
Contribution to the theory of nonfickian diffusion of gas in a polymer
Authors: Samohýl Ivan , Nguyen X. Quang , Šípek Milan
Published: September 2010

Based on the previous work on rational thermodynamics of a fluid-solid mixture in linear approximation, an expression for the diffusion flux was derived. This (with tensor phenomenological coefficients) depends linearly on the temperature gradient and on the isothermal gradient of chemical potential, hence not only on the gas concentration gradient but also on the second deformation gradient of the polymer and on the gradient of the internal parameter (characterizing long-term memory effects in the polymer). Nonequilibrium values of the internal parameter may cause a diffusion flux also directly. However, this is not the case in an isotropic solid or fluid polymer, where the tensor phenomenological coefficients and thus also the diffusion coefficient are reduced to scalars. The results are discussed in relation to the classical diffusion in fluids.
Chromatographic behaviour of aromatic hydrocarbons and heterocyclic compounds on silica gel with a chemically bonded amino phase
Authors: Šmídl Petr , Pecka Karel
Published: September 2010

The chromatographic behaviour of a series of polycyclic aromatic hydrocarbons and heterocyclic compounds was investigated on Separon SIX NH2, a sorbent with chemically bonded amino groups. The effect of substitution and partial hydrogenation of the aromatics on their retention was examined. The achieved separation of aromatic hydrocarbons from their mixtures into groups, each containing substances with the same number of rings, was compared with that published for other, similar chromatographic materials. The effect of structure of some heterocyclic compounds on their affinity for the stationary phase, in comparison with the related aromatic hydrocarbons, is also discussed.
A MO treatment of solvent influence on the amide group rotation in 1-methylnicotinamides
Authors: Hofmann Hans-Jörg , Bartzsch Christine , Weiss Cornelius , Kuthan Josef
Published: September 2010

Using the Huron-Claverie solvation model the conformations of 1-methyl-1,4-dihydronicotinamide (II) and corresponding quaternary ion III have been investigated by the semiempirical NDDO method. The calculated data show that anti-conformers IIb and IIIb should be more stabilized by polar solvents than syn-conformers IIa and IIIa, respectively, mainly due to electrostatic contributions within solvation energy.
The wavenumbers of NO2 stretching vibrations and transmission of substituent effects in 2- and 4-substituted 3-nitropyridine series
Authors: Perjéssy Alexander , Rasala Danuta , Tomasik Piotr , Gawinecki Ryszard
Published: September 2010

The wavenumbers of both the symmetric and asymmetric stretching vibrations of the nitro group were measured in chloroform for the series of 2-X- and 4-X-substituted 3-nitropyridines as well as for o-X-substituted nitrobenzenes. The νas(NO2) and νs(NO2) values of both nitropyridine series were compared with those of corresponding nitrobenzenes. It has been found that the substituent effects in pyridines are transmitted to the 3-nitro group more readily from the 4-position, than from the 2-position. This transmission in 2-X-substituted 3-nitropyridines is comparable with that in the series of o-substituted benzene analogues. The transmission factors, γ, were determined according to Charton's definition for both 2,3- and 4,3-disubstituted pyridine rings. The separation of overall substituent effect into its inductive (field), resonance and steric components is discussed in terms of multiparameter correlation equations for wavenumber of asymmetric NO2 stretching vibration.
Reaction of 3,4a-disubstituted 4,4-dimethyl-5,6β-epoxy-A-homo-5β-cholestane derivatives with reducing agents
Authors: Velgová Helena , Zajíček Jaroslav
Published: September 2010

Reaction of all stereoisomeric 3-acetoxy-4,4-dimethyl-5,6β-epoxy-A-homo-5β-cholestan-4a-ols I-IV with lithium aluminium hydride and reduction of 3-acetoxy-4,4-dimethyl-5,6β-epoxy-A-homo-5β-cholestan-4a-ones XXII and XXIII with sodium borohydride were studied. It was found that reductive opening of the 5β,6β-epoxide ring occured only in the case of the derivatives III and IV due to 5(O)n participation of the 3α-oxygen-containing substituent under formation of the transannular 3α,5α-epoxides VIII and IX, resp. On reduction of the 4a-keto epoxides XXII and XXIII with sodium borohydride the trans-epoxy alcohols III and I were formed. On the basis of 1H NMR data the conformation of the A-ring in the epoxides I-IV, XXII, and XXIII is also discussed.
Inhibition of acetylcholine esterase and butyrylcholine esterase with isoquinoline alkaloids
Authors: Stejskal Jaromír , Kovář Jan , Slavík Jiří
Published: September 2010

The inhibition of the mentioned enzymes with 16 natural and modified isoquinoline alkaloids was investigated. Protoberberines are very strong inhibitors of both enzymes, quaternary tetrahydroprotoberberines and benzylisoquinolines are comparably strong in butyrylcholine esterase and slightly weaker in the case of acetylcholine esterase. Representatives of the pavinane and protopine groups are the weakest inhibitors of both enzymes in the series tested. The results confirm that these substances are bound competitively to butyrylcholine esterase and non-competitively to acetylcholine esterase, and they also show that the charge has a decisive effect on the force of the interaction. On the other hand the effect of the hydrophobicity of the inhibitor molecule on the bond strength is relatively small. Among the substances tested allylberberrubine is the strongest inhibitor of butyrylcholine esterase, its inhibition constant is 1.3 . 10-7.