bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical and model studies of strip footing supported by a reinforced granular fill - soft soil system
Authors: Lee K M , Manjunath V R , Dewaikar D M
Published: April 2011

Laboratory model tests have been carried out using a rigid strip footing supported on dense sand overlying soft clay with and without a layer of geotextile reinforcement at the interface. The study aimed at determining the effect of geotextile reinforcement and the thickness of a sand layer on the ultimate bearing capacity and settlement characteristics of the footing resting on a granular fill - soft soil system. It was found that the bearing capacity increases with an increase in the ratio of sand thickness to footing width until it reaches a critical value, which can be considered as the optimum limit of improvement of the bearing capacity of the layered soil. The installation of a geotextile reinforcement at the interface resulted in an appreciable increase in bearing capacity and decrease in settlement of the footing. The optimum thickness of the sand layer for a geotextile-reinforced foundation was found to be 0.8 times the width of the footing, which was significantly lower than that of an unreinforced foundation. The results of the laboratory model tests were validated by a comparison with the results of a finite element analysis. The results obtained using the finite element model compared well with data obtained from the laboratory tests. Additional parametric study was carried out by the finite element model to supplement the results of the laboratory model tests. Design recommendations are given based on the results of the finite element model and laboratory model studies for a rigid footing supported on a reinforced granular fill - soft soil system. Key words: model tests, footing, bearing capacity, granular fill, clays, finite elements, geotextiles.
Hydraulic conductivity of clays in confined tests under low hydraulic gradients
Authors: Dixon D A , Graham J , Gray M N
Published: April 2011

Clay barriers normally function at hydraulic gradients much lower than are commonly used in laboratory tests for hydraulic conductivity. This paper describes low-gradient tests on compacted illite, Na-bentonite, and sand-bentonite specimens at a range of dry densities. The tests examined the effects of deionized or saline pore fluid, the initial degree of saturation at the time of compaction, and back-pressuring to achieve saturation during permeation. No "critical" or "threshold" gradients were observed. In low-density materials, "transitional" gradients defined two separate regions of Darcian flow. Low flow rates and low hydraulic conductivities were associated with hydraulic gradients below the transitional gradient. Higher conductivities were associated with gradients above the transitional gradient. Hydraulic conductivities decreased with increasing initial density. They appeared independent of initial degree of saturation or back-pressuring. Tests on Na-rich bentonite showed that deionized and saline permeants produced similar hydraulic conductivities. Measured hydraulic conductivities were in reasonable agreement with values computed using the Poiseuille and Kozeny-Carman equations. Key words: hydraulic conductivity, gradient, Darcian, illite, bentonite.
The effect of the bending rigidity of a wall on lateral pressure distribution
Authors: Huang Ching-Chuan , Menq Farn-Yue , Chou Yue-Chin
Published: April 2011

A two-dimensional model retaining wall system was developed to investigate the effect of the bending rigidity of a wall, supported at the top and bottom, on the lateral pressure distribution at completion-of-backfilling condition. A total of 120 000 pieces of 1.96 mm diameter stainless steel rods were placed piece by piece behind the 500 mm high walls in a parallel and dense stack. Ten two-component load cells were mounted to the inner face of the wall to obtain simultaneously normal and shear stresses acting on the wall. The stress-deformation characteristics of the steel-rod assembly and the friction angle between the steel rods and the stainless plate were investigated thoroughly to provide parameters of the backfill material used. Four types of walls with different bending rigidities were employed. The deflections at the half-height of the wall at the moment of completion of backfill ranged between 0.03 and 4.6 mm. A parameter Rr, the relative degree of deflection at the half-height of the wall, was used to evaluate the lateral pressure distribution on the walls for their at-completion conditions. Both the lateral pressure coefficients and the patterns of lateral pressure distribution on the walls were strongly related to Rr.
Centrifuge modelling of laterally loaded single battered piles in sands
Authors: Zhang Limin , McVay Michael C , Lai Peter W
Published: April 2011

Centrifuge lateral load tests were performed on single battered piles at five pile inclinations founded in both medium-dense (relative density Dr = 55%) and loose (Dr = 36%) sands. The effects of pile batter and soil density on lateral resistance were studied. Pile batter had significant effects in dense sands but minor effects in loose sands. Based on the test results, nonlinear p-y curves, where p is the soil resistance in unit length and y is the lateral deflection of the pile, were developed for single piles at any angle (positive or negative) and sand density. The developed p-y curves were subsequently used with a Winkler model (COM624, LPILE, FLPIER, etc.) to predict all the test results with reasonable accuracy.
A transient analysis of slope stability following drawdown after flooding of a highly plastic clay
Authors: Pauls G J , Sauer E Karl , Christiansen E A , Widger R A
Published: April 2011

The stability of slopes at bridge abutments across the Carrot River in east-central Saskatchewan was not influenced significantly by drawdown after flooding in the spring of 1995. Traditional methods of analysis for rapid drawdown predicted the factor of safety of slopes on highly plastic clays of proglacial Lake Agassiz would drop to 0.65 from an initial value of 1.0. Deformation along a well-defined slip plane has persisted at a more or less constant, slow rate since the bridge was constructed in 1975. The river rose approximately 10 m during a flood in the spring of 1995, yet there was only minimal response in piezometers and no measurable increase in the rate of deformation recorded by inclinometers. Pore-water pressures from a steady state seepage model, which was calibrated from piezometer measurements, were integrated into a stability analysis. Changes in pore-water pressures caused by flooding and subsequent drawdown were characterized from a transient seepage model using the flood hydrograph as a flux boundary. The stability analysis integrated with the transient seepage model estimated the factor of safety would drop from 1.0 to 0.91 after drawdown. Field measurements indicated the reduction in factor of safety was even less.
Tire-reinforced earthfill. Part 2: Pull-out behaviour and reinforced slope design
Authors: O'Shaughnessy Vince , Garga Vinod K
Published: April 2011

The disposal of scrap tires has become a major environmental concern. The reuse of scrap tires in the reinforcement of earth structures can provide an attractive solution in reducing the number of used tires disposed in overcrowded landfills. This paper, the second in a series of three papers, discusses the behaviour of slopes reinforced with scrap tires and proposes design recommendations. A mat-reinforced slope can either fail by pull-out of the reinforcement or due to rupture of the attachment tying the tires. A large number of pull-out tests were performed on whole tires and tires with one sidewall removed embedded in sand and cohesive backfill. The pull-out resistance of tire mat reinforcement was primarily governed by the effective shear strength of the soil, and therefore it can provide an efficient means of reinforcement. However, large displacements were required to fully mobilize the ultimate pull-out capacity which must be considered in design.Key words: pull-out tests, scrap tires, reinforced slope, performance, design guidelines.
Nonlinear site effects on strong ground motion at a reclaimed island
Authors: Yang Jun , Sato Tadanobu , Li Xiang-Song
Published: April 2011

Recently there has been an increased interest in the study of the nonlinearity in soil response for large strains through in situ earthquake observations. In this paper, the downhole array acceleration data recorded at a reclaimed island, Kobe, during the 1995 Kobe earthquake are used to study nonlinear site effects. Particular attention is given to the liquefaction-induced nonlinear effects on the recorded ground motions. By using the spectral ratio and the spectral-smoothing technique, the characteristics of the ground motions are analyzed. It is shown that the peak frequencies in spectral ratios were shifted to lower frequencies when the strongest motions occurred. The increase in the predominant period was caused primarily by a strong attenuation of low-period waves, rather than by amplification of long-period motions. Based on the spectral analyses, the nonlinearity occurring in the shallow liquefied layer during the shaking event is identified, manifested by a significant reduction of the shear modulus. A fully coupled, inelastic, finite element analysis of the response of the array site is carried out. The stress-strain histories of soils and excess pore-water pressures at different depths are calculated. It is suggested that the stress-strain response and the build up of pore pressure are well correlated to the variation of the characteristics of ground motions during the shaking history.Key words: site response, ground motion, nonlinearity, soil liquefaction, array records, Kobe earthquake.
Detection of shear zones in a natural clay slope using the cone penetration test and continuous dynamic sampling
Authors: Mahmoud Mahmoud , Woeller David , Robertson Peter K
Published: April 2011

The detection of shear zones along which a mass of soil is moving is essential for understanding the state of stability of natural slopes. Weaker zones in clay soils can be identified from low values of cone penetration test (CPT) tip resistance measured during penetration. This paper presents a case history illustrating the identification of softened shear zones in clay soils using the CPT and the observation of shear surfaces using continuous dynamic sampling (CDS). The analysis and interpretation of the CPT data are discussed in relation to the detection of shear surfaces using the CDS at a site with a history of slope instability. Difficulties encountered in identifying shear zones and detecting shear surfaces are discussed.Key words: cone penetration testing, slope stability, in situ testing, case history, shear zone.
Solid phase assisted synthesis of HIV-1 protease inhibitors. Expedient entry to unsymmetrical substitution of aC2symmetric template
Authors: Oscarsson Karin , Classon Björn , Kvarnström Ingemar , Hallberg Anders , Samuelsson Bertil
Published: April 2011

A solid phase synthesis has been developed leading up to unsymmetrical HIV-1 protease inhibitors that are not readily available by conventional solution phase chemistry (18ag). To prepare these compounds the hydroxyl group of (1S,2R)-()-cis-1-phthalimido-2-indanol (3) was coupled to a Merrifield resin via a dihydropyrane linker. Cleavage of the phthalimido protecting group and reaction of the liberated amine with the bis-activated symmetrical diacid 15 resulted in the resin bound amide 16. Coupling of 16 with amino acids and amines followed by hydrolysis produced the desired unsymmetrical products 18ag from which potent HIV-1 protease inhibitors were identified, e.g., 18e (ki= 0.1 nM), 18a (ki= 0.2 nM) and 18c (ki= 2 nM).Key words: HIV, inhibitor, protease, solid phase.
The directed ortho metalation - palladium catalyzed cross coupling connection. A general regiospecific route to 9-phenanthrols and phenanthrenes. Exploratory further metalation
Authors: Fu Jian-min , Snieckus Victor
Published: April 2011

A new general and regiospecific synthesis of 9-phenanthrols (1 +2 [Formula: see text] 3 [Formula: see text] 4, Scheme 1, Table 1) proceeding by a Directed ortho Metalation (DoM), Suzuki-Miyaura cross coupling, and a new LDA-mediated Directed remote Metalation sequence is described. The facile Pd-catalyzed hydrogenolysis of the phenanthrols 4 into the corresponding phenanthrenes 5 via their triflates 18 translates the original DoM regioselectivity also into a general synthesis of phenanthrenes (Table 2). Further DoM (19 [Formula: see text]20, 21; 24 [Formula: see text]25), cross coupling (20c [Formula: see text]23), as well as oxidation - ring contraction (4b, 4f [Formula: see text]28a, 28b) chemistry of phenanthrene derivatives is reported.Key words: 9-phenanthrols, directed ortho metalation, Suzuki cross coupling, synthesis.
The photolysis of Si,Si-di-tert-butyltetramesitylsiladigermirane in the presence of methylmagnesium iodide
Authors: Samuel Mini S , Baines Kim M , Hughes Donald W
Published: April 2011

The photolysis of Si,Si-di-tert-butyltetramesitylsiladigermirane in the presence of methylmagnesium iodide at 15°C has been investigated. Five products were isolated and identified from the complex product mixture: mesityldimethylgermane, dimesitylmethylgermane, (di-tert-butylmethylsilyl)mesitylmethylgermane, meta-(di-tert-butylmethylsilyl)toluene, and para-(di-tert-butylmethylsilyl)toluene. The characterization of these compounds and proposed mechanisms for their formation will be discussed.Key words: germasilene, Grignard reagents, germylmagnesium compounds.
Trans alkenylpyridine and alkenylamine complexes of platinum
Authors: Shaver Michael P , Vogels Christopher M , Wallbank Andrew I , Hennigar Tracy L , Biradha Kumar , Zaworotko Michael J , Westcott Stephen A
Published: April 2011

Addition of cis-cyclooctene (coe) to K2PtCl4gives trans-[PtCl2(coe)]2(1), which reacts with excess coe to give trans-PtCl2(coe)2(2). Compound 2 was characterized by an X-ray diffraction study and crystals were found to be triclinic, a = 5.7838(5), b = 7.4347(6), c = 9.9972(9) Å, α = 83.924(1), β = 87.844(2), γ = 73.546(1)°, Z = 1, with space group P1-. Addition of 4-vinylpyridine (4vp) to 1 gave trans-PtCl2(4vp)2(5) which was also characterized by an X-ray diffraction study. Crystals of 5 were monoclinic, a = 8.2255(6), b = 12.8254(10), c = 6.9624(5) Å, β = 98.8230(10)°, Z = 2, with space group P21/c. Although alkenylamines react with 1 to give a mixture of products, addition of one equivalent of apve (H2NCH2CH2CH2OCHβCH2) to 1 cleanly afforded the organometallic product trans-PtCl2(coe)(thmo) (thmo = tetrahydro-2-methyl-1,3-oxazine) arising from a metal-catalyzed intramolecular hydroamination of the starting alkenylamine. Initial investigations into the functionalization of metal complexes containing pendant alkene groups have shown that catecholborane can be added in some cases, using a rhodium catalyst, to give the corresponding organoboronate ester platinum compounds.Key words: alkenylamines, alkenylpyridines, hydroamination, hydroboration, platinum.
Substituent effects on stability of oxiranes, oxirenes, and dioxiranes
Authors: Sung Kuangsen
Published: April 2011

Homodesmotic reactions were designed to study substituent effects on stability of oxiranes, oxirenes, and dioxiranes. Good or fair correlation between their homodesmotic stabilization energies and Taft's dual-substituent-parameters has been found. Oxiranes are stabilized by σ-donating and π-donating substituents but destabilized by σ-accepting and π-accepting substituents. The π-effects on oxiranes are comparable to σ-effects for π-acceptor substituents and are much stronger than σ-effects for π-donor substituents. Oxirenes are stabilized by σ-donating, π-donating, and π-accepting substituents but destabilized by σ-accepting substituents. The π-effects on oxirenes are stronger than σ-effects. Oxirenes with strong π-donor substituents such as F, OH, and NH2, or strong σ-donor substituents such as Li and Na are neither real molecules nor transition states. Dioxiranes are stabilized by σ-donating and π-donating substituents but destabilized by σ-accepting and π-accepting substituents. The π-effects on dioxiranes are stronger than σ-effects for π-donor substituents, but weaker than σ-effects for π-acceptor substituentsKey words: oxirane, oxirene, dioxirane, homodesmotic reaction, substituent effect.
Solution multinuclear (31P,111Cd,77Se) magnetic resonance studies of cadmium complexes of heterocyclic aromatic thiones and the structure of [tetrakis(2(1H)-pyridinethione)cadmium] nitrate, [Cd(C5H5NS)4](NO3)2
Authors: Rajalingam Umarani , Dean Philip AW , Jenkins Hilary A
Published: April 2011

The complex salts CdL4(O3SCF3)2 (L = 2(1H)-pyridinethione (Py2SH), 4(1H)-pyridinethione (Py4SH), or 2(1H)-quinolinethione (Q2SH)) have been synthesized by the stoichiometric reaction of Cd(O3SCF3)2 and the appropriate thione. Both ambient-temperature 13C and reduced-temperature 111Cd NMR of CdL4(O3SCF3)2 in solution are consistent with L being bound through sulfur. Reduced-temperature NMR (31P, 77Se, 111Cd, as appropriate) of mixtures of CdL4(O3SCF3)2 and Cd(EPCy3)4(O3SCF3)2 (E = Se, Cy = c-C6H11) and of Cd(EPCy3)4(O3SCF3)2 (E = S, Se) and L in solution provides evidence for various [CdLn(EPCy3)4-n]2+. Similarly, reduced-temperature metal NMR of [CdL4]2+ and [CdL'4]2+ (L, L' = Py2SH, Py4SH, Q2SH; L not equal L') in solution shows the formation of [CdLnL'4-n]2+. Thus it has been demonstrated that at reduced temperature [CdL4]2+ is intact in solution and exchange of L is slow on the timescale of the metal chemical shift differences. From the NMR studies of Cd(EPCy3)4(O3SCF3)2 (E = S, Se):L mixtures, the binding preferences are found to be L > EPCy3 in solution. Similarly, from the reduced temperature metal NMR spectra of mixtures where L and L' compete for Cd(II) in solution, the binding preferences are Py4SH > Py2SH > Q2SH. The structure of Cd(Py2SH)4(NO3)2 (4) has been determined by single crystal X-ray analysis. Colorless crystals of 4 are tetragonal, I4(1)/acd with 8 molecules per unit cell of dimensions a = 18.660(3), c = 15.215(3) Å. The structure is comprised of recognizable NO3- anions and [Cd(Py2SH)4]2+ cations. In the cations, which have S4 symmetry, the ligands are S-bound. A network of NH···O hydrogen bonds links the cations and anions.Key words: aromatic heterocyclic thiones, cadmium complexes, phosphine chalcogenides, 111Cd, 31P, 77Se NMR, X-ray crystallography.
Free radicals and Lewis acid. Chelation-controlled radical allylations of substituted α-halo- or α-phenylseleno-β-alkoxy esters. The endocyclic effect.
Authors: Guérin B , Chabot C , Mackintosh N , Ogilvie W W , Guindon Y
Published: April 2011

The radical allylation of a series of α-halo or α-phenylseleno-β-alkoxy esters in the presence of MgBr2·OEt2 is reported and compared with analogous reactions under non-chelating conditions. The addition of MgBr2·OEt2 gives excellent selectivity favoring anti products; in some cases ratios >100:1 are obtained. Varying the substrate substituents reveals that these reactions are quite tolerant of alkyl functionalities at the β-position. Changes to the alkoxy function indicate that a chelate is involved in the reaction. The reactions are successful with secondary iodides, bromides, and phenylselenides, as well as tertiary iodides, which all give very high ratios under chelation control. Performing less well under the same conditions are substrates with a radical exocyclic to a tetrahydrofuran ring. EDTA titration is used to determine the amount of Mg2+ dissolved in the allylation reaction mixture, and 13C NMR is employed to better define the nature of the complex formed (chelate or monodentate) prior to the reaction. Competition experiments suggest that the chelate and monodentate pathways are in competition for the radical allylation with allyltributyltin.Key words: allylation, radicals, Lewis acid, stereoselectivity, 1,2-induction.
Benzyloxy(4-substituted benzyloxy)carbenes. Generation from oxadiazolines and fragmentation to radical pairs in solution
Authors: Merkley Nadine , Warkentin John
Published: April 2011

Thermolysis of 2,2-dibenzyloxy-5,5-dimethyl-Δ3-1,3,4-oxadiazoline in benzene at 110°C leads to dibenzyloxycarbene. The carbene was trapped with tert-butyl alcohol to afford dibenzyl-tert-butyl orthoformate. In the absence of a trapping agent for the carbene, it fragmented to benzyloxycarbonyl and benzyl radicals, as shown by trapping the latter with TEMPO. In the absence of both TEMPO and tert-butyl alcohol, the radicals were partitioned between coupling to benzyl phenylacetate and decarboxylation, with subsequent formation of bibenzyl. The preferred sense of fragmentation of the analogous carbenes from benzyloxy-(p-substituted-benzyloxy)carbenes was determined by comparing the yields of the two possible esters, ArCH2O(CO)CH2Ph and PhCH2O(CO)CH2Ar. It was found that an electron-withdrawing group in the para position favoured fragmentation to the benzylic radical containing that group. A Hammett plot of the data gave a best fit with σ- substituent constants (r = 0.994, ρ(PhH, 110°C) = 0.7) suggesting that the fragmentation involves charge separation in the sense that increases electron density on the group that is becoming a benzylic radical and decreases electron density on the carbonyl group that is becoming the benzyloxycarbonyl radical.Key words: carbene, dibenzyloxycarbene, fragmentation, substituent effect, radical pair, TEMPO.
Synthesis and photophysical properties of fluorophore-labeled abscisic acid
Authors: Hou X , Abrams S R , Balsevich J J , Irvine N , Norstrom T , Sikorski M , Sinha H K , Steer R P
Published: April 2011

The 8'-benzophenone, 8'-dansylhydrazone, 3'-S-(2-ethyldansylamide), and 3'-S-acetamidofluorescein derivatives of the plant hormone abscisic acid (ABA) have been synthesized for use in photoaffinity labeling (the benzophenone derivative) or fluorescence probe experiments and have been spectroscopically characterized. One of the three fluorescent compounds, the 3'-tethered fluorescein derivative, exhibits spectroscopic and photophysical properties which indicate that it could be an excellent fluorescent probe of ABA interactions in vivo. The 3'-tethered fluorescein and ABA moieties do not interact strongly, so that the fluorescence properties of the fluorescein-labelled hormone are very similar to those of fluorescein itself. Measurements of the absorption, emission, and fluorescence excitation spectra, fluorescence quantum yields, and fluorescence decay parameters of this derivative as a function of pH indicate that the photophysics is dominated by ground and excited state prototropic equilibria involving only the fluorescein moiety. The fluorescein dianion is the only significant absorber and emitter at pH > 6.7, whereas only the cation absorbs and emits at pH < 0. In the intervening pH range, strong emission from the monoanion and weak emission from two neutral species, tentatively assigned to the zwitterion and the lactone of the fluorescein moiety, is observed.Key words: abscisic acid, fluorescein, synthesis, photophysics.
Reactions of the radical cation derived from 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS·+) with amino acids. Kinetics and mechanism
Authors: Aliaga C , Lissi E A
Published: April 2011

Stable free radicals derived from 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS·+) have been extensively employed to monitor the antioxidant capacity of biological fluids and beverages. Besides reacting with typical antioxidants (such as phenols or thiols) these radicals react with a variety of hydrogen or electron donors. The present work reports on the kinetics and mechanism of these radical reactions with several amino acids. Reaction rates notably increase when the pH of the media increases and, when measured under similar conditions, follows the ordercysteine > > tryptophan > tyrosine > histidine > cystineThe kinetics of the process is interpreted in terms of a mechanism comprising an initial pH dependent reversible step, followed by secondary reactions of the substrate derived radical with itself or with another ABTS·+; this simple three-step mechanism leads to very complex kinetic expressions. The specific rate constants of several of the elementary steps were determined by working under a wide range of substrate, radical, and ABTS concentrations. The values obtained for the initial interaction between the ABTS derived radical and the substrate range from 0.5 M1 s1 to 1.9 × 106 M1 s1 for histidine and cysteine, respectively.Key words: ABTS radical cation, 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid), amino acids, kinetics.
Transition state stabilization by micelles: thiolysis of p-nitrophenyl alkanoates in cetyltrimethylammonium bromide micelles
Authors: Tee Oswald S , Yazbeck Ogaritte J
Published: April 2011

Thiolysis of p-nitrophenyl esters (acetate to decanoate) by the anion of 2-mercaptoethanol (ME) is catalyzed by micelles of cetyltrimethylammonium bromide (CTAB) in aqueous solution. At fixed [ME], the observed rate constants (kobs) show saturation with respect to added [CTAB], consistent with ester binding in the micelles. Plots of kobs vs. [ME] are linear in the absence and in the presence of the CTAB, and analysis of the slopes of the plots afford rates constants for thiolate ion attack on the esters in the aqueous phase (kN) and in the micellar phase (kcN). The strengths of substrate binding and transition state binding to the micelles are strongly correlated, with a slope of unity, because they have the same dependence on the ester chain. Consequently, the catalytic ratios (kcN/kN) are independent of the length of the ester. Similar behaviour is found for thiolysis by the dianions of mercaptoacetic acid, 3-mercaptopropionic acid, and cysteine, and also for ester cleavage by the anions of glycine and 2,2,2-trifluoroethanol, as earlier for cleavage by hydroxide ion. The results are consistent with Kirby's dissection of transition state binding into "passive" and "dynamic" components. The passive component involves hydrophobic binding of the ester chain which is more or less the same as in the substrate binding. The dynamic component is associated with reaction in the Stern layer of the micelle, and its magnitude varies with the nucleophiles because of differences in their ease of exchange between the aqueous medium and the Stern layer.Key words: catalysis, esters, thiolysis, micelles.
Oxidative coupling-type mechanism of N,N-dialkylanilines in solvent-free conditions forming crystal violet derivatives. A clay-mediated and microwave-promoted approach
Authors: López-Cortés J G , Penieres-Carrillo G , Ortega-Alfaro M C , Gutiérrez-Pérez R , Toscano R A , Alvarez-Toledano C
Published: April 2011

In the clay-mediated reaction of N,N-disubstituted anilines using microwave radiation as an energy source in the absence of solvent, crystal violet and derivatives, diphenylmethanes, and biphenyls were isolated along with intermediates supporting an oxidative coupling-type mechanism.Key words: clay, dyes, microwave radiation, solvent-free reactions.
Thermodynamics of methanesulfonic acid revisited
Authors: Guthrie J Peter , Gallant Roger T
Published: April 2011

Recently we reported a study of the thermodynamics of methanesulfonic acid and some of its derivatives. The foundation of these results was a measurement of the heat of reaction of S-methyl thioacetate with aq sodium hypochlorite, leading to methanesulfonic acid. We have reinvestigated this reaction and discovered that contrary to the initial stoichiometry experiments, the stoichiometry under the reaction conditions is not as was believed and that the heat of reaction observed was spuriously high. We have found a new reaction, that of sulfite ion with methyl methanesulfonate, which does allow a clean determination of the heat of formation of methanesulfonic acid. Revised thermodynamic quantities for methanesulfonic acid, methanesulfonyl chloride, and methyl methanesulfonate are reported here.Key words: sulfonic acid, heat of reaction, free energy of formation, SN2 reaction.
Thermodynamics of triaryltin chloride adduct complexes
Authors: Asadi Mozaffar , Jamshid Khosrow Aein
Published: April 2011

The stability constants and the thermodynamic data were measured spectrophotometerically for 1:1 adduct formation of triaryltin chlorides, where aryl groups are p-chlorophenyl, phenyl, p-, m-, and o-tolyl, as Lewis acids, with chloride and bromide ions, as Lewis bases, in 50% v/v ethanol-water solvent. The stability constants and the thermodynamic parameters trend, confirmed the following softness trend of tin(IV) in the triaryltin chlorides:(p-, m-, o-tolyl)3SnCl > (phenyl)3SnCl > (p-chlorophenyl)3SnClKey words: tin(IV) complexes, thermodynamic parameters, mixed solvent, adduct formation.
Titanocene(III) catalyzed homogeneous hydrosilation-hydrogenation of pyridines
Authors: Harrod John F , Shu Ronghua , Woo Hee-Gweon , Samuel Edmond
Published: April 2011

The homogeneous catalytic hydrosilation-hydrogenation of pyridines is observed in the presence of Cp2TiMe2 (Cp = η5-C5H5) and CpCp*TiMe2 (Cp* = η5-C5Me5) as catalysts and using PhSiH3 or PhMeSiH2 as the source of Si-H. Under appropriate conditions, and with appropriate ring-substitution, good yields of the N-silyl-dihydropyridine or N-silyltetrahydropyridine products are be obtained. Although complete saturation is not achieved with organosilane alone, carrying out the reaction under moderate H2 pressures can give excellent yields of N-silylpiperidines. Under moderate pressures of H2, [Cp2TiH]2 catalyzes rapid H-D exchange between H2 and the 2- and 6-positions of C5D5N. Under the same conditions, only traces of hydrogenation are observed. This, together with the regioselectivity of 3-picoline hydrosilation-hydrogenation, leads to the conclusion that the key step in the reaction is probably addition of Ti-Si to C=N.Key words: hydrosilation, hydrogenation, pyridines, dimethyltitanocene, catalysis.
Intervalence transfer in a new benzotriazolate bridged ruthenium-iron complex
Authors: Rocha Reginaldo C , Toma Henrique E
Published: April 2011

The unsymmetrical dinuclear rutheniumiron complexes [(NH3)5RubtaFe(CN)5]n(where bta = benzotriazolate; n = 2, 1, 0) were prepared as solid sodium salts from [RuII(NH3)5(bta)]+or [RuIII(NH3)5(bta)]2+and [FeII(CN)5(H2O)]3and characterized in aqueous solution by means of electrochemical and spectroelectrochemical methods. UV-vis, near-infrared, IR, and cyclic and differential pulse voltammetry data suggest that the related mixed valent species belong to a valence trapped formulation, featuring localized Ru(III) and Fe(II) oxidation states. In spite of the class II categorization in the Robin and Day scheme, this system shows a remarkable metalmetal electronic coupling, as deduced from an intense, low-energy, and very broad intervalence band in the near-IR region. In addition, the mixed valence state displays enhanced stabilization in relation to the isovalent state. The intervalence transfer properties are discussed on the basis of Hush's theory.Key words: ammineruthenium complexes, cyanoiron complexes, mixed valence, intervalence, benzotriazole, benzotriazolate.
Solvation of a water molecule in cyclohexane and water
Authors: Graziano Giuseppe
Published: April 2011

Reliable values for the thermodynamic functions associated with the solvation of a water molecule in its own liquid phase and in cyclohexane, at 25°C, are obtained using experimental data from different investigations. They are successfully rationalized by means of a general theory of solvation. The standard Gibbs energy change is given by the balance of two contrasting terms: the work to create a cavity in the solvent suitable to host the water molecule; and the work to turn on the water-solvent interactions. It proves that the work of cavity creation is largely overwhelmed by the formation of two H-bonds in liquid water, whereas it is almost exactly counterbalanced by the establishment of van der Waals interactions in liquid cyclohexane.Key words: water, cavity creation, H-bonds, van der Waals interactions.
Synthesis and characterization of the pentadentate macrobicyclic ligand, 14-thia-1,4,8,11-tetraazabicyclo[9.5.3]nonadecane (L1) and its nickel(II) complexes. X-ray crystal structure of [Ni(L1)(ClO4)](ClO4)·2[Ni(L1)(OH2)](ClO4)2·6H2O
Authors: Coulter Kevin R , McAuley Alexander , Rettig Steven
Published: April 2011

The pentadentate macrobicycle,14-thia-1,4,8,11-tetraazabicyclo[9.5.3]nonadecane (L1), has been synthesized by high dilution cyclization of 1-thia-4,8-diazacyclododecane ([10]aneN2S) (2) with N,N'-bis(α-chloro acetamido) propane (3) and subsequent reduction of the di-oxo intermediate. The structure of the [Ni(L1)(ClO4)](ClO4)·2[Ni(L1)(OH2)](ClO4)2·6H2O complex (monoclinic, P21/c, a = 13.9261(4) Å, b = 30.279(2) Å, c = 17.1248(3) Å, β = 94.5065(3)°) at R = 0.039 (Rw = 0.034) for 911 parameters using 18 266 reflections with I > 3σI has been determined. The ligand adopts a trans-III configuration. The Ni(II) ion is pseudooctahedral with Ni-S = 2.3896(10) Å in [Ni(L1)(ClO4)]+ and 2.4193(10) Å, 2.4225(10) Å, in the two [Ni(L1)(H2O)]2+ cations. Both nickel(II) and nickel(III) complexes are six-coordinate in solution. Oxidation of the [Ni(L1)(OH2)]2+ complex with K2S2O8 in aqueous solution yielded an ESR active Ni(III) species and the frozen solution spectrum displayed axial symmetry with g[Formula: see text] = 2.159 and g|| = 2.024. In CH3CN, the [Ni(L1)(solv)]2+ complex showed two reversible redox waves corresponding to the Ni2+/+ couple at E1/2 = -1.807 V vs. Fc+/0 and Ni3+/2+ couple at E1/2 = 0.715 V vs. Fc+/0.Key words: synthesis, structure, polydentate macrobicycle, nickel(II).
The life, death, and ROMP activity of ruthenium complexes containing the basic, chelating diphosphine bis(dicyclohexyl)-1,4-phosphinobutane
Authors: Amoroso Dino , Yap Glenn PA , Fogg Deryn E
Published: April 2011

Reaction of RuCl2(PPh3)3with bis(dicyclohexyl)-1,4-phosphinobutane (dcypb) under N2affords access to a formerly elusive family of dcypb complexes based on the RuCl2(PP) core. Under Ar or vacuum atmosphere, decomposition occurs via Ru-promoted dehydrogenation of the dcypb ligand. While the N2-stabilized species [RuCl2(dcypb)]2(N2) (4a) is easily handled under N2in nonchlorinated solvents, reaction with chlorinated solvents rapidly yields paramagnetic Ru2Cl5(dcypb)2(5). The N2ligand within 4a is readily displaced under H2or CO atmosphere, yielding Ru2Cl4(dcypb)2(H2) (6) or RuCl2(dcypb)(CO)2, the latter as a mixture of ccc-(7) and tcc-(8) isomers. Benzylidene derivative RuCl2(dcypb)(CHPh) (1a), prepared in situ by reaction of 4a with PhCHN2, proves exceptionally active in ring-opening metathesis polymerization (ROMP) of norbornene. The X-ray crystal structure of 5 is reported: triclinic, a = 13.390(2), b = 15.726(2), c = 19.524(2) Å, α = 77.325(2), β = 70.964(2), γ = 73.478(2)°, with space group P[Formula: see text] and Z = 2.Key words: ruthenium, alkylphosphine, dehydrogenation, carbene, metathesis, crystal structure.
The Heck reaction in the production of fine chemicals
Authors: de Vries Johannes G
Published: April 2011

An overview is given of the use of the Heck reaction for the production of fine chemicals. Five commercial products have been identified that are produced on a scale in excess of 1 ton/year. The herbicide Prosulfuron(tm)is produced via a Matsuda reaction of 2-sulfonatobenzenediazonium on 3,3,3-trifluoropropene. The sunscreen agent 2-ethylhexyl p-methoxy-cinnamate has been produced on pilot scale using Pd/C as catalyst. Naproxen(tm)is produced via the Heck reaction of 2-bromo-6-methoxy-naphthalene on ethylene, followed by carbonylation of the product. Monomers for coatings are produced via a Heck reaction on 2-bromo-benzocyclobutene. A key step in the production of the antiasthma agent Singulair(tm)is the use of the Heck reaction of methyl 2-iodo-benzoate on allylic alcohol (18) to give ketone (20). The high cost of palladium has spurred much research aimed at the development of more active palladium catalysts. Ligandless catalysts are very attractive for production, but work only on reactive substrates. Palladacycles are much more stable than Pd-phosphine complexes and can be used at higher temperatures. The same effect has been reached with pincer ligands. Bulky ligands lead to coordinatively unsaturated Pd-complexes, which are highly active for the Heck reaction. Recycle of palladium catalysts is also very important to reduce cost. Immobilization of catalysts by attaching ligands to solid support is not very useful, because of leaching and reduced activity. In ligandless Heck reactions the catalyst can be precipitated on carriers such as silica, dicalite, or celite. This material can be restored to its original activity by treatment with I2or Br2.Key words: homogeneous catalysis, palladium, arylation, olefination, ligandless, catalyst recycle.
New pathways of site selective aromatic alkylation of palladium complexes: fragmentation to arenes vs. ring closure to hexahydromethano-fluorenes or -phenanthrenes
Authors: Catellani Marta , Cugini Federica , Tiefenthaler Domenico
Published: April 2011

Dimeric arylbicycloheptylpalladium halide complexes of type 1 undergo selective alkylation at the aromatic site by reaction with allyl, styryl, and benzyl bromides (RBr) via hexahydromethanopalladafluorenes (2). Ring closure of the resulting palladium complex (7) on sp2 and sp3 C-H bonds of a suitable R group then occurs with formation of hexahydromethanophenanthrene or hexahydromethanofluorene derivatives. Alternatively, substituted arenes derived from bicycloheptene deinsertion are formed. In some cases the latter can be obtained in substantial amounts when methyl isonicotinate is used as ligand.Key words: alkylations, C-H activation, palladium, palladacycles.
A DFT study of Zr-S rotational barriers of (η5-C5H5)2Zr(Cl)(SR); the origin of an inverse steric effect
Authors: Das P K , Alguindigue Susan Stanislav , Ashby Michael T
Published: April 2011

We have previously reported the experimental rotational barriers about the MS bonds of 16e bent metallocene monothiolates (η5-C5H5)2Zr(Cl)(SR) (R = CH3, CH2CH3, CH(CH3)2, C(CH3)3] (1ad): 32, 33, 35, and 26 kJ mol1, respectively. The ground-state orientation about the ZrS bonds of 1 that maximizes S(pπ) [Formula: see text] M(dπ) bonding (Cl-Zr-S-R [Formula: see text] 90°) also maximizes Cp « R (Cp = η5-C5H5) steric interaction, whereas the rotational transition-state orientation (Cl-Zr-S-R [Formula: see text] 0°) is one that minimizes S(pπ) [Formula: see text] M(dπ) bonding and maximizes Cl « R steric interaction. Deviation from a ground-state orientation that is ideal for S(pπ ) [Formula: see text] M(dπ ) bonding might be expected as the size of the R-group and Cp « R steric interaction increases. The present study employs hybrid density function computational methods to reproduce the experimental rotational barriers. The computational rotational barriers decrease in the order 1a (R = CH3) > 1b (R = CH2CH3) > 1c (R = CH(CH3)2) at low temperature. However, opposing enthalpic factors reverse this trend at higher temperatures. The aberrant trend (unexpectedly low rotational barrier) that is observed for the 1d (R = C(CH3)3) derivative is due to dominant ground-state steric (enthalpic) effects. We conclude the thiolate ligand of 1d is misdirected in the ground-state with respect to the other thiolate derivatives.Key words: misdirected ligands, metallocene, thiolate, structure, bonding, dynamics.
An easy-to-use heterogeneous catalyst for the Knoevenagel condensation
Authors: Siebenhaar Bernd , Casagrande Bruno , Studer Martin , Blaser Hans-Ulrich
Published: April 2011

Physical mixtures of alkali and earth alkali metal carbonates and commercially available zeolites were investigated as solid catalysts for the Knoevenagel condensation. Best results for the model reaction between benzaldehyde and ethyl cyanoacetate were obtained for a 1:4 mixture of Na2CO3 with 4 Å molecular sieves (MS). The effects of the following parameters were investigated: structure of substrate, type and basicity of metal carbonate and zeolite, and temperature. Between 50 and 90°C chemical yields up to >90% were obtained without continuous removal of water and with reasonable catalyst activities and reaction times. Na2CO3  MS 4 Å proved to be active for the condensation of several aldehydes and ketones with a variety of active methylene components.Key words: Knoevenagel condensation, solid basic catalysts, zeolite  sodium carbonate mixtures.
Original disymmetric bolaforms bearing at least one sulfobetaine head; synthesis and surface properties
Authors: Souirti Souad , Baboulène Michel
Published: April 2011

We describe a simple and efficient method for the synthesis of disymmetric bolaforms bearing at least one sulfobetaine head. In this process, we could introduce successively on α, ω-bis(dialkylamino) alkane a sulfobetaine head and a cationic, a sulfobetaine, or a carboxybetaine head, in excellent yield. This is the first synthesis of disymmetric sulfobetaine bolaforms. The method is easily generalized to various types of head functional groups. The wide range of bolaforms produced by this method has been exploited to study their surface properties and to determine the respective roles of the polar heads and the lengths of the spacers (n) on self-aggregation in aqueous media. A critical micellar concentration (cmc) was observed with the compounds with a spacer of 12 carbon atoms (n = 12). Micellization appeared to be consistent with a "wicket-like" conformation, which did not appear to form with the n = 8 compounds.Key words: disymmetric bolaform, sulfobetaine, carboxybetaine, cationic amphiphile, synthesis, surface properties.
A convenient and selective route to a trans-difunctionalized macrocyclic hexadentate N4O2 ligand
Authors: Luo Hongyan , Rogers Robin D , Brechbiel Martin W
Published: April 2011

The synthesis and characterization of a novel difunctionalized tetraaza macrocycle, 1,8-bis(2-hydroxybenzyl)-1,4,8,11-tetraazacyclotetradecane (abbreviated H2bcyclamb), is described. The diprotic hexadentate ligand N4O2 was conveniently synthesized in two steps by the cyclic condensation reaction of 1,4,8,11-tetraazacyclotetradecane (abbreviated cyclam) and salicylaldehyde, followed by NaBH4 reduction of the cyclic hexahydropyrimidine condensate. The difunctionalization was selective and is the first procedure of trans-difunctionalization of a tetraazamacrocycle, without generating mono-, tri-, or tetra-functionalized products, with only 1,8-difunctionalized product being isolated, and with the convenience of the functionalization occurring as a result of deprotection. The trans-arrangement of the two functional groups in H2bcyclamb was verified by X-ray crystallographic studies of the copper(II) complex [Cu(H2bcyclamb)](OAc)2·2H2O. The crystal is monoclinic, P21/c, with a = 10.0931(2), b = 13.8820(1), c = 10.8752(1) Å, β = 106.332(1)°, V = 1462.26(3) Å3. The structure of [Cu(H2bcyclamb)](OAc)2·2H2O also shows the metal ion in an elongated octahedral geometry.Key words: 1,8-difunctionalized, cyclam, copper(II) complex.
Effect of kinetic synergist on transport of copper(II) through a liquid membrane containing P507 in kerosene
Authors: He Dingsheng , Ma Ming , Wang Hui , Zhou Pandeng
Published: April 2011

A new kinetic synergism system for copper(II) transport through a bulk liquid membrane containing mono(2-ethyhexyl)-2-ethyhexyl phosphate and Manoxol OT (OT) was examined. The influence of stripping agent, anion, pH in feed phase, and carrier concentration were investigated. The kinetics of Cu(II) transport could be analyzed in the formalism of two consecutive irreversible first-order reactions, considering both extraction and stripping. The pseudo-first-order apparent rate constants of interfacial reactions in membrane transport are determined by altering the temperature. The activation energy values are 38.1 kJ mol1 for extraction and 32.8 kJ mol1 for stripping. The experiments demonstrated that Manoxol OT is a good kinetic synergist for Cu(II) transport through liquid membranes in this study. The kinetic synergism of OT for extraction of Cu2+ ions is analyzed.Key words: copper ions, kinetic synergist, liquid membrane.
Quinoxaline-1,2,3-dithiazolyls  Synthesis, EPR characterization, and redox chemistry
Authors: Cordes A Wallace , Mingie James R , Oakley Richard T , Reed Robert W , Zhang Hongzhou
Published: April 2011

Oxidation of quinoxalineaminothiol with SCl2 or S2Cl2/Cl2 affords a series of compounds based on the quinoxaline-1,2,3-dithiazole framework QDTA. Under highly oxidizing conditions, the 1,2,3-dithiazolyl ring is opened to afford the acyclic dichlorosulfimino-sulfenyl chlorides Clx-QDTA-Cl3 (x = 0, 1, 2). Reduction of these "trichloro" compounds leads to ring closure. For x = 2, reduction using S2Cl2 affords the dithiazolylium chloride [Cl2-QDTA][Cl]. For all values of x, reduction with iodide ion (3 mol equiv) affords the corresponding dithiazolyl radical [Clx-QDTA]. The radicals can be isolated in good yield in crude form, but attempts to purify them by vacuum sublimation lead to thermal degradation. The radicals have nonetheless been fully characterized by EPR spectroscopy, and the assignments of the observed hyperfine coupling constants cross-matched with those obtained by computation at the B3LYP/6-31G** level. The structures of the trichloro compounds Clx-QDTA-Cl3 (x = 1, 2) have been confirmed by X-ray crystallography. Crystal data: Cl-QDTA-Cl3, monoclinic, space group C2/c, a = 30.561(5) Å, b = 4.9764(9) Å, c = 22.247(4) Å, β = 131.822(14)°, V = 2521.4(8) Å3, Z = 8, R(F) = 0.043, and Rw(F) [I [Formula: see text] σ (I)] = 0.049; Cl2-QDTA-Cl3, orthorhombic, space group Pnma, a = 18.627(12) Å, b = 6.848(4) Å, c = 10.926(7) Å, V = 1393.7(15) Å3, Z = 4, R(F) = 0.047, and Rw(F) [I [Formula: see text] 3σ(I)] = 0.060.Key words: thiazyl radicals, molecular conductors, EPR spectroscopy, quinoxaline, DFT calculations.
Synthesis of highly functionalized naphthoate precursors to damavaricin D  Observation of kinetically stable benzocyclohexadienones in the bromination reactions of highly functionalized β-naphthol derivatives
Authors: Roush William R , Madar David J , Coffey D Scott
Published: April 2011

Selective syntheses of the highly substituted bromonaphthoates 4a, 4b, 19, and 22 are reported. These compounds were targeted as precursors to the naphthoquinone nucleus of damavaricin D; compound 22 ultimately was used in the successful total synthesis. The synthesis of 22 features the DielsAlder reaction of the oxygenated diene 5 and 2,6-dibromo-3-methylbenzoquinone 6 to establish the core naphthalenic unit. The quinone was protected throughout this synthesis as a 1,4-bis-methoxymethyl-1,4-dihydroquinone (see 36). The C-2-carboalkoxy group of 22 was added by carboxylation of the aryllithium intermediate generated from 36, and protected as a β-trimethylsilylethyl ester. Finally, the C-8-Br substituent was introduced by NBS bromination of 38. This reaction proceeds by way of bromobenzocyclohexadienone 39. Related bromobenzo-cyclohexadienones 13 and 29 were observed in the NBS brominations of the highly functionalized β-naphthyl MOM ethers 11 and 28. The bromobenzocyclohexadienones 29 and 39 undergo facile substitution reactions with chloride ion and reduction with bromide ion at rates competitive with base-promoted aromatization. The surprising kinetic stability of these intermediates is attributed to a combination of steric and stereoelectronic factors.Key words: damavaricin D, naphthoate precursors, kinetically stable benzocyclohexadienones, aromatic bromination.