bluuebunny/crossref_metadata_2025 huggingface dataset:
Nickel(III)–tris(di-imine) complexes: a series of strong one-electron oxidants
Authors: Brodovitch J. C. , Haines R. I. , McAuley A.
Published: May 2006

The complexes [Ni(III)(LL)3](ClO4)3 (LL = phen, bipy, and substituted derivatives) have been isolated as products of the electrolysis in acetonitrile of the corresponding nickel(II) species. Electron spin resonance measurements for all nickel(III) species in frozen anhydrous CH3CN and in frozen 4.0 M HClO4 solutions (77 K) show a single near symmetric line shape (g ≈ 2.10) with fine structures appearing only in the presence of mixed solvent systems. In a CH3CN/5% H2O glass (77 K) quintets in the [Formula: see text] and [Formula: see text] regions are observed [Formula: see text]consistent with Jahn–Teller distortion expected for a low-spin d7 system. Ultraviolet–visible spectra are also reported. Electrode potentials for the Ni(LL)33+/2+ couples in CH3CN (0.1 M NaClO4) lie in the range 1.51 V (Ni(4,4′-Me2bipy)33+) to 1.82 V (Ni(5-NO2-phen)33+) and the powerful oxidizing nature of these species has been confirmed in reaction with both organic and inorganic substrates.
An experimental study of the reactivity of the hydroxide anion in the gas phase at room temperature, and its perturbation by hydration
Authors: Tanner Scott D. , Mackay Gervase I. , Bohme Diethard K.
Published: May 2006

Flowing afterglow measurements are reported which provide rate constants and product identifications at 298 ± 2 K for the gas-phase reactions of OH− with CH3OH, C2H5OH, CH3OCH3, CH2O, CH3CHO, CH3COCH3, CH2CO, HCOOH, HCOOCH3, CH2=C=CH2, CH3—C≡CH, and C6H5CH3. The main channels observed were proton transfer and solvation of the OH−. Hydration with one molecule of H2O was observed either to reduce the rate slightly and lead to products which are the hydrated analogues of the "nude" reaction, or to stop the reaction completely, k ≤ 10−12 cm3 molecule−1 s−1. The reaction of OH−•H2O with CH3—C≡CH showed an uncertain intermediate behaviour.
Annelation of β-keto thiolesters and synthetic application
Authors: Liu Hsing-Jang , Ho Li-Kang , Lai Hoi Kiong
Published: May 2006

The use of β-keto thiolesters in the construction of fused (e.g. 8) and bridged (e.g. 12) ring systems possessing a functionalized substituent at the angular position is described. Some synthetic applications of the annelation procedure are demonstrated including: selective reduction of the thiol ester group; the concomitant removal of ketone carbonyl and reduction of thiolester to the alcohol level via thioketal intermediate; and direct conversion of the ketone carbonyl to a gem-dimethyl group using lithium dimethylcuprate.
Water elimination from the keto and enol tautomers of ionised ethylacetate
Authors: Holmes J. L. , Burgers P. C. , Terlouw J. K.
Published: May 2006

The keto and enol forms of ionised ethylacetate both lose H2O to generate the keto and enol ions of methylvinylketone, probably via common reacting configurations. All hydrogen atoms and both oxygen atoms participate in this mechanistically complex reaction; the degree of their involvement depends upon the internal energy content of the fragmenting ions.
Interfacial excess entropies and solvent structures
Authors: Hills Graham , Silva Fernando
Published: May 2006

Detailed consideration is given to thermodynamic relationships describing the temperature dependence of the properties of electrified interfaces. Excess entropies are derived for multicomponent systems and in particular it is shown that the effect on the residual excess entropy, S*, of the specifically adsorbed organic species can be directly determined by experiment. Values of S* in the presence of thiourea (TU) can be understood in terms of the surface excesses of TU and the degree of solvent orientation. The preferred orientation of water is shown to be charge-dependent, under all conditions to be zero at −3 µC cm−2, and largely determined by its molecular polarisability. Temperature-invariant capacities are shown to occur widely and are not easily explained in terms of cluster models or time-dependent solvent orientation.
Solvent accessibility and hydrophobicity in the adsorption of alkylammonium cations at air/water and Hg/water interfaces. Part 1. Behavior at the air/water interface in relation to hydration properties
Authors: Bennes R. , Conway B. E.
Published: May 2006

By means of adsorption and surface-potential studies on a series of R4−nN+Hn perchlorates at the air/water interface, the role of hydrophobic and hydrophilic interaction in the adsorption and ion distribution of these salts near the air/water interface is examined. While the adsorption of the alkylamine ions increases as n decreases from three to zero, inclusive, the surface-potential change accompanying the adsorption decreases. This effect is interpreted in terms of opposing hydrophilic, electrostatic and hydrophobic interactions between the organic ion and water near the liquid surface, leading to a progressive change of double-layer ion distribution. In Part II, comparative studies of the same series of compounds at the Hg/water interface are reported.
Glycosides from Muscari comosum. 1. Eucosterol glycoside and structure of its methanolysis products
Authors: Parrilli Michelangelo , Lanzetta Rosa , Dovinola Vincenzo , Adinolfi Matteo , Mangoni Lorenzo
Published: May 2006

A mixture of at least four glycosides has been isolated from bulbs of Muscari comosum. Acidic methanolysis of this mixture afforded a crystalline fraction consisting of four diols 1a differing in the configuration at the epimerizable C-20 and/or C-24 centers. Benzoylation of this diol fraction allowed the isolation of one pure dibenzoate, mp 175–176 °C, to which structure 1b was assigned on the basis of chemical and spectral evidence. This allowed the deduction that one of the aglycone moieties was 27-norlanostane triterpene eucosterol 4a. This conclusion has been confirmed by identification of 4a as the major product of the enzymatic hydrolysis of the glycoside mixture.
The conformational properties of seven-membered heterocycles: 1,3-dioxacyclohept-5-ene and its 2-substituted derivatives
Authors: St-Amour R. , St-Jacques M.
Published: May 2006

1,3-Dioxacycloheptene and its 2-CH3, 2-OCH3, 2-t-Bu, and 2,2-dimethyl derivatives were studied by 1H and 13C dnmr methods. Substituent effects and the interpretation of spectral changes in 13C nmr at low temperature allow the determination of the most stable conformation of these compounds (TB for 1–4b and C for 5b) and the characterization of the dynamic processes observed for 2b, 4b, and 5b. The differences between the conformational and dynamic properties of the above compounds and their benzo analogs are rationalized in terms of different torsional interactions in the two series.
Pyrolysis of bacterial polyalkanoates
Authors: Morikawa Hiromichi , Marchessault Robert H.
Published: May 2006

Pyrolysis products from bacterial polyesters, poly-β-hydroxybutyrate (PHB), and from a heteropolyester (β-hydroxyvalerate and β-hydroxybutyrate) were identified. Different physical forms of PHB were studied: PHB purified by dissolution in chloroform, native granules of PHB, and PHB in bacterial cells. The products were characterized by gc, ms, and nmr analysis. The yield of crotonic acid obtained by the pyrolysis of purified PHB was 60 to 65%. Pyrolysis of PHB native granules yielded crotonic acid as well as oligomers of PHB with a terminal crotonate. Upon direct pyrolysis of dry bacterial cells, the yield of crotonic acid was 20 to 25% of the PHB in the cells. From the heteropolymer, 2-pentenoic acid and terminally unsaturated oligomers of polyhydroxyvalerate were obtained. The usefulness of the pyrolysis method for obtaining vinyl compounds from bacterial cultures containing polyalkanoates is discussed.
Synthesis and bromination of 3-alkyl-5α-cholestan-2-one
Authors: Horiuchi C. Akira , Satoh J. Yasuo
Published: May 2006

3β-Alkyl-5α-cholestan-2-ones (R = CH3, C2H5, and CH3CH2CH2) were prepared by the direct alkylation of 5α-cholestan-2-one with alkyl iodide and potassium tert-butoxide in a reflux of tert-butyl alcohol – benzene. The bromination of these 3β-alkyl ketones gave 3α-bromo-3β-alkyl-5α-cholestan-2-one.
Spectrophotometric investigation on the interaction of acridine orange with methylene blue, phenosafranine, and disulphine blue in aqueous medium
Authors: Ghosh Suhaschandra , Moulik Satya P. , Das Akhil R.
Published: May 2006

The results of dye–dye interactions for the pairs, acridine orange – methylene blue, acridine orange – phenosafranine, and acridine orange – disulphine blue have been presented. It has been found that at comparable concentrations the interaction is rather weak, and the formation of mixed entities is only possible at relatively high proportions of one of the components. However, the evidence of mixed dimers in the form of a new absorption band is lacking. Phenosafranine remarkably promotes dimerization of acridine orange. An experimental demonstration of the dimer spectra of acridine orange has thus been possible. The interaction of the anionic dye disulphine blue with cationic acridine orange has been observed to be the weakest of all the pairs, indicating the vital role of the structural parity for interaction. At comparable low concentrations, none of the dye-pairs studied have revealed compound metachromasy in the presence of a polyelectrolyte, suggesting unfavorable mixed dye aggregation under ordinary conditions.
Acidité dans les mélanges H2O–ODPN. I. Etude de l'acidité dans l'oxydipropionitrile pur
Authors: Persin M. , Gal J. Y.
Published: May 2006

The study of acid–base reactions in oxydipropionitrile (ODPN) by means of glass and hydrogen electrodes allows us to determine the pKA's of several acid–base pairs. Use of Strehlow's hypothesis leads to a correlation of acidity scales in water, acetonitrile and oxydipropionitrile. Because of solvent degradation in highly alkaline solution it proved impossible to determine the ionic product of the medium and consequently the pKB's of several acid–base pairs. The weak basicity of ODPN allows for the easy titration of very weak bases such as urea, DMSO, and HMPT in water. For weak acid the importance of homoconjugation is clearly shown leading to the weak ability of the medium to solvate both anions and protons. Some homoconjugation constants have been determined by the analysis of the potentiometric titration curves. Finally a study of the quinone–hydroquinone couple shows that this is also a pH indicator in ODPN. At the present time our studies provide a pK scale of practical use over 20 units. [Journal translation]
l-Sterpurene-3,12,14-triol and 1-sterpurene, metabolites of silver-leaf disease fungus Stereum purpureum
Authors: Ayer William A. , Saeedi-Ghomi M. Hussein
Published: May 2006

Two new sterpurane-type sesquiterpenes, sterpurene-3,12,14-triol (4) and 1-sterpurene (5), 2,6,10,10-tetramethyltricyclo-[6.3.0.03,6]undec-1-ene, have been isolated from among the neutral metabolites of the fungus Stereum purpureum. The structures were determined mainly on the basis of mass and nuclear magnetic resonance spectrometry.
Carbon-13 isotopic selectivity in the infrared multiphoton photolysis of CF2Cl2–O2 mixtures
Authors: Nip W. S. , Hackett P. A. , Willis C.
Published: May 2006

The infrared multiphoton chemistry of CF2Cl2–O2 mixtures has been studied at laser frequencies where the product CF2O is highly enriched in carbon-13. Yield enhancements with no loss of isotopic selectivity are attributed to suppression of radical–atom recombination reactions. It is demonstrated that addition of up to 60 Torr of either excess O2 or N2 suppresses a thermal, non-selective channel important at higher fluences. A selectivity factor greater than 30 is observed for 4 Torr CF2Cl2 in the presence of 80 Torr of oxygen.
The hydrolyses of benzamides, methylbenzimidatium ions, and lactams in aqueous sulfuric acid. The excess acidity method in the determination of reaction mechanisms
Authors: Cox Robin A. , Yates Keith
Published: May 2006

The excess acidity method has been applied to hydrolysis rate data for a number of benzamides, methylbenzimidatium ions, and lactams, obtained as a function of sulfuric acid concentration and temperature. All of the substrates studied except β-propiolactam (8) and methyl-2,6-dimethylbenzimidatium ion (7) were found to follow the AOT2 mechanism at all acidities. The excess acidity method provided considerable mechanistic detail; in dilute acid the transition state contains O-protonated (or methylated) substrate and three water molecules (large negative ΔS≠), but in more concentrated solutions a one-water-molecule mechanism takes over (smaller negative ΔS≠). In strong acid bisulfate ion acts as the nucleophile (positive ΔS≠). N-protonated intermediates are not involved for "normal" substrates, being observed in this work only for 8, which follows the AND1 pathway. Observed differences between benzamide and methylbenzimidatium ion (4) hydrolyses are due to their differing activity coefficient behaviour, the mechanism being the same for both. The hydrolysis of 7 involves a one-water-molecule SN2 displacement at the O-methyl group. Comparison with 7 shows that this displacement is not likely to occur under the reaction conditions for 4; however, for the N-methyl and N,N-dimethyl derivatives studied it is probably an important reaction pathway. A comprehensive mechanistic framework for amide hydrolyses in strong acid media is given.
The synthesis and X-ray crystal structure of triiodotellurium(IV) hexafluoroarsenate(V), TeI3AsF6
Authors: Passmore Jack , Sutherland George , White Peter S.
Published: May 2006

TeI3AsF6 was prepared quantitatively from the reaction of iodine, tellurium, and arsenic pentafluoride in sulphur dioxide solution. Single crystals of TeI3AsF6 are monoclinic, a = 8.243(2), b = 10.755(2), c = 12.660(2) Å; β = 100.91(2)°, V = 1102 Å3. The structure was refined in the space group P21/c to a conventional R factor of 0.075 for 1551 independent reflections with I ≥ 2σ(I). The structure consists of essentially discrete TeI3+ cations and AsF6– anions with some cation–anion interaction. The TeI3+ cation has approximate C3v symmetry with an average Te—I distance of 2.667 Å and I—Te—I angle of 99.90°.
Standard electrode potentials of the silver – silver phosphate and silver – silver arsenate electrodes in formamide at different temperatures
Authors: Dash Upendra Nath , Nayak Surendra Kumar
Published: May 2006

For the emf measurements of cells of the type Ag, AgCl/NaCl(m)|Na3X(m/3)/Ag3X, Ag where X is PO4 or AsO4, the standard potentials of the silver–silver phosphate and silver–silver arsenate electrodes have been determined in formamide at five different temperatures ranging from 5 to 45 °C. The standard molal potentials of the electrodes have been expressed through the equations[Formula: see text]The standard thermodynamic quantities, ΔG0, ΔH0, ΔS0 and ΔCp0 for the respective electrode reactions have been evaluated from the Em0's of the electrodes at these temperatures. The solubility products of silver phosphate and silver arsenate have also been calculated in formamide at these temperatures.
A theoretical study on the bimolecular hydrogen exchange aminonitrene → trans-diimide. Comparison with formaldehyde photochemistry
Authors: Kemper M. J. H. , Buck H. M.
Published: May 2006

Ab initio calculations on the rearrangement aminonitrene → trans-diimide are reported. It is shown that a bimolecular hydrogen exchange is much easier than a unimolecular 1,2 hydrogen shift: the reactions have activation energies of 4 and 94 kcal/mol, respectively. The hydrogen exchange starts from dimers which have a fairly large stabilization energy. Infrared and Raman frequencies of these dimers are calculated in order to facilitate experimental studies. Some striking similarities are indicated between diimide chemistry and the photochemistry of formaldehyde. It is shown that results from one field are transferable to the other one. From this, some new experiments are suggested.
Heat capacities and volumes of NaCl, MgCl2, CaCl2, and NiCl2 up to 6 molal in water
Authors: Perron Gèrald , Roux Alain , Desnoyers Jacques E.
Published: May 2006

It has been claimed by Enderby and co-workers that changes in long-range order occur in NiCl2 aqueous solutions at high concentrations. To investigate the possibility of a transition, the partial molar heat capacities and volumes of NiCl2, CaCl2, MgCl2, and NaCl were measured and compared in water at 25 °C up to 6 mol kg−1. In the case of NaCl, data were also measured at 5 and 45 °C. A slight change in slope of [Formula: see text] is observed for NiCl2 around 4 mol kg−1 which may suggest a third or higher order transition. However, the change is too small to support unambiguously any particular model for the high concentration region.
Chemistry of thujone. IV. Cyclopropane derivatives and analogs of pyrethrins
Authors: Kutney James P. , Choudhury Manash K. , Decesare John M. , Jacobs Helen , Singh Ashok K. , Worth Brian R.
Published: May 2006

Thujone 1 was degraded to the thujaketonic acids 5 and 18 which were used as starting materials for the synthesis of pyrethroid analogs 8, 12–17, 21–24, and 27–35.
1,3-Dinitrobenzene – hydroxide ion interactions. Equilibrium constants for σ-complex formation in the dimethylformamide–water solvent system
Authors: Buncel Erwin , Zabel Allen W.
Published: May 2006

The results of a uv–visible spectroscopic study of the interaction of 1,3-dinitrobenzene (DNB) with hydroxide ion in aqueous dimethylformamide (DMF) media are reported. Formation of several spectral species has been discerned, depending on factors such as the relative concentrations of the reactants, the time scale of the experiments, and the medium composition. The principal interaction is formation of the 1-hydroxy-2,4-dinitrocyclohexadienate anion. The molar absorptivities of this σ-complex, and the equilibrium constants (Ke) for its formation, have been determined as a function of medium composition. Values of Ke increase from 7.5 M−1 to 3 × 105M−1 as the DMF content of the medium is changed from 57.4 to 95.8 mol% DMF. A solvent isotope effect, Ke(D2O)/Ke(H2O), of ca. 0.4 has been observed. Structural and medium effects in this and related systems are evaluated. Correlations between log Ke and H− are examined using the stoichiometric as well as the calculated free hydroxide ion concentrations. Attention is drawn to an important condition for equilibrium constant measurement in systems where one of the interacting species contributes significantly to the overall basicity, or to another property of the medium.
Hydrogen exchange studies. XIV. Kinetics and mechanism of base-catalyzed hydrogen exchange in 1,3-dinitrobenzene in aqueous dimethylformamide and relationship with σ-complex formation
Authors: Buncel Erwin , Zabel Allen W.
Published: May 2006

Kinetic data have been evaluated for hydrogen exchange in 1,3-dinitrobenzene (DNB), occurring at the 2-position, in dimethylformamide (DMF) – D2O mixtures containing deuteroxide ion. The pseudo first order rate constants for exchange, kobs, show inverse dependence on the initial DNB concentration, which can be quantitatively related to the extent of σ-complex formation in these systems. The profile for kobs as function of medium composition exhibits a maximum at ca. 70 mol% DMF, and εapp for σ-complex formation reaches a plateau at about the same medium composition. The equilibrium constants for σ-complex formation, Ke, are used to calculate the free, or uncomplexed, deuteroxide ion concentrations, which then allow one to calculate k2, the second order rate constants for exchange. The k2 values show a uniformly increasing tendency with increased DMF content. Correlations with medium basicity are examined, and the nature of the log k2 and log Ke vs. H− plots afford insight into the origin of the medium dependence of proton exchange. The results of the present study are consistent with the σ-complex being an unreactive form of the substrate towards exchange, which occurs via uncomplexed DNB present in small concentration. The study also rules out the possibility that the colored species present in these systems is the carbanion formed on deprotonation of DNB.
Heat capacity measurements of liquids with a Picker mixing flow microcalorimeter
Authors: Simard Marc-André , Fortier Jean-Luc
Published: May 2006

The Picker mixed flow microcalorimeter has been used without modification as a differential thermal balance to measure the volumetric heat capacity of liquids. The precision on volumetric heat capacity change is evaluated to be ±0.5% or better, and the limit of detection is ± 5 × 10−5 J K−1 cm−3. As a check, the apparent molar heat capacities of an aqueous solution of NaCl in the range 0.01 to 6 mol kg−1 were measured at 298.15 K. The performance of this instrument is compared with that of the Picker heat capacity flow microcalorimeter.
High resolution nuclear magnetic resonance studies of platinum(II) – guanosine-5′-monophosphate interactions in aqueous solutions
Authors: Polissiou Moschos , Viet Minh Tan Phan , St-Jacques Maurice , Theophanides Theophile
Published: May 2006

A detailed 400 MHz 1H nmr study was carried out on platinum complexation products of GMP by K2PtCl4. Coupling constant values show that platination on N7 induces a conformational change on the ribose moiety: the 3E form of the ring and the gt conformer about the C(4′)—C(5′) bond are favoured upon complexation. The results are compared to the conformational changes induced by N7 protonation and methylation.
A 1H and 13C nmr study of the radiation-induced degradation products of 2′-deoxythymidine derivatives: N-(2′-deoxy-β-D-erythropentofuranosyl) formamide
Authors: Cadet J. , Nardin R. , Voituriez L. , Remin M. , Hruska F. E.
Published: May 2006

N-(2′-Deoxy-β-D-erythropentofuranosyl) formamide is an ionizing radiation-induced degradation product of 2′-deoxythymidine. This work describes a facile chemical synthesis of this molecule, and discusses the results of an 1H and 13C nmr study. The rotational barrier to cis–trans isomerization about the amide linkage is calculated, and details of the molecular conformation of the cis and trans isomers in aqueous solution are presented.
Adsorption enhancement in square wave polarography
Authors: Ramaley Louis , Dalziel John A. , Tan Wee Tee
Published: May 2006

Reduction peaks in single drop square wave polarography (SDSWP) for metal ions such as Cd(II) and Pb(II) in the presence of picolinic acid gave peak currents that can be an order of magnitude or more greater than diffusion-limited peaks. Various studies using techniques such as controlled-potential electrolysis, tast polarography, staircase voltammetry, and SDSWP demonstrated that this enhancement effect was due to the adsorption of metal–picolinate complexes on the electrode surface. Since it provides a detection limit of about 0.2 ppb with ions such as Cd(II), adsorption enhancement appears to be of use in trace analysis under certain circumstances. Linearity is observed only up to 1 × 10−5 M and any substance capable of adsorption is a potential interferent.
Coulometric determination of several water-insoluble aromatic nitro compounds with electrogenerated chromium(II)
Authors: Al-Daher I. M. , Kratochvil B.
Published: May 2006

The electrochemical reduction of a series of water-insoluble aromatic nitro compounds with coulometrically generated chromium(II) has been investigated. Samples ranging from 0.2 to 0.5 μmol could be determined for several substances with a precision and accuracy of about 1%. The number of electrons involved in the reductions corresponded in most cases to the formation of hydroxylamines or amines, but in some instances to dihydrazo products.
Studies related to biological detoxification of Kraft pulp mill effluent. II. The biotransformation of isopimaric acid with Mortierella isabellina
Authors: Kutney James P. , Singh Mahatam , Dimitriadis Eugene , Hewitt Gary M. , Salisbury Philip J. , Worth Brian R. , Servizi James A. , Martens Dennis W. , Gordon Robert W.
Published: May 2006

A study related to the biological detoxification of Kraft pulp mill effluent is presented. Several fungal and bacterial preparations were evaluated for their action on isopimaric acid (IPA), one of the effluent constituents toxic to fish. Mortierella isabellina was the organism selected for the biodegradation of IPA and subsequent chemical studies established the structures of three diterpenoid substances with very much lower acute toxicity.
Synthèse et étude chimique préliminaire des pentadiényl-2,4-phosphines
Authors: Santini Catherine C. , Mathey François
Published: May 2006

A penta-2,4-dienylphosphine oxide is easily obtained by reaction of methylmagnesium iodide with 1-oxa-2-phosphacyclo-hepta-4,6-diene followed by two more intermediate steps. The corresponding phosphine may be obtained either by trichlorosilane reduction of the oxide or nickelocene reduction–complexation of the sulfide. It seems that the dienic part of penta-2,4-dienylphosphines cannot be involved in a η4-complexation for steric reasons. The oxides are valuable precursors for conjugated trienes through Wittig–Horner reactions with carbonyl compounds.
Ullmann condensation using copper or copper oxide as the reactant. Arylation of active hydrogen compounds (imides, amides, amines, phenol, benzoic acid, and phenylacetylene)
Authors: Yamamoto Takakazu , Kurata Yasundo
Published: May 2006

Ullmann condensation using Cu or copper oxide as the reactant and using no base has been studied. Reactions of active N—H, O—H, and C—H compounds, RZH (imides, amides, amines, phenol, benzoic acid, and phenylacetylene), with mixtures of aryl halides and more than a stoichiometric amount of Cu or copper oxide (Cu2O or CuO) without addition of base lead to facile arylation of the active hydrogen compounds. In the arylation reaction Cu and copper oxides serve not only as the catalyst but also as the acceptor of halogen from aryl halide. The reactivity of phenyl halide, PhX, increases in the order PhCl < PhBr < Phl. Cu generally gives higher yields than Cu2O and CuO and, of the two copper oxides, Cu2O has the higher activity. The stronger the acidity of the active hydrogen compound (RZH), the more easily the compound is phenylated by the mixture of PhX and Cu; a roughly linear correlation between Ti, the temperature where the phenylation starts, and the pKa value of the active hydrogen compound has been observed. A mechanism involving initial formation of an RZ—Cu species by the reaction between RZH and Cu or copper oxide and ensuing attack of organic halide at the RZ—Cu species is proposed.
The retroaldol reaction of 3-methyl-2-butenal
Authors: Guthrie J. Peter , Dawson Brian A.
Published: May 2006

In aqueous sodium hydroxide solutions at 25 °C, 3-methyl-2-butenal, 1c, undergoes retroaldol cleavage to acetone and acetaldehyde. The kinetics of the retroaldol reaction were followed spectrophotometrically at 242 nm and showed simple first order behavior. When 3-methyl-3-hydroxybutanal, 2c, was added to aqueous sodium hydroxide solutions at 25 °C, there was an initial increase in absorbance at 242 nm, attributed to formation of 1c, followed by a 20-fold slower decrease; the rate of the slow decrease matches the rate of disappearance of 1c under the same conditions. Analysis of the kinetics allows determination of the three rate constants needed to describe the system: khyd = 0.00342; kdehyd = 0.00832; kretro = 0.0564; all M−1 s−1. The equilibrium constant for enone hydration is 0.41. Rate constants for the analogous reactions for acrolein and crotonaldehyde could be obtained from the literature. There is a reasonable rate–equilibrium correlation for the retroaldol step. For the enone hydration step, rate and equilibrium constants respond differently to replacement of hydrogen by methyl. It is proposed that this results from release of strain after the rate-determining step by rotation about a single bond; this decrease in strain is reflected in the equilibrium constant but not in the rate constant.
Structural studies of organoboron compounds. XIII. Preparation and crystal and molecular structure of bis[(salicylaldoximato(2−))phenylboron]
Authors: Rettig Steven J. , Trotter James
Published: May 2006

The reaction of (C6H5)2BOH with salicylaldoxime yielded [(C7H5NO2)BC6H5]2 via a boron–carbon bond cleavage reaction. Crystals of bis[(salicylaldoximato(2−))phenylboron] are triclinic, a = 9.219(1), b = 11.240(1), c = 12.086(1) Å, α = 100.682(7), β = 112.224(6), γ = 92.189(7)°, Z = 2, space group [Formula: see text]. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.036 and Rw = 0.049 for 3433 reflections with I ≥ 3σ(I). The molecule, which has approximate C2 symmetry, contains a system of five fused six-membered rings including the first crystallographically characterized B2N2O2 ring. The compound is stabilized both by intramolecular N → B coordination and by resonance delocalization and contains boron atoms in a distorted tetrahedral environment. Bond lengths (corrected for libration) are: O—B, 1.469(2)–1.488(2), N—B, 1.602(2) and 1.575(2), C—B, 1.598(2) and 1.599(2) Å.
1-(Dialkylaminomethyl)-azetidin-2-ones. Intermediates in a highly stereoselective preparation of trans-3,4-disubstituted azetidin-2-ones
Authors: Hamlet A. Bevin , Durst Tony
Published: May 2006

The use of dialkylaminomethyl derivatives as a new β-lactam N—H protecting group is described. The group is stable to basic reagents but is readily removed with dilute aqueous acids. 1-Dialkylaminomethyl derivatives bearing a 4-substituent are converted in good yield and with high stereoselectivity into trans-3,4-disubstituted derivatives via reaction with LDA and subsequent addition of electrophiles. The products of several of these sequences are of interest as intermediates to thienamycin related substances.
Methylenecyclohexenes: inversion barriers from the far-infrared spectra
Authors: Smithson Tracy L. , Ibrahim Nan , Wieser Hal
Published: May 2006

The far-infrared spectra of 3-methylenecyclohexene, 4-methylenecyclohexene, and 1-methyl-3-methylenecyclohexene in the region of 80–400 cm−1 are reported and interpreted mainly with a view to the two lowest out-of-plane deformations of the cyclohexene ring. Typical C-type band sequences are observed and interpreted in terms of ring inversion modes. Barriers to inversion are determined by means of a one-dimensional Hamiltonian with a quadratic-quartic potential function. Possible ground state geometries and forms of the inversion coordinates are discussed and compared to those thought to occur in the analogous cyclohexenones.
Effect of the partial pressures of oxygen and water vapour on the dispersity of α-Cr2O3 obtained by thermal decomposition of hydrated chromium(III) oxide
Authors: Klissurski Dimitar G. , Bluskov Vladimir N.
Published: May 2006

The effect of water vapour and oxygen partial pressure on the thermal decomposition of hydrated chromium (III) oxide has been studied. A decrease in the water vapour partial pressure from 20 to 1 × 10−3 mm Hg has been found to produce a sharp increase in the specific surface area of the decomposition product (α-Cr2O3). Decomposition in an argon atmosphere leads to highly dispersed α-Cr2O3 even at relatively high temperatures (400–500 °C).
Coupling of allylic pivalates with lithium and magnesium organocopper reagents. Reversal of regiochemistry
Authors: Liu Hsing-Jang , Ho Li-Kang
Published: May 2006

Allylic pivalates undergo efficient coupling with both lithium diorganocuprates and RMgX–Cul (2:1) complexes resulting in the predominant formation of the "SN2"-type and the "SN2′"-type products respectively.
Barriers to rotation of the cyclopentadienyl ligand: spin-lattice relaxation time measurements and atom–atom potential calculations on cyclopentadienyl manganese and rhenium tricarbonyl and vanadium tetracarbonyl complexes
Authors: Gilson D. F. R. , Gomez G. , Butler I. S. , Fitzpatrick P. J.
Published: May 2006

The barriers to cyclopentadienyl ring rotation in the solid phase have been measured by spin-lattice relaxation time methods for the organometallic complexes CpMn(CO)3 (7.24 kJ mol−1), CpRe(CO)3 (7.15 kJ mol−1), and CpV(CO)4 (7.07 kJ mol−1), where Cp = η5-C5H5. Nonbonded atom–atom potential calculations of the barriers in these complexes and in BzCr(CO)3 (Bz = η6-C6H6) show that the molecular conformation of the Mn and Re compounds is determined by crystal packing forces and that concerted ring motions are possible for the cyclopentadienyl complexes, but not for the benzene chromium tricarbonyl.
Nuclear mean free paths and transparency at intermediate energies
Authors: Karol Paul J.
Published: May 2006

The soft-spheres model of nuclear reaction cross sections incorporating tapered density distributions is used to evaluate nucleon mean free paths and transparencies at intermediate energies. Comparison with similar calculations employing uniform density distributions shows the latter to give misleading results that nevertheless have been used in recent years as evidence that the physics of the nucleon–nucleon interaction within nuclei is incompletely understood.
Molecular models for recombination and disproportionation of radicals
Authors: Benson Sidney W.
Published: May 2006

The modified Gorin model of recombination as a long range interaction of weakly bound radicals, constrained only by steric forces, is rederived to give a collision impact parameter 11% larger than rmax, the separation at the centrifugal maximum. This larger impact parameter resolves some of the earlier difficulties with secondary and tertiary radicals. By imposing a new constraint, that the orientation of the radicals be such as to permit exchange forces to act, a new model is developed in which kr = 1/4 Zr α, where a represents the product of fractions of active surface areas of each radical available for bonding. Excellent agreement is obtained in estimating values of kr.Analysis of disproportionation is made to show that it cannot be described by the tight transition state but must also be governed by similar, long range exchange forces between the bond being attacked and the same "active surface" of the abstracting radical. Using an ad hoc radius for [Formula: see text]equal to 4 Å it is possible to reproduce the data on alkyl radical disproportionation to within ± 10%.The model predicts a small decrease in rate of recombination with increasing temperature. This decrease is more pronounced for bulkier radicals and at higher temperatures (> 900 K).
Quenching of by O(3P), O2(a1Δg), and other gases
Authors: Kenner Rex D. , Ogryzlo Elmer A.
Published: May 2006

Spectroscopic and kinetic results for the quenching of [Formula: see text] are presented, including the first reported laboratory observation of gas phase emission from vibrational levels greater than zero for this state. In addition, the absolute rate constants for quenching of the lowest vibrational level by O(3P), O2(a1Δg), [Formula: see text], CO2, SF6, HE, and Ar are given. These results are compared with the results of atmospheric modeling studies. Qualitative evidence is presented for the formation of O2(a1Δg) and [Formula: see text] in the quenching of this state.
ipso Halogenation. II. Bromination of phenols, isomerization and disproportionation of bromophenols, and dienone–phenol rearrangement of bromodienones
Authors: Fischer Alfred , Henderson George Narayanan
Published: May 2006

Bromination of p-cresol, 2-bromo-p-cresol, 3,4-dimethylphenol, and mesitol in trifluoromethanesulfonic acid gives as the main product the bromo derivative with bromine meta to hydroxyl, a result attributed to the intermediate formation of a bromodienone and its rearrangement. Phenol does not give m-bromophenol in trifluoromethanesulfonic acid. 4-Bromo-2,4,6-trimethylcyclohexa-2,5-dienone rearranges to 3-bromomesitol in trifluoromethanesulfonic acid and, similarly, 2,4,6-tribromo-4-methylcyclohexa-2,5-dienone rearranges to 2,3,6-tribromo-4-methylphenol. Under appropriate conditions debromination of bromodienones is competitive with rearrangement. Tetramethylammonium bromide in trifluoromethanesulfonic acid is an effective reagent for isomerization and disproportionation of bromophenols. Tetramethylammonium iodide in trifluoromethanesulfonic acid is an effective reagent for selective debromination of bromophenols at the ortho and para positions.
Heterogeneous processes in the pyrolysis of ethane in contact with surfaces of SiO2, C, KCl, and PbO
Authors: Pacey Philip D. , Wimalasena Jayantha H.
Published: May 2006

Heterogeneous termination reactions in the pyrolysis of ethane have been investigated by three methods, involving measurements of the reductions in the steady state rates of formation of C2H4 and C4H10 and of the reduction in the induction period in the presence of active surfaces. Equations were developed for the approach of the concentration of C2H5 to its steady state value when both first and second order termination reactions occur. Experiments have been performed at about 904 K with from 2.8 × 10−4 to 2.3 × 10−3 mol L−1 of C2H6 in the presence of surfaces of SiO2, PbO, KCl, and C. Data from the literature have been reinterpreted. The data may be most simply explained if the main surface termination on most surfaces is first order with respect to gaseous C2H5. Collisional termination probabilities, γ, for this reaction were calculated to be: KCl, 905 K, 3 × 10−4; C, 903 K, 3 × 10−4; SiO2, 894 K, 6 × 10−5; 823 K, 10−5; PbO, 833 K, 6 × 10−5; Pyrex, 833 K, 4 × 10−6.
A total synthesis of (±)-biotin
Authors: Whitney Ralph Allen
Published: May 2006

A total synthesis of (±)-biotin 1 based on the photochemical cycloaddition reaction of 1,3-diacetylimidazolin-2-one 2 with 3,4-dihydro-2-methoxy-2H-pyran 3 is described. The photoadduct 4 was converted into the lactone 6, which bears the complete carbon framework and all the requisite stereochemical features, via hydrolysis, Wittig olefination, and catalytic hydrogenation to the cyclobutanol 5 followed by oxidative rearrangement. Subsequent conversion of the lactone to (±)-biotin followed from literature precedent (5).
On the positional reactivity order in the sulfuric acid sulfonation of the two naphthalenesulfonic acids
Authors: de Wit Peter , Cerfontain Hans
Published: May 2006

The sulfonation in 98.5% H2SO4 at 25.0 °C of naphthalene-1-sulfonic acid yields 58% 1,5-, 32% 1,6-, and 10% 1,7-disulfonic acids and that of the 2-sulfonic acid 4% 1,3-, 74% 1,6-, 18% 1,7-, and 4% 2,6- + 2,7-disulfonic acids. Further sulfonation of the latter disulfonic acid mixture in 105.2% H2SO4 at 25.0 °C yields 78% 1,3,6- and 12% 1,3,5- + 1,3,7-trisulfonic acids. Reaction of naphthalene-1,5-disulfonic acid with 105.2% H2SO4 at 25 °C yields 5-sulfonaphthalene-1-sulfonic anhydride.Partial rate factors for the sulfonation of naphthalene-1- and -2-sulfonate in highly concentrated aqueous sulfuric acid (where the sulfonating entity is H2S2O7) are reported. They are discussed in terms of the difference in the reactivity of the α- and β-positions of the naphthalene skeleton and the electronic and steric effects of the sulfonate substituent already present.
Molecular rearrangements. Part XX. Thermolysis of carboxylic acid esters
Authors: Aly M. M. , Badr M. Z. A. , Fahmy A. M. , Mahgoub S. A.
Published: May 2006

Thermolysis of phenyl benzoate on heating under reflux for ca. 10 days in a nitrogen atmosphere gives phenol, o- and p-hydroxy biphenyl, biphenyl, and carbon monoxide. Phenyl phenylacetate under the same conditions gives toluene, bibenzyl, stilbene, phenol, o- and p-benzylphenol, 9-phenylxanthene, water, and carbon monoxide. Thermolysis of benzyl benzoate is accompanied by decarboxylation and the formation of toluene, diphenylmethane, bibenzyl, stilbene, and biphenyl. Thermolysis of benzyl phenylacetate proceeds smoothly, affording carbon dioxide, toluene, bibenzyl, and stilbene. It was concluded that thermolyses of esters proceeds through a free radical mechanism involving homolytic fission of either the O—CO or O–alkyl bond with subsequent decomposition of the radicals so formed.
Electrical and thermal properties of Na2SO4 doped with NaVO3, Ln2(SO4)3 (Ln = Eu, Pr)
Authors: Imanaka Nobuhito , Adachi Gin-Ya , Shiokawa Jiro
Published: May 2006

In order to develop useful solid electrolytes for SO2 detectors, Na2SO4, Na2SO4–Eu2(SO4)3, Na2SO4–NaVO3, and Na2SO4–NaVO3–Ln2(SO4)3 (Ln = Eu, Pr) systems have been prepared, and their electrical and thermal properties have been measured. By doping Na2SO4 with Eu2(SO4)3, the electrical conductivity increases and the apparent activation energy of the Na2SO4–Eu2(SO4)3 system shows a value between those of Na2SO4-III and Na2SO4-I. Addition of NaVO3 and Ln2(SO4)3 (Ln = Eu, Pr) to Na2SO4 suppressed the phase transformation, by stabilizing the structure of the Na2SO4-I phase even at a relatively low temperature.
Rate enhancements for the nickel(II)–PADA complexation in mixed anionic micelles
Authors: Fletcher Paul D. I. , Hicks Joanne R. , Reinsborough Vincent C.
Published: May 2006

Rate enhancements for the [Formula: see text] and pyridine-2-azo-p-dimethylaniline (PADA) reaction have been obtained in four simple equimolar binary micellar systems: sodium dodecylsulfate – sodium decylsulfate, sodium dodecylsulfate – sodium octylsulfate, sodium octylsulfate – sodium hexylsulfate, and sodium octylsulfate – sodium octanesulfonate. The rate enhancement curves were similar to those obtained for pure surfactants and were consistent with a 1:1 mixed micelle except for the third system where the micelle was richer in sodium octylsulfate. The kinetic analysis revealed no dramatic changes in hydrophobic or electrostatic forces on forming the mixed micelles
A quadruply bonded dimolybdenum compound containing a novel bridging and chelating hexadentate ligand
Authors: Breakell Kenneth R. , Rettig Steven J. , Storr Alan , Trotter James
Published: May 2006

The synthesis, physical properties, and molecular structure of (N2C3H)+[Mo2(μ-CH3CO2)[CH3Ga(N2C3H3)O]4]−•2(C4H8O) are reported. Crystals of pyrazolium (μ-acetato)[1,3,5,7-tetramethyl-1,3,5,7-tetrakis(pyrazol-1-yl)cyclotetragalloxanato(4−)]dimolybdate(II)-bis(tetrahydrofuran) are orthorhombic, a = 10.638(2), b = 32.779(4), c = 12.617(1) Å, Z = 4, space group Cmcm. The structure was solved by Patterson and Fourier syntheses and was refined by full-matrix least-squares procedures to R = 0.032 and Rw = 0.041 for 1957 reflections with I ≥ 3σ(I). The structure consists of THF molecules and (N2C3H5)+[Mo2(μ-CH3CO2)[CH3Ga(N2C3H3)O]4]− ion-pair units, the latter displaying exact C2v symmetry. The pyrazolium cation is joined to the complex anion by a pair of strong [Formula: see text] hydrogen bonds [Formula: see text]. The Mo24+ unit is bridged by a single acetato group, the remaining coordination sites being occupied by the hexadentate bridging and chelating [CH3Ga(N2C3H3)O]44− ligand. Bond lengths are: Mo—Mo = 2.127(I), Mo—N = 2.151(3), Mo—O = 2.090(4) and 2.115(4), Ga—O = 1.853(2) and 1.861(2), Ga—N = 1.961(3), and Ga—C = 1.950(6) Å.
The thermal decomposition of azobenzene
Authors: Barton Donald , Hodgett Michael , Skirving Paul , Whelton Michael , Winter Keith , Vardy Cathy
Published: May 2006

The rate of nitrogen formation during the thermal decomposition of azobenzene in static and stirred-flow systems was measured over the temperature range of 368.9 °C to 437.4 °C. The first order rate constant was found to be given by the expression[Formula: see text]A consideration of the equilibrium constant between cis-azobenzene and trans-azobenzenc, and the rate of attainment of equilibrium, leads to the conclusion that a small concentration of cis-azobenzene is always present, at equilibrium with the trans isomer. Since the cis isomer is likely to be more reactive than the trans isomer the rate constant cannot be ascribed to the trans isomer alone. No effect of variation of surface-to-volume ratio could be detected. Some preliminary experiments in which toluene and ethylene were employed as additives indicated that these did not affect the rate of formation of nitrogen. Nevertheless, because of a certain amount of scatter in the results, a small effect could not be excluded. There were at least nine products, in addition to nitrogen.
β-Lactams. XI. Synthesis of N-phosphorylated mono- and bicyclic β-lactams
Authors: Just George , Dugat Denise , Liu Whi-Yu
Published: May 2006

Starting from appropriately.substituted monocyclic β-lactam, N-phosphorylated mono- and bicyclic β-lactams have been synthesized.
Infrared spectra of crystalline n-alkanes. Changes observed during the phase I → phase II transition
Authors: Casal Hector L. , Cameron David G. , Mantsch Henry H.
Published: May 2006

Detailed measurements of the changes in the infrared spectra of n-nonadceanc and n-heneicosane on transition from the orthorhombic to the so-called "hexagonal" or "rotator" phase are reported.
Comparative nitrosation of etintidine and cimetidine
Authors: Montzka Thomas A. , Juby Peter F. , Matiskella John D. , Holava Henry M. , Crenshaw R. R.
Published: May 2006

Etintidine (4), a new histamine H2-receptor antagonist, was compared with cimetidine (1) for susceptibility to in vitro nitrosation at pH 1 and pH 3. Each agent formed two mono-N-nitrosoguanidine derivatives: N-cyano-N′-{2-[(5-methyl-1H-imidazol-4-yl)methylthio]ethyl}-N″-nitroso-N″-(2-propynyl)guanidine (5) and N-cyano-N′-{2-[5-methyl-1H-imidazol-4-yl)methylthio]ethyl}- N′-nitroso-N″-(2-propynyl)guanidine (6) from etintidine and N-cyano-N′-methyl-N″-{2-[(5-methyl-1H-imidazol-4-yl)methylthio]ethyl}- N′-nitrosoguanidinc (2) and N-cyano-N′-methyl-N"-{2-[(5-methyl-1H-imidazol-4-yl)methyl-thio]ethyl}-N′-nitrosoguanidine (11) from cimetidine. The N-nitroso derivative 5 from etintidine cyclized to 2-cyanoimino-3-{2-((5-methyl-1H-imidazol-4-yl)methylthio]ethyl}-N″-methylene-1-nitroso-imidazoline (7) at neutral or basic pH's. Both agents were nitrosated less at pH 3 than at pH 1, and at both pH's nitrosation of etintidine was considerably less than that of cimetidine. At pH 1, with a nitrite concentration about 150–500 times that expected in fasting human gastric juice, formation of 5 and 6 from etintidine was barely detectable (each < 0.5%). Comments are made on the standard WHO conditions for investigating nitrosation of drugs.
Heteroanthracyclines. 1. 4-Demethoxyxanthodaunomycinone (6,7,9,11-tetrahydroxy-9-acetyl-7,8,9,10-tetrahydrobenzo(B)xanthen-12-one)
Authors: Wong Chiu-Ming , Haque Wasimul , Lam Hing-Yat , Marat Kirk , Bock E. , Mi Ai-Qiao
Published: May 2006

Two heteroanthracyclinones, namely 4-demethoxyxanthodaunomycinone (29) and its epimer 4-demethoxy-7-epixantho-daunomycinone (30), were synthesized using 2-acetyl-5,8-dimethoxytetralin (12) as starting material. Condensation of 12 with 2-methoxybenzoic acid followed by hydrolysis and oxidative cyclization gave xanthones 17 and 18 which were converted to 19 and 20 for the purpose of separation and structure assignment by dipole moment. Hydrolysis of 19 followed by alkylation with chloromethyl methyl ether and oxidation with molecular oxygen gave 26 and 27, which on acid hydrolysis gave 4-demethoxyxanthodaunomycinone (29) and 4-demethoxy-7-epixanthodaunomycinone (30). Preliminary biological assays with MCF-7, a human breast cancer cell line, showed that both 29 and 30 were weakly active while daunomycinonc, the aglycone of 2, showed no activity under similar conditions.