bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthetic applications and spectroscopic investigations of the (NSCl)3–SO2Cl2 system
Authors: Apblett Allen , Chivers Tristram
Published: April 2011

Solutions of (NSCl)3 in the presence of excess SO2Cl2 behave as a source of the synthetic equivalent "NSCl3" in reactions with methacrylonitrile or thioacetamide to give 4-cyanoisothiazole (78%) or 5-methyl-1,3,2,4-dithiadiazolium chloride (63%), respectively. In the reaction of this reagent with thiobenzamide both 5-phenyl-1,3,2,4-dithiadiazolium chloride (42%) and 3,5-diphenyl-1,2,4-thiadiazole (51%) are produced. The treatment of the (NSCl)3-SO2Cl2 system with 2-aminobenzenethiol yields 2,4-C6H3Cl2NSCl2, which is converted to 2,4-(C6H3Cl2N)2S upon heating at 80 °C in toluene or by reduction with Ph3Sb or mercury. The reaction of 2-aminobenzenethiol with excess SO2Cl2, in the absence of (NSCl)3, produces 2,4,6-C6H2Cl3NSCl2. Attempts to characterize the active species in the (NSCl)3-SO2Cl2 system by 14N and 33S nmr, Raman and infrared spectroscopy are also described. Keywords: cyclotrithiazyl chloride, isothiazole, dithiadiazolium, arylimidosulfurous dichloride, 14N nmr.
Mechanistic studies on diamine oxidase: oxidation of α,ω-diamines does not involve an enamine intermediate
Authors: Gavin Stephen S. , Equi Angela M. , Robins David J.
Published: April 2011

Three β,β,β′,β′-2H4-labelled α,ω-diamines were synthesized and incubated with pea seedling diamine oxidase. The aminoaldehydes formed by oxidative deamination cyclized to the corresponding imines, which were trapped with benzoylacetic acid. In all three cases the acetophenone derivatives produced were shown by NMR and mass spectrometry to contain four deuterium atoms. The retention of all four deuterium atoms demonstrates that oxidative deamination of α,ω-diamines catalyzed by pea seedling diamine oxidase does not involve an enamine intermediate as previously suggested.
Site-directed mutagenesis of farnesyl diphosphate synthase; effect of substitution on the three carboxyl-terminal amino acids
Authors: Koyama Tanetoshi , Saito Kazuhiro , Ogura Kyozo , Obata Shusei , Takeshita Ayumi
Published: April 2011

Site-directed mutation was introduced into the gene for the farnesyl diphosphate synthase of Bacillus stearothermophilus. To investigate the significance of the three C-terminal amino acids, where arginine is completely conserved throughout the farnesyl diphosphate synthases of prokaryotes and eukaryotes, three kinds of mutant enzymes, R295V, D296G, and H297L, which have replacements of arginine-295 with valine, aspartate-296 with glycine, and histidine-297 with leucine, respectively, were overproduced and purified to homogeneity. All of the three mutant enzymes showed similar catalytic activities to that of the wild-type enzyme, indicating that the basic amino acids including the conserved arginine in the C-terminal region are not essential for catalytic function. They were also similar to the wild-type enzyme with respect to pH optima, thermostability, reaction product, and kinetic parameters for allylic substrates. However, their Km values for isopentenyl diphosphate are approximately twice that of the wild type.
Biosynthesis of pyrrolizidine alkaloids: putrescine and spermidine are essential substrates of enzymatic homospermidine formation
Authors: Böttcher Frank , Ober Dietrich , Hartmann Thomas
Published: April 2011

sym-Homospermidine, the first pathway-specific intermediate of pyrrolizidine alkaloid (PA) biosynthesis, is formed from two moles of putrescine in an NAD+-dependent reaction catalyzed by homospermidine synthase (HSS). In the overall process catalyzed by HSS, NAD+ seems to function as hydride acceptor in the first part of the reaction and subsequently as hydride donor in the second part. This was proved with chirally Cl-deuterated putrescines. Both a bacterial HSS (isolated from Rhodopseudomonas viridis) and the enzyme from PA-producing Eupatorium cannabinum transformed (R)-[1-2H]putrescine and (S)-[1-2H]-putrescine into homospermidine with a 100% retention of deuterium. Studies with deuterated and 14C-labeled substrates revealed that in the presence of putrescine spermidine is a substrate of HSS. The putrescine semialdehyde moiety of spermidine is combined with putrescine and 1,3-diaminopropane is released. Kinetic studies with plant HSS documented that the putrescine semialdehyde moiety of spermidine is incorporated into homospermidine with the same affinity (Km) and activity (Vmax) as putrescine. Plant HSS is highly specific for putrescine and spermidine; spermidine is not a substrate in the absence of putrescine. It is suggested that in the biosynthesis of homospermidine and thus PAs, one of the two C4 units is derived from spermidine and the other one from putrescine. A scheme of the HSS-catalyzed reaction is proposed that fully accounts for the enzymatic data and the results of previous tracer studies. Bacterial HSS is less substrate specific and not as well adapted as plant HSS to accept spermidine as a substrate.
Dynamics of silicate exchange in highly alkaline potassium silicate solutions
Authors: Vallazza Eva , Bain Alex D , Swaddle Thomas W
Published: April 2011

The problem of measuring the kinetics of Si exchange between aqueous silicate species by 29Si NMR has been revisited, using highly alkaline KOH solutions (2.8 mol SiIV per kg solvent, [SiIV]/K2O = 0.43) at 60-90°C to minimize the number of silicate species present. Longitudinal 29Si relaxation times T1 and apparent rate constants estimated from line-shape analysis (LSA) varied markedly with the degree of purity of the KOH used, but rate constants k obtained by selective inversion-recovery (SIR) using the CIFIT data-fitting program were independent of the source of KOH and were smaller than those obtained from LSA by at least an order of magnitude. Although only four kinetically significant silicate anions (monomer M, dimer D, linear trimer L, and cyclic trimer C) were present, overlap of the D and L resonances prevented complete analysis of the SIR data. True rate constants could therefore be obtained only for the M-D exchange (for formation of D, k1 (90°C) = 0.13 ± 0.01 kg mol -1 s-1, Δ H1dagger = 67.4 kJ mol-1, Δ S1dagger = -78 J K-1 mol-1; for dissociation of D, k-1 (90°C) = 1.4 ± 0.1 s-1, Δ H-1dagger = 64.7 kJ mol-1, and Δ S1dagger = -66 J K-1 mol-1). Models that included L as the precursor of C (MDLC mechanism) showed, within the limitations imposed by D-L band overlap, that the reactivities of M, D, L, and C in Si-O-Si link formation or dissociation were all roughly comparable. Good fits of the experimental data, however, and equally reliable rate constants for the M-D exchange, could be obtained with models that ignored the presence of L entirely (MDC mechanism). The simple MDC model also provides consistent apparent rate constants kC and k-C for the overall formation of C from M + D and the reverse process, respectively, by SIR of either M or C ( Δ HCdagger = 76.5 kJ mol-1, Δ SCdagger = -57 J K-1 mol-1; Δ H-Cdagger = 88.6 kJ mol-1, and Δ S-Cdagger = -7 J K-1 mol-1).Key words: kinetics, silicates, 29Si NMR.
A calculational and ultraviolet photoelectron spectroscopic study of distorted amides
Authors: Werstiuk N H , Muchall H M , Roy C D , Ma J , Brown R S
Published: April 2011

Distorted amides 3,4-dihydro-2-oxo-1,4-ethanoquinoline (1a), 3,4-dihydro-2-oxo-1,4-propanoquinoline (1b), 3,3,4,5-tetrahydro-2-oxo-1,5-ethanobenzazepine (1c), and 3,3,4,5-tetrahydro-2-oxo-1,5-propanobenzazepine (1d) and the model compounds 2,N-dimethyl-acetanilide (2a), 2,N,N-trimethylaniline (3), and benzoquinuclidine (4) have been studied calculationally and with He(I) ultraviolet photoelectron spectroscopy. We find good agreement between experimentally obtained ionization energies for 1b, 1c, 1d, 2a, 3, and 4 and values calculated with HAM/3 using the equilibrium geometries obtained at the HF/6-31G** level of theory. An excellent correlation between experimental ionization energies and orbital energies from Becke3LYP/6-31+G* calculations led to the characterization of the highest occupied molecular orbitals for these compounds and for 1a, whose photoelectron spectrum could not be obtained due to its reactivity in the solid state.Key words: distorted amides, He(I) photoelectron spectroscopy, Becke3LYP, molecular orbitals.
A benzo-fused oxapenem from a β-lactam-4-ylidene
Authors: Couture Philippe , Warkentin John
Published: April 2011

Spiro-fused β -lactam oxadiazoline 2a was prepared from acetone semicarbazone in five steps. Thermolysis of 2a at 100°C in benzene led to carbene 3a, which cyclized to the benzo-fused oxapenem derivative 4 via intramolecular OH insertion. Compound 10, with a β -lactam ring linked to an azetidinedione ring, was a minor product.Key words: benzoxapenem, carbene, β -lactam-4-ylidene, OH insertion.
Article
Authors: Sun Sengen , Britten James F , Cow Christopher N , Matta Chérif F , Harrison Paul HM
Published: April 2011

The crystal structure of 3,4,7,8-tetramethylglycoluril (5) was determined by X-ray diffraction. The structure reveals a hydrogen-bonding motif in the crystal lattice that differs from that present in related glycolurils. The two sides of each molecule form part of two independent, but parallel, infinite helical chains. These chains are formed by the NH donor and C==O acceptor on one side of a glycoluril molecule, forming H-bonds to two different molecules at adjacent positions within the helix. On the other side of the same molecule, a similar motif generates another helix of opposite helicity to the first. The molecule has a crystallographic plane of symmetry through the two bridgehead carbon atoms and the two bridgehead methyl groups, which are syn-periplanar. Thus, 5 is similar to 3,4-dimethylglycoluril (3), but differs from some glycolurils, where there is a significant dihedral angle between the two bridgehead-to-bridgehead substituent bonds. Bond lengths and angles in 5 resemble those reported for 3, but bond lengths around the bridgehead positions are slightly lengthened relative to 3.Key words: glycoluril, 1,2,5,8-tetramethyl-2,6,7,8-tetraazabicyclo[3.3.0]octane-3,7-dione, X-ray diffraction, crystal structure, hydrogen-bond array.
Synthesis, spectroscopic characterization, and structural studies of organogermanium tri- and monothiocarbonates. Crystal structures of Me2Ge[S2CSEt]2, Ph3Ge[SCO2Me], Ph3Ge[SCO2(i-Pr)], and Ph2Ge[SCO2Me]2
Authors: Drake John E , Yang Jincai
Published: April 2011

Two series of S-alkyl trithiocarbonate derivatives of imethylgermane, Me2Ge[S2CSR]2, and halodiphenylgermane, Ph2GeX[S2CSR], where R = Me, i-Pr, n-Pr, n-Bu and X = Cl, Br, and three series of O-alkyl monothiocarbonate derivatives of triphenylgermane, Ph3Ge[SCO2R], diphenylgermane, Ph2Ge[SCO2R], and trimethylgermane, me3Ge[SCO2R], where R = Me, i-Pr, and n-Pr, have been prepared in 73-92% yields by the reaction of the potassium or sodium salt of the appropriate tri- or monothiocarbonic acid with dichlorodimethyl-, chlorotriphenyl-, dichlorodiphenyl-, and chlorotrimethylgermane. The compounds were principally characterized by infrared, Raman, and 1H and 13C NMR spectroscopy, including some variable temperature studies, as well as by mass spectrometry. Me2Ge[S2CSEt]2, 1: P21/m (No. 11) with cell parameters a = 6.647(4) Å, b = 7.423(2) Å, c = 16.290(4) Å, β = 91.07(3)°, V = 803.6(4) Å3, Z = 2, R = 0.0484,Rw = 0.0485. Ph3Ge[SCO2Me],13: P1bar (No. 2) with cell parameters a = 9.970(4) Å, b = 10.660(3) Å, c = 9.853(2) Å, α = 101.78(2)°, β = 109.98(2)°, γ = 89.76(3)°, V = 961.0(5) Å3, Z = 2, R = 0.0534, Rw = 0.0451. Ph3Ge[SCO2(i-Pr)], 14: P 1bar (No. 2) with cell parameters a = 14.386(7) Å, b = 18.598(6) Å, c = 9.223(3) Å, α = 102.85(3)°, β = 94.58(3)°, γ = 108.13(3)°, V = 2256(1) Å3, Z = 2, R = 0.0545, Rw = 0.0552. Ph2Ge[SCO2Me]2, 16: Cc, (No. 9) with cell parameters a = 11.790(4) Å, b = 13.696(5) Å, c = 23.232(6) Å, β = 92.26(3)°, V = 3748(2) Å3, Z = 8, R = 0.0563, Rw = 0.0512. The immediate environment about Ge is that of tetrahedral but the orientations of the thiocarbonate groups display interesting features.Key words: structure, germanium, phenyl, methyl, thiocarbonates.
Ultrasonic velocity and volumetric properties of isomeric butanediols plus water systems
Authors: Hawrylak Brent , Gracie Kim , Palepu R
Published: April 2011

Ultrasonic velocities and densities of binary aqueous solutions of isomeric butanediols were measured in the temperature range 298-318 K at 10 degree intervals over the entire composition range, and 5 degree intervals in the water-rich region. The experimental data in the dilute region, with mole fraction of water less than 0.1, was analysed to determine the partial molar volumes and adiabatic compressibilities of water at infinite dilution. The standard thermodynamic transfer functions were calculated to evaluate the environment of water at infinite dilution in these systems. From the compressibility isotherms, as a function of temperature in the water-rich region, the formation and the composition of clathrate-like structures in the liquid solutions was determined, and the nature of these structures was discussed.Key words: ultrasonic velocity, adiabatic compressibility, density, partial molar quantities, standard thermodynamic transfer functions.
Article
Authors: Zhao Yixing , Freeman Gordon R
Published: April 2011

As a foundation for a future measurement of solvated electron mobilities in alcohol-water mixed solvents, the electrical conductances of sodium tetraphenylboride (STPB) in methanol-water, ethanol-water, and 2-propanol-water were measured at different temperatures. The molar conductivity LAMBDA 0 (10-4 S m2 mol-1) of STPB at 298 K is 70 in pure water and 82 in pure methanol; in methanol-water mixed solvents it passes through a minimum, the value being 45 at 70 mol% water. In 2-propanol-water LAMBDA 0 (10-4 S m2 mol-1) at 298 K decreases rapidly from 70 in pure water to 22.6 in 80 mol% water, then gradually to 16.5 in pure 2-propanol. Behavior in ethanol-water is intermediate, with a minimum of 29.5 in 70 mol% water, gradually increasing to 35.5 in pure ethanol. The product of LAMBDA 0 and the solvent viscosity eta has a maximum at about 75 mol% water in methanol, 90 mol% water in ethanol, and 95 mol% water in 2-propanol. The effects are attributed to changes of solvent structure and of solvated ion radius as alcohol is added to water.Key words: alcohol-water mixed solvents, electrical conductivity, large ions, solvent effects, activation energy.
Remarkable efficiency of iron(III) versus manganese(III) tetraphenylporphyrins as catalysts for fast and quantitative oxidation of sulfides into sulfones by hydrogen peroxide
Authors: Marques Antonio , Matteo Massimo di , Ruasse Marie-Françoise
Published: April 2011

The efficiency of various metallo-phtalocyanines (Pht) and -tetraphenylporphyrins (TPP) as catalysts for the H2O2 oxidations of dibenzylsulfide, phenylchloroethylsulfide, and thioanisole is investigated in ethanol and acetonitrile, using imidazole as a cocatalyst. Neither PhtNiII nor TPPCoII exhibits any catalytic activity. PhtMnII and TPPMnIIICl accelerate markedly these reactions but do not promote quantitative oxidations, at most 70% of the sulfides being transformed into sulfoxides. In contrast, with PhtFeII sulfoxides are obtained with a 100% yield from sulfides. Finally, the only catalyst able to oxidize sulfides rapidly (<5 min), completely and quantitatively (100% sulfone) is TPPFeIIICl in EtOH. The absence of any by-product, disulfide in particular, suggests that a free sulfenium radical cation is not an active intermediate in these reactions. The marked differences in the behaviour of TPPMnIIICl and TPPFeIII Cl are analyzed by comparing the rates of the catalyst decomposition, of the sulfoxide and sulfone formation as a function of the hydrogen peroxide concentration. The results are discussed in terms of a competition between the several oxidative pathways and a possible mechanism for the oxygen transfer to sulfides.Key words: sulfide, oxidation, H2O2, manganese(III) or iron(III) tetraphenylporphyrin.
Article
Authors: Manners Ian
Published: April 2011

Ring-opening polymerization (ROP) of strained ring-tilted metallocenophanes can be achieved thermally, via anionic or cationic initiation, or by the use of transition-metal catalysts and provides access to a wide range of high molecular weight (Mw = 105-106, Mn > 105) poly(metallocenes). These materials possess a variety of interesting properties and many are very easy to prepare. This article provides an overview of our work, giving background to and an account of the initial discovery, and discusses work on the synthesis and properties of new poly(metallocenes) and related materials with particular emphasis on recent research directions.Key words: metallocene, ring-opening polymerization, ferrocenophane, organometallic polymer.
Isotope effects in nucleophilic substitution reactions X. The effect of changing the nucleophilic atom on ion-pairing in an SN2 reaction
Authors: Fang Yao-ren , Lai Zhu-gen , Westaway Kenneth Charles
Published: April 2011

The effect of ion-pairing in an SN2 reaction is very different when the nucleophilic atom is changed from sulfur to oxygen, i.e., changing the nucleophile from thiophenoxide ion to phenoxide ion. When the nucleophile is sodium thiophenoxide, ion-pairing markedly alters the secondary α -deuterium kinetic isotope effect (transition state structure) and the substituent effect found by changing the para substituent on the nucleophile. When the nucleophile is sodium phenoxide, ion-pairing does not significantly affect the secondary α -deuterium or the chlorine leaving group kinetic isotope effects (transition state structure) or the substituent effects found by changing a para substituent on the nucleophile or the substrate. The different effects of ion-pairing may occur because the electron density on the hard oxygen atom of the sodium phenoxide is not affected significantly by ion-pairing.Key words: nucleophilic substitution, SN2, kinetic isotope effect, transition state, substituent effects, ion-pair.
Are mesoionic compounds aromatic?
Authors: Simas Alfredo Mayall , Miller Joseph , de Athayade Filho Petrônio Filgueiras
Published: April 2011

We have evaluated the experimental evidence relevant to the structure and character of mesoionic compounds, accumulated for more than 100 years and including X-ray diffraction studies. We have also evaluated relevant theoretical studies. All these, including our own extensive work, lead us to conclude that mesoionic compounds are not aromatic. According to our recent definition “mesoionic compounds are planar five-membered heterocyclic betaines with at least one side chain whose α-atom is also in the ring plane and with dipole moments of the order of 5 D. Electrons are delocalized over two regions separated by what are essentially single bonds. One region, which includes the a-atom of the side chain is associated with the HOMO and negative π-charge whereas the other is associated with the LUMO and positive π-charge.” Key words: mesoionic compounds, betaines, aromaticity.
Article
Authors: Hunter Duncan H , McRoberts Chantelle , Vittal Jagadese J
Published: April 2011

Attempts to prepare 2,4-bisthiosemicarbamoylpentanediones 1 via literature precedent from 2,4-pentanedione and three different thiosemicarbazides resulted instead in the formation of cyclic pyrazolines 5. The preparation was attempted with thiosemicarbazide, 4-methylthiosemicarbazide, and 4-ethylthiosemicarbazide, respectively. A single-crystal X-ray structure study of the product from 4-methylthiosemicarbazide confirmed the pyrazoline structure. This observation serves to correct earlier misassignments of structure.Key words: pentanedione, bisthiosemicarbazone, pyrazoline, ethylenediamine.
Theoretical study of O - > X (S, Se, Te) coordination in organic compounds
Authors: Minyaev Ruslan M , Minkin Vladimir I
Published: April 2011

Ab initio (RHF/LanL2DZ, MP2(fc)/LanL2DZ, MP2(fc)/6-31G**, and MP2(fc)/6-311++G**) calculations were performed for a series of β -chalcogenovinylaldehydes, 1,6-dioxa-6a-chalcogenopentalenes, and bimolecular complexes of formaldehyde with chalcogen hydrides and chlorides. The calculations reproduce well the existence and experimentally observed structural peculiarities of the intra- and intermolecular Ο - > chalcogen attractive interactions that stabilize the hypervalent T-shaped bond configuration at a chalcogen atom. These interactions increase in the order S, Se, Te and with the increasing electronegativity of a substituent attached to the chalcogen center. The ab initio calculations performed predict the existence of sufficiently stable bimolecular complexes H2CO . . .XR1R2 (X = S, Se, Te; R1, R2 = H, Cl) with a complexation energy comparable to the energy of a strong hydrogen bond.Key words: ab initio calculations, chalcogen-containing compounds, intramolecular coordination.
Mechanism of the benzidine disproportionation of (arylhydrazo)pyridines. The reactions of 4-(4-chlorophenylazo)pyridine and -hydrazo)pyridine in acid media
Authors: Cox Robin A , Cheon Kap-Soo , Keum Sam-Rok , Buncel Erwin
Published: April 2011

A kinetic and product analysis study of the reactions of 4-(4-chlorophenylhydrazo)pyridine (1) and 4-(4-chlorophenylazo)pyridine (2) in acid media is reported. The disproportionation of two moles of 1 in aqueous sulfuric acid gives one mole of the oxidized product 2, and one mole each of the reduced products 4-chloroaniline and 4-aminopyridine. The azo compound 2, a product of the reaction of 1, undergoes a slower hydroxylation reaction in acid media, and this process was also investigated. The first-formed product in the reaction of 2 is probably 4-(4-hydroxyphenylazo)pyridine, the 4-chlorine being displaced. At the low substrate concentrations used for the kinetic measurements both reactions are straightforward, but at the much higher concentrations used for product isolation studies a complex product mixture results, one of the products being a dimer. The complexity is increased because 1 had to be used as its hydrochloride salt for reasons of stability, and the chloride ion can also react with the diprotonated substrates; chloride ion also accumulates in the system as it is displaced from 2 during the hydroxylation. Thus chloride ion competes with bisulfate ion (present in large excess) for the diprotonated substrates. Nevertheless, complete mechanistic schemes accounting for all of the observed products, including the dimer, could be derived and are presented. Values of pK BH2 2+ for 2 and two of the azo products, needed for the kinetic analysis, were measured using the excess acidity equilibrium method. The nucleophile reacting with protonated 2 in the rate-determining step of the hydroxylation was positively identified as being bisulfate ion by an excess acidity analysis. A comparison of the reaction of 1 with the equivalent reactions of two previously studied 4-(arylhydrazo)pyridines, 9 and 10, reveals that the benzidine disproportionation of these molecules is an A1 process with the second protonation being a pre-equilibrium; pK BH2 2+ values for the hydrazo compounds could not be measured as they react too quickly, but they could be determined from the kinetic data, using the excess acidity method. The rate-determining step is a thermally allowed 10-electron electrocyclic process of the diprotonated substrate, giving rise to an intermediate that undergoes fast reaction with a molecule of protonated substrate in a thermally allowed 14-electron electrocyclic process to give the observed products.Key words: azopyridines, benzidine, disproportionation, excess acidity, hydrazopyridines, hydroxylation, mechanism.
Thermodynamics of methanesulfonic acid, methanesulfonyl chloride, and methyl methanesulfonate
Authors: Guthrie J Peter , Stein Allan R , Huntington Anthony P
Published: April 2011

The heat of formation of liquid methanesulfonic acid, -178.09 ± 1.48, was determined by measuring the heat of reaction of methyl thiolacetate with aqueous hypochlorite solution to give aqueous methanesulfonate and acetate. The heats of formation of liquid methanesulfonyl chloride, -126.91 ± 1.54, and methyl methanesulfonate, -164.34 ± 1.58, were determined by measuring the heats of reaction of methanesulfonyl chloride with water or methanol in the presence of a suitable basic catalyst. Heats of vaporization (based on vapor-pressure data), entropies (based on ab initio molecular orbital calculations), and free energies of transfer from gas phase to aqueous solution were calculated leading to values for the free energies of formation in aqueous solution. The free energies of formation so determined were methanesulfonic acid, -151.72 ± 2.68, methanesulfonyl chloride, -101.29 ± 1.96, and methyl methanesulfonate, -127.28 ± 2.08. From these values the free energies of hydrolysis (leading to unionized methanesulfonic acid) are methanesulfonyl chloride, -25.11 ± 3.04, and methyl methanesulfonate, -9.90 ± 2.48.Key words: sulfonic acids, heat of formation, free energy of formation, hydrolysis.
Article
Authors: Zhang X -Z , Francis R C , Dutton D B , Hill R T
Published: April 2011

Peracetic acid (Pa) is now being used for totally chlorine-free delignification and bleaching of wood pulps. During the process, metals desorb from the pulp fibers into the aqueous solution. Of the relevant metals in bleaching systems, cobalt(II) and vanadium(V) are the most potent in wastefully decomposing Pa to O2. In the present study, radical scavenging by N,N'-(5-nitro-1,3-phenylene)-bisglutaramide (GAMID) indicates that free-radical mechanisms are operative. Kinetic data support a free-radical decomposition mechanism previously described for Co(II). A similar type of mechanism, involving VO(OH)2(aq) and VO(OH)3(aq), is postulated to partially explain catalysis by vanadium.Key words: peracetic acid, peroxymonosulfuric acid, transition metals, free radicals, acetoxy radical, peracetoxy radical.
Highly diastereoselective synthesis of 1,2-amino alcohols via nucleophilic addition of organocerium reagents to 4- and 5-oxazolidinonecarbaldehydes
Authors: Wee Andrew GH , Tang Fuxing
Published: April 2011

The reaction of chiral, non-racemic 4- and 5-oxazolidinonecarbaldehydes, 6 and 13, with organocerium reagents proceeds efficiently with good to excellent diastereoselectivity to give syn and anti alcohols, respectively. A model to explain the observed diastereoselectivity of the reaction of 6 and 13 is provided. The utility of this method for the synthesis of amino alcohols is exemplified by the synthesis of C-18-D-ribo-phytosphingosine from the anti alcohol 14f.Key words: oxazolidinonecarbaldehydes, organocerium, diastereoselective, amino alcohols, C-18-ribo-phytospingosine.
A new diaza heteroaromatic crown of 3,5-disubstituted 1H-pyrazole which forms solid dinuclear complexes with lipophilic phenethylamines
Authors: Sanz Ana M , Navarro Pilar , Gomez-Contreras Fernando , Pardo Mercedes , Pèpe Gèrard , Samat André
Published: April 2011

The cyclic stannoxane obtained from N-methyldiethanolamine and dibutyltin oxide reacts with 1H-pyrazole-3,5-dicarbonyl dichloride to afford the new 26-membered diaza tetraester crown 3. In neutral medium, the above crown forms 1:2 solid dinuclear complexes with phenethylamine (3a) and homoveratrylamine (3b), which, after crystallization from acetonitrile, were isolated in high yield (90% and 85%, respectively). The 3, 3a, and 3b structures were identified from their analytical and spectroscopic (1H, 13C NMR, and MS (FAB)) data. The spectroscopic properties of 3a and 3b are demonstrating that, in each complexation centre, simultaneously to the strong participation of the four pyrazole nitrogens, an additional weaker interaction between the aliphatic nitrogen of the side chain and the amine is involved. Comparison of the total interaction energies calculated (GenMol software) for phenethylamine-derived complex (3a) and homoveratrylamine-derived one (3b) suggests that the o-dimethoxy substitution of the guest aromatic ring could be improving the stability of 3b in relation to 3a.Key words: diazacrown, 1H-pyrazole, dinuclear, complexes, phenethylamines.
Computer simulation of time correlation functions and matter transport coefficients for a model order–disorder alloy
Authors: Qin Ziqiang , Allnatt Alan R , Allnatt E Loftus
Published: April 2011

The time correlation functions associated with the Onsager phenomenological coefficients for isothermal matter transport have been calculated by Monte Carlo simulation for a binary system (A,B) at the equiatomic composition according to the Kikuchi-Sato model of an order-disorder alloy with vacancy transport mechanism. The diagonal (AA) time correlation functions are positive, decay monotonically to zero, and exhibit a long time tail where they vary as t-n where t is time; the exponent n varies weakly with temperature at high temperatures and more rapidly as the temperature is lowered through the order-disorder transition temperature. In the region of short-range order the off-diagonal (AB) time correlation function is negative but otherwise shows similar behaviour to the diagonal one, although as the transition temperature is approached n varies more rapidly. At the transition temperature and below, the off-diagonal time correlation function increases from an initial negative value to a maximum where it is positive and then, at later times, decreases to zero. The implications of these observations for approximate theoretical calculations of the phenomenological coefficients are briefly indicated.Key words: diffusion, non-equilibrium phenomena, statistical mechanics, transport properties.
Article
Authors: Jacobs Patrick WM , Vernon Marcia L
Published: April 2011

New crystal potentials have been developed for rubidium chloride, bromide, iodide, and sulphide, and also strontium chloride, by first calculating the pair-interactions in the electron-gas approximation and then refitting the potential parameters to available crystal properties. These potentials were then further tested by calculating the phonon dispersion in these materials along principal symmetry directions, with generally good agreement with experiment (except for rubidium sulphide for which no experimental neutron scattering data are available). The potentials were then used in the HADES computer code to calculate the energies of formation and migration of point defects in these materials. Our calculations indicate that several transport mechanisms may be important in the Rb halides and this has been verified in the case of RbCl by a recent very detailed analysis of the ionic conductivity of pure and doped RbCl.Key words: rubidium halides, defect energies, ionic transport, phonon dispersion, strontium chloride, rubidium sulphide.
Article
Authors: Horton J Hugh , Rasmusson Johann , Shapter Joseph G , Norton Peter R
Published: April 2011

The adsorption of the organometallic compounds bis(hexafluoroacetylacetonato)zinc(II) (Zn(hfac)2) and bis(hexafluoroacetylacetonato)nickel(II) (Ni(hfac)2) on the surface of Si(111)-7×7 were studied by a combination of scanning tunnelling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). These compounds are analogues of the compound bis(hexafluoroacetylacetonato)copper(II), which is an important precursor for the chemical vapour deposition of copper that we have previously studied. Both XPS and STM results indicate that the Zn(hfac)2 is adsorbed intact on the surface, and remains intact on the surface at temperatures up to 300 K. The XPS shows a transition from a physisorbed state to a chemisorbed state at temperatures between 160 and 300 K. At higher temperatures Zn(hfac)2 decomposed to form Zn and fluorocarbon fragments. The metal component diffused into the substrate. The Ni(hfac)2 complex could not be successfully adsorbed on the Si surface: it was shown that this was due to decomposition of the molecule in the vapour phase, probably due to the higher temperatures needed to evaporate this relatively involatile compound.Key words: scanning tunnelling microscopy, chemical vapour deposition, zinc, copper.
Article
Authors: Asgari Faraj , Argyropoulos Dimitris S
Published: April 2011

The complex interaction of softwood residual kraft lignin with oxygen at elevated temperatures, pressures, and pH's was investigated by isolating and systematically oxidizing the lignin, as a function of time and temperature. The isolation of the oxidized lignin was carried out using a multistep procedure developed specifically to recover all species. Detailed quantitative 31P NMR measurements provided, for the first time, three-dimensional plots describing the formation and (or) elimination of the various functional groups. Oxidative demethoxylation reactions were found to induce the formation of catechols, which are, most likely, reactive intermediates of the oxidation. The rate of carboxylic acid formation and guaiacyl phenol elimination was found to follow two distinct phases: a rapid initial phase followed by a slower phase. More specifically, the rate of carboxylic acid group formation was found to dramatically increase as the reaction temperature increased, analogous to the profiles obtained for the elimination of guaiacyl phenolic units. At reaction temperatures typical of conventional commercial oxygen delignification installations (80-100°C), only minor oxidation was found to occur within the lignin. At these temperatures, increasing the reaction time did not significantly aid the formation of carboxylic acid groups on lignin despite the idealized two-phase homogeneous conditions. The technological ramifications of these data imply that a three-phase oxygen delignification system, operating at temperatures below 100°C, causes only minor oxidative changes to the structure of the lignin in the fibre. It was also possible to isolate the effect of alkali and temperature on the structure of residual kraft lignin through experiments in which pressurized oxygen was replaced by nitrogen. These data revealed a concealed set of alkali-induced condensation and fragmentation reactions.Key words: bleaching, catechols, carboxylic acids, delignification, guaiacyl, kinetics, oxygen, phenols, phosphorus, nuclear magnetic resonance (nmr), residual kraft lignin.
Article
Authors: Machin William D
Published: April 2011

A new technique for the generation of negative pressure in liquids is described, based on the pressure difference that exists across a curved liquid-vapour interface. Menisci in pores having very small radii may induce large negative pressures, or tensions, within the liquid phase. The magnitude of this tension is readily controlled through the pressure of the external vapour phase. Liquid butane when contained in hollow capsules, or Bertholet tubes, with walls formed from Vycor porous glass (pore radius ca. 5 nm) has developed negative pressures as large as -4 MPa for brief periods and lesser tensions for much longer times. This tension approaches the theoretical limit (ca. -6 MPa) calculated from the Laplace equation. Maximum possible tensions based on the theory of homogenous nucleation and on spinodal decomposition are much larger and, in principle, may be reached by reducing the pore size. Our unsuccessful attempts to do so are described.Key words: Bertholet tube, liquid, negative pressure, nucleation.
Article
Authors: Borecka-Bednarz Bozena , Bree Alan V , Patrick Brian O , Scheffer John R , Trotter James
Published: April 2011

Second-harmonic generation in the solid state is restricted to materials that crystallize in non-centrosymmetric space groups. Unfortunately, the vast majority of solids crystallize in centrosymmetric space groups and are therefore SHG-inactive. The requirement for solid-state asymmetry is addressed in a new series of organic salts. The acid p-nitrophenylglycine, SHG-inactive due to its centrosymmetric (P1) packing, was coupled to six optically pure amines to form salts and (or) complexes that, by virtue of their chiral counterion, crystallized in non-centrosymmetric space groups. The 1064 nm output from a Nd:YAG laser produced 532 nm second-harmonic generation from each of the six salts, with three of the salts producing second-harmonic intensities at least an order of magnitude greater than that of our standard, urea. X-ray crystallographic analysis was carried out on five of the six salts, and an attempt was made to rationalize the second-harmonic intensity of each of these five salts based on the orientation of its molecular charge-transfer axis in the unit cell and on its chromophore density.Key words: second-harmonic generation, nonlinear optics, chiral organic salts, crystal structures.
Article
Authors: Alavi A , Lynden-Bell R M , Willis P A , Swainson I P , Brown RJC
Published: April 2011

Ab initio density functional calculations have been carried out on the ordered phase of ammonium chloride and the results compared with experimental data. Powder neutron diffraction measurements have been carried out on 14ND4Cl and 15ND4Cl at a temperature of 5 K; the lattice parameter is 3.8224(4) Å and the N-D bond length is 1.0318(8) Å. Calculated structural and spectroscopic quantities agree well with the results of the neutron diffraction refinements, and with measured spectroscopic data. The calculated barrier to reorientation of the ammonium ion about the fourfold axis is 29 kJ mol-1, and the calculated compressibility is 3.78 × 10-11 Pa-1. The octopole moment of the ammonium ion in the crystal has been estimated from the calculated electron density, and is about 10-20% greater than for the free ion. The octopole moment does not vary appreciably with the orientation of the ammonium ion in the lattice. There is no evidence of any covalent interaction between the ammonium and chloride ions.Key words: ammonium chloride, density functional theory, neutron diffraction, ab initio calculations.
Article
Authors: Bensebaa F , Ellis T H , Kruus E , Voicu R , Zhou Y
Published: April 2011

Layered materials composed of metal-alkanethiolate units have been synthesized and characterized. The self-assembly occurs at the interface between a metal-ion-containing aqueous phase and an alkanethiol-containing organic phase. Key features of the structure have been determined from X-ray diffraction and infrared spectroscopy measurements. The highly ordered bilayers are characterized by tilted, all-trans alkyl chains. A new model for the in-plane structure has been presented, which is based on a hexagonal arrangement of metal atoms in the central plane.Key words: self-assembly, alkanethiolates, layered materials, vibrational spectroscopy.
The ultra high pressure conjugate addition of indoles to electron-deficient olefins
Authors: Harrington Paul , Kerr Michael A
Published: April 2011

The addition of indole and methyl indole at both high and ambient pressures to a series of Michael acceptors under the influence of ytterbium triflate was investigated. Under ambient pressure the more reactive and less sterically hindered electrophiles gave the expected 3-alkylated indoles in good to excellent yields. The more problematic Michael acceptors were subjected to pressures of 13 kbar. In all cases a dramatic reduction in reaction time and a significant improvement in yields was observed. In the cases involving 3-methylcyclohex-2-en-1-one, a by-product was formed and was characterized by single crystal X-ray diffraction. alpha , beta-Unsaturated ketones gave the best yields. Enals tended to polymerize while enoates proved to be much too unreactive. A particularly reactive malonate derived ester and beta-nitrostyrene gave good yields at ambient pressures.Key words: hapalindole, indole, Michael addition, high pressure, ytterbium triflate, Lewis acid.
Calculation of octanol-water partition coefficients of organic solutes from their molecular volumes
Authors: Edward John T
Published: April 2011

Bodor and Buchwald (8) have produced a two-parameter equation for calculating the logarithm of the partition coefficient (log P) of an organic solute between n-octanol and water. They computed the first parameter, a van der Waals volume of the of the solute molecule, using an algorithm combining analytical and numerical techniques. This parameter can be obtained more simply by addition of increments for the various atoms making up the molecule. The second parameter N, an integer, is obtained by summation of the integral N values associated with the different polar groups present in the molecule, as long as these polar groups are not too close to each other. The N term results in a decrease in log P. The N parameter is thought to measure the total number of H-bonds between the hydrogen of water and H-acceptor bonding sites of the various polar groups of the solute molecule. The detailed nature of the hydrogen bonds between a polar group and water can be elucidated by calculations involving N and V 0 , the partial molal volume in water of a solute molecule containing this group.Key words: partition coefficient, molecular volume, hydrogen bonding, van der Waals volume.
Ketonization of (Z)-2-methoxy-1,2-diphenylvinyl alcohol. Quantitative evaluation of the remarkable kinetic stability of this enol
Authors: Jefferson E A , Kresge A J , Matthew L , Wu Z
Published: April 2011

Rates of ketonization of (Z)-2-methoxy-1,2-diphenylvinyl alcohol were measured in aqueous perchloric acid and sodium hydroxide solutions as well as in formic acid and ammonium ion buffers, and the results were used to construct a rate profile for this reaction. These data show this substance to be a remarkably stable enol with a lifetime of 3.6 h at the bottom of its rate profile and a hydrogen ion catalytic coefficient 660 000 times less than that for the enol of acetophenone. Comparison with simple models allows partition of this rate factor into a 440-fold retardation for the β-phenyl substituent and a 1500-fold retardation for the β-methoxy substituent. A global rate of enolization of the keto isomer producing both Z and E enol isomers was also measured, and this leads to pKE > 5.4 as the lower limit of the keto-enol equilibrium constant for the Z enol. This result could be dissected into an enol-content enhancing effect of δ pKE = 3.2 for the β-phenyl group and a surprising enol-content diminishing effect of δ pKE > 0.6 for the β-methoxy group. Key words: enol ketonization, enol stability, keto-enol equilibrium, β-phenyl and β-methoxy substituent effects in keto-enol systems.
Article
Authors: Boucher Gregory D , MacDonald Aaron C , Hawrylak Brent E , Marangoni D Gerrard
Published: April 2011

A family of two-headed surfactants, the disodium 4-alkyl-3-sulfonatosuccinates, has been synthesized by the monoesterification of maleic anhydride and the addition of sodium bisulfite to the corresponding monoester. The properties the micelles formed by these compounds in aqueous solution, and the conformations of the chains comprising the micellar interior, have been investigated using a combination of 1-D nmr experiments and homonuclear and heteronuclear 2-D nmr techniques. The critical micelle concentrations (cmc's) and the aggregation numbers determined from the nmr experiments indicate that, in agreement with the earlier literature on other two-headed surfactant systems, these amphiphiles have high cmc's and low aggregation numbers when compared to single-headed surfactants of comparable chain length. All these results are interpreted in terms of the effect of adding a second headgroup to a single-headed, single-tailed surfactant.Key words: micelles, surfactants, nmr spectroscopy, chemical shifts, aggregation numbers.
Structure reassignment of the major isomer from the Diels-Alder reaction of acryloyl chloride and 4,5,6,6a-tetrahydropentalene
Authors: Parvez M , Rauk A , Sorensen T S , Sun F
Published: April 2011

After hydrogenation and hydrolysis, the two adducts formed from the Diels-Alder reaction of acryloyl chloride and 4,5,6,6a-tetrahydropentalene were originally assigned 7-exo- and 7-endo-carboxylic acid structures 3 and 4. Based on unexpected results in using these acids as starting materials for a superacid carbocation study, a reinvestigation of these structural assignments was carried out. From an extensive series of 2D NMR experiments, we conclude that 4 is correctly assigned, but that the other isomer is the 9-endo carboxylic acid 8. The formation of these two isomers (out of eight possible modes of addition) can be rationalized. Finally, an X-ray study of 8 was carried out as a final proof of structure.Key words: Diels-Alder reaction, facial selectivity, regioselectivity, X-ray structure, MO calculation.
A combined QM/MM study of ligand substitution enthalpies in the L2Fe(CO)3, RuCpL2Cl, and RuCp*L2Cl systems
Authors: Cavallo Luigi , Woo Tom K , Ziegler Tom
Published: April 2011

A combined density functional and molecular mechanics approach (QM/MM) has been validated in a study of the substitution reactions: (i) (PH3)2Fe(CO)3 + 2ER3 ⇆ (ER3)2Fe(CO)3 + 2PH3(ER3 = PMe3, PEt3, PMePh2, PPh3, PCyPh2, PiPr3, PBz3, PCy3, AsEt3, AsPh3); and (ii) Cp'Ru(PH3)2Cl + 2ER3 ⇆ Cp'Ru(ER3)2Cl + 2PH3 (Cp' = C5H5, C5(CH3)5; ER3 = PMe3, PEt3, PnBu3, PMe2Ph, PMePh2, PPh3, AsEt3, P(OMe)3, P(OPh)3, P(OCH2)3CEt). The steric influence of the R substituents on the substitution enthalpies correlates well with experimental data. The combined QM/MM approach is also able to afford molecular structures in good accord with experimental estimates. Key words: combined QM/MM, ligand substitutions, organometallic complexes.
Article
Authors: Saravanamuttu Kalaichelvi , Du Xin Min , Najafi S Iraj , Andrews Mark P
Published: April 2011

The solution sol-gel method is used to produce thin films of photosensitive hybrid organic-inorganic glass on silicon. Glasses consisted of photoinitiator, methacryloxypropyltrimethoxysilane, methacrylic acid, and zirconium oxide. Clear, low optical loss films are obtained, indicating nanophase homogeneity in the samples. The nanocomposite films are shown to be suitable for fabricating optical components such as ridge wave guides and Bragg diffraction gratings. The increase in the refractive index of the glass relative to the surrounding material during photolithographic processing is identified as a key material parameter in device fabrication. Accordingly, electronic and vibrational spectroscopy are used to provide insight into the structural changes that occur when glasses are irradiated with continuous narrow band 4.9 eV and pulsed 6.4 eV light. Arguments are advanced, linking the changes in refractive index to collateral densification leading to volume compaction of the silicate network during organic free-radical polymerization. This was shown by following the time evolution of relevant IR absorption bands. Free silanol and unreacted methoxysilane are consumed in the process. Matrix densification is indicated by shifts to low wave number in the transverse optical phonon mode associated with decreasing Si-O-Si bond angles of the antisymmetric stretching vibration (compression). Growth in the Si-O-Si framework is observed through increased intensity in this IR absorption. Similar behaviour is observed for films irradiated with 6.4 eV light from an excimer laser. A phase mask in combination with pulsed 6.4 eV light is used to inscribe a 1.5 mm, high-reflectivity polarization-independent Bragg grating into a ridge wave guide. The high reflectivity is thought to arise from a periodic modulation of the volume compaction of the matrix. Overall, the organic component of the glass confers unique properties on the material that allow it to be densified even with 4.9 eV light. By comparison, sol-gel silica with no organic component must be densified at nearly twice the photon energy.Key words: sol-gel, wave guide, Bragg grating, photochemistry, densification, refractive index, photolithography.