bluuebunny/crossref_metadata_2025 huggingface dataset:
Total synthesis of (±)-9-deoxygoniopypyrone. Application of the iodocyclofunctionalization reaction of bold α-allenic alcohol derivatives
Authors: Friesen Richard W , Bissada Suzanne
Published: April 2011

The synthesis of ( ±)-9-deoxygoniopypyrone (1) from the α-allenic alcohol 5 is described. Iodocyclofunctionaliztion of the N-tosyl carbamate derivative of 5 using I2and Ag2CO3provided, in a highly diastereoselective and regioselective fashion, the vinyl iodo syn-vicinal diol 4. Two routes were explored in order to introduce the third stereogenic centre in the molecule. Reductive deiodination of the vinyl iodide and diastereoselective epoxidation of the derived acetonide14 using mCPBA provided a mixture of epoxides 15 and 16 (2:1) in which the desired threo diastereomer predominated. Alternatively, dihydroxylation of acetonide 14 (OsO4, NMO) yielded a mixture of diols 21 and 22 (2:3) which were separated after monosilylation (TBDMSCl) of the primary alcohol. The major silyl ether erythro diastereomer 24 was converted to the desired epoxide 15 by mesylation (MsCl, Et3N) and epoxide formation (TBAF) with inversion of stereochemistry. The minor threo diastereomer 23 was also converted to the desired epoxide 15 (TBAF; ArSO2Cl; NaOMe). Epoxide opening was effected with lithium acetylide and the resulting alkyne 27 was carbonylated (MeLi, ClCO2Me) to afford the α , β-acetylenic ester 28. Semi hydrogenation over Lindlar's catalyst followed by protecting- group removal under acidic conditions provided ( ±)-8-epigoniodiol 30. Finally, conversion of 30 to ( ±)-9-deoxygoniopypyrone 1 was effected under basic conditions (DBU).Key words: ( ±)-9-deoxygoniopypyrone, α-allenic alcohol, iodocyclofunctionalization, syn-diol.
Article
Authors: Ohta Kiyohisa , Ueda Youko , Nakaguchi Satoshi , Mizuno Takayuki
Published: April 2011

The photocatalytic reduction of CO2using copper-loaded silicate rocks has been reported. The Cu-silicate rock powders suspended in the solution were illuminated with sunlight. Amphibolite, gneiss, granite, granodiorite, phyllite, quartzdiorite, and shale, which are quite ordinary rocks, were tested as substrates (silicate rock) of the catalyst. These catalysts were specific for the formation of formic acid. The effects of amounts of copper, illumination time, and temperature were investigated on photoreduction of CO2. The 30% Cu-loaded quartzdiorite (0.3 g/g) in these Cu rocks was the best catalyst. The formation of formic acid on the Cu-silicate rock increased with time up to 10 h after which the formation decreased, and then became constant. The formic acid formation decreased with temperature for 10 h sunlight illumination. For the photochemical reduction of CO2, a relatively low temperature was suitable. With photochemical reduction, the maximum yield of formic acid was 54 nmol/g under optimum experimental conditions. The carbon dioxide reduction system developed might well become of practical interest for the photochemical production of raw materials for the photochemical industry.Key words: photocatalytic reduction of carbon dioxide, formic acid, copper-loaded silicate rocks, temperature effect, illumination time.
Article
Authors: Refvik Mitchell D , Schwan Adrian L
Published: April 2011

Lithium (E)-1-hexenesulfenate (5a) was treated with a number of TMS-X (TMS = trimethylsilyl) reagents to afford N,N-bis(trimethylsilyl)-(E)-1-hexenesulfenamide (7a) and (or) di((E)-1 hexenyl) disulfide (8), usually in low yield. The cleanest reactions, those from use of TMS-Cl (to afford 7a) and TMS-CN (which yields 8) were analyzed by variable temperature NMR. It was found that the low-temperature silylation reaction using TMS-Cl affords 7a and thiosulfinate 12 as initial products. Warming the mixture coerces the decomposition of 12. Treatment of 5a with TMS-CN also yields thiosulfinate 12 which is reduced to disulfide 8 as the temperature warms, possibly by action of cyanide ion. Evidence is presented that allows a confident structural assignment of the transient thiosulfinate 12, and mechanisms are suggested for the formation of 12. The study also led to the NMR observation of (E)-1-hexenesulfenate (5a).Key words: sulfenate, thiosulfinate, variable temperature NMR (VT NMR), silylation.
Lactams in sulfuric acid. The mechanism of amide hydrolysis in weak to moderately strong aqueous mineral acid media
Authors: Cox Robin A
Published: April 2011

Reaction rate constants obtained in moderately concentrated sulfuric acid for the hydrolysis of simple lactams of ring sizes five, six, seven, and eight as a function of acidity and temperature have been analyzed using the excess acidity kinetic method. The basicity constants for these substrates have been recalculated; the 13C NMR spectra used to obtain these values are very sensitive to medium effects. It was found that the basicities of the lactams at 0.003-0.1 M lactam concentration were over half a pK unit more basic than they were at 0.5 M lactam, presumably because of the medium effect. Apart from this, the rate constant results obtained at different times by different groups using different techniques for monitoring the kinetics are in adequate agreement. The excess acidity analysis showed that the kinetics could be fitted according to the "three-water-molecule followed by one-water-molecule" mechanistic scenario previously found, or could just as well be fitted by a "one-water-molecule followed by unknown mechanism" scenario, with the mechanistic change taking place at 50 wt.% sulfuric acid for all the substrates. Other evidence makes the latter seem the more likely possibility of the two, and activation parameters based upon the "one-water-molecule" process were determined. Sufficient data points to enable the unknown mechanism to be established were not present; possible mechanisms applicable in media more concentrated than 50 wt.% sulfuric acid are discussed. Previously obtained values of the parameter r, the number of water molecules involved with the substrate in A2 processes, are now questionable.Key words: amides, lactams, excess acidity, hydrolysis, mechanism.
Carbon versus oxygen nucleophilic selectivity in the reaction of the aryloxide ions, 2,6- and 3,5-di-tert-butylphenoxide, with the 2-[(nitro)\dn6 xaryl]-4,6-dinitrobenzotriazole 1-oxide series of super-electrophiles. Stereoelectronic factors on C-7 Meisenheimer complex formation versus C-1' SNAr displacement
Authors: Dust Julian M , Manderville Richard A
Published: April 2011

The 2-[(nitro)xaryl]-4,6-dinitrobenzotriazole 1-oxides (1, Pi-DNBT (x = 3); 2, DNP-DNBT (x = 2); 3, NP-DNBT (x = 1)) are electron-deficient nitro-substituted heteroaromatic substrates that possess two sites for nucleophilic attachment: C-7 and C-1'. Generally, attack at the super-electrophilic C-7 site yields spectroscopically observable anionic sigma -bonded adducts, whereas attack at C-1' leads to displacement products in an overall process of nucleophilic aromatic substitution (SNAr). To gain an understanding of the factors affecting C-1' versus C-7 attack by potentially ambident aryloxide (C- and O-)nucleophiles, we have monitored the reactions of 1-3 with 2,6-di-tert-butylphenoxide (2,6-ArO-) and 3,5-di-tert-butylphenoxide (3,5-ArO-) using 400 MHz 1H NMR spectroscopy (deuterated dimethyl sulfoxide solvent at ambient temperature). The results indicate that 2,6-ArO- acts only as a C-nucleophile with O-attack precluded, presumably by the sterically demanding tert-butyl groups flanking the O-nucleophilic centre. Although 2,6-ArO- reacts preferentially at C-7 of 1-3, the biphenyl derivative that arises from C-1' attack is also observed with 1, the first time that C-nucleophilic attack has been seen at this electrophilic site. In contrast, 3,5-ArO- acts only as an O-nucleophile, also as a consequence of the steric hindrance to the C-4 position; this aryloxide reacts entirely at C-1' of Pi-DNBT but also exclusively at C-7 of 3. However, with DNP-DNBT, 2, both the C-7 O-adduct and C-1' displacement products are noted; attack at C-1' is dominant. The selectivity (C-7 versus C-1') found in these reactions is discussed with emphasis given to stereoelectronic factors that may stabilize the putative C-1' O-adducts.Key words: aryloxides, super-electrophiles, Meisenheimer complexes, 2-[(nitro)xaryl]-4,6-dinitrobenzotriazole 1-oxides.
New heterocycles from thienopyridocinnolines
Authors: Badr M ZA , Geies A A , Abbady M S , Dahy A A
Published: April 2011

3-Cyano-4-(p-tolyl)pyrido[3,2-c]cinnolin-2(1H) thione 3 was reacted with α -halo ketones, esters, or amides to give the intermediates, S-alkylated products 5b-h, respectively, which underwent intramolecular ring closure reactions with ethanolic sodium ethoxide to give thienopyridocinnolines 6a-h. Pyrimidothienopyridocinnolines 9 and 11 were obtained by treatment of oxazino compound 8 with hydrazine hydrate and ammonium acetate. Treatment of hydrazino derivative 13 with acetylacetone, triethylorthoformate, carbon disulphide, ethyl chloroformate, and acetic anhydride afforded triazolopyrimidothienopyridocinnolines 14-16, 18, and 21, while with nitrous acid the corresponding tetrazolo compound 19 was produced.Key words: thienopyridocinnolines; their pyrimido, triazolopyrimido, and heteroannelated systems.
Article
Authors: Ruelle Paul , Kesselring Ulrich W
Published: April 2011

The volume fraction solubilities of a number of solid n-fatty alcohols and sterols are predicted in neat organic nonpolar, polar, and hydrogen-bonded solvents including water. In the frame of the mobile order thermodynamics, the predictions are based on the knowledge (a) of the melting properties of the alcohols, which affect the fluidization process, (b) of their molar size, which mainly rules the exchange entropy and the hydrophobic effect, and (c) of the group interaction stability constants, which are responsible for the balance between the competing self-association and strong intermolecular interactions of the alcohols in solution. Owing to its ability to deal properly with these various elementary processes, the proposed thermodynamic solubility model derived from the mobile order theory in H-bonded liquids represents an advance towards reliable and comprehensive estimates of the solubilizing capacity of common solvents for nonideal complexing systems, i.e., the solid alcohols.Key words: solubility prediction, solution thermodynamics, mobile order theory, n-fatty alcohols, sterols.
On the possibility of conversion of strained bridgehead alkenes into carbenes via 1,2 hydrogen and 1,2 carbon migrations. A theoretical study of the rearrangements in the adamantene and protoadamantene systems
Authors: Shustov Gennady V , Liu Michael TH
Published: April 2011

Rearrangements of 2-adamantene 3, adamantylidene 4, and 4-protoadamantylidene 5 have been studied theoretically using high level ab initio computations. Adamantene 3 and adamantylidene 4 have singlet ground states. The conversion of 3 into 4 via 1,2 hydrogen migration ( Δ Gdouble dagger = 69.1 kcal mol-1) cannot compete with 1,2 carbon migration of 3 to 5 (30.3 kcal mol-1). The singlet carbene 5 rearranges to 2,4-dehydroadamantane 6 and 4,5-protoadamantene 9 via 1,3H and 1,2H shifts, respectively, with identical activation barriers of 8.8 kcal mol-1. The 1,2 migration of the bridge hydrogen in 5 leading to 3,4 protoadamantene 8 has a higher activation barrier (37.2 kcal mol-1). A retro Diels-Alder cycloaddition of 3 to 5-allyl-3-methylenecyclohex-1-ene 7 is the main channel of the unimolecular conversion of 3 ( Δ Gdouble dagger = 20.5 kcal mol-1). A predicted ratio of 7 > > 6 approx 9 of the products of thermolysis of 3 is in agreement with experimental data. The rearrangement of 4 into 6 via the 1,3H shift ( Δ Gdouble dagger = 11.8 kcal mol-1) dominates over the 1,2C shift of 4 to 8 (13.5 kcal mol-1), also in accord with experiment.Key words: adamantene, protoadamantenes, carbenes, rearrangements, ab initio, computation.
On the role of copper and iron in DNA cleavage by ochratoxin A. Structure-activity relationships in metal binding and copper-mediated DNA cleavage
Authors: Ardus Jason A , Gillman Ivan G , Manderville Richard A
Published: April 2011

Ochratoxin A (OTA, 1: X = Cl) is a fungal carcinogen that facilitates single-strand DNA cleavage and DNA adduction when metabolically activated. To determine if redox-active transition metals induce OTA-mediated DNA damage, we have examined the toxin's ability to bind Cu(II) and Fe(III) in aqueous media and facilitate DNA cleavage in their presence using agarose gel electrophoresis and supercoiled plasmid DNA. Using fluorescence spectroscopy, 1 was found to bind Cu(II) readily at physiological pH, while acidic conditions (pH 2.6) were employed to study Fe(III) binding due to the formation of Fe-oxide precipitates at higher pH values. Structure-activity relationships employing synthetic derivatives of 1 implied that 1 binds both Cu(II) and Fe(III) by its phenolic oxygen, while the carboxylic acid of its phenylalanine moiety binds Cu(II), but does not appear to play a role in Fe(III) coordination at pH 2.6. In terms of metal-mediated DNA cleavage, no role for 1 could be detected in Fe-induced DNA strand scission. With Cu(II), DNA cleavage by the 1:1 copper-bound complex of 1 could only be initiated by addition of a suitable reducing agent (sodium ascorbate). However, 1 was found to facilitate DNA cleavage by the Cu(II) complex of 1,10-phenanthroline (Cu(OP)2); a prototypical Cu-mediated nuclease system that cleaves DNA upon activation by an external reducing agent. Structure-activity relationships employing analogs lacking the chlorine atom, ochratoxin B (2: X = H), and the lactone (12), indicated that the chlorine atom is essential for activity of the OTA in potentiating DNA cleavage by Cu(OP)2. The implications of our findings to the genotoxic properties of 1 are discussed.Key words: ochratoxin, DNA cleavage, copper, iron, 1,10-phenanthroline.
Catalysis by topologically anchored metal complexes. Liquid-phase hydroxylation of benzene by H2O2 in the presence of zeolite-supported Fe(II) phthalocyanine
Authors: Zefirov Nikolai S , Zakharov Alexandre N
Published: April 2011

Fe(II) phthalocyanine topologically anchored on NaA zeolite has been prepared. The catalytic activity of zeolite-supported Fe(II) phthalocyanine has been studied in the liquid-phase hydroxylation of benzene by H2O2. The main product of the reaction at room temperature is phenol. By refluxing, the reaction proceeds to give the products of subsequent oxidation, i.e., hydroquinone and p-benzoquinone, in low yields.Key words: topologically anchored Fe(II) phthalocyanine, catalysis, oxidation, benzene, phenol.
C-(2-Hydroxyaryl)-N-(2-hydroxyphenylmethyl)nitrones as regioselective bidentate ligands in boron chelate formation. Crystal and molecular structures of a diphenylboron complex and its parent ligand
Authors: Kliegel Wolfgang , Metge Jörg , Rettig Steven J , Trotter James
Published: April 2011

The C-(2-hydroxyaryl)-N-(2-hydroxyphenylmethyl)nitrones 5 are synthesized by the condensation of variously substituted salicylaldehydes with N-(2-hydroxyphenylmethyl)-hydroxylamine. These nitrones react with diphenylborinic acid anhydride to form seven-membered diphenylboron chelates 6. Crystals of C-(4-diethylamino-2-hydroxyphenyl)-N-(2-hydroxyphenylmethyl)nitrone, 5d, are monoclinic, a = 6.911(2), b = 10.663(2), c = 22.951(1) Å, β = 97.33(1)°, Z = 4, space group P21/n, and those of 4-dimethylamino-8-(2-hydroxyphenylmethyl)-6,6-diphenyl-5,7-dioxa-8-azonia-6-borata-6,7-dihydro-5H-benzocycloheptene-ethanol, 6d·EtOH, are monoclinic, a = 9.069(2), b = 29.881(1), c = 11.1883(6) Å, β = 109.426(9)°, Z = 4, space group P21/n. The structures were solved by direct methods and refined by full-matrix least-squares procedures to R = 0.032 and 0.039 (R w = 0.031 and 0.036) for 2510 and 4162 reflections with I > 3σ(I), respectively. Key words : C-(2-hydroxyaryl)-N-(2-hydroxyphenylmethyl)nitrones, organoboron compounds, crystal structures.
Article
Authors: Veinot Jonathan GC , Galloro Josie , Pugliese Linda , Bell Valerie , Pestrin Robert , Pietro William J
Published: April 2011

The preparation, characterization, properties, and reactivity of a novel quantum-confined CdS nanocluster containing a chemically active aniline surface are described, along with three general methods for the covalent attachment of a wide scope of molecular moieties to the cluster surface. The formation of facile covalent linkages via DCC mediated amidization, secondary amine formation, and thiourea condensation is discussed and, as the introduction of surface functionality is crucial for the eventual realization of molecular electronic devices fabricated from such nanoclusters, several derivatized nanoclusters bearing interesting chromophoric, fluorescent, electroactive, and chiroptical tethered species are described. All three derivatization techniques occur under very mild conditions that have been demonstrated not to disturb the integrity of the nanocluster core.Key words: quantum dot, nanocluster, semiconductor, surface-functionalized, nanostructured.
Formation of mixed-ligand fluoroboron cations involving C=N donors. A 19F and 11B NMR study
Authors: Hartman J Stephen , Ilnicki Elizabeth I , Shoemaker James AW , Szerminski Wojciech R , Yuan Zheng
Published: April 2011

Mixed-donor difluoroboron and chlorofluoroboron cations DD'BF2+ and DD'BFCl+ involving at least one C=N donor molecule can be formed by Cl- displacement from the mixed boron trihalide adducts D·BF2Cl and D·BFCl2, provided that the steric hindrance of D' and especially D is not too great. The DD'BF2+ cations can also be formed by selective displacement of one donor molecule in certain D2BF2+ cations, present in acetone as their PF6- salts, allowing isolation of the first salt of a mixed-donor difluoroboron cation, (quinuclidine)(pyridine)BF2+·PF6-. In less favourable cases, however, either no reaction occurs or the reaction continues to give D'2BF2+. Reactivities and 19F and 11B NMR parameters of mixed boron trihalide adducts and fluoroboron cations of a number of C=N donors are reported.Key words: fluoroboron cations, mixed-ligand, fluorine-19 NMR, boron-11 NMR, oxazolines, thiazolines, C=N donors.
Gold nanoclusters reductively deposited on porous silicon: morphology and electronic structures
Authors: Coulthard I , Degen S , Zhu Y -J , Sham T K
Published: April 2011

Utilizing porous silicon as a reducing agent and a substrate, gold complex ions [AuCl4]- were reduced from aqueous solution to produce nanoparticles of gold upon the surface of porous silicon. Scanning electron microscopy (SEM) was utilized to study the morphology of the porous silicon layers and the deposits of gold nanoparticles. It is found that preparation conditions have a profound effect on the morphology of the deposits, especially on porous silicon prepared from a p-type wafer. The gold nanoparticles, varying from micrometric aggregates of clusters of the order of 10 nm, to a distribution of nearly spherical clusters of the order of 10 nm, to strings of ~10 nm were observed and compared to bulk gold metal using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS). These techniques confirm and complement the SEM findings. The potential for this reductive deposition technique is noted.Key words: gold nanostructures, reductive deposition, porous silicon, morphology, X-ray spectroscopy.
Synthesis and characterization of homoleptic ruthenium(II) imidazole complexes, and a carbonyl species derived by CO abstraction from DMF
Authors: Baird Ian R , Rettig Steven J , James Brian R , Skov Kirsten A
Published: April 2011

[Ru(II)(L)6]2+ complexes were synthesized from [Ru(DMF)6][CF3SO3]3; DMF = dimethylformamide, L = imidazole (Im), N-methylimidazole (NMeIm) and 5-methylimidazole (5MeIm). The 2-methylimidazole complex trans-[Ru(CO)(DMF)(2MeIm)4][CF3SO3]2 (4) was also synthesized via a reaction involving abstraction of CO from DMF; 4 loses CO reversibly at ambient temperature to form [Ru(DMF)(2MeIm)4][CF3SO3]2 (5), and the DMF can be removed to generate a [Ru(CF3SO3)x(2MeIm)4][CF3SO3]y species (x = 2, y = 0, or x = 1 = y), containing coordinated triflate. The complexes were characterized by elemental analysis, conductivity, UV-vis, NMR, and IR spectroscopies. The structures of [Ru(Im)6][CF3SO3]2 (1), [Ru(NMeIm)6][CF3SO3]2 (2), and [Ru(5MeIm)6][CF3SO3]2 (3) were established by X-ray crystallographic analyses. Crystals of 1, are triclinic, a = 7.4010(6), b = 9.9846(15), c = 11.275(2) Å, α = 113.469(5), β = 92.419(2), γ = 94.737(2)°, Z = 1, space group P1 ; those of 2, are trigonal, a = 11.558(2), c = 8.109(3) Å, Z = 1, space group P3; and those of 3, are trigonal, a = 12.6547(4), c = 20.4078(12) Å, Z = 3, space group R3. The structures were solved by Patterson methods and refined by full-matrix least-squares procedures to R(F) = 0.029, 0.034, and 0.034 (R w (F2) = 0.055, R w (F) = 0.031, and R w (F2) = 0.058), respectively. Key words: hexakis(imidazole)ruthenium(II) triflates, crystal structures, CO abstraction.
Synthesis, structure, and reactivity of macro cyclic heterobimetallic complexes of (Co, Cu), (Co, Ni), (Co, Zn), (Zn, Cu), (Zn, Ni) combinations
Authors: Golchoubian H , Waltz W L , Quail J W
Published: April 2011

A series of macrocyclic heterobimetallic complexes of type [Mc(tntnam)Mo](PF6)n and [Mc'(tntnim)Ni](PF6)n where Mc = Co(III) and Zn(II), Mc' = Co(II), Co(III), and Zn(II), and Mo = Ni(II), Cu(II), and Zn(II) have been synthesized and characterized. The macrocyclic ligands tntnim 2 and tntnam 3 contain two geometrically distinct compartments, 6-coordinate (closed site) and 4-coordinate (open site), which are bridged by phenolic oxygens. The heterobimetallic complexes with Zn(II) or Ni(II) in the open site are primarily formed as 5-coordinate with a chloride ion as a fifth ligand; the latter can be removed by Ag+ ion. The crystal structures of [Zn(tntnim)NiCl]PF6·C2H5OH, 5, [Zn(tntnam)Ni](PF6)2, 11, [Zn(tntnam)Cu](PF6)2, 12, and [Co(tntnam)Ni(H2O)](PF6)3·4H2O, 14 were determined. Crystal data for 5: monoclinic, T = 123 K, a = 15.822(2), b = 15.6230(10), c = 16.432(2) Å, β = 104.570(10)°, Z = 4, space group Pc, R = 0.0371 (wR2 = 0.0843) for 5826 reflections with I [Formula: see text] 2σ(I). Crystal data for 11: tetragonal, T = 123 K, a = b = 24.122(2), c = 14.397(7) Å, Z = 8, space group P41212, R = 0.0625 (wR2 = 0.1549) for 3250 reflections with I [Formula: see text] 2σ(I). Crystal data for 12: tetragonal, T = 123 K, a = b = 24.180(2), c = 14.281(4) Å, Z = 8, space group P41212, R = 0.0588 (wR2 = 0.1219) for 3452 reflections with I [Formula: see text] 2σ(I). Crystal data for 14: triclinic, T = 287 K, a = 12.664(2), b = 12.983(2), c = 16.216(3) Å, α = 80.317(14)°, β = 69.585(12)°, γ = 74.791(12)°, Z = 2, space group P[Formula: see text], R = 0.0573 (wR2 = 0.1332) for 3443 reflections with I [Formula: see text] 2σ(I). The structures were solved by direct methods and refined by full-matrix least-squares procedures. The crystal structures demonstrate that the expected trans pyridine structures are formed. The magnetic moments, electrospray mass spectra, electronic absorption and emission spectra, and redox couples are reported. Key words: cobalt, copper, nickel, zinc, heterobimetallic, macrocycle.
Synthesis, structure, and solution dynamics of indenyl rhodium complexes containing bulky phosphine ligands: molecular structures of (η5-1-CH3-C9H6)Rh(η2-C2H4)(PCy3) (Cy = cyclohexyl) and (η5-1-CH3-C9H6)Rh(dcpe) (dcpe = Cy2PCH2CH2PCy2)
Authors: Westcott Stephen A , Kakkar Ashok K , Taylor Nicholas J , Roe D Christopher , Marder Todd B
Published: April 2011

Reactions of (η5-1-CH3-C9H6)Rh(η2-C2H4)2 with PCy3 (Cy = cyclohexyl) and 1,2-bis(dicyclohexylphos - phino)ethane (dcpe = Cy2PCH2CH2PCy2) gave complexes (η5-1-CH3-C9H6)Rh(η2-C2H4)(PCy3) (1) and (η5-1-CH3-C9H6)Rh(dcpe) (2), respectively, in high yields. Complexes 1 and 2 were characterized by x-ray diffraction studies and by multinuclear NMR spectroscopy. Variable temperature 31P{1H} NMR spectra allowed for evaluation of energy barriers associated with indenyl ring rotation. While 1 and 2 displayed similar degrees of slip-fold distortion with respect to bonding of the indenyl ligand to the RhL2 fragment, a lower energy barrier to ring rotation was calculated for the mixed ethylene-phosphine complex 1. Yellow crystals of 1 are orthorhombic, Pbca with 16 molecules per unit cell of dimensions a = 11.341(3), b = 32.915(10), and c = 29.413(9) Å. Yellow crystals of 2 are triclinic, P1 with two molecules per unit cell dimensions a = 9.327(3), b = 10.117(3), c = 18.934(6) Å, α = 104.28(2)°, β = 101.34(2)°, and γ = 92.99(2)°.Key words: indenyl, rhodium, phosphines, ring-slippage.
Electronic effects on enol acidity and keto-enol equilibrium constants for ring-substituted 2-tetralones
Authors: Yao Xudong , Pollack Ralph M
Published: April 2011

Equilibrium constants for the ionization of a variety of phenyl-substituted 2-tetralones (pKaK), for the ionization of their enols (pKaE), and for keto-enol tautomerization (pKE) were determined. Hammett plots of pKaKand pKaEvs. σ-are linear with slopes (-ρ) of -1.66 ± 0.06 and -0.90 ± 0.03, respectively, except for deviations of the points corresponding to 6-nitro-2-tetralone (1b) and its enol. We have previously attributed the negative deviation of 1b from the correlation for the acidities of the ketones obtained with the more limited set of data to the lack of a free electron pair on C-1 of the free tetralone (Nevy et al.). The negative deviation of the point for 1b from the correlation for the acidities of the enols suggests that charge transfer from the hydroxyl group of the enol to the nitro group is less important than it is for phenols. This study represents the first systematic study of electronic effects on equilibria among ketone, enol, and enolate in aqueous solution. Key words: enol, acidity, equilibrium, substituent, conjugation.
The properties of a family of two-headed surfactant systems: the 4-alkyl-3-sulfosuccinates 2. Surface properties of alkyl sulfosuccinate micelles
Authors: MacInnis Judith A , Boucher Greg D , Palepu R , Marangoni D Gerrard
Published: April 2011

The micellar properties of a family of two-headed surfactants, the alkyl sulfosuccinates, were investigated employing fluorescence, ultra-violet spectroscopy, and acid-base titrations, as a function of the chain length of the surfactant. Polarity of the micellar interior was investigated using pyrene and the ionic probe 8-anilino-1-naphthalensulfonic acid ammonium salt (ANS). Pyrene I1/I3 ratios were used to probe the microenvironment of the probe in the palisade layer of the micelle. The pKa values of both of the anionic head groups were determined using acid-base titrations. Surface potential measurements were obtained from the measurement of the pKa of the hydrophobic indicator, 7-hydroxycoumarin, at the sulfosuccinate micellar interface. All of these results were used to examine the surface properties of the alkyl sulfosuccinate micelles and the polarity of the micellar interior.Key words: micellization, pKa, surface potential, surface charge density, 7-hydroxycoumarin, pyrene.
Apparent molar volumes of glycine, L-alanine, and L-serine in water + ethanol mixtures at 298.15 K
Authors: Ren Xiaoling , Lin Ruisen , Ni Yaming , Zong Hanxing
Published: April 2011

Densities of glycine, L-alanine, and L-serine have been measured with an oscillating-tube densimeter at 298.15 K in water + ethanol (EtOH) mixtures ranging from pure water to 45% ethanol by mass. From these densities, apparent molar volumes and limiting apparent molar volumes of the three amino acids in the mixtures have been calculated. Transfer volumes are interpreted in terms of the structure-making or structure-breaking effects of water on addition of these amino acids in the mixtures. The relative contributions of hydrophilic and hydrophobic interactions in these solutions have been inferred.Key words: glycine, L-alanine, L-serine, water + ethanol mixtures, densities.
Self-assembly of one-dimensional polymers by coordination and hydrogen bonding in palladium(II) complexes
Authors: Qin Zengquan , Jenkins Hilary A , Coles Simon J , Muir Kenneth W , Puddephatt Richard J
Published: April 2011

The ligands L = pyridine- or quinoline-carboxylic acid easily give complexes trans-[PdCl2L2], which self-assemble through hydrogen bonding between carboxylic acid groups to give one-dimensional polymers, as proved by structure determinations when L = NC5H4COOH-4, NC5H4COOH-3, and 2-Ph-NC9H5COOH-4.Key words: polymer, hydrogen-bonding, palladium, coordination.
New chloride anion receptors: trifluoromethyl sulfonylated polyamines
Authors: Lee H S , Yang X Q , McBreen J , Vyprachticky D , Okamoto Y
Published: April 2011

A new chloride anion receptor, derivatized oligoethylene oxide CF3SO2 substituted tetraamine (3), was synthesized. This compound exhibited strong Cl-1 ion binding properties in nonpolar solvents such as benzene. Neutral red and Nile blue chloride dye molecules do not dissolve in benzene. However, when compound (3) was added to a benzene solution containing the solid dye compounds, the color of the solution immediately turned to dark blue, and the intensity of the color proportionally increased with the concentration of (3). The phenomena indicated that the Cl- ions of Neutral red or Nile blue chloride are complexed with (3), thereby resulting in an increase in the solubility of the Neutral red or Nile blue cations in benzene. The dissociation of chloride anions from 4,4',4''-trimethoxytriphenyl chloromethane in a benzene solution proceeded with addition of compound (3) and increased with increasing time at room temperature. In contrast, another tetraamine compound (4) which was substituted with a less electron withdrawing group, CH3SO2, did not complex with Cl- anions in a benzene solution.Key words: Cl- anion receptor, trifluoromethyl sulfonated tetraamine, ion pair dissociation.
A complex of gallium with a Schiff base - bis(orthoquinone) ligand
Authors: Brown Martyn A , Castro Jesus A , McGarvey Bruce R , Tuck Dennis G
Published: April 2011

The electrochemical oxidation of gallium in a cell containing a solution of 3,5-di-tert-butylcatechol (H2dbc) in a mixture of liquid ammonia and diethyl ether gives rise to the complex Ga(dbqdi)2, where dbqdi is a tridentate ligand formed by the condensation of two molecules of H2dbc and ammonia. The same paramagnetic molecule can be prepared by treating GaCl3 with H2dbc in ethanol with concentrated aqueous ammonia, with subsequent aerial oxidation. The crystal parameters are triclinic, space group P[Formula: see text], a = 11.6140(8), b = 12.3415(9), c = 20.765(1) Å, α = 89.491(1)°, β = 74.287(1)°, γ = 75.748(1)°, Z = 2, and R = 0.0542 for 7578 unique reflections. The structure, which is based on a GaO4N2 kernel, is discussed on the basis of crystallographic and ESR results.Key words: gallium, electrochemical synthesis, electron spin resonance, X-ray crystallography.
Keto><enol equilibria for and oxidative cyclization to benzofurans of 2,2-ditipyl-1-R-ethenols. Comparison with dimesityl analogs
Authors: Frey Joseph , Rappoport Zvi
Published: April 2011

2,2-Ditipyl-1-R-ethenols (R = H, Me, t-Bu; tipyl (Tip) = 2,4,6-triisopropylphenyl) were equilibrated in hexane with their carbonyl isomers. The equilibration was accompanied by an oxidative cyclization of the enols to substituted 2-R-3-tipyl-4,6-diisopropylbenzofurans, which became more facile with the increase in the bulk of R. At 77.5°C in hexane the KEnolvalues were 90, 0.11, and 0.0011 for R = H, Me, t-Bu, respectively. Comparison with KEnolvalues for the 2,2-dimesityl analogs indicate a higher value for the 2,2-ditipyl derivative with R = H, but lower values for R = Me and t-Bu. The factors affecting this difference are discussed.Key words: 2,2-ditipyl-1-R-ethenols, keto–><-enol equilibria, enols oxidative cyclization.
The reversible enolization and hydration of pyruvate: possible roles of keto, enol, and hydrated pyruvate in lactate dehydrogenase catalysis
Authors: Esposito A , Lukas A , Meany J E , Pocker Y
Published: April 2011

The reversible enolization and hydration of pyruvic acid and pyruvate anion were monitored using spectrophotometric methods at several temperatures. Widely varying values for the equilibrium constant for the enolization of pyruvic acid and pyruvate ion appear in the literature. To accurately determine the position of equilibrium for the enolization reaction, we have developed a method that gives consistent results in which purified samples of sodium pyruvate are first "titrated" with triiodide ion to remove any triiodide-scavenging impurities such as those resulting from aldol condensation reactions. After reequilibration to allow the regeneration of enol pyruvate, the addition of small quantities of triiodide result in an initial burst in the decrease of absorbance at 353 nm, followed by the much slower zero-order decrease due to the formation of new enol pyvuvate molecules. The absorbance change during the burst phase of the reaction is proportional to the enol concentration plus that of any triiodide-scavenging impurity which may be present in the original pyruvate solution. Thus, as the quantity of triiodide used in the pretreatment stage of the experiments is increased, these burst absorbance changes, ΔA, decrease until a constant value of ΔA is reached. Accordingly, this final ΔA value is proportional to enol pyruvate (or enol pyruvic acid) in the absence of triiodide-scavenging impurity, allowing the accurate and reproducible determinations of Kenol. The equilibrium constants for both pyruvate and pyruvic acid are relatively temperature insensitive and, typically, Kenol (pyruvate anion) = 2.6 × 10-5 and Kenol (pyruvic acid) = 7.8 × 10-5 at 25.0°C. The zero-order phase of the reaction of triiodide ion may be used to calculate rate constants for enolization. The hydration and dehydration of pyruvic acid were followed directly by following absorbance changes in the peak at 340 nm due to the keto group. The thermodynamic and kinetic results reported in this paper are used to help determine whether the observed "substrate" inhibition of the lactate dehydrogenase catalyzed reduction of pyruvate is actually caused by keto, hydrated, or enol pyruvate.Key words: pyruvate, enolization, hydration, lactate dehydrogenase.
A mechanism for efficient proton-transfer catalysis. Intramolecular general acid catalysis of the hydrolysis of 1-arylethyl ethers of salicylic acid
Authors: Barber Sarah E , Dean Kathryn ES , Kirby Anthony J
Published: April 2011

The tert-butyl (1) and 1-arylethyl ethers (2) of salicylic acid are hydrolyzed with efficient general acid catalysis by the ortho-COOH group. The half-life of the neutral COOH form of the tert-butyl ether is 15.2 min at 39°, and the estimated acceleration by the COOH group of 2, X = Me, Y = H is 2.13 × 105. The salicylate leaving group from 2 (X = Me, Y = H) has an effective pKaof 2.9, compared with a nominal pKaof 8.52. Analysis of substituent effects in both arylethyl and leaving groups provides the most detailed available mechanistic insight into a reaction involving efficient intramolecular proton-transfer catalysis. The mechanism is very different from classical general acid-base catalysis. Proton transfer takes place very rapidly within a developing strong hydrogen bond, and though an integral part of the CO cleavage process is practically uncoupled from it. "Strategic delay" of the proton-transfer step, relative to CO cleavage, makes a significant contribution to efficiency by setting up the conditions for the formation of the strong, intramolecular hydrogen bond.Key words: catalysis, carboxyl, hydrogen bond, proton transfer, enzyme mechanism.
Spectroscopic studies on effects of triptycyl group on structures and reactivities of triplet arylcarbenes
Authors: Tomioka Hideo , Nakajima Junichi , Mizuno Hidehiko , Iiba Eiji , Hirai Katsuyuki
Published: April 2011

A series of triplet 9-triptycyl(aryl)carbenes, where aryl groups are phenyl, 1- and 2-naphthyl, and 9-anthryl, is generated by photolysis of the corresponding diazomethanes and observed directly by spectroscopic means. Their structures are characterized by electron spin resonance (ESR) spectroscopy in a 2-methyltetrahydrofuran matrix at 77 K, and the reactivities are investigated by laser flash photolysis in degassed benzene solution at room temperature. Comparison of the data with other arylcarbenes bearing a series of substituents, i.e., hydrogen, phenyl, naphthyl, and anthryl groups, revealed an interesting relationship between structures and reactivities of triplet arylcarbenes.Key words: steric protection, stability of triplet carbenes, electron spin resonance, laser flash photolysis, structure-reactivity relationship.
Hypervalent iodine oxidation of α-substituted 2,4-dihydroxyacetophenones: synthesis of novelo-iodophenoxy ethers via rearrangement of iodonium ylides
Authors: Prakash Om , Sharma Vijay , Tanwar Madan P
Published: April 2011

α-Substituted 2,4-dihydroxyacetophenones (1a-1i) have been oxidized with phenyliodonium diacetate (PIDA) under three conditions (i) PIDA-KOH-MeOH (basic) at 0°C, (ii) PIDA-MeOH (neutral) at reflux temperature, and (iii) PIDA-AcOH (acidic) at reflux temperature, to afford novel o-iodophenoxy ethers (4a-4i) via rearrangement of respective iodonium ylides (5a-5i). Key words: hypervalent iodine reagents, phenyliodonium diacetate, α-substituted 2,4-dihydroxyacetophenones, α-substituted 2-hydroxy-3-iodo-4-phenoxyacetophenones, iodonium ylides rearrangement
Formation and nucleophilic capture of N-nitrosiminium ions
Authors: Chahoua Latifa , Vigroux Alain , Chiang Yvonne , Fishbein James C
Published: April 2011

A study of the solvolysis of a series of (N-nitrosomethylamino)arylmethyl esters and azides and the products of nucleophilic trapping of the corresponding N-nitrosiminium ion intermediates in aqueous media, 25°C, ionic strength 1 M is reported. Structure-reactivity data for the forward and reverse reactions have been obtained. In three cases, the rate constants for reactions of the cations with nucleophiles have been measured directly by laser flash photolysis. The data allow a comparison of the degree to which the N-methyl-N-nitroso functionality enhances cation stability from a thermodynamic and kinetic perspective. It has been possible to deduce that the carbon basicity of azide ion is less than 1 kcal/mol greater than that of acetate ion.Key words: nitrosiminium ions, α-acetoxynitrosamines, carbocations, iminium ions, nucleophilicity.
Photocycloelimination of α,α-dichlorocyclobutanones
Authors: Ramnauth Jailall , Lee-Ruff Edward
Published: April 2011

Direct irradiation of a series of α,α-dichlorocyclobutanones in benzene solutions results in photocycloelimination to give 1,1-dichloroalkenes in yields ranging from 30-65%. The α,α-dichlorocyclobutanones were formed in good yields from the [2+2] cycloaddition of the terminal olefins with dichloroketene. This two-step sequence formally represents a "metathesis" of two olefinic functions and provides an easy access to functionalized 1,1-dichloroalkenes. Irradiation of the dichlorocyclobutanones in the solid state led to poor yields of 1,1-dichloroalkenes and polymeric mixtures, however, photoreactions performed in zeolites gave similar yields as those run in benzene solutions.Key words: dichlorocyclobutanones, dichloroalkenes, olefin metathesis, photocycloelimination.
Dimethyltellurium(IV) derivatives with mixed 1,1-dithio ligands. Crystal structures of Me2Te[S2CNMe2][S2COEt] and Me2Te[S2CNEt2][S2COMe]
Authors: Drake John E , Khasrou Layla N , Mislankar Anil G , Ratnani Raju
Published: April 2011

Mixed ligand derivatives of Me2TeLL'2, where L = N,N-dialkyl dithiocarbamate or O,O-alkylene dithiophosphate and L' = O-alkyl dithiocarbonate, have been synthesized and characterized by elemental analysis, 1H, 13C, 31P, and 125Te NMR spectroscopy and infrared and Raman spectroscopy, and X-ray crystallography. Me2Te[S2CNMe2][S2COEt], 8: P[Formula: see text] (no. 2), with cell parameters a = 10.073(3) Å, b = 10.139(2) Å, c = 9.108(2) Å, α = 92.36(2)°, β = 115.55(2)°, γ = 111.19(2)°, V = 760.7(4) Å3, Z = 2, R = 0.0343, Rw = 0.0296. Me2Te[S2CNEt2][S2COMe], 9: P21/c (no. 14) with cell parameters a = 9.881(4) Å, b = 17.671(3) Å, c = 10.149(4) Å, β = 113.65(3)°, V = 1623.3(10) Å3, Z = 4, R = 0.0567, Rw = 0.0514. The immediate environment about tellurium in both molecules is essentially that of a saw-horse structure in which the lone pair is apparently stereochemically active and occupying an equatorial position in a distorted trigonal bipyramid. The S-Te-S angles in the two molecules are 166.87(6)° and 162.0(1)° for 8 and 9, respectively. In both molecules, the TeS bonds to the dithiocarbamate groups are slightly shorter than those to dithiocarbonates. The dithiocarbamate groups are oriented to give secondary interactions involving the apparently terminal sulfur atoms resulting in TeS distances of 3.205(2) and 3.277(4) Å, respectively, in 8 and 9. However, only in 9 is there a similar TeS distance of 3.346(5) Å involving the S2COMe group because in 8, the OEt group of S2COEt, rather than the terminal S atom, is oriented toward Te. Key words: structure, tellurium, methyl, dithiocarbamates, dithiocarbonates, dithiophosphates.
Polynuclear Co(II) and Cu(II) complexes of tetraacetylethane: CuII2(dpa)2(tae)(O2CCF3)2, {[CuII2(dpa)2(tae)(4,4'-bipy)](O2CCF3)2}n, and [CoII2(dpa)4(tae)](O2CCH3)2(H2O)2, dpa = 2,2'-dipyridylamine, tae = tetraacetylethane dianion
Authors: Zhang Yousheng , Breeze Steven R , Wang Suning , Greedan John E , Raju N P , Li Lijuan
Published: April 2011

The syntheses and structures of copper(II) and cobalt(II) complexes employing tetraacetylethane as the bridging ligand have been investigated. The reaction of Cu(O2CCF3)2 with tetraacetylethane (tae) and 2,2'-dipyridylamine (dpa) yielded a dinuclear complex CuII2(dpa)2(tae)(O2CCF3)2 (1), which has an extended hydrogen-bonded chain structure in the solid state. The reaction of 4,4'-dipyridyl (4,4'-bipy) with compound 1 resulted in the formation of a polymeric compound {[CuII2(dpa)2(tae)(4,4'-bipy)](O2CCF3)2}n (2), where the dinuclear unit is cross-linked by the 4,4'-dipyridyl ligand. The reaction of Co(O2CCH3)2 with tetraacetylethane and 2,2'-dipyridylamine yielded a helical dinuclear complex [CoII2(dpa)4(tae)](O2CCH3)2(H2O)2 (3), which forms a hydrogen-bonded band architecture in the solid state. The three-dimensional structure of 3 has molecular sieve-like channels that host methanol molecules reversibly. While only either negligible or weak magnetic exchanges appear to be present in compounds 1 and 2, there appears to be a significant ferromagnetic exchange in 3, which is likely caused by orbital orthogonality of the Co(II) ions, as supported by the crystal structure and EHMO calculations.Key words: cobalt, copper, polynuclear, tetraacetylethane complex, magnetism.
On combination lines in the NMR spectra of strongly coupled spin systems
Authors: Bain Alex D
Published: April 2011

Strongly coupled spin systems provide many curious and interesting effects in NMR spectra, one of which is the presence of unexpected (from a first-order viewpoint) lines. A physical reason is given for the presence of these combination lines. The X part of the spectrum of an ABX spin system is analysed as an example. For an ABX system, it is well known that the AB nuclei give a spectrum consisting of two AB-type spectra, corresponding to the two orientations of the X nucleus. It can also be shown that the X part of the spectrum corresponds to the X nucleus undergoing a transition in the presence of an AB-like spin system. For weakly coupled systems, the four observed lines correspond to the four different orientations of the A and B nuclei. For a strongly coupled system, two additional lines may appear, the combination lines. The resulting six lines correspond to the four spin orientations, plus the two zero-quantum transitions. It is shown that these six lines are such that there is no net excitation of the AB-like spin system associated with the X transitions. There is no AB coherence created directly by a pulse applied to X. AB coherence is created as the system evolves, and this is responsible for many of the curious effects. This is shown to be true for all spin sub-systems, which are weakly coupled to a strongly coupled sub-system.Key words: NMR, strong coupling, second-order spectra, ABX spin system, combination lines, spectral analysis.
Étude thermodynamique des acides phtalique, isophtalique et téréphtalique
Authors: Sabbah Raphaël , Perez Laurence
Published: April 2011

A thermodynamic study of phthalic, isophthalic, and terephthalic acids (general formula: C8H6O4) was carried out by sublimation calorimetry and differential thermal analysis. With values of combustion enthalpy taken from the literature, it was possible to determine their enthalpies of formation in the gaseous state and at 298.15 K and their resonance energy. The results enabled us to do a comparative study of the relative stability of the three acids, on the one hand, and of different benzene disubstituted derivatives, on the other hand. From the enthalpy of sublimation, it was possible to determine the energetic contribution of the different intermolecular forces in the crystals of the three acids.Key words: thermodynamic, calorimetry, differential thermal analysis, phthalic, isophthalic, terephthalic acids, enthalpy of fusion, of sublimation, of formation, of intermolecular bonds, resonance energy, triple point temperature.
Chelated fluoroboron cations. I. Synthesis and NMR studies involving the tertiary-amine ligandsN,N,N',N'-tetramethylethylenediamine andN,N,N',N",N''-pentamethyldiethylenetriamine
Authors: Shoemaker James AW , Hartman J Stephen
Published: April 2011

Several possible methods of synthesis of chelated fluoroboron cations are explored, using the tert-amines N,N,N',N'-tetramethylethylenediamine (Me4en) and N,N,N',N",N"-pentamethyldiethylenetriamine (Me5dien) as model chelating ligands. Both ligands displace pyridine from (pyr)2BF2+(as its PF6-salt) to form the bidentate (Me4en)BF2+and (Me5dien)BF2+cations. The same cations, as well as the corresponding BFCl+and BFBr+cations, can also be prepared by displacement of the donor molecule (D = pyridine or isoxazole) and the heavy halide ion (Cl-or Br-) from the neutral D·BF2X and D·BFX2adducts. The central nitrogen of Me5dien becomes chiral when it and one terminal nitrogen are coordinated, and the prochiral and magnetically nonequivalent fluorines of (Me5dien)BF2+give19F NMR signals separated by 1.2 ppm. In (Me5dien)BFCl+the boron is a second chiral centre and the two diastereomers, distinguishable by NMR with19F chemical shifts differing by 3.0 ppm, form in a 3:1 ratio. The bidentate BFBr+cations of Me4en and Me5dien are insoluble in non-coordinating solvents but have been detected by positive ion FAB mass spectrometry and11B MAS NMR. The tridentate complex (Me5dien)BF+2does not form under our conditions.Key words: N,N,N',N'-tetramethylethylenediamine, N,N,N',N",N"- pentamethyldiethylenetriamine, chelated fluoroboron cations, fluorine-19 NMR, boron-11 NMR, pyridine, isoxazole, chiral, magnetically nonequivalent.
Estimation of particle size distribution in Athabasca oil sands by indirect instrumental neutron activation analysis
Authors: Schutte Robert , Thompson Gordon R , Donkor Kingsley K , Duke M John M , Cowles Roger , Li Xiu Ping , Kratochvil Byron
Published: April 2011

Instrumental neutron activation analysis (INAA) was used to predict the relative amounts of various sizes of fine particles in Athabasca oil sands. The method is based on regression analysis of element concentration data for 529 oil sand test portions, determined by INAA, against particle size distributions determined by three currently used methods. The most important elements for the estimation of particle sizes below 44 µm were found to be aluminum, sodium, and manganese. The INAA estimation method works because variation in elemental composition within particle size fractions in oil sands up to at least 44 µm is relatively small, whereas the variation between size fractions is significant. The new method does not involve the use of organic solvents, is faster and simpler to perform than the methods currently in use, and is comparable in precision. It has the added advantages that it can be readily automated, and concentrations of elements of special interest in oil sand processing, such as chlorine, are obtained simultaneously.Key words: instrumental neutron activation analysis, oil sand, particle size distribution.