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Elimination/readdition Reactions (elimination + reaction)
Selected AbstractsZirconocene-Induced Cocyclization/Elimination Reactions of 2-Heterosubstituted 1,6-Dienes and 1,6-Enynes.CHEMINFORM, Issue 52 2005David R. Owen No abstract is available for this article. [source] Indium(I) Bromide Promoted Stereoselective Preparation of (E)-,,,-Unsaturated Ketones via Sequential Intermolecular Aldol-Type Coupling/Elimination Reactions of ,,,-Dichloroketones with Aldehydes.CHEMINFORM, Issue 19 2007Clovis Peppe Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] The Effect of Brine Ingredients on Carrot Texture during Thermal Processing in Relation to Pectin Depolymerization due to the ,-Elimination ReactionJOURNAL OF FOOD SCIENCE, Issue 9 2006Trong Son Vu ABSTRACT:, Thermal texture degradation of carrots was studied at a temperature of 100 °C in aqueous solutions containing sodium chloride, citric acid, ascorbic acid, and ethylenediaminetetraacetic acid (EDTA) at different concentrations. To enhance the texture of the final product, the carrot samples were pretreated at 65 °C for 30 min in an aqueous calcium chloride solution (5 g/L). For all case studies considered, the pH of the solutions was adjusted to pH = 6.0. In parallel, both the changes in degree of esterification (DE) and the progress of the ,-elimination reaction of carrot pectin under the same conditions were investigated. The kinetic parameters for texture degradation (rate constant kt and final texture value [TP,/TP0]) were estimated using a fractional conversion model. The results indicate that both the rate constant for texture degradation (kt) and the rate constant for the ,-elimination reaction (kb) increased with increasing additive concentration, while the final texture values (TP,/TP0) and DE decreased with increasing additive concentration in all systems studied. A high correlation was observed between the relative rate constant for texture degradation and the relative rate constant for the ,-elimination reaction on the one hand, and the relative final texture value and the relative rate constant for the ,-elimination reaction on the other hand, suggesting that the influence of the solutes on texture degradation can be explained by their influence on the ,-elimination reaction. [source] Serum Albumin-Catalyzed Trigger System by Using a Tandem Kemp Elimination/,-Elimination ReactionCHEMBIOCHEM, Issue 5 2005Guillaume Boucher Dr. Prodrug activation: Serum albumins (BSA or HSA) are shown to catalyze a reaction cascade that involves the ring-opening of an isoxazole ring followed by a ,-elimination reaction, as per the scheme. The 4-(aryloxymethyl)isoxazole derivative of estrone is selectively removed in vitro by albumins, thus demonstrating the potential of this new protective group. [source] ChemInform Abstract: Zinc Homologation,Elimination Reaction of ,-Sulfinyl Carbanions as a New Route to Olefins.CHEMINFORM, Issue 5 2009Adi Abramovitch Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Palladium-Catalyzed Elimination Reaction of Acyclic (E)-Allylic Acetates: The Stereochemistry Elucidated by "syn-Effect".CHEMINFORM, Issue 30 2005Hiroyuki Takenaka Abstract For Abstract see ChemInform Abstract in Full Text. [source] Dimethyl Sulfoxide Mediated Elimination Reactions in 3-Aryl 2,3-Dihalopropanoates: Scope and Mechanistic Insights.CHEMINFORM, Issue 50 2007Wei Li Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Manganese-Promoted ,-Elimination Reactions: Totally Stereoselective Synthesis of (E)-,,,-Unsaturated Esters.CHEMINFORM, Issue 23 2006Jose M. Concellon Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Photoinduced Metalation of Nonactivated C,Cl Bonds with Samarium Diiodide: Synthesis of Alkenes with High (Z)-Selectivity Through ,-Elimination Reactions.CHEMINFORM, Issue 18 2006Jose M. Concellon Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Carbocupration/Zinc Carbenoid Homologation and ,-Elimination Reactions for a New Synthesis of Allenes , Application to the Enantioselective Synthesis of Chiral Allenes by Deracemization of sp3 -Organometallic Derivatives.CHEMINFORM, Issue 16 2003Jos P. Varghese Abstract For Abstract see ChemInform Abstract in Full Text. [source] Unexpected SN2,-Type Addition,Elimination Reactions of 1-Aryl-2,3-allenols with LiX.CHEMINFORM, Issue 47 20023-dienes., Synthesis, Synthetic Application of 1-Aryl-3-halo- Abstract For Abstract see ChemInform Abstract in Full Text. [source] Hydration/elimination reactions of trapped protonated fluoroalkyl triazinesJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 2 2008Gianluca Giorgi [source] Fragmentations of (M,H), anions of underivatised peptides.MASS SPECTROMETRY REVIEWS, Issue 1 2009Part 2: Characteristic cleavages of Ser, of disulfides, other post-translational modifications, together with some unusual internal processes Abstract In a previous review (Bowie, Brinkworth, & Dua (2002); Mass Spectrom Rev 21:87,107) we described the characteristic backbone cleavages and side chain fragmentations which occur from (M,H), parent anions of underivatized peptides. This work is briefly summarized in the present review. Cys was not described in the previous review: here we describe the Cys characteristic side chain loss of H2S, together with its , backbone cleavage. These processes are compared with those of the related Ser. All experimental observations are backed up with theoretical studies at the HF/6-31G(d)//AM1 level of theory, a level of theory which we have shown gives good geometries and acceptable relative energies. The negative ion cleavages of a number of post-translational modifications are described. Negative ion mass spectrometry is the method of choice for identification of disulfides in both peptides and proteins. Intramolecular disulfides are identified by the presence of the fragment anion [(M,H),,H2S2], and CID MS2 of this fragment normally identifies the positions of the two Cys residues and often the full sequence of the peptide. An unsymmetrically substituted intermolecular disulfide can give up to eight characteristic fragment anions, and CID MS2 of some, or all of these often provides the full sequence of those peptides which form the initial intermolecular disulfide linkage. Negative ion cleavages of disulfides are the most energetically favored of all peptide negative cleavages studied to date. Negative ion mass spectrometry is also valuable for the identification of pyroglutamates, sulfates and phosphates. Finally, some unusual fragmentations are described which involve cyclization/elimination reactions which require the decomposing (M,H), parent anions to adopt the same helical conformation that these peptides have in solution. © 2008 Wiley Periodicals, Inc., Mass Spec Rev 28:20,34, 2009 [source] Metal Effects on the Asymmetric Synthesis of a New Heterobidentate As/P=S LigandEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2010Mengtao Ma Abstract The cycloaddition reaction between 3,4-dimethyl-1-phenylarsole and diphenylvinylphosphane sulfide was promoted by chiral palladium and platinum complexes containingortho -metalated (S)-[1-(dimethylamino)ethyl]naphthalene. They exhibited similar stereoselectivity; the palladium cycloadducts could not be separated via column chromatography and fractional crystallization, however, the corresponding platinum complexes could be successfully converted into their enantiomerically pure counterpart. A formal arsanylidene elimination reaction was observed on the liberated free As/P=S bidentate ligand. [source] Synthesis and Structure of Aminopyridinato-Stabilized Yttrium and Lanthanum Amides and Their Reactivity towards Alkylaluminium CompoundsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 3 2009Christian Döring Abstract A series of aminopyridinato-stabilized (amido)lanthanide complexes has been synthesized and characterized. The bulky aminopyridines (2,6-diisopropylphenyl)[6-(2,4,6-triisopropylphenyl)pyridin-2-yl]amine (1a) and [6-(2,4,6-triisopropylphenyl)pyridin-2-yl](2,4,6-trimethylphenyl)amine (1b) were introduced by amine elimination reaction with [Ln{N(SiHMe2)2}3(thf)2] (Ln = Y, La, thf = tetrahydrofuran, Me = methyl) to obtain the corresponding mono(aminopyridinato) complexes. Single-crystal X-ray analyses were carried out for the yttrium derivatives. The complexes are not able to undergo coordinative chain transfer polymerization with ethylene in the presence of alkylaluminium compounds as the corresponding dialkyl complexes do. Investigations of the reactions of the lanthanide aminopyridinato complexes with triethylaluminium or diisobutylaluminium hydride reveal a fast transfer of the aminopyridinato ligand to the aluminium atom. The products of this transfer reaction are aminopyridinato-stabilized dialkylaluminium compounds. One example of these aluminium complexes was characterized by X-ray crystal structure analysis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Synthesis and Reaction of MnII Iodides Bearing the ,-Diketiminate Ligand: the First Divalent Manganese N-Heterocyclic Carbene Complexes [{HC(CMeNAr)2}MnI{C[N(iPr)CMe]2}] and [{HC(CMeNAr)2}MnNHAr{C[N(iPr)CMe]2}] (Ar = 2,6- iPr2C6H3)EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 24 2003Jianfang Chai Abstract The manganese mono-iodide [HC(CMeNAr)2]MnI(THF) (Ar = 2,6- iPr2C6H3) (3) was prepared in good yield from the reaction of [HC(CMeNAr)2]K with MnI2 in THF. Treatment of 3 under reflux in toluene and removing all the volatiles in vacuo afforded the dimeric compound [{HC(CMeNAr)2}Mn]2(,-I)2 (4). Displacement of the coordinated THF in 3 by a strong Lewis base C[N(iPr)CMe]2 or by adding C[N(iPr)CMe]2 to the toluene solution of 4 readily gave the N-heterocyclic carbene adduct [{HC(CMeNAr)2}]MnI{C[N(iPr)CMe]2} (5). Reduction of 5 with sodium/potassium alloy at room temperature unexpectedly resulted in the formation of the monomeric compound [{HC(CMeNAr)2}]MnNHAr{C[N(iPr)CMe]2} (6). Alternatively 6 was obtained by the salt elimination reaction of 5 with LiNHAr. Compounds 5 and 6 are the first examples of divalent manganese N-heterocyclic carbene adducts and the first manganese non-carbonyl carbene complexes. The single crystal X-ray structural analyses reveal that compounds 3 and 6 are monomeric and compound 4 is dimeric in the solid state. The manganese centers in these compounds exhibit a distorted tetrahedral geometry. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Kinetics of elimination reactions of 1,2-diphenyl ethyl substrates in acetonitrile: A mechanistic change in the presence of a strong baseINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 8 2008D. Santhosh Kumar Kinetics of elimination of methanesulfonic acid from 1,2-diphenylethylmethane sulfonate and its 1- p -methylphenyl- and 1- p -chlorophenyl-substituted derivatives is studied. The results show that the elimination reaction is unimolecular (E1) as reported in the case of 1-chloro-1-(4-methoxyphenyl)-2-phenylethane. The rate of the elimination reaction in the presence of added weak base pyridine is independent of the concentration of the base, but in the presence of a strong base piperidine the rate shows a linear upward drift and this is due to the appearance of a bimolecular component along with the unimolecular pathway. The shift from the unimolecular to bimolecular process takes place independently of the nature of the leaving group and the parasubstituent in the 1,2-diphenylethyl substrate. © 2008 Wiley Periodicals, Inc. 40: 481,487, 2008 [source] The Effect of Brine Ingredients on Carrot Texture during Thermal Processing in Relation to Pectin Depolymerization due to the ,-Elimination ReactionJOURNAL OF FOOD SCIENCE, Issue 9 2006Trong Son Vu ABSTRACT:, Thermal texture degradation of carrots was studied at a temperature of 100 °C in aqueous solutions containing sodium chloride, citric acid, ascorbic acid, and ethylenediaminetetraacetic acid (EDTA) at different concentrations. To enhance the texture of the final product, the carrot samples were pretreated at 65 °C for 30 min in an aqueous calcium chloride solution (5 g/L). For all case studies considered, the pH of the solutions was adjusted to pH = 6.0. In parallel, both the changes in degree of esterification (DE) and the progress of the ,-elimination reaction of carrot pectin under the same conditions were investigated. The kinetic parameters for texture degradation (rate constant kt and final texture value [TP,/TP0]) were estimated using a fractional conversion model. The results indicate that both the rate constant for texture degradation (kt) and the rate constant for the ,-elimination reaction (kb) increased with increasing additive concentration, while the final texture values (TP,/TP0) and DE decreased with increasing additive concentration in all systems studied. A high correlation was observed between the relative rate constant for texture degradation and the relative rate constant for the ,-elimination reaction on the one hand, and the relative final texture value and the relative rate constant for the ,-elimination reaction on the other hand, suggesting that the influence of the solutes on texture degradation can be explained by their influence on the ,-elimination reaction. [source] Experimental and theoretical studies of the elimination kinetics of 3-hydroxy-3-methyl-2-butanone in the gas phaseJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 7 2005Mariana Graterol Abstract The kinetics of the gas-phase elimination of 3-hydroxy-3-methyl-2-butanone was investigated in a static system, seasoned with allyl bromide, and in the presence of the free chain radical inhibitor toluene. The working temperature and pressure range were 439.6,489.3°C and 81,201.5,Torr (1,Torr,=,133.3,Pa), respectively. The reaction was found to be homogeneous, unimolecular and to follow a first-order rate law. The products of elimination are acetone and acetaldehyde. The temperature dependence of the rate coefficients is expressed by the following equation: log[k1(s,1)],=,(13.05±0.53),(229.7±5.3),kJ,mol,1 (2.303RT),1. Theoretical estimations of the mechanism of this elimination suggest a molecular mechanism of a concerted non-synchronous four-membered cyclic transition-state process. An analysis of bond order and natural bond orbital charges suggests that the bond polarization of C(OH),C(O),, in the sense of C(OH),+&·C(O),,, is rate limiting in the elimination reaction. The rate coefficients obtained experimentally are in reasonably good agreement with the theoretical calculations. The mechanism of 3-hydroxy-3-methyl-2-butanone elimination is described. Copyright © 2005 John Wiley & Sons, Ltd. [source] Origin of the formation of the 4-butenyl end group in zirconocene-catalyzed propylene polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 11 2006Bernabe Quevedo-Sanchez It has been proposed that the 4-butenyl end group in polypropylene is formed by isomerization of the 2-butenyl end group. Prior experimental evidence has shown that the isomerization is not produced thermally or upon an acidic treatment during the workup or analysis of the polymer. We postulate that the production of the 4-butenyl end group by isomerization might be catalyzed by a zirconocene hydride complex that forms during the ,-hydride elimination reaction. The isomerization of a preformed olefinic-end-group isotactic polypropylene with a well-known transition-metal hydride shows the disappearance of the 2-butenyl end group concomitant with the appearance of the 4-butenyl end group. [source] Serum Albumin-Catalyzed Trigger System by Using a Tandem Kemp Elimination/,-Elimination ReactionCHEMBIOCHEM, Issue 5 2005Guillaume Boucher Dr. Prodrug activation: Serum albumins (BSA or HSA) are shown to catalyze a reaction cascade that involves the ring-opening of an isoxazole ring followed by a ,-elimination reaction, as per the scheme. The 4-(aryloxymethyl)isoxazole derivative of estrone is selectively removed in vitro by albumins, thus demonstrating the potential of this new protective group. [source] Oxidant-Free Dehydrogenation of Alcohols Heterogeneously Catalyzed by Cooperation of Silver Clusters and Acid,Base Sites on AluminaCHEMISTRY - A EUROPEAN JOURNAL, Issue 10 2009Ken-ichi Shimizu Dr. Abstract Trifunctional green catalysis: In-depth characterization shows that oxidant-free selective oxidation of alcohols by silver nanoparticles on ,-Al2O3, as a new heterogeneous catalyst, proceeds through cooperation of silver, acid, and base sites (see figure). A ,-alumina-supported silver cluster catalyst,Ag/Al2O3,has been shown to act as an efficient heterogeneous catalyst for oxidant-free alcohol dehydrogenation to carbonyl compounds at 373,K. The catalyst shows higher activity than conventional heterogeneous catalysts based on platinum group metals (PGMs) and can be recycled. A systematic study on the influence of the particle size and oxidation state of silver species, combined with characterization by Ag,K-edge XAFS (X-ray absorption fine structure) has established that silver clusters of sizes below 1,nm are responsible for the higher specific rate. The reaction mechanism has been investigated by kinetic studies (Hammett correlation, kinetic isotope effect) and by in situ FTIR (kinetic isotope effect for hydride elimination reaction from surface alkoxide species), and the following mechanism is proposed: 1),reaction between the alcohol and a basic OH group on the alumina to yield alkoxide on alumina and an adsorbed water molecule, 2),CH activation of the alkoxide species by the silver cluster to form a silver hydride species and a carbonyl compound, and 3),H2 desorption promoted by an acid site in the alumina. The proposed mechanism provides fundamental reasons for the higher activities of silver clusters on acid,base bifunctional support (Al2O3) than on basic (MgO and CeO2) and acidic to neutral (SiO2) ones. This example demonstrates that catalysts analogous to those based on of platinum group metals can be designed with use of a less expensive d10 element,silver,through optimization of metal particle size and the acid,base natures of inorganic supports. [source] Intramolecular Carbolithiation of Allyl o -Lithioaryl Ethers: A New Enantioselective Synthesis of Functionalized 2,3-DihydrobenzofuransCHEMISTRY - A EUROPEAN JOURNAL, Issue 18 2005José Barluenga Prof. Dr. Abstract A new and easy method for the diastereoselective synthesis of 3-functionalized 2,3-dihydrobenzofuran derivatives from allyl 2-bromoaryl ethers is described. The key step of this transformation involves an intramolecular carbolithiation reaction of allyl 2-lithioaryl ethers. The substituents in both the allyl and the aryl moieties play an important and decisive role in stopping the reaction at the benzofuran thus avoiding a ,-elimination reaction. Finally, this process is amenable to the synthesis of enantiomerically enriched compounds by using (,)-sparteine as a chiral inductor. Se describe un método nuevo y sencillo para la síntesis diastereoselectiva de derivados de 2,3-dihidrobenzofurano funcionalizados en la posición 3 a partir de alil 2-bromoaril éteres. El paso clave de esta transformación implica una reacción de carbolitiación intramolecular de alil 2-litioaril éteres. La presencia de sustituyentes tanto en el resto alílico como en el arílico desempeña un papel decisivo e importante para poder detener la reacción en el estadio de benzofurano, evitando así la reacción de , -eliminación. Finalmente, este proceso puede ser aplicado a la síntesis de compuestos enantioméricamente enriquecidos mediante el uso de (,)-esparteína como inductor quiral. [source] Highly Stereoselective Synthesis of Phenylseleno- and p -Tolylsulfonyl Substituted 1,3-Dienes from Functionalized Allyl AlcoholsCHINESE JOURNAL OF CHEMISTRY, Issue 2 2004Mei-Hua Xie Abstract Phenylseleno- and p -tolylsulfonyl substituted 1,3-dienes were conveniently prepared with high stereoselectivity by the elimination reaction of phenylseleno- and p -tolylsulfonyl substituted allyl alcohols in the presence of BF3 · Et2O in acetic anhydride. The products were characterized by 1H NMR, MS, IR and elemental analysis. The single crystal structure of 2a was determined by X-ray diffraction analysis. [source] Using Chiral Ligand Substituents To Promote the Formation of Dinuclear, Double-Stranded Iron, Manganese, and Zinc MesocatesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 33 2007Stuart D. Reid Abstract The synthesis and structures of dinuclear manganese, iron, and zinc complexes of chiral di-iminodipyrromethane ligands (L) are reported. Schiff base condensation reactions between 5,5,-diformyl-2,2,-dipyrromethane and the chiral amines (,)-(R)-CH(Me)tBu and (+)-(R)-CH(Me)Ph result in the straightforward synthesis of the new, chiral ligands H2L2 and H2L3, respectively. Salt elimination reactions between K2L and divalent Mn and Fe halides, and protonolysis reactions between ZnMe2 and H2L result in the formation of the new dinuclear complexes [M2(L)2]. Investigation of the structures of these compounds in solution and in the solid state reveal that chiral mesocates are formed for L = L2, whereas for L = L3, a racemic mixture of helicates is present.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Towards Cationic Gallium Derivatives: Metallacycles from the Reactions of Organogallium Compounds with Tetraorganodichalcogenoimidodiphosphinates and a New N -(Diphenylthiophosphinyl)thioureato LigandEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2004Virginia Montiel-Palma Abstract The organometallic complexes of general formulae [Me2Ga{,2 - E,E, -[R2P(E)NP(E,)R,2]}] [R = R, = Ph, E = E, = O (1); R = R, = Ph, E = E, = S (2); R = R, = Ph, E = E, = Se (3); R = R, = Ph, E = O, E, = S (4); R = Me, R, = Ph, E = S, E, = O (5)] and [Me2Ga{,2 - S,S, -[Ph2P(S)NC(S)(C9H10N)]}] (6) were obtained by facile methane elimination reactions from GaMe3 and the acidic ligands L1H [(XPPh2)2NH (X = O, S, Se), (OPPh2)(SPPh2)NH, and (OPMe2)(SPPh2)NH] and L2H [Ph2P(S)NHC(S)(C9H10N)] in toluene. Replacement of one phosphorus atom by a carbon atom in the ligand skeleton of L1H gave the new ligand L2H, which, upon reaction with GaMe3, gave compound 6, which shows no significant structural differences with respect to 1,5. Therefore, L2H does not induce partial planarity in the six-membered ring, indicating the necessity for replacing both phosphorus atoms of the ligand by carbon atoms, as in the ,-diketonate-type derivatives, in order to impose ring planarity. Thus, despite originating from a variety of ligands with differing donor atoms and substituents at the phosphorus atoms, all complexes show little structural differences. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Kinetics of elimination reactions of 1,2-diphenyl ethyl substrates in acetonitrile: A mechanistic change in the presence of a strong baseINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 8 2008D. Santhosh Kumar Kinetics of elimination of methanesulfonic acid from 1,2-diphenylethylmethane sulfonate and its 1- p -methylphenyl- and 1- p -chlorophenyl-substituted derivatives is studied. The results show that the elimination reaction is unimolecular (E1) as reported in the case of 1-chloro-1-(4-methoxyphenyl)-2-phenylethane. The rate of the elimination reaction in the presence of added weak base pyridine is independent of the concentration of the base, but in the presence of a strong base piperidine the rate shows a linear upward drift and this is due to the appearance of a bimolecular component along with the unimolecular pathway. The shift from the unimolecular to bimolecular process takes place independently of the nature of the leaving group and the parasubstituent in the 1,2-diphenylethyl substrate. © 2008 Wiley Periodicals, Inc. 40: 481,487, 2008 [source] Homogeneous, unimolecular gas-phase elimination kinetics of ethyl esters of glyoxylic, 2-oxo-propanoic, and 3-methyl-2-oxo-butanoic acidsINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 5 2007Andreina Reyes The rates of elimination of several ethyl esters of 2-oxo-carboxylic acid were determined in a seasoned static reaction vessel over the temperature range 350,430°C and pressure range 33,240 Torr. The reactions, in the presence of a free-radical inhibitor, are homogeneous, unimolecular, and follow a first-order rate law. The overall and partial rate coefficients are expressed by the Arrhenius equation. Ethyl glyoxalate Ethyl 2-oxo-propionate Ethyl 3-methyl-2-oxo-butyrate The mechanisms of these elimination reactions are described in terms of concerted cyclic transition state structures. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 268,275, 2007 [source] Reaction of tetraazathiapentalene and thiadiazolopyrimidine derivatives with heterocumulenes: Cycloaddition and elimination reactions via hypervalent sulfur intermediatesJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 1 2004Noboru Matsumura Tetraazathiapentalene derivative 1 reacts with heterocumulenes such as diphenylketene (2) and 2-pyridylisothiocyanate (5) to give heterocycles 3, 6 and 7 with elimination of methylisothiocyanate. The reactions of thiadiazolopyrimidine derivatives 8a-b with ethoxycarbonyl isothiocyanate (9) and carbon disulfide (11) gives heterocycles 10 and 12 via thermal decomposition of 1:1 cycloadducts C and D which have a hypervalent sulfur. The mechanistic and reactivity features of these reactions are described. [source] Applications of deuterium isotope effects for probing aspects of reactions involving oxidative addition and reductive elimination of H,H and C,H bonds,JOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 11-12 2007Gerard Parkin Abstract The various types of deuterium isotope effects that are observed for reactions involving oxidative addition and reductive elimination reactions of H,H and C,H bonds with a transition metal center are reviewed. Copyright © 2007 John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||||||||