bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stoichiometry and Structure of the Complexes Between Lanthanide Ions and Macrocyclic Crown Ethers Containing from Four to Seven Coordinating Sites
Authors: Bünzli J.‐C. G. , Wessner D. 
Published: November 2013

AbstractThe factors influencing the stoichiometry and the structure of the complexes between trivalent lanthanide perchlorates, hexafluorophosphates, nitrates, trifluoroacetates, chlorides, bromides, isothiocyanates and the polyethers 12‐crown‐4, 15‐crown‐5, 18‐crown‐6, dibenzo‐18‐crown‐6 and 21‐crown‐7 are reviewed. The properties of divalent lanthanide and Ce(IV) complexes with crown ethers are presented and discussed.
Cation Transport at 25°C from Binary Cd2+–Mn+ Mixtures in a H2O‐CHCl3–H2O Liquid Membrane System Containing a Series of Macrocyclic Carriers[1]
Authors: Izatt Reed M. , Izatt Steven R. , Mcbride Don W. , Bradshaw Jerald S. , Christensen James J. 
Published: November 2013

AbstractMacrocycle‐mediated fluxes of Cd(NO3)2 and of several binary mixtures of Cd(NO3)2 with the nitrate salt of either Na+, K+, Rb+ Cs+, Ag+, Ca2+, Sr2+, Pb2+, Zn2+, or Cu2+ have been determined in a H2O‐CHCl3–H2O liquid membrane system. Of the macrocycles studied, 2.2 and 2.2DD most successfully transported Cd2+ In the Cd2+–Mn+ mixtures, Cd2+ was transported selectively with 2.2 when Mn+ was either an alkali or an alkaline earth cation. However, when Mn+ was either Ag+, Pb2+, or Cu2+ the Cd2+ flux was reduced sharply. Generally, cation flux was greater for 2.2DD than for 2.2 with selectivity for Cd2+ being altered also in several cases. Relative fluxes from binary cation mixtures depend on metal cation radius, macrocycle cavity diameter, ligand ring substituent and log K for metal ion‐macrocycle interaction.
Structures of the (4S, 14S)‐4, 14‐Dimethyl‐3,6,9,12,15‐pentaoxa‐21‐azabicyclo[15.3.1] heneicosa‐1(21) 17,19‐Triene‐2,16‐dione Complexes of R‐and S‐α‐(1‐Naphthyl)ethylammonium Perchlorate
Authors: Davidson Richard B. , Kent Dalley N. , Izatt Reed M. , Bradshaw Jerald S. , Campana Charles F. 
Published: November 2013

AbstractCrystal data for the more stable (R) and less stable (S) 1:1 macrocycle‐cation complexes are as follows: R cation: Mr = 625.08, orthorhombic P212121, a = 8.47(1), b = 11.78(1), c = 31.19(6) A, V = 3112.0(123) Å3, Z = 4, Dx = 1.333 kg m−3, λ(Mo Kα) = 0.71073 μ = 1.90 cm−1, F(000) = 1320, T = 295 K, R = 0.17 for 1680 reflections. S Cation: Mr = 625.08, monoclinic, P21, a = 8.654(2), b = 11.954(3), c = 15.130(4) Å, β = 97.39(2)°, V = 1552.2(12) Å3, Z = 2, Dx = 1.337 kg m−3, λ(Mo Kα) = 0.71073, μ = 1.91 cm−1, F(000) = 660, T = 295K, R = 0.081 for 2751 unique reflections. Crystals of the complexes were prepared by the authors. The greater thermodynamic stability of the R cation complex is consistent with the observation that this cation experiences less steric interaction with the methyl substituent of the ligand than does the S cation.
Protonation of Macrocyclic Polyethers
Authors: Jagur‐Grodzinski Joseph 
Published: November 2013

AbstractProton affinity of various “crown” ethers is discussed. Equations are given for simultaneous calculation of the complexation and the dissociation constants from conductivity data. pKf in 1.2‐dichloroethane is 8.6 and 8.3, respectively, for the cis‐syn‐cis and the cis‐anti‐cis isomers of dicyclohexyl‐18‐CR‐6, the most basic among the investigated “crown” ethers. pKf = 8.2 for the mixture of these isomers in acetonitrile (AN). The effect of water on pKf of “crown” ethers in aprotic solvents is discussed. It is suggested that a monohydrate of the “oxonium‐crown” rather than a “hydronium‐crown” may be formed. The proton binding capacity of “crown” ethers may be applied for extraction of acids and in catalysis. Dicyclohexyl‐24‐CR‐8 has been found to be an equally effective extractant for HNO3 as the Dicyclohexyl‐18‐CR‐6.
Ring Size Effect on the Chemical Properties of Monovalent Nickel Complexes with Tetraazamacrocyclic Ligands in Aqueous Solutions
Authors: Jubran Nusrallah , Cohen Haim , Meyerstein Dan 
Published: November 2013

AbstractThe chemical properties of the monovalent nickel complexes, NiLi+, where L1 = 1,4,7,10 tetraazacyclotridecane and L3 = 1,4,8,12 tetraazacyclopentadecane, in aqueous solutions were studied electrochemically and pulse‐radiolytically. The results are compared with those for L2 = 1,4,8,11 tetraazacyclotetradecane which were earlier reported. The redox potentials for the NiLi2+/NiLi+ couples are < −1.70, −1.56 and −1.50 V vs. Ag/AgCl for L1, L2 and L3 respectively. NiL+2 has the longest half‐life in neutral solutions, ca 2 s and NiL1 the shortest ca 100 μs. NiL+1 and NiL+2 react with N2O to yield NiLi3+ in fast reactions; this reaction cannot be studied for NiL+3. CO−2 radicals reduce NiL2+1 and NiL2+2 in a reaction approaching the diffusion controlled limit via the bridged mechanism. No reaction between CO−2 and NiL3(H2O)2+2 is observed.
Reactions of Trivalent Silver with One‐Electron Reducing Agents
Authors: Kirschenbaum Louis J. , Borish Edward T. , Rush James D. 
Published: November 2013

AbstractKinetic and stoichiometric data are reported for the reduction of Ag(OH)−4 with Fe(CN)4−6, MnO2−4 and Mo(CN)4−8. The rate constants for reduction to Ag(II) are 1.1 × 105 M−1 s−1, 1.3 × 104 M−1 s−1 and < 1 × 102 M−1 s−1, respectively, at 25°C and μ = 1.2 M. Reaction with Mo(CN)4−8 results in an apparent one‐electron equilibrium, indicating a Ag(OH)−4/[Ag(II)]n potential near that of the Mo(V)/MO(IV) couple. In the Fe(CN)4−6 and MnO2−4 reactions, there is a competition between transfer of a second electron to silver and polymerization of silver(II). A general mechanism for these reactions is presented.
Stability Constants of Oximes of 4‐Substituted‐2‐acetylphenols [1]
Authors: Shai Y. , Warshawsky A. 
Published: November 2013

AbstractProton‐ligand stability constants (pKd) and metal‐ligand stability constants for six oximes of 4‐substituted‐2‐acetyl phenol in H2O: Dioxane (1:3) are obtained by the spectrophotometric method of Magnusson et al. as modified by Patel et al.
A Mechanistic Aspect of the Remote Asymmetric Transmission Observed During Substrate Reduction with Chiral NADH Model Compounds
Authors: Baba Naomichi , Hoshide Fumitoshi , Oda Jun'Ichi , Inouye Yuzo 
Published: November 2013

AbstractAsymmetric reduction of ethyl benzoylformate were conducted using chiral NADH model compounds with various substituents at the 3‐ and N1‐positions of the dihydronicotinamide. In one case, in which l‐prolinamide resides at the terminal of the N1‐substituent, the optical yield was 90%; the remote asymmetric induction was ascribed to a stereospecific blockage of one of the diastereotopic faces in the dihydronicotinamide by an interaction of the amide functions with magnesium.
Anion Exchange Kinetics in Resins of High Selectivity. Part II. The Case of Chloride/Sulphate Exchange
Authors: Helfferich F. G. , Liberti L. , Petruzzelli D. , Passino R. 
Published: November 2013

AbstractFive kinetic models potentially applicable to ion exchange with ions of high selectivity, discussed in Part I of this study, are systematically applied to experimental data on chloride/sulfate forward and reverse exchange and sulfate isotopic exchange with three different types of resins (quaternary ammonium, tertiary amine, and secondary amine groups) and highly dilute solutions (< 0.006 N). Interpretation of these data shows conceivably that the system is controlled by film diffusion, with a small contribution from intraparticle diffusion in forward and isotopic exchange and especially for the resin of highest sulfate selectivity.
Selective Potentiometric Gas‐Sensing Membrane Electrodes
Authors: Rechnitz G.A. 
Published: November 2013

AbstractPotentiometric gas‐sensing membrane electrodes have been investigated for both the CO2 and NH3 systems from the point of view of selectivity and dynamic response. Selectivity is found to be primarily determined by the acid‐base properties, not the volatility, of the interferents. The dynamic response characteristics, on the other hand, are a function of the internal electrolyte layer and the osmolarity of the sample solution.
Transition Metal‐Chelating Phase Transfer Agents from 3,4‐Disubstituted Benzylhalides
Authors: Warshawsky Abraham , Deshe Abraham , Shai Yehiel 
Published: November 2013

AbstractA unified approach to the synthesis of chelating phase transfer agents which uses attachment of various side‐chains to a single chelating molecular precursor (such as 2‐acetyl‐4‐chloromethyl phenol, 4‐chloromethyl salicylaldehyde, 5‐chloromethyl‐8‐hydroxyquinoline), by alkylation at carbon (on aromatic substrates), at oxygen (on alkanols, oligoethylene glycols) or at nitrogen (dialkylamines), is presented. The reaction of a model precursor, 2‐acetyl‐4‐chloromethyl phenol, is studied in detail. The proton–ligand and proton–metal stability constants and Cu(II) phase transfer properties is determined.
Uranium Recovery from Phosphoric Acid with Selective Resins
Authors: Belfer Sofia , Korngold Emmanuel 
Published: November 2013

AbstractThe synthesis and performance of resins selective for adsorbing uranium from wet‐process phosphoric acid were studied. The resins' capacity for uranium was determined in batch experiments and in columns. The morphology of the resin was examined by scanning electron microscopy. The conditions of column loading and elution were found and the concentration of uranium in the eluent was increased more than 50‐fold from 0.15 g/l to 5–7.
Synthesis and Cycloaromatization of Allenyl Ethynyl Sulfides and Selenides [1]
Authors: Braverman Samuel , Duar Ytzhak , Freund Meir 
Published: November 2013

Abstractγ,γ‐Dimethylallenyl 1‐alkynyl sulfides 8a–d have been prepared by reaction of the corresponding alkynyllithium with γ,γ‐dimethylallenyl thiocyanate while the selenide analogs 10a,b have been obtained by an SN2′ reaction of the appropriate alkynyl selenide with α,α‐dimethylpropargyl bromide. Sulfides 8a–d display a high thermal reactivity, undergoing cyclization to the corresponding thiophenic derivatives 11a–d, together with thiophenic dimers such as 12–15, and some polymerization, under certain conditions. In contrast, selenides 10a,b are generally unreactive. The reaction exhibits a remarkable solvent effect. In isopropanol, only monomeric products are observed and the yield is greatly improved. An intramolecular free radical mechanism, involving the diradical intermediate 19, is suggested on the basis of the observed dimerization, solvent effect, deuterium labeling and a kinetic study of the reaction. The differences in reactivities between the analogous sulfides 8 and selenides 10 can be attributed to the varying ability of the respective heteroatom to stabilize the vinyl radical intermediate.
Optical Activity of Nascent Twisted Allene and its Induction by Circularly Polarized Light
Authors: Chiu Ying‐Nan 
Published: November 2013

AbstractThe evolution of optically active twisted allene (D2 symmetry) from orthogonal (D2d) and planar (D2h) structures is traced by construction of “chiral” molecular orbitals as a function of the twist angle. By substitution it is shown that cis‐L, cis‐R, trans‐L and trans‐R enantiomers are all possible. The consistency of these orbitals is shown by their interconversion upon mirror reflection and their reduction to those of orthogonal and planar allenes. For a doubly degenerate excited state in D2d, it is demonstrated that the Jahn—Teller effect due to the torsional vibration of pseudoscalar symmetry can have an equal chance of generating left or right (D2) enantiomers in a symmetrical double‐well potential. A second‐order interaction with circularly polarized light, that is also of pseudoscalar symmetry, is derived and shown to destroy theoretically the parity of the double‐well resulting in a preference for one enantiomer over the other. The magnitude of this radiative interaction and the time factors relative to tunneling frequency are briefly discussed. Potential use of this pseudoscalar and “chiral” vibration in allene as a surrogate for circularly polarized light in asymmetric synthesis is alluded to.
Phase Transfer Catalysis An Account of its Development and Future
Authors: Starks Charles M. 
Published: November 2013

AbstractThat part of chemistry which has come to be known as “Phase Transfer Catalysis,” or simply “PTC” presents to those of us who have watched and participated in its developments for the last 20 years with a rather classical picture of how and why scientific knowledge becomes generated, recognized, communicated, and eventually absorbed into our box of common and useful tools for practicing chemistry. The first PTC results, scattered over the world in the hands of many independent chemists, gave birth to the concept of Phase Transfer Catalysis, and the formal recognition of this and related concepts brought together a number of people who built the basic theoretical foundation on which PTC rests, who discovered many of the experimental facets of PTC, and who suggested many of the ideas for future development. This “PTC” Past has evolved into the “PTC Present,” which is following a still sharply‐increasing learning curve, with the development of new uses, methods, concepts, theoretical development, and world‐wide recognition. The “PTC Future” is thought by this author to be bright, not through its simple extension to old chemical reactions but because it provides a tool to handle future chemical problems in highly material‐ and energy‐efficient ways.
Studies on Methylation of Anomeric Hydroxyl Groups Under Phase‐Transfer Catalysed Conditions
Authors: Szeja Wieslaw 
Published: November 2013

AbstractReaction derivatives of monosaccharides possessing a free anomeric hydroxyl group with methyl sulfate under phase‐transfer catalysed conditions is described. Under phase‐transfer conditions, which permit equilibrium control, the proportions of α‐ to β‐glycosides are determined by the relative acidity of anomers. In the presence of alcohols the proportions of α to β‐D‐gluco‐ and galactopyranosides have been shifted in favor of the equatorial anomer.
Dehydrating Effect of Concentrated Aqueous Alkaline Solutions in Aliphatic Nucleophilic Substitutions Carried out in Aqueous‐Organic Two‐Phase Systems. The Different Behavior of Various Phase‐Transfer Catalysts: Quaternary Salts, Crown Ethers and Cryptands
Authors: Landini Dario , Maia Angelamaria , Montanari Fernando 
Published: November 2013

AbstractConcentrated aqueous NaOH and KOH solutions affect the hydration and hence the reactivity of anions (Cl−, Br−, I−, SCN−, N−3) in aliphatic nucleophilic substitutions catalyzed by lipophilic quaternary onium salts, cryptands and crown ethers under phase‐transfer (PTC) condtions. In the presence of aqueous 50% NaOH or 53% KOH non‐hydrated anions are transferred from the aqueous into the organic phase by quaternary salts. The anionic reactivity thus becomes identical to that found under anhydrous homogeneous conditions in non‐polar organic media. Unlike quaternary salts, in the presence of cryptates water is not completely removed even at the highest KOH concentration, i.e. conditions in which aH2O ∼ 0. Residual hydration depends on the nature of the anion and is the highest for anions with localized and/or less polarizable charge, such as Cl−, Br− and N−3. As a consequence, rate constants noticeably increase in comparison with those found under conventional PTC conditions, but don't reach those of anhydrous solutions. Behavior of crown ethers is in between that of quaternary salts and cryptates, since residual hydration in the presence of 53% aqueous KOH is lower than that of cryptates, whereas anionic reactivity become practically identical to that found under anhydrous conditions. A comparison of the catalytic efficiency of lipophilic quaternary salts, cryptands and crown ethers under various reaction conditions is also included.
Quaternary Onium Salts Immobilized on Inorganic Matrices
Authors: Tundo Pietro , Venturello Paolo , Angeletti Enrico 
Published: November 2013

AbstractOnium salts immobilized on silica gel and alumina show unusual properties because of the presence of the polar inorganic support. Under liquid—liquid phase‐transfer catalysis conditions these systems can also catalyze reactions carried out without stirring, and unlike the corresponding onium salts supported on polystyrenic matrix, they do not need the use of polar solvent. Moreover, different matrices with different geometries in the micropores are differently functionalized and may induce selectivity towards reagents with different molecular size. The polar and hydrophilic matrix strongly affects the affinities of the immobilized onium salts in the anion exchange process, producing a higher affinity towards hydrophilic inorganic and lipophilic organic anions, with respect to that observed for the homogeneous and polystyrene supported onium salts. In aqueous solution the onium salts supported on inorganic matrices are able to adsorb the reactants and to vary the reaction microenvironment as the micellar catalysts do.
The Geometrical Nature of Transition State Variation
Authors: Harris J. Milton , Paul J. Lawrence 
Published: November 2013

AbstractThe proposal that the movement of transition states on potential energy surfaces is controlled by the geometry of the surface is examined by use of a nonchemical, mathematical model of surfaces. We conclude that the chemical rules of Thornton, Jencks, and More O'Ferrall for predicting TS movement have an underlying geometrical origin. The model permits ready visualization of the rules for predicting TS movement, and the model facilitates predicting TS movement for surfaces in which the saddle point lies off the diagonals connecting the corners of the surface.
Temperature Dependence of the Radical Addition to Alkenes
Authors: Giese Bernd , Feix Christine 
Published: November 2013

AbstractIn addition reactions of primary n‐hexyl, secondary cyclohexyl and tertiary butyl radicals to the alkene pair fumarodinitrile/methyl α‐chloroacrylate, the selectivities and the differences of the selectivities decrease with increasing temperature. An isoselective relationship is found with an isoselective temperature of about 280°C. Below this temperature, the frontier molecular orbital theory can be applied to explain the substituent effects on the selectivities. The previously observed breakdown of the reactivity‐selectivity principle for radical addition reactions to alkenes is, therefore, not a temperature effect.
A Demonstration of the Reactivity—Selectivity Principle for the Thiol—Disulfide Interchange Reaction
Authors: Hupe D.J. , Pohl E. R. 
Published: November 2013

AbstractEquilibrium constants for the reaction of aryl thiol anions with hydroxyethyl disulfide have been measured which, along with literature data, demonstrate a slope of 1.21 for a plot of log KS− (R'S‐ + RSSR ⇌ R'SSR + ‐SR) vs pKa. Rate constants were measured also for these endothermic reactions of aryl thiol anions with hydroxyethyl disulfide and also for the exothermic reactions of alkyl thiol anions with the mixed disulfide of mercaptoethanol and 4‐nitro‐2,3,5,6‐tetrafluorothiophenol. These kinetic data, obtained over a range of KS− of 1021, show the gradual curvature expected for Hammond postulate type behavior. A quantitative measure of this curvature in terms of the Marcus formalism was carried out for these two data sets along with four others having more moderate values of ΔG. The data were fit with a value for the intrinsic barrier, λ/4 = 11.6 kcal, and a value for the work term Wr = 4.0 kcal. A comparison is made of these values with the similar values found for alkyl, proton and acyl transfer reactions. The importance of using a variety of substrates with a series of bases or nucleophiles, rather than a single substrate, is discussed, as are the cause for curvature other than Hammond postulate behavior.
Cation—Anion Combination Reaction of Substituted Tropylium Ions with Borohydride Ion in Acetonitrile: Regioselectivity in a Diffusion‐Controlled Region
Authors: Takeuchi Ken'ichi , Yasuda Sumio , Kitagawa Toshikazu , Senzaki Yoshihide , Okamoto Kunio 
Published: November 2013

AbstractThe relative rates and regioselectivities were determined for the reaction of unsubstituted and substituted tropylium ions containing methoxy, methylthio, methyl, phenyl, methoxycarbonyl or cyano with borohydride ion in acetonitrile at 25°C. The rate increases in the order methoxy‐ < methylthio‐ < methyl‐ < unsubstituted‐, but it levels off for unsubstituted‐, phenyl‐, methoxycarbonyl‐ and cyano‐tropylium ions. From the lower limit of the rate constant of the methoxytropylium ion, which was estimated by the stopped‐flow technique, and the logarithmic plot of the relative rates against those of the one‐electron reduction of the tropylium ions with Cr(II) ion, the reaction with the borohydride ion at the level‐off region was concluded to be diffusion‐controlled. In spite of the diffusion‐controlled behavior, these tropylium ions show regioselectivities. The data indicate that the present cation—anion combination reaction is not a one‐step reaction, but proceeds via a cation—anion encounter‐pair (or charge‐transfer) intermediate, providing a clear example of the presence of intramolecular selectivity in the absence of intermolecular selectivity. CNDO/2 SCF MO calculations suggest that the regioselectivity is primarily frontier orbital controlled.
Constant Selectivity in Proton Exchange Reactions Between Aqueous Sulphuric Acid and Acetylenes
Authors: Chokotho Norris C. J. , Johnson C. David 
Published: November 2013

AbstractLinear Pfluger plots of unit slope are obtained from logarithmic rate constants for acid–catalysed hydration of phenylacetylene and its substituted derivatives p‐OCH3, p‐CH3, m‐CH3, p‐Br, m‐Cl, m‐NO2, p‐NO2 in aqueous sulphuric acid solution. This direct experimental observation of absence of any dependence on selectivity gives evidence for the applicability of the magnified image kinetic acidity function in these systems.
Ionization of Acetylacetone in Me2SO—Water Mixtures. Reactivity—Selectivity Principle or Principle of Imperfect Synchronization?
Authors: Bernasconi Claude F. , Bunnell Richard D. 
Published: November 2013

AbstractRate constants for the reversible deprotonation of acetylacetone were measured in carboxylate and amine buffers in water and in 50%, 90% and 95% Me2SO at 20°C. The Brønsted plot for the carboxylate ions is curved in the Me2SO—water mixtures, but straight in water. The curvature is in the direction predicted by the Reactivity—Selectivity Principle (RSP). However, the Brønsted plot for the reaction with primary amines is straight in all solvents. This suggests that the curvature observerd with the carboxylate ions is caused by loss of solvation of the base; this loss of solvation is ahead of bond formation in the transition state rather than being a manifestation of the RSP. (Note that all Brønsted plots are based on pKavalues measured in the respective solvents.) The intrinsic rate constant (k0) for proton transfer increases with the addition of Me2SO, and more so with the carboxylate buffers than with the amines. This increase ink0is attributed to delayed solvation of the developing enolate ion in the transition state; with the carboxylate buffers, an additional factor is the early loss of solvation of the base. The various solvation effects observed in this study can all be understood in the context of the Principle of Imperfect Synchronization (PIS).