Hydride Ion Transfer Reactions Research Articles

On the limiting stage of oxidation of alkylarenes by potassium permanganate

The first stage of hydrocarbon benzyl C–H bond oxidation with permanganate is considered. Using a thermochemical approach, three possible mechanisms of this stage are analyzed: electron transfer from hydrocarbon to oxidant, homolytic abstraction of H-atom from benzyl C–H bond, insertion of O-atom into benzyl C–H bond. The reaction enthalpies were used as a characteristic of the thermodynamic favorability of these reactions. The thermochemical characteristics of the species involved in oxidation reactions and the reaction enthalpies were calculated with the quantum chemical method PM7. It is the most accurate among the semi-empirical methods. The calculated reaction enthalpies of various oxidant species formed during the oxidation of the cumene with KMnO 4 showed that their reactivity increases in the series MnO 4 – < HMnO 4 < H 2 MnO 4 + < MnO 3 + . It is established that the protonation of the oxidant species increases their reactivity both in homolytic reactions, where after the neutral H-atom abstraction free radical is formed, and in heterolytic ones, when electron or hydride ion transfer occurs. The obtained fact of increasing the reactivity of the species in oxidation reactions due to protonation explains the experimentally established significant effect of medium acidity on the rate of permanganate reactions with C–H bonds in hydrocarbon functionalization processes, and also provides understanding of the significant role of acidity in the oxidation of organic matter by permanganate. It should be noted that dehydration (removal of water molecule) of the oxidant species increases its reactivity in oxidation reactions. The results of the calculations of the enthalpies of the reactions show greater thermochemical favorability of hydride ion transfer reactions in comparison with reactions that proceed through homolysis of the C–H bond is shown. Keywords: potassium permanganate, oxidative functionalization, alkylarenes, PM7 method.

Stereoselective Total Synthesis of (S)-Stigmolone: A Fruiting-Body-Inducing Pheromone

The total synthesis of (S)-stigmolone, a pheromone from the myxobacterium Stigmatella aurantiaca that induces the formation of fruiting bodies, is described. Sharpless asymmetric epoxidation followed by tert-butyldimethylsilyl trifluoromethanesulfonate/Hunig’s base mediated intramolecular hydride ion transfer reactions were used to install the C-5 stereogenic center. Commercially available isovaleraldehyde is used as a starting material.

Submolecular regulation of cell transformation by deuterium depleting water exchange reactions in the tricarboxylic acid substrate cycle

The naturally occurring isotope of hydrogen (1H), deuterium (2H), could have an important biological role. Deuterium depleted water delays tumor progression in mice, dogs, cats and humans. Hydratase enzymes of the tricarboxylic acid (TCA) cycle control cell growth and deplete deuterium from redox cofactors, fatty acids and DNA, which undergo hydride ion and hydrogen atom transfer reactions. A model is proposed that emphasizes the terminal complex of mitochondrial electron transport chain reducing molecular oxygen to deuterium depleted water (DDW); this affects gluconeogenesis as well as fatty acid oxidation. In the former, the DDW is thought to diminish the deuteration of sugar-phosphates in the DNA backbone, helping to preserve stability of hydrogen bond networks, possibly protecting against aneuploidy and resisting strand breaks, occurring upon exposure to radiation and certain anticancer chemotherapeutics. DDW is proposed here to link cancer prevention and treatment using natural ketogenic diets, low deuterium drinking water, as well as DDW production as the mitochondrial downstream mechanism of targeted anti-cancer drugs such as Avastin and Glivec. The role of 2H in biology is a potential missing link to the elusive cancer puzzle seemingly correlated with cancer epidemiology in western populations as a result of excessive 2H loading from processed carbohydrate intake in place of natural fat consumption.

Molecular Dynamics Simulation Study on Stabilities and Reactivities of NADH Cytochrome B5 Reductase

Binding free energies between coenzyme (FAD and NADH) and the apoenzyme of NADH-cytochrome b5 reductase (b5R) were estimated by applying the continuum Poisson-Boltzmann (PB) model to structures sampled from molecular dynamics simulations in explicit water molecules. Important residues for the enzymatic catalysis were clarified using a computational alanine scanning method. The binding free energies calculated by applying an alanine scanning method can successfully reproduce the trends of the measured steady-state enzymatic activities kcatNADH/KmNADH. Significant decreases in the binding free energy are expected when one of the four residues Arg91, Lys110, Ser127, and Thr181 is mutated into Ala. According to the results of the molecular dynamics simulation, Thr181 is considered to be one of the key residues that helps NADH to approach the isoalloxazine in FAD. Finally, we have constructed very simplified model systems and carried out density functional theory calculations using B3LYP/LANL2DZ//ROHF(or RHF)/LANL2DZ level of theory in order to elucidate a realistic and feasible mechanism of the hydride-ion transfer from NADH to FAD affected by HEME(Fe3+) as an electron acceptor. Our calculated results suggest that the electron and/or hydride-ion transfer reaction from NADH to FAD can be accelerated in the presence of HEME(Fe3+).

The role of mass spectrometric methods in ionic reaction mechanistic studies

The role of various mass spectrometric methods, including electron ionization, collisional activation, metastable peak shapes, analysis of neutrals from ionic unimolecular dissociations, field ionization kinetics, drift cell, and Fourier transform ion cyclotron resonance spectrometry, in ionic reaction mechanistic studies is described. This is illustrated by selected examples of research performed in the author’s group over the last three decades. They comprise inter alia intramolecular acid–base, anchimeric assistance, nucleophilic attack, isomerization, cycloaddition, S N2, and hydride ion transfer reactions.

Intramolecular reactions. An explanation for [M−H]+ ions in the chemical ionization mass spectra of some ring C-substituted methyl dehydroabietate derivates

The formation of [M−H]+ ions in the chemical ionization mass spectra of ring C-substituted methyl dehydroabietates, when methane is used as reagent gas, has been investigated. Two mechanisms, one involving H2 loss from [M−H]+ ions, and the other, hydride ion transfer reactions to the methane reagent ions, have been proposed to account for [M−H]+ ion abundances. For methyl 12,14-diaminodehydroabietate, protonation of the amino group on C-14, followed by the loss of H2 by an intramolecular reaction via a cyclic transition state, is proposed as the predominant mechanism. Hydride ion transfer from the benzylic C-7 has been suggested to provide a major contribution to the formation of [M−H]+ ions of methyl 12-amino-14-nitrodehydroabietate. These conclusions are also consistent with results obtained using ammonia as reagent gas. © 1997 John Wiley & Sons, Ltd.

2-Methylhexane Cracking on Y Zeolites: Catalytic Cycles and Reaction Selectivity

We have formulated a quantitative kinetic model for analyzing the catalytic cracking of 2-methylhexane over USY-zeolite-based catalysts. The model is based on carbocation chemistry which includes carbenium ion initiation, isomerization, olefin desorption, β-scission, oligomerization, and hydride ion transfer reactions. It describes the complex product distribution at different reaction conditions and for catalysts with different Brønsted acid strengths. Three catalytic cycles dominate this reaction and determine activity and selectivity: the initiation/desorption, initiation/β-scission, and hydride ion transfer/β-scission cycles. The rates of these cycles decrease with increasing steaming severity, which reduces catalyst acid strength. The overall site time yield for 2-methylhexane cracking decreases as severity of steaming increases. Because the cycles do not produce excess paraffins, the paraffin to olefin ratio is always lower than 1. β-Scission reactions follow initiation and hydride ion transfer reactions and are important reactions of 2-methylhexane cracking. Olefin adsorption–desorption reactions determine surface coverage of carbenium ions, and although these reactions are in quasi-equilibrium, they play a crucial role in influencing the rates of other surface processes.

Catalytic and Potentiometric Characterization of E201D and E201Q Mutants of Trypanosoma congolense Trypanothione Reductase

Trypanothione reductase is a member of the structurally and functionally well-characterized family of flavoprotein reductases, which catalyze the reduced pyridine nucleotide dependent reduction of their disulfide, peroxide, or metal ion substrates. Trypanothione reductase is found in a wide variety of Trypanosoma species, where the enzyme serves physiologically to protect the organism from oxidative stress and assists in maintaining low intracellular levels of hydrogen peroxide. The redox potential of the flavin and the hydride ion transfer reaction of the pro-S hydrogen of NADPH to N5 of FAD have been proposed to be influenced by the presence of a conserved Lys-Glu (K60-E201) ion pair at the bottom of the nicotinamide binding pocket. We have evaluated this hypothesis by making modest substitutions for both the Lys and Glu residues using site-directed mutagenesis. Replacement of the K60 residue with an arginine led to a poorly expressed, and completely inactive, enzyme. Replacement of the Glu201 residue with either a glutamine (E201Q) or an aspartate (E201D) residue led to expressed enzymes which could be readily purified in > 20 mg amounts using protocols developed for the WT enzyme, and which had significant residual trypanothione-reducing activity. These enzymes have now been characterized to determine their redox potentials, catalytic activities, and nucleotide specificities. Relative to the WT enzyme, both E201D and E201Q exhibit ca. 5% of WT trypanothione-reducing activity using NADPH as reductant, but significantly enhanced quinone reductase activity. The oxidase activity of both mutants is enhanced by over 50-fold compared to that of the WT. The redox potential of the WT enzyme has been determined to be -273 mV, while both the E201D and E201Q exhibit more positive redox potentials (-259 and -251 mV, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Dynamics of the Hydride Ion Transfer Reaction between CD3+ and CH4: A Crossed Beam Scattering Study

Dynamics of the Hydride Ion Transfer Reaction between CD3+ and CH4: A Crossed Beam Scattering Study

Isobutane Cracking over Y-Zeolites: II. Catalytic Cycles and Reaction Selectivity

We describe the activity and selectivity of isobutane cracking on Y-zeolite-based catalysts in terms of catalytic cycles composed of initiation, β-scission, oligomerization, olefin desorption, isomerization, and hydride ion transfer reactions involving carbenium ions. Olefin desorption and isomerization reactions are at quasi-equilibrium, with the former reactions determining the surface carbenium ion coverages. Microcalorimetric measurements of ammonia adsorption show that catalyst steaming leads to a decrease in the number and strength of acid sites. Decreasing the strength of Brønsted acid sites results in decreasing surface carbenium ion coverages and decreasing rates of all reactions. The hydride ion transfer cycles are affected most by catalyst steaming, leading to lower paraffin selectivities. Lower temperatures and higher conversions increase carbenium ion coverages and favor hydride ion transfer cycles, leading to higher paraffin selectivities.

Hydride ion transfer reactions in the gas phase. Pressure dependence of reaction efficiency as a criterion for the recognition of anchimeric assistance

The efficiency (kobs/kcoll) of the gas phase hydride ion transfer from 2,2-dimethylbutane to tert-butyl cation displays a pronounced positive pressure dependence, which suggests significant anchimeric assistance of the methyl groups of 2,2-dimethylbutane adjacent to the departing CH2 hydride in the transition state.

Catalytic Cycles and Selectivity of Hydrocarbon Cracking on Y-Zeolite-Based Catalysts

Environmental concerns have created the need for selective catalysts that increase the yield of desirable products (e.g., isobutylene from hydrocarbon cracking units) or reduce the production of polluting byproducts. The development of selective catalysts may be facilitated by understanding the chemical factors controlling the rates of the various catalytic cycles available to the reactants and products. The authors have developed a kinetic model based on carbenium and carbonium ion surface chemistry for isobutane cracking and extended it to 2-methylhexane cracking over USY-based catalysts. Catalytic cycles for isobutane cracking that include initiation reactions lead to olefin production, while cycles that include hydride ion transfer reactions lead to paraffin production. The overall chemistry of the major catalytic cycles is the same for isobutane and 2-methylhexane cracking, although additional reaction pathways are available for the larger 2-methylhexane molecule. Paraffins and olefins with three or more carbon atoms can be produced from 2-methylhexane by cycles that include both initiation and hydride ion transfer reactions and the paraffin to olefin ratio cannot be greater than 1. By allowing one to build catalytic cycles, such models help identify similarities and differences in reactivity patterns for various reactants.

Thermal ion–molecule reactions in oxygen-containing molecules. Proton and hydride ion transfer reactions in acetaldehyde

The proton and hydride ion transfer reactions in acetaldehyde have been studied on a modified time-of-flight mass spectrometer. The appearance potentials and the ionization efficiency curves of fragment and product ions were measured by the r.p.d. technique and the precursors of the product ions were determined from an analysis of the shapes of these curves. Rate constants for the formation reactions of CH3CHOH+ and CH3CO+ were obtained. The positions from which proton and/or hydrogen atom transfer occur were clarified using [2H3]2,2,2-acetaldehyde. The rate constant of proton and/or hydrogen atom transfer from the formyl group is larger than that from the methyl group by a factor of two. It was also confirmed that CH+3 abstracts only the hydrogen of the formyl group in the hydride ion transfer reaction. The hydride ion transfer involving CH+3 from methane was studied in acetaldehyde + methane mixtures and its rate constant is larger than that in pure acetaldehyde.

Temperature dependences of some fast ion-polar molecule proton transfer and of slow hydride(1-) ion transfer reactions

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTTemperature dependences of some fast ion-polar molecule proton transfer and of slow hydride(1-) ion transfer reactionsM. Meot-Ner and F. H. FieldCite this: J. Am. Chem. Soc. 1975, 97, 8, 2014–2017Publication Date (Print):April 1, 1975Publication History Published online1 May 2002Published inissue 1 April 1975https://doi.org/10.1021/ja00841a003RIGHTS & PERMISSIONSArticle Views70Altmetric-Citations26LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (459 KB) Get e-Alerts Get e-Alerts

Radiation-initiated Thermal Cracking of <i>n</i>-Octane Vapor

The radiation-initiated thermal cracking (RTC) of n-octane vapor was studied at temperatures from 184 to 551°C and at atmospheric pressure. Vapor-phase ionic chain reactions, which were completely suppressed by the addition of ammonia, were found to proceed simultaneously with radical chain reactions. The main ionic chain products were C3∼C5 paraffins and olefins containing quantities of branched products and β-olefins which were not formed by the thermal cracking of n-octane. For example, the G-values of isobutane and isopentane reached 82 and 78, respectively, at 524°C. The proportion of the ionic chain products to the overall products was about 10mol%. Isomerization of C8H17+ ion, its thermal decomposition, and subsequent hydride ion transfer reaction from n-octane molecule to the fragment ion are proposed for the ionic chain mechanism. Carrier ions are carbonium ions of C3∼C5.Several similarities are pointed out between the ionic products from the RTC and those from catalytic reactions over acidic sites.

Pulse Radiolysis of Neopentane in the Gas Phase.

The pulse radiolysis of gaseous neopentane has been investigated in the absence and presence of electron scavengers (SF6, CD3I, CCl4). Deuterium labeling experiments show that the stable product molecules can be accounted for by (a) radical combination reactions involving mainly CH3 and H; (b) hydride ion transfer reactions involving C2H3 +, C2H5 +, and C3H5 +; (c) neutralization reactions of C4H9 + and C5H11 +; and (d) unimolecular dissociation of the parent ion (C5H12 +) and of electronically excited neopentane. Neutralization of the t-C4H9 + ion, which is the major positive ion in the system occurs as follows: (a) t-C4H9 + + e → i-C4H8 + H and (b) t-C4H9 + + e → 2CH3 + C3H6. It is shown that C5H11 + produced in hydride ion transfer reaction C n H m + + neo-C5H12 → C n H m+1 + C5H11 + (where C n H m + = C2H3 +, C2H5 +, and C3H5 +) rearranges to the CH3C+(CH3)CH2CH3 structure prior to neutralization. A detailed accounting of all products produced in the unimolecular and bimolecular reactions led to the conclusion that the ratio of neutral electronically excited molecules to parent ions (Nex/N+) is 0.28.

Transformations of geraniol in aqueous acid solutions

Geraniol decomposition in aqueous oxalic acid yields twenty-three identified products, most of which retain the oxidation level of geraniol and result from simple hydration and proton-transfer reactions. However, a large quantity of the reduced alcohol, citronellol, is formed along with cymenol, the oxidation product of α-terpineol, indicating that hydride ion transfer reactions play a major role in these terpene alcohol interconversions.

Anthocyanidins and related compounds—XVI: The dimerization of flavylium salts in aqueous solutions

7-Hydroxyflavylium salts dimerize in aqueous acetic acid solutions to form benzopyrylium salts substituted at position 4 with the corresponding dihydrochalcone nucleus. It is proposed that this dimerization involves initial condensation of the flavylium salt and its carbinol base to give a product which then undergoes a series of intermolecular hydride ion transfer reactions. It is also suggested that flavones are formed as by-products in these flavylium dimerization reactions.

Cationic polymerization of cyclic dienes. X. Cationic polymerization of 1‐vinylcyclohexene and 3‐methyl‐1,3‐pentadiene

Abstract1‐Vinylcyclohexene (VCH), which has one of the double bonds in the ring and the other outside the ring, was synthesized and polymerized by cationic catalysts. The reactivity of VCH was very large in the polymerizations catalyzed by boron trifluoride etherate (BF3OEt2) and stannic chloride–trichloroacetic acid complex. Similar to other cyclic dienes, the polymerization of VCH was a nonstationary reaction having a very fast initiation step. The polymerization proceeded by either a 1,2‐ or a 1,4‐propagation mode in which vinyl group was always involved. Particularly when BF3OEt2 was used as a catalyst, an intramolecular proton or an intramolecular hydride ion transfer reaction took place, resulting in the formation of methyl groups in the polymer. The degree of polymerization of polymer formed was about 10. This indicates the preponderance of monomer transfer reaction. To investigate the reason for the high reactivity of cyclic dienes, cationic copolymerizations of VCH and 3‐methyl‐cis/trans‐1,3‐pentadiene (cis/trans‐MPD) was carried out. The relative reactivity of monomers decreased in the order VCH > trans‐MPD > cis‐MPD. On the other hand, the resonance stabilization of monomers decreased in the order VCH > trans‐MPD > cis‐MPD. Therefore, it could be considered that the monomer reactivity is mainly determined by the stability of carbonium ion intermediate. The relative stability of carbonium ion must be VCH > trans‐MPD > cis‐MPD. Thus the influence of the conformation of ion on its stability was clearly demonstrated.

Reactions of Ions in the Radiolysis of Liquid Propane

Abstract The reactions of ions, especially fragmentation of excited ions and the subsequent reactions of fragment ions in the radiolysis of liquid propane have been investigated by the use of charge scavengers such as sulfur hexafluoride (SF6) and ammonia (NH3). It has been confirmed that the fragment ions are produced by the dissociation of the excited parent ion prior to the parent ion-electron recombination. The yields of C2H5+ and C3H7+ have been measured by the use of the reaction, RH++ NH3→R+ NH4, with the results G≥0.28 and ∼1.1 respectively. These ions neutralize with electrons to form ethylene or propylene. The hydride ion transfer reaction between C2H5+ and propane may be competing with the neutralization of C2H5+ by electron in the absence of an additive. The yields of fragment ions are compared in the radiolysis of several saturated hydrocarbons.