On the methods of pore size distribution and the multilayer thickness

Summary Pore-volume-area distribution was achieved for a wide variety of silica gels, employing six computational procedures, and using botht-estimates ofCranston andInkley, andButt. The mathematical induction procedure outlined byRoberts proved to be as good as the more exact procedures. S _eum values evaluated by employing theButt estimate of multilayer thickness were exclusively higher than SBET data. The tabulatedt-values ofCranston andInkley yielded relatively reasonableS _eum results than those obtained above but are also higher thanS _BET. An overlooked parameter was suggested to be partly the cause of the divergence between the varioust-evaluations, namely: the thickness of a monolayer. Recalculation of all data, and using a value of 4.132 Å for the adsorbed monolayer, in botht-estimates ofLippens andButt, resulted in an excellent agreement betweenS _eum andS _BET in most of the cases. It is suggested that the multilayer thickness, as determined from adsorption data on non-porous solids, might not necessarily be of value in pore-size distribution analysis.     

Zur Kenntnis organischerLewis-Säuren, 36.Cis—trans-Gleichgewichte und Konformationen von 2,(x)-Dialkyl-1-dicyanomethylencyclohexanen. Wahlweise einfache Darstellung dercis- odertrans-Formen

Knoevenagel condensation of malononitrile withcis- andtrans-2,5-dimethylcyclohexanone (1 c and1 t, respectively) leads to2 c and2 t, respectively, and withtrans-1-decalone to4 t. The equilibria2 c2 t and4 c4 t have been determined as well as, by means of 270-MHz-¹H-NMR, the conformations of these four compounds. The dicyanomethylene group is found to induce axial positions of neighbouring alkyl residues on the cyclohexane ring (or when this is impossible, as in the case of4 t, the twist form of the cyclohexane ring). This results in a strong predominance of thecis isomers in the equilibria2 c2 t and4 c4 t whereas thetrans isomers strongly predominate in the equilibria among the starting ketones. This situation allows the optional preparation of2 c or2 t, and of4 c or4 t, from the more stable starting ketone (or ketone mixture). The free conformational energy of the distorted twist form of4 t amounts to 17 kJ/mol.

Herrn Prof. Dr.E. Ziegler, Graz, zum 70. Geburtstag in aufrichtiger Verbundenheit gewidmet.     

Neue Ergebnisse über die Adsorption von Celluloseglykolat aus kolloiden Lösungen an Textilfasern

Summary Studies on the slow coagulation of Prussian blue sol have been made in the light of the New Equation,C=a+m·1/t/n+1/t, whereC andt are the concentration of the electrolyte and time of coagulation, respectivelya, m andn are parametric constants.

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Zusammenfassung Es wurde die langsame Koagulation von Preu\isch-Blau-Sol unter Verwendung der neuen Gleichung:C=a+m·1/t/n+1/t untersucht. Dabei istC die Konzentration des Elektrolyts undt die Koagulationszeit;a, m undn sind Parameter.

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Grateful thanks are due to Professor A. K. Bhattacharya, D. Sc., F. R. I. C. (London), for his valuable guidance and helpful suggestions in these investigations.     

Vapour phase alkylation of ethylbenzene with t -butyl alcohol over mesoporous Al-MCM-41 molecular sieves

The alkylation of ethylbenzene witht-butyl alcohol was studied over Al-MCM-41 (Si/Al = 50 and 90) and Al, Mg-MCM-41 (Si/(Al+Mg) = 50) in the vapour phase from 200 to 400°C. The products werep-t-butylethylbenzene (p-t-BEB),p-t- butylvinylbenzene (p-t-BVB) andm-t-butylethylbenzene (m-t-BEB). Ethylbenzene conversion decreased with increase in temperature and increase in the ethylbenzene content of the feed. The reaction between the freely diffusing ethylbenzene in the channel and thet-butyl cations remaining as charge compensating ions yieldedp-t- BEB.p-t-BVB, an unexpected product in this investigation, was produced by dehydrogenation ofp-t-BEB over alumina particles present in the channels of the molecular sieves. Adsorption of ethylbenzene on Br?nsted acid sites and its subsequent reaction with very closely adsorbedt-butyl cations proved to be necessary to obtainm-t-BEB. Thoughm-t-BEB was obtained, the correspondingm-t-butylvinylbenzene was not observed in this study. Study of time durations indicated rapid and slow catalyst deactivation at lower and higher streams respectively.     

Untersuchung iiber die Wechselwirkung Polymere-Tenside

Zusammenfassung Es wurde der Einfluß von Polyvinylpyrrolidon (PVP) auf die kritische Mizellenbildungskonzentration (CMC) der Natriumsalze gesättigter und ungesättigterC ₁₆- undC ₁₈-Fettsäuren studiert. Die Oberflachenspannungskurven wiesen die Knickpunktet ₁ undt ₂ auf, die dem Adsorptionsbeginn bzw. der Polymersättigung an Tensidionen entsprechen. Wahrendt ₁ nur von der CMC des Tensids abhangt, istt ₂ an die CMC des Tensids und an die Polymerkonzentration gebunden. Die Gegenwart von Polymer-Tensid-Adsorptionskomplexen in Lösung verschiebt die CMC gegen höhere Konzentrationen, die dert ₂-Konzentration entsprechen. Die Polymer-Tensid-Wechselwirkung nimmt mit steigender PVP-Konzentration (im Konzentrationsbereich 0,25–0,50%) und mit der Verstarkung des hydrophoben Characters der Tenside in der Reihe:Stearat > Palmitat > Elaidinat > Oleat zu. Die Leitfahigkeitskurven zeigen keine Übergangspunkte.

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Summary The influence of polyvinylpyrrolidone (PVP) on the critical micellar concentration (CMC) of the sodium salts of saturated and unsaturatedC ₁₆ andC ₁₈ carboxylic acids was investigated. The surface tension curves displayed transition pointst ₁ andt ₂ corresponding to the adsorption outset and to the saturation of the polymer in tensid ions, respectively. Whilet ₁ only depends on the CMC of the tensid,t ₂ depends both on the CMC of the tensid and on the polymer concentration. The presence in solution polymer-tensid adsorption complexes shifts the CMC towards higher concentrations, corresponding to thet ₂ concentration. The polymer-tensid interaction increases with the increasing PVP concentration (in the concentration range 0.25–0.50%) and with the strengthening of the hydrophobic character of the tensids, in the order: stearate > palmitate > elaidinate > oleate. Conductivity curves did not display the two transition points.

     

A representation of chemical transformations by labeled graphs

A transitional labeling of a graphG is an assignment of one of the elements of the set (1, -1, 0) to each vertex and edge ofG so that each edge labeled 0 is incident only with vertices labeled 0, and no edge labeled 1 (respectively, -1) is incident with a vertex labeled -1 (respectively, 1). Chemical transformations can be represented by graphs possessing a transitional labeling. The positive (negative) graph of a transitional labelingt of a graphG is the subgraph ofG consisting of the nonnegative (nonpositive) elements ofG. The linking graph oft is the subgraph consisting of the zero elements ofG. A maximum common subgraph of two given graphsG ₁ andG ₂ is a graphF isomorphic to a common subgraph ofG ₁ andG ₂ such that the sum of the number of vertices and number of edges ofF is maximum. A transitional labelingt of a graphG is a transform if there exists an extensiont oft to a supergraphG of G such that the linking graph oft is a maximum common subgraph of the positive and negative graphs oft. Transforms are used to model chemical reaction pathways. Transforms and related concepts are studied in this paper. A characterization of transforms is also given.Dedicated to Professor Frank Harary on the occasion of his 70th birthday Research supported in part by Office of Naval Research Contract N00014-91-J-1060.     

Kinetics of aquation ofcis- andtrans-chloro-nitrobis-(ethylene-diamine)cobalt(III) ion in binary aqueous mixtures

Kinetics of aquation ofcis- andtrans-[Co(en)₂NO₂Cl]⁺ were investigated in aqueous mixtures of MeOH, EtOH,i-PrOH andt-BuOH at 298.1 K. The values of transfer functions corresponding to the transfer of reactant and activated complex from H₂O to the solvent mixtures were calculated from kinetic measurements and from solubilities of the complex salt. The results of the analysis of solvent effect are discussed in terms of D and I_d mechanisms. TMC 2676     

13C and1H NMR spectroscopic characterization of titanium(IV) alkylperoxo complexes Ti(OOtBu)n(OiPr)4?n with n=1, 2, 3, 4

Using¹³C and¹H NMR spectroscopy, titanium(IV) alkylperoxo complexes Ti(OOtBu)_n(OiPr)_4−n with n=1, 2, 3 and 4 were characterized in the reaction of Ti(OiPr)₄ withtBuOOH in CH₂Cl₂ and CDCl₃.     

A study of the protonation and alkylation oft-butyl isocyanide intrans-[M(CNBu-t 2(Ph2PCH2CH2PPh2)2] (M = Mo or W): Formation of carbyne-type complexes and theirtrans- tocis-isomerization

Summary Treatment of complexestrans-[M(CNBu-t)₂(dppe)₂][(1) M = Mo or W, dppe = Ph₂PCH₂CH₂PPh₂] with protic acid gives a mixture of the aminocarbyne complexestrans- pluscis-[M(CNHBu-t)(CNBu-t)(dppe)₂]⁺ (2) and the hydridocompounds [MH(CNBu-t)₂(dppe)₂]⁺ (3), whereas reaction with an alkylating agent (R⁺) appears to give the dialkylaminocarbyne compounds [M(CNRBu-t)(CNBu-t)(dppe)₂]⁺ (4) also as a mixture of thetrans andcis isomers.     

Lifetime prediction for polymers via the temperature of initial decomposition

The temperature of initial decompositionT _id was determined from TG and DTG curves of mass loss during thermooxidative polymer decomposition in an environmental air atmosphere. The values ofT _id were applied for comparison of the thermal stabilities of several polymers, e.g. PC-A, PBT, PET, PPO and PVC. Both the activation energies of initial decompositionE _id and the preexponential termsA _id of the Arrhenius equation were calculated by using the Kissinger approach. The initial mass loss is proposed as a criterion for calculation of the time to failuret _f from the known values ofE _id andA _id, and hence for a prediction of the lifetime of polymer materials.The following thermal stability sequence was found for the investigated polymer materials: PC-A (st)>PC-A (nst)>PBT>PET>PPO>PVC (e)>PVC (c). The activation energy of initial decomposition had a mean value ofE _id=83 kJ mol^–1 for PC-A, PBT, PET and PPO, andE _id=73 kJ mol^–1 for the PVC samples.The calculated time to failure,t _f, for PC-A, PET and PVC under specified conditions was in reasonable agreement with published experimental data.The proposed parameters of thermal decompositionT _id,E _id andt _f, can be applied for the characterization and comparison of various polymer materials, and for a prediction of their lifetime.Financial support from the Polish Scientific Research Committee, the grant No. 7 761791 02, is gratefully acknowledged.     

Photophysical properties of the extract of endometallofullerenes La@C2n inortho-dichlorobenzene. Picosecond laser photolysis

The kinetics of relaxation of optical anisotropy induced by polarized light in endometallofullerenes La@C_2n inortho-dichlorobenzene was studied by picosecond laser photolysis. Decay of the optical absorption signal due to the excited states of La@C_2n follows the biexponential law with two values of relaxation time:t ₁=35±3 ps andt ₂=1100±200 ps. The lifetimet or decay of the optical anisotropy is 19±5 ps and determined by the orientational diffusion of La@C_2n . The experimentally determined lifetime of optical anisotropy agrees satisfactorily with the value yielded by the theoretical model of orientational diffusion under slip boundary conditions at the interface of the La@C_2n molecule with the solvent. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya No. 10, pp. 1921–1923, October, 1999.     

Synthesis of some substituted benzimidazoles with potential antimicrobial activity

Summary The synthesis andin vitro antimicrobial evaluation of several benzimidazole derivatives with different heterocyclic nuclei at position-2 are described.

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Synthese einiger substituierter Benzimidazole mit potentieller antimikrobieller Aktivität

Zusammenfassung Die Synthese und antimikrobielle Prüfung einiger Benzimidazole mit verschiedenen heterozyklischen Substituenten in 2-Stellung wird beschrieben.

     

Thermodynamic study of binary mixtures of isomeric butylamines with methanol enthalpy of hydrogen bonded complex

Heats of mixing of the binary mixtures ofn-, sec-, iso- andt-butylamines with methanol were determined in the entire concentration range. All the four systems showed a strong exothermic behaviour. The exothermic heats of mixing vary in the ordert-BuNH₂ >n-BuNH₂ > sec-BuNH₂ > iso-BuNH₂. The enthalpy of hydrogen bond in the methanol-butylamine complexes was calculated by means of a thermochemical cycle and found to vary in the ordert-BuNH₂ >n-BuNH₂ > iso-BuNH₂ > sec-BuNH₂. This order is different than that found for the hydrogen bond due to self-association. The difference has been explained in the light of steric and electromeric effects arising out of the substitution of the methyl groups in the alkyl chain of the butylamine. NCL Communication No. 2356 (Part of the Ph.D. Thesis submitted to the Bombay University by the first author).     

Molecular structure of cyclobutanones resulting from cycloaddition of Moore's ketene to styrene, 1-vinylnaphthalene andp-methoxystyrene

Styrene or 1-vinylnaphthalene react with Moore's ketene (t-butylcyanoketene) to give cyclobutanones1a and1b, respectively, withcis configuration of the vicinal bulkyt-butyl and aryl groups. Steric crowding is reduced by (i) nonplanarity distortion of the cyclobutanone ring (ca. 20°), (ii) elongation to ca. 1.6 Å of the C₂-C₃ bond (which is flanked by the bulky groups), (iii) deviation of the vicinal bulky groups by ca. 22° from the eclipsed conformation, and (iv) increased bond angles of thet-Bu-C₂-C₃ and Ar-C₃-C₂ groups.p-Methoxystyrene reacts with Moore's ketene to give cyclobutanone2a with the vicinal bulkyt-butyl and aryl groups in thetrans configuration. In contrast to1a and1b, (i) the cyclobutanone ring is planar, (ii) the C₂-C₃ bond is shorter (1.59 Å), and the bond angles (iii) and (iv) are each reduced by 12.5°. It is concluded that in the case of styrene and 1-vinylnaphthalene the cycloaddition reaction is seemingly concerted and occurs according to a_{2 s}+2 _a reaction mode, whereasp-methoxystyrene reacts stepwise with Moore's ketene, giving the thermodynamically more stable cyclobutanone isomer.     

Kinetics of oxidation ofcis-, andtrans-chlorobis(ethylenediamine)isothiocyanatocobalt(III)ion with peroxodisulphate in aqueous alcoholic mixtures

Summary The effect of organic cosolvent on the rate constants and activation parameters of oxidation of coordinativelybound thiocyanate with peroxodisulphate was investigated in mixtures of water with methanol,i-propanol andt-butanol. The thermodynamic transfer functions, corresponding to the transfer of reactants and activated complex from water to the solvent mixtures were evaluated from kinetic measurements and from the solubilities of corresponding salts. The experimental results are interpreted in terms of the solvation of both the initial state and the activated complex.     

Prins-Reaktionen mit Arylaldehyden, 3. Mitt.

By reaction of excess benzaldehyde with cyclohexene in presence of sulfuric acid besider-2,c-4-diphenyl-(t-4aH,c-8aH)-hexahydro-4H-1,3-benzodioxin (2) andr-4-phenyl-(t-4aH,c-8aH)-hexahydro-4H-1,3,2-benzodioxathiin-2,2-dioxide (3),trans-2-benzyloxycyclohexyl phenyl ketone (5) and (E)-3-benzylidene-1-cyclohexenyl phenyl ketone (6) are obtained. The formation of5 and6 is shown to proceed via an acid catalyzedCannizzaro reaction of benzaldehyde.

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2. Mitt.:H. Griengl undK. P. Geppert, Mh. Chem.107, 675 (1976).     

Electrochemical nucleation of lead and copper on indium-tin oxide electrodes

The nucleation process of Pb and Cu onto indium-tin oxide electrodes was studied by single potentiostatic steps using 0.1×10^–4 mol L^–1 Cu(NO₃)₂ and 2×10^–2 mol L^–1 Pb(NO₃)₂ solutions in aqueous 1.0 mol L^–1 NaNO₃. The current, I_max, and the time, t_max, corresponding to the maximum, were evaluated by 3D nucleation with a diffusion-controlled growth model for instantaneous and progressive nucleation. The non-dimensional plots of (I/I_max)² vs. t/t_max showed that Cu and Pb nucleation closely followed the response predicted for instantaneous nucleation. Other parameters, such as I vs. t^1/2 and I²_maxt_max, as well as nuclei micrographs, were analyzed, corroborating the results obtained.     

Thermochemical study of the solvation of alkanes in mixtures of methanol with butyl alcohol isomers

A calorimetric method was applied at 25 °C to measure the enthalpies of dissolution of cyclohexane, heptane, and decane in the methanol-n-butanol mixed solvent and hexadecane in mixtures of methanol withn-, iso-, andtert-butyl alcohols. The standard enthalpies of dissolution of alkanes were determined. It was shown that the equation proposed in the literature for calculation of the enthalpies of dissolution of alkanes in mixtures with nonspecific intermolecular solvent-solvent interactions describes satisfactorily the enthalpies of dissolution of alkanes in mixtures of methanol withn- andiso-butyl alcohols. It was suggested that there is no preferential solvation of alkanes by one of the mixed solvent components in the MeOH−BuⁿOH and MeOH−BuⁱOH mixtures; in the MeOH−Bu^tOH system, the composition of alkane solvation shell differs slightly from the solvent composition in the bulk. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 271–274, February, 1999.     

Technetium-99m labeling of hippuric and p-amino-hippuric acid in the presence of DTPA: Biological and pharmacokinetic evaluation and comparison with99mTc-DTPA

^99mTc-Hipp as a modified^99mTc-DTPA, and^99mTc-PAH as a new renal agent are developed. Each veal of lyophilised kit contain hippuric (Hipp) or p-aminohippuric acid (PAH), diethyltriaminepentaacetic acid as calciumtrisodium salt (CaNa₃DTPA) and stannouschloride (SnCl₂·xH₂O), in molar ratio Hipp/PAH:DTPA=4∶1. They are high radiochemical purity radiopharmaceuticals, with hydrophilic character and low percentage of protein binding. The ITL chromatography and HPLC analyses of these labeled compounds have shown almost identical results as^99mTc-DTPA, but their biological behavior in rats confirm certain differences.^99mTc-Hipp is a renal agent clearing by the glomerular system, with better pharmacokinetical parameters than^99mTc-DTPA:t _1/2(α)=4.1 min,t _1/2(β)=198.6 min,K _cl=1.2·10⁻²min⁻¹ and a twofold value for blood clearance (Cl=2.07 ml/min).^99mTc-PAH is a quite different renal agent, rapidly secreted by kidney as a tubular secretion agent. Its pharmacokinetical parameters:t _1/2(α)=2.5 min,t _1/2(β)=41.7 min andK _cl=5.1·10⁻⁴ min⁻¹ are almost equal to those of^99mTc-MAG₃, but the blood clearance of Cl=5.22 ml/min is even higher than that of IOH clearance.