High Yields (high + yield)

Distribution by Scientific Domains
Distribution within Chemistry

Kinds of High Yields

  • very high yield

  • Terms modified by High Yields

  • high yield synthesis

  • Selected Abstracts

    The First Example of Magnesium Carbenoid 1,3-CH Insertion Reaction: A Novel Method for Synthesis of Cyclopropanes from 1-Chloroalkyl Phenyl Sulfoxides in High Yields.

    CHEMINFORM, Issue 20 2005
    Tsuyoshi Satoh
    Abstract For Abstract see ChemInform Abstract in Full Text. [source]

    Stable Nickel Catalysts for Fast Norbornene Polymerization: Tuning Reactivity

    Juan A. Casares
    Abstract The air-stable complexes trans -[Ni(C6Cl2F3)2L2] (L = SbPh3, 1; AsPh3, 2; AsCyPh2, 3; AsMePh2, 4; PPh3, 5) have been synthesized by arylation of [NiBr2(dme)] (dme = 1,2-dimethoxyethane) in the presence of the corresponding ligand L (for compounds 1,4) or by ligand substitution starting from 1 (for compound 5). The structures of 1, 2, and 5 have been determined by X-ray diffraction and show an almost perfect square-planar geometry in all cases. Their catalytic activity in insertion polymerization of norbornene have been tested showing a strong dependence of the yield and molecular mass of the polymer on the ligand used and the solvent. High yield and high molecular mass values are obtained using complexes with ligands easy to displace from NiII (SbPh3 is the best) and noncoordinating solvents. Complexes 1,3 are suggested as convenient bench-catalysts to have available in the lab. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

    Comparison of methods for determining the numbers and species distribution of coliform bacteria in well water samples

    R.M. Niemi
    R.M. NIEMI, M.P. HEIKKILÄ, K. LAHTI, S. KALSO AND S.I. NIEMELÄ. 2001. Aims: Enumeration of coliform bacteria and Escherichia coli is the most widely used method in the estimation of hygienic quality of drinking water. The yield of target bacteria and the species composition of different populations of coliform bacteria may depend on the method. Three methods were compared. Methods and Results:,Three membrane filtration methods were used for the enumeration of coliform bacteria in shallow well waters. The yield of confirmed coliform bacteria was highest on Differential Coliform agar, followed by LES Endo agar. Differential Coliform agar had the highest proportion of typical colonies, of which 74% were confirmed as belonging to the Enterobacteriaceae. Of the typical colonies on Lactose Tergitol 7 TTC agar, 75% were confirmed as Enterobacteriaceae, whereas 92% of typical colonies on LES Endo agar belonged to the Enterobacteriaceae. LES Endo agar yielded many Serratia strains, Lactose Tergitol 7 TTC agar yielded numerous strains of Rahnella aquatilis and Enterobacter, whereas Differential Coliform agar yielded the widest range of species. Conclusions: The yield of coliform bacteria varied between methods. Each method compared had a characteristic species distribution of target bacteria and a typical level of interference of non-target bacteria. Identification with routine physiological tests to distinct species was hampered by the slight differences between species. High yield and sufficient selectivity are difficult to achieve simultaneously, especially if the target group is diverse. Significance and Impact of the Study: The results showed that several aspects of method performance should be considered, and that the target group must be distinctly defined to enable method comparisons. [source]

    High yield of aromatics from CH4 in a plasma-followed-by-catalyst (PFC) reactor

    AICHE JOURNAL, Issue 9 2006
    Xiao-Song Li
    First page of article [source]

    Controlling particle size during anatase precipitation

    AICHE JOURNAL, Issue 9 2001
    Sekhar Sathyamoorthy
    Titanium dioxide particles in the form of anatase are precipitated from concentrated titanyl sulfate solution in the sulfate process, which are then recovered by a filtration process downstream of the precipitation stage. A previous study by Sathyamoorthy et al. showed that the final anatase particles are aggregates (1-2 ,m) consisting of numerous crystals (7,8 nm) arranged in primary agglomerates (60,100 nm). Pigment quality is determined by crystal and primary agglomerate size. One way of improving filtration rate is by the formation of larger aggregates, while maintaining the crystal and primary agglomerate size at optimum values. In a new seeding procedure proposed, the controlled inoculation of seeds used in industry is combined with a new type of seed (Large Seeds). The new seeding procedure has the potential to increase downstream filtration efficiency by increasing aggregate size, while maintaining crystal and primary agglomerate sizes close to the values correctly obtained in industry. High yield in the precipitation process is also maintained. [source]

    Iron,Palladium Association in the Preparation of Indoles and One-Pot Synthesis of Bis(indolyl)methanes

    Vincent Terrasson
    Abstract Indoles were prepared by annulation of the parent alkynylanilines with the use of a new FeCl3,PdCl2 catalytic combination. High yields were obtained by using low loadings of the transition-metal complex (FeCl3,PdCl2: 2 and 1 mol-%, respectively). One-pot accesses to bis(indolyl)methanes and trisubstituted indoles through annulation/Friedel,Crafts alkylation and annulation/1,4-Michael addition sequences, in which FeCl3 acts both as a cooxidant and a Lewis acid are described.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

    Vegetative growth and development of irrigated forage turnip (Brassica rapa var. rapa)

    GRASS & FORAGE SCIENCE, Issue 4 2008
    J. E. Neilsen
    Abstract Field and greenhouse experiments were conducted to identify visual markers and predictors of changes in the vegetative growth rate of forage turnip (Brassica rapa var. rapa) as a potential tool to improve the timing of inputs of N and irrigation to periods of maximum demand. The onset of root expansion, which was associated with a colour change and the death of cotyledons, was identified as a critical marker for the beginning of the rapid growth of the crop and the accumulation of starch in the storage root but indicators of subsequent changes in vegetative growth rate were not identifiable. The results suggested that management inputs can be more readily targeted to the beginning of the exponential growth phase but targeting of later vegetative growth stages will remain arbitrary. The vegetative growth and development of the crop was also studied to elucidate the process of leaf emergence and senescence (turnover) as they affected both leaf and root yield. The sequential senescence of leaves, which began immediately after cotyledon death, and translocation of carbohydrate to the storage root, coupled with high leaf area index (LAI), probably account for the high growth rates of 220 kg ha,1 day,1 maintained for periods of 10 weeks after the onset of root expansion. High yields can be expected if high LAI is maintained by ensuring that leaf emergence rates are not limited by nutrient or water deficiencies and leaves are protected from insect pests. Forage turnip is particularly robust because new leaf continues to emerge as older and damaged leaves senesce and carbohydrate is stored as starch in the storage root. [source]

    An in situ Generated Ruthenium Catalyst for the Tishchenko Reaction

    Marc-Olivier Simon
    Abstract A simple and efficient catalytic system for the selective dimerization of aldehydes, the Tishchenko reaction, is described. High yields of symmetrical esters were generally achieved using an in situ generated ruthenium catalyst in association with the electron-rich and hindered cyclohexyl(diphenyl)phosphane (CyPPh2) ligand. [source]

    Rapid and efficient microwave assisted method for the regioselective synthesis of 8,8,-methylene-bis-4-oxo-1H and 2H -chromeno[4,3- C]pyrazoles

    Adki Nagaraj
    The ethyl ester of 5,5,-methylene-bis-salicyclic acid 3 was prepared by the esterification of 5,5,-methylene-bis-salicylic acid 2. The compound 3 on reacting with ethylacetoacetate yields 6,6,-methylenebis-(3-acetyl-4-hydroxycoumarin) 4. The compound 4 was regioselectively converted into either 8,8,-methylene-bis-(4-oxo-1H -chromeno[4,3- c]pyrazoles) 6 or 8,8,-methylene-bis(-4-oxo-2H -chromeno[4,3- c]-pyrazoles) 7 under microwave irradiation. High yields are achieved even on a gram scale, while reaction times are considerably shortened compared to conventional heating conditions. [source]

    Turnip yellow mosaic virus: transfer RNA mimicry, chloroplasts and a C-rich genome

    SUMMARY Taxonomy:,Turnip yellow mosaic virus (TYMV) is the type species of the genus Tymovirus, family Tymoviridae. TYMV is a positive strand RNA virus of the alphavirus-like supergroup. Physical properties:, Virions are non-enveloped 28-nm T = 3 icosahedrons composed of a single 20-kDa coat protein that is clustered in 20 hexameric and 12 pentameric subunits. Infectious particles and empty capsids coexist in infected tissue. The genomic RNA is 6.3 kb long, with a 5,m7GpppG cap and a 3, untranslated region ending in a tRNA-like structure to which valine can be covalently added. The genome has a distinctive skewed C-rich, G-poor composition (39% C, 17% G). Viral proteins:, Two proteins, whose open reading frames extensively overlap, are translated from the genomic RNA. p206, which contains sequences indicative of RNA capping, NTPase/helicase and polymerase activities, is the only viral protein that is necessary for genome replication in single cells. It is produced as a polyprotein and self-cleaved to yield 141- and 66-kDa proteins. p69 is required for virus movement within the plant and is also a suppressor of gene silencing. The coat protein is expressed from the single subgenomic RNA. Hosts and symptoms:, TYMV has a narrow host range almost completely restricted to the Cruciferae. Experimental host species are Brassica pekinensis (Chinese cabbage) or B. rapa (turnip), in which diffuse chlorotic local lesions and systemic yellow mosaic symptoms appear. Arabidopsis thaliana can also be used. Clumping of chloroplasts and the accumulation of vesicular invaginations of the chloroplast outer membranes are distinctive cytopathological symptoms. High yields of virus are produced in all leaf tissues, and the virus is readily transmissible by mechanical inoculation. Localized transmission by flea beetles may occur in the field. [source]

    Controllable Synthesis of Shuttle-Shaped Ceria and Its Catalytic Properties for CO Oxidation

    Chunwen Sun
    Abstract Shuttle-shaped ceria was obtained in a high yield via a surfactant octadecylamine and urea assisted solvothermal process. The crystalline structure and morphology were characterized with powder X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM). Preliminary catalytic measurement shows that the shuttle-shaped CeO2 exhibits an enhanced activity for CO oxidation, which may be attributed to its higher porosity and more oxygen vacancies.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

    Metal Complexes of 4,11-Dimethyl-1,4,8,11-tetraazacyclotetradecane-1,8-bis(methylphosphonic acid) , Thermodynamic and Formation/Decomplexation Kinetic Studies

    Ivona Svobodová
    Abstract The macrocyclic ligand with two methylphosphonic acid pendant arms, 4,11-dimethyl-1,4,8,11-tetraazacyclotetradecane-1,8-bis(methylphosphonic acid) (1,8-H4Me2te2p, H4L3), was synthesized by a new simple approach. The product of the reaction of quarternized formaldehyde cyclam aminal with the sodium salt of diethyl phosphite was hydrolyzed to give a very high yield of the title ligand. The (H6L3)2+ cation in the solid state is protonated on all ring nitrogen atoms and on each phosphonate group. In the solid-state structure of [Cu(H3L3)][Cu(H2L3)]PF6·3H2O, neutral as well as positively charged complex species are present. Molecular structures of both species are very similar having the copper(II) ion in a coordination environment between square-pyramidal and trigonal-bipyramidal arrangements (, = 0.43 and 0.48) with one pendant arm non-coordinated. The ligand forms stable complexes with transition-metal ions showing a high selectivity for divalent copper atoms. The formation of complexes of the ligand with CuII, ZnII and CdII is fast, confirming the acceleration of complexation due to the presence of the strongly coordinating pendant arms. Acid-assisted decomplexation is fast for all three metal ions. Therefore, the copper(II) complex is not suitable for medicinal applications employing copper radioisotopes, but the title ligand motive can be employed in copper(II) separation. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

    Breaking Infinite CuI Carboxylate Helix Held by Cuprophilicity into Discrete Cun Fragments (n = 6, 4, 2)

    Yulia Sevryugina
    Abstract A new copper(I) carboxylate complex with 3,5-bis(trifluoromethyl)benzoate ligands, [Cu(O2C(3,5-CF3)2C6H3)] (1), has been prepared in high yield and fully characterized. An X-ray diffraction study revealed a remarkable infinite double-helical chain motif held together by cuprophilic interactions ranging from 2.69 to 3.14 Å. Both left- and right-handed helices are present in the unit cell of the centrosymmetric structure of 1 thus making the crystalline compound racemic. Complex 1 shows bright emission at ca. 594 nm upon UV/Vis radiation in the solid state (,ex = 350 nm). The Cu···Cu contacts in 1 are easily broken in the gas phase to afford copper clusters of ascertained nuclearity upon sublimation with various polyaromatic hydrocarbons. Several polyarenes such as fluoranthene (C16H10), pyrene (C16H10), and coronene (C24H12) were selected to cover a broad temperature range from 130 to 220 °C for the gas-phase co-deposition reactions. As a result of the successive temperature increase, cleavage of the infinite copper(I) chain into [Cun(O2C(3,5-CF3)2C6H3)n] fragments of decreasing nuclearity, n = 6, 4, and 2, has been achieved. The isolation of these units represents the first instance where various polynuclear copper(I) complexes are prepared and structurally characterized for the same carboxylate ligand.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

    The Transient Titanocene(II): Direct Synthesis from Solvated Titanium(II) Chloride and Cyclopentadienylsodium and Ensuing Interception with Diphenylacetylene as 1,1-Bis(cyclopentadienyl)-2,3,4,5-tetraphenyltitanacyclopentadiene,

    John J. Eisch
    Abstract For the first time the unstable titanocene(II) has been directly synthesized by the Wilkinson metallocene approach, namely the interaction of a THF-soluble form of titanium(II) chloride with two equivalents of cyclopentadienylsodium in THF solution at 0°,25 °C. Because of the transient existence of the titanocene(II) thereby obtained, it could only be chemically trapped in high yield as 1,1-bis(cyclopentadienyl)-2,3,4,5-tetraphenyltitanacyclopentadiene by two equivalents of diphenylacetylene, if the acetylene was added at 25 °C, without removal of the by-product LiCl and NaCl. If the addition of the acetylene was delayed, in order to filter off the LiCl and NaCl from the reaction mixture, then no trace of the titanacyclopentadiene derivative was found upon hydrolytic workup. Instead, a significant portion of the acetylene was found to have undergone hydrotitanation. This finding is clear evidence that the titanocene(II) had undergone a precedented rearrangement to a known dimer having the structure of a titanocene(III) hydride with a fulvalene bridge between the titanium centers. We suggest that the LiCl and NaCl present in the unfiltered reaction mixture form a dichloro complex with titanocene(II) and thereby retard its dimerizing rearrangement to the titanocene(III) hydride. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

    A Facile One-Step Synthesis of a Lipophilic Gold(I) Carbene Complex ,X-ray Crystal Structures of LAuCl and LAuC,CH (L = 1,3-di- tert- Butylimidazol-2-ylidene)

    Sanjay Singh
    Abstract The reaction of Au(CO)Cl with 1,3-di- tert -butylimidazol-2-ylidene and 1,3-dimesitylimidazol-2-ylidene in toluene at room temperature results in CO evolution and readily affords in high yield the adducts 1a and 1b, respectively. The reaction of 1a and 1b with ethynylmagnesium chloride in THF yields 2a and 2b, respectively. The crystal structures of 1a, 1b, and 2a were determined. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

    Synthesis and Structural Characterization of Three-Coordinate MnII, FeII, and ZnII Complexes Containing a Bulky Diamide Ligand [DippN(CH2)3NDipp]2, (Dipp = 2,6- iPr2C6H3)

    Jianfang Chai
    Abstract The reaction of DippNH(CH2)3NHDipp (1) (Dipp = 2,6- iPr2C6H3) with 2 equiv. of MeLi in diethyl ether resulted in the formation of the monomeric dilithium salt [(Dipp)N(CH2)3N(Dipp)][Li(OEt2)]2 (2) in high yield. Further reactions of 2 with MnCl2, FeCl2, and ZnCl2, respectively, afforded the complexes [M2{N(Dipp)(CH2)3N(Dipp)}2] [M = Mn (3), Fe (4), Zn (5)] with three-coordinate metal centers. Complexes 2,5 were characterized by X-ray structural analysis. The complexes contain a nonplanar MNMN central core. The diamide ligand in complexes 3,5 displays a boat conformation and is both chelating and bridging, so that one of the nitrogen atoms is three-coordinate and the other four-coordinate. Complexes 3,5 are the first examples with diamide ligands in such a bonding mode. The magnetic investigations of compounds 3 and 4 reveal an antiferromagnetic exchange between the metal atoms. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

    Coordination Modes of 9-Methyladenine in cis -Platinum(II) Complexes with Dimethyl(phenyl)phosphanes as Ancillary Ligands , Synthesis and Characterization of cis -[PtL2(9-MeAd)2](NO3)2, cis -[PtL2{9-MeAd(,H)}]3(NO3)3, and cis -[L2Pt{9-MeAd(,H)}PtL2](NO3)3

    Bruno Longato
    Abstract Treatment of 9-methyladenine (9-MeAd) with cis -[PtL2(NO3)2] (1) (L = PMe2Ph) in a 2:1 molar ratio generated the bis(adduct) cis -[PtL2(9-MeAd)2](NO3)2 (2), which was isolated and fully characterized by multinuclear (1H, 31P, 13C, 195Pt and 15N) NMR analysis, which showed that the two nucleobases are selectively coordinated through the N1 atom. Small amounts of a mono(adduct) cis -[PtL2(S)(9-MeAd)]2+ (3) (S = solvent) and of a diplatinated species cis -[L2Pt(S){9-MeAd(,H)}PtL2]3+ (4) are formed in DMSO solution when 9-MeAd is present in smaller quantities than 1. Complex 3 is platinated at N1, with a solvent molecule representing the fourth ligand around the metal center. Complex 4 contains an adenine molecule deprotonated and platinated at N1,N6,N7, with two cis -L2Pt units bonded to nitrogen atom N1 and to nitrogen atoms N6 and N7, respectively. With increasing relative concentration of the nucleobase, both complexes 3 and 4 progressively convert into the bis(adduct) 2, the only species detectable in solution when the Ad/Pt molar ratio is 2:1. The trinuclear compound cis -[L2Pt{9-MeAd(,H)}]3(NO3)3 (5) (L = PMe2Ph), containing an NH2 -deprotonated nucleobase bridging the metal centers through the N1 and N6 atoms, is quantitatively formed when the dinuclear hydroxo complex cis -[Pt(,-OH)L2]2(NO3)2 (6) reacts with 9-MeAd in CH3CN solution. The isolated complex was fully characterized by multinuclear NMR spectroscopy and mass spectrometry. It appears to be stable in solution in CH3CN and chlorinated solvents, whereas in DMSO it partially converts into a new species, probably the dinuclear analog cis -[PtL2{9-MeAd(,H)}]2(NO3)2, in which the adenine maintains its coordination mode. At equilibrium the trinuclear/dinuclear species molar ratio is 20:1. Through the addition of a stoichiometric amount of nitrate 1 to a DMSO solution of 5 we were able to generate the diplatinated compound 4 in high yield. Complex 4 displays a new coordination mode for the adeninate ion, with N1 bonded to one platinum atom whereas N6 and N7 are chelated to a second one. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

    Regioselectivity in the Addition of Grignard Reagents to Bis(2-benzothiazolyl) Ketone: C - vs.

    O -Alkylation Using Aryl Grignard Reagents
    Abstract The reaction between bis(2-benzothiazolyl) ketone (1) and a series of ring-substituted phenyl Grignard reagents gives, in considerable amount, the unexpected O -alkylation product derived from the attack of the Grignard reagent to thecarbonyl oxygen atom, thus extending the range of rarely reported cases in which O -alkylation can occur. The expected classic 1,2-addition product and that derived from O -alkylation have been obtained in a relative molar ratio dependent on the substituent on the phenyl ring. Bis(2-benzothiazolyl) aryl carbinols, the classic 1,2-addition products to the carbonyl group of 1, were obtained in high yield through an alternative synthetic route that permitted the limit imposed by O - vs. C -alkylation competition to be overcome. [source]

    Hydrolytic Deallylation of N -Allyl Amides Catalyzed by PdII Complexes

    Naoya Ohmura
    Abstract Hydrolytic deallylation of N -allyl amides to give amides and propanal can be achieved with PdII catalysts. The optimized catalyst consists of Pd(OCOCF3)2 and 1,3-bis(diphenylphosphanyl)propane (DPPP). Several kinds of open-chain N -allyl amides and N -allyl lactams undergo hydrolytic deallylation to give the corresponding amides and lactams in good to high yield. A mechanism which includes isomerization to enamides and subsequent hydrolysis is proposed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

    Facile Access to Optically Active Ferrocenyl Derivatives with Direct Substitution of the Hydroxy Group Catalyzed by Indium Tribromide

    Paola Vicennati
    Abstract Ferrocene derivatives have found many different uses and applications in organometallic chemistry, material chemistry, and catalysis. We have shown that using a catalytic amount (5,10 mol-%) of commercially available indium tribromide, at room temperature, many carbon nucleophiles, such as indoles, allylsilane, enolsilane, silyl ketene acetal, diketone, and trimethylsilylcyanide, smoothly react with different optically active ferrocenyl alcohol derivatives to afford the desired products in high yield, with retention of configuration. Also, many different N-nucleophiles (azide, carbamates) and O-nucleophiles (alcohols) react as well, again with retention of configuration. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

    Regiospecific Synthesis of 4-Deoxy- D - threo -hex-3-enopyranosides by Simultaneous Activation,Elimination of the Talopyranoside Axial 4-OH with the NaH/Im2SO2 System: Manifestation of the Stereoelectronic Effect

    Emanuele Attolino
    Abstract A new and high-yielding method for the regioselective preparation of 4-deoxy- and 2,4-dideoxy-2-acetamido-,- D - threo -hex-3-enopyranosides has been developed. The process involves a simultaneous activation,elimination of the OH-4 group of ,- D -talopyranosides and 2-acetamido-2-deoxy-,- D -talopyranosides, mediated by the NaH/N,N,-sulfuryldiimidazole system at ,30 °C. The same reaction applied on the analogous ,- D -galactopyranosides takes place without any regioselectivity, affording mixtures of hex-3- and hex-4-enopyranosides. In the case of the methyl 2,3,6-tri- O -benzyl-,- D -talo- and ,- D -galactopyranosides, the corresponding 4- O -imidazylates can be isolated by quenching the reactions at ,30 °C. Upon warming these crude products to room temperature, the ,- talo -4- O -imidazylate gives the corresponding hex-3-eno derivative in very high yield, but its ,- galacto analogue gives the hex-4-enopyranoside enol ether in poor yield. The different regiochemical outcome between the talo and the galacto series has been attributed to the stereoelectronic effect exerted, exclusively in talo -configured compounds, by the axially disposed C-2 electronegative substituent, which selectively accelerates the breaking of the antiperiplanar C(3),H bond. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

    Facile Preparation of 3-Amino-4-(arylamino)-1H -isochromen-1-ones by a New Multicomponent Reaction

    Till Opatz
    Abstract Reactions between 2-formylbenzoic acid, various anilines and HCN result in the formation of 3-amino-4-(arylamino)-1H -isochromen-1-ones in high yield. The mechanism of this three-component condensation involves the intermediate formation of an ,-aminonitrile and subsequent cyclization through nucleophilic attack of the ortho -carboxylate at the nitrile carbon. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

    Highly Enantioselective Synthesis of No-Carrier-Added 6-[18F]Fluoro- L -dopa by Chiral Phase-Transfer Alkylation

    Christian Lemaire
    Abstract [18F]Fluoro- L -dopa, an important radiopharmaceutical for positron emission tomography (PET), has been synthesized using a phase-transfer alkylation reaction. A chiral quaternary ammonium salt derived from a Cinchona alkaloid served as phase-transfer catalyst for the enantioselective alkylation of a glycine derivative. The active methylene group of this Schiff-base substrate was deprotonated with cesium hydroxide and rapidly alkylated by the 2-[18F]fluoro-4,5-dimethoxybenzyl halide (X = Br, I). The reaction proceeded with high yield (> 90%) at 0 °C or room temperature in various solvents such as toluene or dichloromethane. Preparation of the [18F]alkylating agent on a solid support was developed. After labelling, the labeled [18F]fluoroveratraldehyde was trapped on a tC18 cartridge and then converted on the cartridge into the corresponding benzyl halide derivatives by addition of aqueous sodium borohydride and gaseous hydrobromic or -iodic acid. Hydrolysis and purification by preparative HPLC made 6-[18F]fluoro- L -dopa ready for human injection in a 25,30% decay-corrected radiochemical yield in a synthesis time of 100 min. The product was found to be chemically, radiochemically and enantiomerically pure (ee > 95%). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

    Efficient Synthesis of Doubly Connected Primary Face-to-Face Cyclodextrin Homo-Dimers

    Thomas Lecourt
    Abstract "Head-to-head" type ,- and ,-cyclodextrin homo-dimers in which the two primary rims are doubly ligated through alkyl chains have been synthesised in high yield by acyclic diene metathesis (ADM), followed by ring-closing metathesis (RCM). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

    A Novel Approach to 2-Chloro-2-fluorostyrenes

    Valentine G. Nenajdenko
    Abstract A new general catalytic olefination reaction (COR) of aromatic and heteroaromatic aldehydes and ketones was applied to synthesise 2-chloro-2-fluorostyrenes. The two-stage procedure includes the transformation of carbonyl compounds into hydrazones followed by treatment with CFCl3 mediated by copper catalysis. Trichlorofluoromethane was used as a chlorofluoromethylene transfer reagent. The reaction proceeds stereoselectively and the target alkenes were obtained in high yield. A proposed mechanism for the reaction is discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

    High-Yield Synthesis and Electrochemical and Photovoltaic Properties of Indene-C70 Bisadduct

    Youjun He
    Abstract [6, 6]-Phenyl-C61 -butyric acid methyl ester (PC60BM) is the widely used acceptor material in polymer solar cells (PSCs). Nevertheless, the low LUMO energy level and weak absorption in visible region are its two weak points. For enhancing the solar light harvest, the soluble C70 derivative PC70BM has been used as acceptor instead of PC60BM in high efficiency PSCs in recent years. But, the LUMO level of PC70BM is the same as that of PC60BM, which is too low for the PSCs based on the polymer donors with higher HOMO level, such as poly (3-hexylthiophene) (P3HT). Here, a new soluble C70 derivative, indene-C70 bisadduct (IC70BA), is synthesized with high yield of 58% by a one-pot reaction of indene and C70 at 180 °C for 72 h. The electrochemical properties and electronic energy levels of the fullerene derivatives are measured by cyclic voltammetry. The LUMO energy level of IC70BA is 0.19 eV higher than that of PC70BM. The PSC based on P3HT with IC70BA as acceptor shows a higher Voc of 0.84 V and higher power conversion efficiency (PCE) of 5.64%, while the PSC based on P3HT/PC60BM and P3HT/PC70BM displays Voc of 0.59 V and 0.58 V, and PCE of 3.55% and 3.96%, respectively, under the illumination of AM1.5G, 100 mW cm,2. The results indicate that IC70BA is an excellent acceptor for the P3HT-based PSCs and could be a promising new acceptor instead of PC70BM for the high performance PSCs based on narrow bandgap conjugated polymer donor. [source]

    Aspergillus nidulans,-galactosidase of glycoside hydrolase family 36 catalyses the formation of ,-galacto-oligosaccharides by transglycosylation

    FEBS JOURNAL, Issue 17 2010
    Hiroyuki Nakai
    The ,-galactosidase from Aspergillus nidulans (AglC) belongs to a phylogenetic cluster containing eukaryotic ,-galactosidases and ,-galacto-oligosaccharide synthases of glycoside hydrolase family 36 (GH36). The recombinant AglC, produced in high yield (0.65 g·L,1 culture) as His-tag fusion in Escherichia coli, catalysed efficient transglycosylation with ,-(1,6) regioselectivity from 40 mm 4-nitrophenol ,- d -galactopyranoside, melibiose or raffinose, resulting in a 37,74% yield of 4-nitrophenol ,- d -Galp -(1,6)- d -Galp, ,- d -Galp -(1,6)-,- d -Galp -(1,6)- d -Glcp and ,- d -Galp -(1,6)-,- d -Galp -(1,6)- d -Glcp -(,1,,2)- d -Fruf (stachyose), respectively. Furthermore, among 10 monosaccharide acceptor candidates (400 mm) and the donor 4-nitrophenol ,- d -galactopyranoside (40 mm), ,-(1,6) linked galactodisaccharides were also obtained with galactose, glucose and mannose in high yields of 39,58%. AglC did not transglycosylate monosaccharides without the 6-hydroxymethyl group, i.e. xylose, l -arabinose, l -fucose and l -rhamnose, or with axial 3-OH, i.e. gulose, allose, altrose and l -rhamnose. Structural modelling using Thermotoga maritima GH36 ,-galactosidase as the template and superimposition of melibiose from the complex with human GH27 ,-galactosidase supported that recognition at subsite +1 in AglC presumably requires a hydrogen bond between 3-OH and Trp358 and a hydrophobic environment around the C-6 hydroxymethyl group. In addition, successful transglycosylation of eight of 10 disaccharides (400 mm), except xylobiose and arabinobiose, indicated broad specificity for interaction with the +2 subsite. AglC thus transferred ,-galactosyl to 6-OH of the terminal residue in the ,-linked melibiose, maltose, trehalose, sucrose and turanose in 6,46% yield and the ,-linked lactose, lactulose and cellobiose in 28,38% yield. The product structures were identified using NMR and ESI-MS and five of the 13 identified products were novel, i.e. ,- d -Galp -(1,6)- d -Manp; ,- d -Galp -(1,6)-,- d -Glcp -(1,4)- d -Glcp; ,- d -Galp -(1,6)-,- d -Galp -(1,4)- d -Fruf; ,- d -Galp -(1,6)- d -Glcp -(,1,,1)- d -Glcp; and ,- d -Galp -(1,6)-,- d -Glcp -(1,3)- d -Fruf. [source]

    The effect of temperature and ventilation condition on the toxic product yields from burning polymers

    FIRE AND MATERIALS, Issue 1 2008
    A. A. Stec
    Abstract A major cause of death or permanent injury in fires is inhalation of toxic gases. Moreover, every fire is unique, and the range of products, highly dependant on fire conditions, produces a wide variety of toxic and irritant species responsible for the most fire fatalities. Therefore, to fully understand each contribution to the toxicity it is necessary to quantify the decomposition products of the material under the test. Fires can be divided into a number of stages from smouldering combustion to early well-ventilated flaming through to fully developed under-ventilated flaming. These stages can be replicated by certain bench-scale physical fire models using different fuel-to-oxygen ratios, controlled by the primary air flow, and expressed in terms of the equivalence ratio (the actual fuel/air ratio divided by the stoichiometric fuel/air ratio). This work presents combustion product yields generated using a small-scale fire model. The Purser Furnace apparatus (BS7990 and ISO TS 19700) enables different fire stages to be created. Identification and quantification of combustion gases and particularly their toxic components from different fire scenarios were undertaken by continuous Fourier transform infrared spectroscopy. The relationship between type of the fire particularly the temperature and ventilation conditions and the toxic product yields for four bulk polymers, low-density polyethylene, polystyrene (PS), Nylon 6.6 and polyvinyl chloride (PVC) is reported. For all the polymers tested, except PVC, there is a dramatic increase in the yield of products of incomplete combustion (CO and hydrocarbons) with increase in equivalence ratio, as might be expected. For PVC there is a consistently high level of products of incomplete combustion arising both from flame inhibition by HCl and oxygen depletion. There is a low sensitivity to furnace temperature over the range 650,850°C, except that at 650°C PS shows an unexpectedly high yield of CO under well-ventilated conditions and PVC shows a slightly higher hydrocarbon yield. This demonstrates the dependence of toxic product yields on the equivalence ratio, and the lack of dependence on furnace temperature, within this range. Copyright © 2007 John Wiley & Sons, Ltd. [source]

    Supercritical carbon dioxide extraction of 2-acetyl-1-pyrroline and volatile components from pandan leaves

    Natta Laohakunjit
    Abstract The ,avour of pandan (Pandanus amaryllifolius Roxb.) leaves was extracted by supercritical ,uid with CO2 (SC-CO2) under different conditions of pressure, temperature and contact time to determine the yield of 2-acetyl-1-pyrroline (ACPY) and various other components; 14 volatile compounds on the gas chromatogram were identi,ed, and the predominant constituents were ACPY and 3-methyl-2(5H)-furanone. The interaction of different conditions signi,cantly in,uenced the yield of ACPY and various volatile compounds. There is a potential for high yield of ACPY by SC-CO2 at 200 bar, 500 °C and 20 min. The SDE,ether extract was found to have a very small amount of ACPY and an undesirable odour, as compared to the dark green ethanol extract, which contains a relatively larger quantity of ACPY and even more 3-methyl-2(5H)-furanone. Although at least 34 new components were uncovered from SC-CO2, SDE, and ethanol extraction, both ACPY and 3-methyl-2(5H)-furanone were the components tentatively obtained by all three methods. Copyright © 2004 John Wiley & Sons, Ltd. [source]

    Supercritical carbon dioxide separation of bergamot essential oil by a countercurrent process

    Marco Poiana
    Abstract The ef,ciency of separation of bergamot essential oil, performed by a countercurrent column ,lled with Raschig rings and using supercritical carbon dioxide as partition solvent, is affected by various parameters. In the experiments explained in this work, the direct effect of CO2 density was shown and the ratio between the amount of oil loaded to on the column and the amount of CO2 used were discussed. The conditions that produced extracts with a similar volatile fraction composition of starting material and with a high yield (more than 80% of recovery) were those with a low feed:solvent ratio; the lowest bergaptene content was obtained at low CO2 density or at high feed:solvent ratio. A good result was observed at a CO2 density of 206 g/dm3 (8 MPa of pressure and a temperature gradient of 46,50,54 °C) and a feed:solvent ratio of 9.4,9.6; in this separation, a yield of 74,77% and a bergaptene content lower than 0.01% was measured. Copyright © 2003 John Wiley & Sons, Ltd. [source]