- A methodical selection process for the development of ketones and esters as bio-based replacements for traditional hydrocarbon solvents
-
A "top down" approach to the development of sustainable, greener, low-polarity solvents is presented. Methyl butyrate, ethyl isobutyrate, methyl pivalate and pinacolone were identified as potential target solvents from trends in Hansen solubility parameters and known physical properties. Solubility, flammability and physical properties were determined which showed their potential to replace traditional, hazardous, volatile, non-polar solvents such as toluene. Each new candidate then demonstrated their suitability to replace these traditional solvents in solubility tests, despite being esters and ketones, each candidate demonstrated their similarity to traditional volatile non-polar solvents in terms of their solubility properties by their ability to dissolve natural rubber, a particularly low-polarity solute. This was reinforced by their performance in a model Menschutkin reaction and a radical-initiated polymerisation for the production of pressure-sensitive adhesives, where their performance was found to be similar to that of toluene. Importantly, a preliminary toxicity test (Ames test) suggested non-mutagenicity in all candidates. Each of the four candidates can be synthesised via a catalytic route from potentially renewable resources, thus enhancing their green credentials.
- Byrne, Fergal P.,Forier, Bart,Bossaert, Greet,Hoebers, Charly,Farmer, Thomas J.,Hunt, Andrew J.
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supporting information
p. 4003 - 4011
(2018/09/11)
-
- Hydrogenation of Ketones and Esters Catalyzed by Pd/C?SiO2
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Hydrogenation of unsaturated ketones and esters with molecular hydrogen on the 5%Pd/C?SiO2 heterogeneous catalyst has been studied. The reaction direction and yield are determined by the starting compounds structure. Hydrogenation of unsaturated ketones containing phenyl group at the double carbon–carbon atom is accompanied by the reduction of the ketone group into the alcohol one. Hydrogenation of unsaturated esters is accompanied by transesterification.
- Akchurin,Baibulatov,Dokichev
-
p. 195 - 198
(2018/03/26)
-
- Synthesis of Multivalent Organotellurium Chain-Transfer Agents by Post-modification and Their Applications in Living Radical Polymerization
-
Functionalized or multivalent organotellurium chain-transfer agents (CTAs) for living radical polymerization were synthesized by post-modification, which involved the condensation between a carboxylic-acid-functionalized CTA and various amines in excellent yields without affecting the reactive tellurium moiety. The CTAs exhibited high synthetic versatility for radical polymerization and gave structurally well-controlled polymers, such as multiarmed polymers, from various monomers. Because all new CTAs are easily available on a large scale by simple purification, the current method significantly facilitates macromolecular engineering based on organotellurium-mediated radical polymerization (TERP).
- Fan, Weijia,Nakamura, Yasuyuki,Yamago, Shigeru
-
supporting information
p. 17006 - 17010
(2016/11/16)
-
- NANOEMULSIONS
-
An oil-in-water emulsion comprises an emulsifier which is a non-gelled branched polymer (e.g. a branched vinyl polymer), wherein the ends of at least some of the chains of said polymer terminate in an alkyl chain of 5 carbon atoms or more, and wherein the oil-in-water emulsion takes the form of particles having a z-average diameter of no greater than about 1000 nm. This is useful in, for example, facilitating the carrying of hydrophobic materials within aqueous systems, to enhance oral drug delivery. The oil-in-water emulsion may be prepared by mixing an oil phase with an aqueous phase in the presence of an emulsifier, wherein said emulsifier is a non-gelled branched polymer, wherein the ends of at least some of the chains of said polymer terminate in an alkyl chain of 5 carbon atoms or more, and wherein the oil-in-water emulsion takes the form of particles having a z-average diameter of no greater than about 1000 nm. The oil phase may comprise a further solvent which is miscible with the oil, said solvent being allowed to evaporate to produce the final emulsion.
- -
-
Page/Page column 20
(2016/09/22)
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- Mixed-ligand complexes of paddlewheel dinuclear molybdenum as hydrodehalogenation catalysts for polyhaloalkanes
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We developed a hydrodehalogenation reaction of polyhaloalkanes catalyzed by paddlewheel dimolybdenum complexes in combination with 1-methyl-3,6-bis(trimethylsilyl)-1,4-cyclohexadiene (MBTCD) as a non-toxic H-atom source as well as a salt-free reductant. A mixed-ligated dimolybdenum complex Mo2(OAc)2[CH(NAr)2]2 (3a, Ar = 4-MeOC6H4) having two acetates and two amidinates exhibited high catalytic activity in the presence of nBu4NCl, in which [nBu4N]2[Mo2{CH(NAr)2}2Cl4] (9a), derived by treating 3a with ClSiMe3 and nBu4NCl, was generated as a catalytically-active species in the hydrodehalogenation. All reaction processes, oxidation and reduction of the dimolybdenum complex, were clarified by control experiments, and the oxidized product, [nBu4N][Mo2{CH(NAr)2}2Cl4] (10a), was characterized by EPR and X-ray diffraction studies. Kinetic analysis of the hydrodehalogenation reaction as well as a deuterium-labelling experiment using MBTCD-d8 suggested that the H-abstraction was the rate-determining step for the catalytic reaction. This journal is
- Tsurugi, Hayato,Hayakawa, Akio,Kando, Shun,Sugino, Yoshitaka,Mashima, Kazushi
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p. 3434 - 3439
(2015/05/27)
-
- Why are organotin hydride reductions of organic halides so frequently retarded? kinetic studies, analyses, and a few remedies
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Kinetic data for reduction of organic halides (RX) by tri-n-butylstannane (SnH) reveal a serious flaw in the current view of the kinetic radical chain: the tacit but unproven assumption that the speed of reaction is determined by the slowest propagation step. Our results show this is rarely true for reductive chains and that the observed rate is in fact controlled by unseen side-reactions of propagating R? and Sn? radicals with the solvent (notably, benzene!) or solvent impurities (e.g., trace benzophenone dryness indicator in THF) or, crucially, with allylic-CH and conjugated unsaturated groups in substrates and products. Most R? and/or Sn? radicals are therefore converted into relatively inert delocalized species A? and/or B? that inhibit the chain. Retardation in the degraded chain is given by a simple sum of terms, each being the ratio of the chain-transfer rate divided by the rate of chain-return. The model kinetic equation is linear and easy to ratify, interpret, and apply: to calculate retarding rate constants, optimize reaction conditions, and identify additives or "remedies" that repair the chain and accelerate reaction. The present work is thus expected to have a helpful impact on the practice and design of SnH radical chain based (and related) syntheses.
- Ingold,Bowry, Vincent W.
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p. 1321 - 1331
(2015/02/19)
-
- Expanding ester biosynthesis in Escherichia coli
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To expand the capabilities of whole-cell biocatalysis, we have engineered Escherichia coli to produce various esters. The alcohol O-acyltransferase (ATF) class of enzyme uses acyl-CoA units for ester formation. The release of free CoA upon esterification with an alcohol provides the free energy to facilitate ester formation. The diversity of CoA molecules found in nature in combination with various alcohol biosynthetic pathways allows for the biosynthesis of a multitude of esters. Small to medium volatile esters have extensive applications in the flavor, fragrance, cosmetic, solvent, paint and coating industries. The present work enables the production of these compounds by designing several ester pathways in E. coli. The engineered pathways generated acetate esters of ethyl, propyl, isobutyl, 2-methyl-1-butyl, 3-methyl-1-butyl and 2-phenylethyl alcohols. In particular, we achieved high-level production of isobutyl acetate from glucose (17.2 g l -1). This strategy was expanded to realize pathways for tetradecyl acetate and several isobutyrate esters.
- Rodriguez, Gabriel M,Tashiro, Yohei,Atsumi, Shota
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p. 259 - 265
(2014/04/03)
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- Scope and mechanism of the electrochemical Reformatsky reaction of α-haloesters on a graphite powder cathode in aqueous anolyte
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Six α-haloesters and eighteen carbonyl compounds were submitted to electrochemical coupling on a graphite powder cathode using aqueous anolyte free of organic solvents. Preparative yields of coupling products could be obtained with ethyl 2-bromoisobutyrate and aromatic aldehydes. Ethyl 2-bromopropionate was much less efficient. Extensive variation of applied potential, electrolyte composition, stoichiometry, catalyst, leaving halogen and activating substituents on the carbonyl compound led to the conclusion that the reaction mechanism in most cases proceeds via a radical intermediate generated from the halide reduction. Ethyl chloroacetate produced only trace amounts of coupling product, most probably by a carbanionic mechanism.
- De Souza, Carlos A.,Navarro, Marcelo,Bieber, Lothar W.,Areias, Madalena C.C.
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p. 118 - 126
(2014/05/06)
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- A strategy for separating and recycling solid catalysts based on the pH-triggered pickering-emulsion inversion
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Turn you inside out: A novel method for performing in situ separation and recycling of submicrometer-sized solid catalysts is developed based on the pH-triggered inversion of Pickering emulsions (see scheme; o=oil, w=water). Solid catalysts can be recycled 36 times without significant loss of activity. The method differs from conventional methods in terms of speed, energy consumption, catalyst separation, and recycling effectiveness. Copyright
- Yang, Hengquan,Zhou, Ting,Zhang, Wenjuan
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supporting information
p. 7455 - 7459
(2013/07/26)
-
- Arylazolylthioacetanilide. Part 11: Design, synthesis and biological evaluation of 1,2,4-triazole thioacetanilide derivatives as novel non-nucleoside HIV-1 reverse transcriptase inhibitors
-
A series of novel 1,2,4-triazole thioacetanilide derivatives has been designed, synthesized and evaluated for their anti-HIV activities in MT-4 cells. Half of these compounds showed moderate to potent activities against wild-type HIV-1 with an EC50 ranging from 38.0 μM to 4.08 μM. Among them, 2-(4-(2-fluorobenzyl)-5-isopropyl-4H-1,2,4-triazol-3-ylthio)-N-(2-nitrophenyl) acetamide 7d was identified as the most promising compound (EC50 = 4.26 μM, SI = 49). However, no compound was active against HIV-2. The preliminary structure-activity relationships among the newly synthesized congeners are discussed.
- Li, Zhenyu,Cao, Yuan,Zhan, Peng,Pannecouque, Christophe,Balzarini, Jan,De Clercq, Erik,Shen, Yuemao,Liu, Xinyong
-
p. 968 - 973
(2014/01/06)
-
- Highly conserved progesterone 5β-reductase genes (P5βR) from 5β-cardenolide-free and 5β-cardenolide-producing angiosperms
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Most cardenolides used in the therapy of cardiac insufficiency are 5β-configured and thus the stereo-specific reduction of the Δ4,5-double bond of a steroid precursor is a crucial step in their biosynthesis. This step is thought to be catalysed by progesterone 5β-reductases. We report here on the isolation of 11 progesterone 5β-reductase (P5βR) orthologues from 5β-cardenolide-free and 5β-cardenolide-producing plant species belonging to five different angiosperm orders (Brassicales, Gentianales, Lamiales, Malvales and Solanales). Amino acid sequences of the P5βR described here were highly conserved. They all contain certain motifs qualifying them as members of a class of stereo-selective enone reductases capable of reducing activated CC double bonds by a 1,4-addition mechanism. Protein modeling revealed seven conserved amino acids in the substrate-binding/catalytic site of these enzymes which are all supposed to exhibit low substrate specificity. Eight P5βR genes isolated were expressed in Escherichia coli. Recombinant enzymes reduced progesterone stereo-specifically to 5β-pregane-3,20-dione. The progesterone 5β-reductases from Digitalis canariensis and Arabidopsis thaliana reduced activated CC double bonds of molecules much smaller than progesterone. The specific role of progesterone 5β-reductases of P5βRs in cardenolide metabolism is challenged because this class of enone reductases is widespread in higher plants, and they accept a wide range of enone substrates.
- Bauer, Peter,Munkert, Jennifer,Brydziun, Margareta,Burda, Edyta,Müller-Uri, Frieder,Gr?ger, Harald,Muller, Yves A.,Kreis, Wolfgang
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scheme or table
p. 1495 - 1505
(2010/11/05)
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- INFANT FORMULA CONTAINING AN AROMA COMPOSITION FOR USE AS FRAGRANCE
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The invention relates to a nutraceutical composition such as infant formula or infant food comprising a) a defined aroma composition; b) a methodology for developing, maintaining certain aroma constituents in the infant formula and an aroma or fragrance composition to be used to increase the acceptance of a person or an object by the baby or new born.
- -
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-
- Arylthiols as highly chemoselective and environmentally benign radical reducing agents
-
(Chemical Equation Presented) Arylthiols serve as excellent environmentally benign reducing agents for organotellurium, organostibine, and organobismuthine compounds under radical conditions. Both small molecules and macromolecules possessing these heteroatom groups are reduced under moderate thermal conditions to give near quantitative yields in most cases. The reduction shows high chemoselectivity with respect to the heteroatom compounds; the reactivity decreases in the order alkylbismuthines, alkylstibines, and alkyltellurides, while simple alkyl iodides could not be reduced. Alkyltellurides are selectively reduced in the presence of alkyl iodides even when an excess amount of arylthiol is used. Furthermore, alkylstibines are also selectively reduced in the presence of alkyltellurides. Moreover, the reduction conditions are compatible with the presence of a variety of polar functional groups in the substrates, products, and solvents, which are not tolerant under ionic and metal-catalyzed conditions. Carbon-carbon bond formation is possible with use of the carbon-centered radicals that are generated. The results clearly reveal the synthetic utility of arylthiols in organic synthesis.
- Yamago, Shigeru,Matsumoto, Atsushi
-
supporting information; experimental part
p. 7300 - 7304
(2009/05/09)
-
- Acylation and alkoxycarbonylation of benzoxazoline-2-thione and benzothiazoline-2-thione
-
Acylation of benzoxazoline-2-thione (1) and benzothiazoline-2-thione (2) with acetic anhydride (3) and acyl chlorides (4) gave N-acyl (5, 6) and/or S-acyl (7, 8) derivatives depending on the nature of acylating agents and bases used. Alkoxycarbonylation of 1 with aralkyl chlorocarbonates (9) gave N-alkoxycarbonyl derivatives (10) mainly, while that of 2 with aralkyl chloroccarbonates (9) gave S-alkoxycarbonyl derivatives (12) exclusively. Photolysis of N-acyl derivatives (5 or 6) in the presence of alcohols afforded 1 or 2, respectively, together with esters (16).
- Nishio, Takehiko,Shiwa, Kiyoko
-
p. 313 - 324
(2007/10/03)
-
- Structure-function correlation in lipase catalysed esterification reactions of short and medium carbon chain length alcohols and acids
-
An attempt has been made to correlate the carbon chain lengths of acids and alcohols to the extent of esterification in the Rhizomucor miehei lipase catalyzed esterification reactions involving acids of carbon chain length C2-C5 and alcohols of carbon chain length C1-C8.
- Divakar, Soundar
-
p. 1919 - 1922
(2007/10/03)
-
- Kinetics and mechanism of oxidation of aliphatic acetals with peroxomonosulphate
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The oxidation of fifteen aliphatic acetals of normal aliphatic aldehydes and substituted aliphatic aldehydes with aliphatic and substituted aliphatic as well as with aromatic alcohols by peroxomonosulphate in aqueous acetic acid medium is first order each in [oxidant] and [acetal] and yields the corresponding esters as the main product. The oxidation reaction is independent of change in dielectric constant of the medium. The activation enthalpies and entropies of the reactions are linearly related. A mechanism involving hydride ion shift is proposed.
- Janakiram,Venkataraman,Basheer Ahamed
-
p. 339 - 341
(2007/10/03)
-
- Kinetics and mechanism of oxidation of aliphatic acetals with N-chlorobenzamide
-
The oxidation kinetics of thirteen aliphatic acetals of normal aliphatic aldehydes and substituted aliphatic aldehydes with aliphatic and substituted aliphatic as well as with aromatic alcohols by N-chlorobenzamide (NCB) in aqueous acetic acid medium follows first order and zero order dependence in [NCB] and [acetal] respectively and yields the corresponding esters as the main product of oxidation. (H2OCl)+ has been postulated as the oxidizing species.
- Basheer Ahamed
-
p. 222 - 224
(2007/10/03)
-
- 29. Synthesis of Indole Derivatives by [2 + 2] Photocycloaddition of Indoline-2-thiones with Alkenes and Photodesulfurization of Indoline-2-thiones
-
The photochemical synthesis of indole derivatives starting from the indoline-2-thiones 1 is described. Irradiation of indoline-2-thiones 1 in the presence of alkenes 3 gave 2-alkyl-3H-indoles 4-7 or 2-alkylindoles 8-22 through the ring cleavage of the intermediates, spirocyclic amino-thietanes, initially derived by [2 + 2] cycloaddition of the C=S bond of 1 and the C=C bond of 3. Irradiation of 1 in the presence of trialkylamines 26 gave desulfurization products 27-32 and unexpected 3-alkylindoles 33-40. N-Acylindoline-2-thiones 1l-p yielded the deacylated products, indoline-2-thiones 1a-b, and ethyl esters 43 through γ-H abstraction by the excited thioamide S-atom when irradiated in CDCl3/EtOH or benzene/EtOH. Oxygen analogues 2a-d also underwent intramolecular H abstraction to give the indolin-2-ones 2e-f and ethyl esters 43 in a similar way.
- Nishio, Takehiko,Oka, Mitsuru
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p. 388 - 397
(2007/10/03)
-
- Reversible protonation of isobutane in liquid superacids in competition with protolytic ionization
-
The deuterium distribution observed in isobutane recovered after short contact times with the DF-SbF5 superacid at 0°C shows that a very fast reversible protonation of all C-H bonds occurs before ionization of the alkane, in accord with the Olah σ-basicity concept. Comparison of the amounts of hydrogen with the amount of tert-butyl ions generated during ionization shows that the reaction is purely protolytic in HF containing up to 20 mol % SbF5, but becomes oxidative at higher concentrations.
- Sommer, Jean,Bukala, Jozef,Hachoumy, Mohammed,Jost, Roland
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p. 3274 - 3279
(2007/10/03)
-
- Oxygen Atom Transfer With Niobocene Ketenes; Baeyer-Villiger Chemistry with Unusual Regioselectivities
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Niobocene ketene complex 1 has been utilized as an oxygen atom transfer reagent, converting ketones and aldehydes to esters and carboxylic acids.The steric properties of compound 1 give rise to a series of relative migratory aptitudes that differs from those seen for peracids.The process may be rendered catalytic in 1 with methyltrifluoromethyldioxirane (4). Key Words: Baeyer-Villiger reaction, niobocene complexes, ketenes, oxygen transfer, dioxiranes
- Fermin, Maria C.,Bruno, Joseph W.
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p. 7545 - 7548
(2007/10/02)
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- Electrochemical activation of zinc in the coupling reaction of α-bromoesters with carbonyl compounds
-
The Reformatsky reaction has been examined using a mild and effective method of electrochemical zinc activation, based on the cathodic reduction of a catalytic amount of zing bromide in acetonitrile.
- Rollin, Y.,Gebehenne, C.,Derien, S.,Dunach, E.,Perichon, J.
-
-
- Selective Carbonylation of Propane in HF-SbF5: The Role of Carbon Monoxide in the Halogen-Promoted Activation Step
-
The halogen-promoted regioselective carbonylation of propane in HF-SbF5 shows a strong dependence of the rates on the partial pressure of CO indicating that carbon monoxide is associated with the halogen in the activation step.
- Bukala, Jozef,Culmann, Jean-Christophe,Sommer, Jean
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p. 481 - 483
(2007/10/02)
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- REACTION OF PHOSPHORUS THIOACID CHLORIDES WITH ETHYL ISOBUTYRIMIDATE HYDROCHLORIDE, PROPERTIES OF PHOSPHORYL THIOIMIDATES
-
Phosphorus thioacid chlorides react with ethyl isobutyrimidate with the formation of 1-ethoxy-1-methylpropylideneamidothiophosphates, which can be hydrolyzed at both C=N and P-N bonds.
- Krongauz, Yu. I.,Potapova, V. V.,Sandakov, V. B.,Koroleva, T. N.,Bogomolova, L. M.
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p. 345 - 348
(2007/10/02)
-
- Pentacarbonylmanganese enolate and dienolate complexes. Preparative and mechanistic considerations
-
Reactions of pentacarbonyl manganate anion with 4-halocrotonate esters or 2-halocarboxylate esters result in a complex set of inorganic and organic products, usually including the expected dienolate (or enolate) complexes.The reaction variables include the counterion, solvent, and halo group.The mechanism of the reaction has been investigated by conducting a thorough characterization of the reaction products under various conditions and also by carrying out model reactions.One can rationalize most of the non-organometallic products using either a radical or carbanion mechanism, but the latter seems to fit the available data better.Experimental procedures for optimizing the yield of the organometallic dienolate or enolate complexes have been worked out.
- Masters, Andrew P.,Sorensen, Ted S.
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p. 492 - 501
(2007/10/02)
-
- A HIGHLY EFFICIENT DEOXYDATION OF α-OXYGENATED ESTERS VIA SmI2-INDUCED ELECTRON TRANSFER PROCESS
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A variety of α-oxygenated esters, such as α-acetoxy, α-methoxy-, α-OTPH, and α-hydroxy esters were easily reduced at room temperature to give the corresponding saturated esters in good to excellent yields with the aid of an efficient electron transfer system, SmI2-THF-HMPA.The method was succesfully applied to the direct conversion of (R,R)-tartrates to (R)-malates.
- Kusuda, Kazuhiro,Junji, Inanaga,Yamaguchi, Masaru
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p. 2945 - 2948
(2007/10/02)
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- NOUVELLES METHODES DE DESHALOGENATION ET DE FORMATION D'ALKYLTRIMETHYLACETALS DE CETENE PAR ACTION DE iPr2NLi SUR QUELQUES α-BROMOESTERS
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A previously described method consisting in reacting LDA with α-bromoketones has been extended to α-bromoesters.Deshalogenation (after hydrolysis) and formation of ketene alkyltrimethylsilyl acetals (after SiMe3Cl addition) occur and show the generality of the method.
- Lion, Claude,Lebbar, Kadija,Boukou-Poba, Jean-Paul
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p. 227 - 234
(2007/10/02)
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- SODIUM HYDROGEN TELLURIDE: A MECHANISTIC CHAMELEON
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Relative rates of reduction of several α,β-unsaturated esters and styrenes added to recently obtained results from other substrates show that sodium hydrogen telluride (NaTeH) can react according to different mechanisms : nucleophilic substitution, hydride transfer, hydrogen atom transfer and electron transfer.
- Barton, Derek H. R.,Bohe, Luis,Lusinchi, Xavier
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p. 6609 - 6612
(2007/10/02)
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- ENZYMATIC REACTIONS IN ORGANIC SYNTHESIS: 2- ESTER INTERCHANGE OF VINYL ESTERS
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Ester interchange of vinyl esters appears to be a rapid and efficient way to obtain esters of primary and secondary alcohols, provided there is a hydrogen atom on the carbon adjacent to the carbonyl of the acyl moiety.
- Degueil-Castaing, M.,Jeso, B. De,Drouillard, S.,Maillard, B.
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p. 953 - 954
(2007/10/02)
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- S,S-Bis Dithiocarbonate. A New Reactive Coupling Agent for the Direct Esterification of Carboxylic Acids
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S,S-Bis dithiocarbonate, prepared from 4,6-dimethyl-2-pyrimidinethiol hydrochloride and phosgene in the presence of triethylamine in dichloromethane/toluene, is a new reactive coupling agent for the direct esterification of carboxylic acids with alcohols.
- Kim, Sunggak,Kim, Sung Soo
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p. 1017 - 1019
(2007/10/02)
-
- Kinetics and Mechanism of the Lewis Acid-catalyzed Addition of Alcohols to Ketenes in Diethyl Ether Solution
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A kinetic study is reported of the addition of alcohols to dimethyl- and diphenyl-ketene in diethyl ether solution at 25 deg in the presence of HgCl2, ZnCl2, SbCl3, and Bun2SnCl2.Except for HgCl2, which forms insoluble complexes with the reactants, the metal halides catalyse the addition to dimethylketene.The catalysed addition involves the reaction of metal halide-alcohol adducts with the ketene.In general, the stronger the adduct as a Broensted acid, The faster is the addition of the alcohol to the ketene, although C-O, as well as C-H, bond formation is propably significant kinetically.A cyclic transition state is suggested.For diphenylketene, strongly acidic adducts transfer alcohol to the ketene so slowly that inhibition of alcoholysis is observed.Inhibition arises because the spontaneous alcoholysis is reduced as free alcohol is removed as unreactive adduct.However, weak-metal halide acids probably lead to catalysis.It is concluded (a) that the different behaviour of the two ketenes in these reactions is in keeping with their behaviour observed when they react with carboxylic acids in ether, and (b) that metal halide-catalysed alcoholysis of ketenes is generally similar to that observed with aryl isocyanates, except that tin-based catalysts are relatively more effective with isocyanates.
- Poon, Nai L.,Satchell, Derek P. N.
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p. 1551 - 1554
(2007/10/02)
-
- A Simple and Mild Esterification Method for Carboxylic Acids Using Mixed Carboxylic-Carbonic Anhydrides
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A simple and mild esterification method using mixed carboxylic-carbonic anhydrides has been developed.Simple aliphatic carboxylic esters are prepared in high yields by the reaction of acids with equimolar amounts of chloroformates (2,2,2-trichloroethyl chloroformate is an exception) and triethylamine in the presence of a catalytic amount of 4-(dimethylamino)pyridine.Although aromatic acids give a mixture of the ester, the acid anhydride, and the carbonate under normal conditions utilized in this study, it is found that increasing the amount of 4-(dimethylamino)pyridine drastically decreases the formation of the acid anhydride and the carbonate, affording a satisfactory yield of the ester.This method reaches a limit with sterically hindered acids and the formation of the acid anhydride and the carbonate is favored.
- Kim, Sunggak,Lee, Jae In,Kim, Youn Chul
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p. 560 - 565
(2007/10/02)
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- Carbene Reactions with Cis Azo Functions. Formation of Ester Azines from Δ3-1,3,4-Oxadiazolines
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Thermolysis of a 2-alkoxy-2,5,5-trialkyl-Δ3-1,3,4-oxadiazoline (1), either neat or in a solvent such as benzene, leads to a carbonyl ylide intermediate which fragments to carbonyl compounds and carbenes.The latter attack the parent oxadiazoline at the azo function, presumably to form azomethine imine ylides.The latter ylides then fragment to form carbonyl compounds and azines such as R1(R2O)C=NN=C(OR2)R1, R1(R2O)C=NN=C(R3)2 and (R3)2C=NN=C(R3)2.The mechanism proposed is supported by results of studies of the dependence of the azine and propeneyields on the initial oxadiazoline concentration.More propene and less (R3)2C=NN=C(R3)2 are obtained at low oxadiazoline concentrations, as would be expected if both arise from dimethyl carbene.
- Keus, Diane,Kaminski, Maciej,Warkentin, John
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p. 343 - 347
(2007/10/02)
-
- THE ELECTRON SPIN RESONANCE SPECTRA OF THE ANNULENE (CYCLOBUTADIENE) RADICAL CATIONS, R4C4+.
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A series of simple (R=R') and mixed (RR') cyclobutadiene radical cations, R2R'2C4+., have been prepared by photolysis of the alkynes, RCCR' or of mixtures of the alkynes RCCR and R'CCR', in dichloromethane in the presence of aluminium chloride, and the e.s.r. spectra have been recorded.The magnitude of the 13C hyperfine coupling in Et4C4+. confirms that it is a ?-radical, with no evidence for out-of-plane or in-plane (Jahn-Teller) distortion.The values of a(Hβ) for the radicals (RCH2)4C4+. and (RCH2)2R'2C4+. indicate that, as the bulk of the alkyl substituents increases, the group R is pushed out of the plane of the ring.Some unusual temperature effects on a(Hβ) are ascribed to interaction of the radical cation with the solvent or with the counterion.As the bulk of the alkyl groups increases, the g-value decreases from 2.0030 to about 2.0022. cis- and trans-Isomers of the radicals Me2tBu2C4+., Et2tBu2C4+., iBu2tBu2C4+., and propably Me2Et2C4+. have been identified, and the spectra of cis- and trans-Me2tBu2C+. are analysed in terms of breaking of the degeneracy of the molecular orbitals of the cyclobutadiene system by differential electron release by the alkyl groups (tBu > Me).
- Courtneidge, John L.,Davies, Alwyn G.,Lusztyk, Ewa,Lusztyk, Janusz
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p. 155 - 164
(2007/10/02)
-
- A HIGH YIELD ROUTE TO ETHYL ESTERS OF CARBOXYLIC ACIDS
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Diethyl trichloromethylphosphonate reacts with carboxylic acids to yield their ethyl esters, via transesterification; even the hindered mesitoic acid is esterified in high yield.
- Downie, Ian M.,Wynne, Neil,Harrison, Stephen
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p. 1457 - 1458
(2007/10/02)
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- PHOTOCHEMICAL ACTIVATION OF THE CARBOXYL GROUP VIA N-ACYL-2-THIONOTHIAZOLIDINES
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Photolysis of N-acyl derivatives of 2-thionothiazolidine in the presence of ethanol affords ethyl esters; a mechanism involving γ-hydrogen abstraction by sulfur is postulated.
- Burton, Lester P.J.,White, James D.
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p. 3147 - 3150
(2007/10/02)
-