Search results for "Reaction"
showing 10 items of 6134 documents
Efficient Synthesis of 5-Chalcogenyl-1,3-oxazin-2-ones by Chalcogen-Mediated Yne-Carbamate Cyclisation: An Experimental and Theoretical Study
2014
A very efficient synthesis of 5-chalcogenyl-1,3-oxazin-2-ones has been accomplished by the chalcogen-mediated yne–carbamate cyclisation of chiral, non-racemic N-Cbz-protected propargylic amines using PhXY (X = Se, S, Te; Y = Br or Cl) as electrophile sources. The reactions gave good-to-excellent yields for a wide range of substrates. In all cases the reaction was totally regioselective, occurring by a 6-endo-dig process regardless of the nature of the reagent and of the substituents in the starting material. This methodology permits the formation of the 1,3-oxazin-2-one moiety as well as the simultaneous installation of a chalcogen functionality onto the heterocyclic ring. The experimental …
Benzyl alcohol to benzaldehyde oxidation on MnOx clusters: Unraveling atomistic features
2021
Abstract The catalytic oxidation of benzyl alcohol with O 2 is a promising option for the production of benzaldehyde, from both environmental and economical viewpoints. In particular, highly dispersed MnO x systems feature good activity and selectivity in a wide range of temperatures, although deactivation phenomena by over-oxidation and/or poisoning of active sites are generally recorded. On this account, a density functional theory study was performed on cluster-sized catalyst models, namely Mn 4 O 8 and over-oxygenated Mn 4 O 9 fragments, to predict the reactivity pattern of MnO x catalysts in the selective aerobic oxidation of benzyl alcohol. Several pathways concur to determine the who…
Graphical Analysis of Electrochemical Impedance Spectroscopy of Two Consecutive Irreversible Electron Transfers. 1. Theoretical Study of the Anodic D…
2006
A general function for the faradaic impedance associated to a two consecutive single electron transfer mechanism followed by a irreversible first-order step has been obtained on the basis of formal kinetics. Kinetic parameters associated to this reaction mechanism can be obtained from the different kind of plots of the impedance function: Nyquist, Cole-Cole, and different Bode plots. A strategy for obtaining all parameters is suggested and analyzed on a detailed flowchart.
Theoretical Study of the Gas Phase Decomposition of Glycolic, Lactic, and 2-Hydroxyisobutyric Acids
1997
The reaction mechanism associated with the decomposition of three α-hydroxycarboxylic acids (glycolic, lactic, and 2-hydroxyisobutyric) in the gas phase to form carbon monoxide, water, and the corresponding carbonyl compounds has been theoretically characterized by using ab initio analytical gradients at the MP2 level of theory with the 6-31G** and 6-31++G** basis sets. A detailed characterization of the potential energy surface points out the existence of three competitive reaction pathways for the decomposition process. The first pathway describes a two-step mechanism, with water elimination and formation of an α-lactone intermediate, achieved by the nucleophilic attack of the carbonylic …
Propan-2-ol dehydration on H-ZSM-5 and H-Y zeolite: a DFT study
2012
The catalytic dehydration of propan-2-ol over H-Y and H-ZMS-5 aluminated zeolite models, mimicking both internal cavities and external surfaces, was studied by DFT calculations to investigate the reaction mechanism. After the adsorption of propan-2-ol on the zeolite, the dehydration mechanism starts with alcohol protonation, occurring by one acidic –OH group of the zeolite fragment, followed by a concerted β-elimination to give propene. The catalytic activity is affected by the size of the zeolite cavity, which is larger in the H-Y than in the H-ZMS-5 zeolite. The adsorption energy of the reagent, as an example, decreases in the order: H-Y cavity ≃ H-ZMS-5 surface > H-ZMS-5 cavity, pointing…
Synthesis, Reactivity and Theoretical Study of B3H8−and Related Derivatives
1996
Abstract Octahydrotriborate salts, B3H8 −, have been prepared by the reaction of NaBH4 with Lewis acids such as BX3·BDMA (BDMA = benzyldimethylamine, × = Cl,Br) or C2H5I in diglyme. The presence of BH3·BDMA as a by-product in the former reaction provides new insight into the reaction mechanism of B11H14 − formation. In acetonitrile-water solutions of HCl or CH3CO2H, the B3H8 − anion reacted to give B3H7CH3CN or B3H7CH3CO2 − characterized by 11B NMR spectroscopy. Their kinetic hydrolysis study was consistent with NMR analysis. Reaction of Bu4NB3H8 and CuCl2 at 0°C produced pure B3H6Cl2 −. An AM1 theoretical study of the substituted derivatives B3H7L (L = Cl−, CH3CN, CH3CO2 −, OH−) and B3H6L2…
Reversible Dimerization and Polymerization of a Janus Diradical To Produce Labile C−C Bonds and Large Chromic Effects
2016
Conducting polymers can be synthesized by irreversible diradical monomer polymerization. A reversible version of this reaction consisting of the formation/dissociation of σ‐dimers and σ‐polymers from a stable quinonoidal diradical precursor is described. The reaction reversibility is made by a quinonoidal molecule which changes its structure to an aromatic species by forming weak and long intermolecular C−C single bonds. The reaction provokes a giant chromic effect of about 2.5 eV. The two opposite but complementary quinonoidal and aromatic tautomers provide the Janus faces of the reactants and products which produces the observed chromic effect. A reaction mechanism is proposed to explain …
Electrocatalytic carboxylation of chloroacetonitrile at a silver cathode for the synthesis of cyanoacetic acid
2008
Abstract The electrocatalytic carboxylation of chloroacetonitrile to cyanoacetic acid performed at silver cathodes was investigated both theoretically and experimentally. Silver exhibits powerful electrocatalytic activities towards the reduction of chloroacetonitrile. In CO 2 -saturated CH 3 CN, reduction of NCCH 2 Cl occurs at potentials that are about 0.7 V more positive than those observed at glassy carbon and gives cyanoacetic acid in good yields. Theoretical considerations on the effect of operative parameters on the performances of the process were confirmed by electrocarboxylation experiments performed in undivided cells equipped with sacrificial anodes both in a bench-scale electroc…
Effect of axially bound anions on the electroreduction of tin(IV) porphyrins in tetrahydrofuran
1989
The spectroscopic characterization and electrochemistry of SnL(X)2 is presented where L is the dianion of tetra-p-tolylporphyrin or tetra-m-tolylporphyrin and X is ClO4–, Br–, Cl–, F–, or OH–. In all cases, electroreduction leads to porphyrin π anion radicals and dianions which were characterized in tetrahydrofuran by spectroelectrochemistry and e.s.r. spectroscopy. Dissociation of one ClO4– ion from SnL(ClO4)2 occurs before electroreduction of the complex but no dissociation is observed either before or after electroreduction of SnL(F)2 or SnL(OH)2. In contrast, one Br– ion dissociates after the first electron addition to SnL(Br)2 while one Cl– ion dissociates from SnL(Cl)2 after the secon…
In situ spectroelectrochemical study of the reductive coupling of benzaldehyde catalyzed by Ti(III) complexes in the presence of Mg(II)
2003
Abstract The UV–vis spectroelectrochemical technique has been used to visualize for the first time, the formation of a trimetallic intermediate Ti(III)Mg(II)Ti(III) during the reductive coupling of benzaldehyde in the presence of electrogenerated Ti(III) and MgCl 2 . This intermediate is supposed to induce the high diastereoselectivity of the reaction. We have built a special thin layer cell adapted from the scheme proposed by A. Neudeck and L. Dunsch [‘J. Electroanal. Chem. 370 (1994) 17; J. Electroanal. Chem. 386 (1995) 135’] which allows the simultaneous recording of the cyclic voltammogram and of a great quantity of UV–vis spectra at a frequency of 1 spectrum per second by means of a …