Formation Of Alkoxides Research Articles

Neptunium Alkoxide Chemistry: Expanding Alkoxides to the Transuranium Elements.

Two oxo-containing neptunium(IV) tert-butoxides, [Np3O(OtBu)10] (1) and [K4Np2O(OtBu)10] (2), were synthesized using the ligand substitution between neptunium(IV) silylamides and HOtBu, whereas the salt metathesis between [NpCl4(DME)2] (DME = dimethoxyethane) and various amounts of LiOtBu resulted in the formation of oxo-free alkoxides [Np(OtBu)4(py)2] (3; py = pyridine) and [Li(THF)]2[Np(OtBu)6] (4; THF = tetrahydrofuran). These complexes are the first structurally characterized neptunium(IV) alkoxides using single-crystal X-ray diffraction and solid-state absorption spectroscopy, which provide data for the development of anhydrous metal-organic neptunium chemistry.

Theoretical and Experimental Evaluation of the Reduction Potential of Straight-Chain Alcohols for the Designed Synthesis of Bimetallic Nanostructures.

Recently, the development of bimetallic nanoparticles with functional properties has been attempted extensively but with limited control over their morphological and structural properties. The reason was the inability to control the kinetics of the reduction reaction in most liquid-phase syntheses. However, the alcohol reduction technique has demonstrated the possibility of controlling the reduction reaction and facilitating the incorporation of other phenomena such as diffusion, etching, and galvanic replacement during nanostructure synthesis. In this study, the reduction potential of straight-chain alcohols has been investigated using molecular orbital calculations and experimentally verified by reducing transition metals. The alcohols with a longer chain exhibited higher reduction potential, and 1-octanol was found to be the strongest among alcohols considered. Furthermore, the experimental evaluation carried out via the synthesis of metallic Cu, Ni, and Co particles was consistent with the theoretical predictions. The reaction mechanism of metallic particle formation was also studied in detail in the Ni-1-octanol system, and the metal ions were confirmed to be reduced via the formation of nickel alkoxide. The results of this investigation were successfully implemented to synthesize Cu-Ni bimetallic nanostructures (core-shell, wire, and tube) via the incorporation of diffusion and etching besides the reduction reaction. These results suggest that the designed synthesis of a wide range of bimetallic nanostructures with more refined control has become possible.

Influence of Confinement on Barriers for Alkoxide Formation in Acidic Zeolites

AbstractThe influence of the confinement imposed by eight different zeotypes on the formation of the alkoxides of 13 primary alcohols is studied using dispersion corrected density functional theory calculations with the PBE‐D3 functional. Adsorption energies of the alcohols are computed along with barriers for formation of the alkoxides, which is the first step of the stepwise dehydration mechanism. We find that variations in the adsorption and transition state energies are largely governed by van der Waals interactions between substrates and the zeolite framework. Trends between different reactants, on the other hand, are largely due to the size of the molecules, which can be described quantitatively by the number of atoms constituting them. We find that the stabilization of adsorbates is largest for frameworks that are neither too small, leading to repulsive interaction, nor too spacious leading only to weak interaction.

Selective oxidation of glycerol to dihydroxyacetone over N-doped porous carbon stabilized CuxO supported Au catalysts

In this work, N-doped porous carbon stabilized CuxO (Cu-NPCs) were synthesized by a one-pot method using copper nitrate as copper precursor with the aid of Pluronic F127 under acidic condition. The characterization results confirmed that CuxO species (CuO and Cu2O) existed in NPC in a highly dispersed state due to the strong interaction between CuxO and the doped N atoms. The obtained Cu-NPCs were used as supports to prepare Au catalysts for glycerol (GLY) oxidation to dihydroxyacetone (DHA) under base-free conditions. During the reaction, GLY preferentially adsorbed onto Au nanoparticles via the secondary OH groups due to the porous characteristics of the supports, the enhanced surface basicity from the N functionalities accelerates the alkoxide formation by abstracting proton from GLY, and the surface Cu+ sites instead of Au nanoparticles activate O2 molecules to produce active oxygen species, as a result, Au/Cu-NPC-15 %-H, which is the best catalyst in Au/Cu-NPCs, exhibited much higher catalytic activity and selectivity than those of Au/CuO. Moreover, due to the stabilization of CuxO species by NPC, relatively stable surface Cu+ content, and the strong interaction between Au nanoparticles and the supports, Au/Cu-NPC-15 %-H also possessed much better catalytic stability than that of Au/CuO during four consecutive catalytic runs.

β-Mannosylation via O-Alkylation of Anomeric Cesium Alkoxides: Mechanistic Studies and Synthesis of the Hexasaccharide Core of Complex Fucosylated N-Linked Glycans.

A number of structurally diverse D-mannose-derived lactols, including various deoxy-D-mannoses and conformationally restricted bicyclic D-mannoses, have been synthesized and investigated in mechanistic studies of β-mannosylation via Cs2CO3-mediated anomeric O-alkylation. It was found that deoxy mannoses or conformationally restricted bicyclic D-mannoses are not as reactive as their corresponding parent mannose. This type of β-mannosylation proceeds efficiently when the C2-OH is left free, and protection of that leads to inferior results. NMR studies of D-mannose-derived anomeric cesium alkoxides indicated the predominance of the equatorial β-anomer after deprotonation. Reaction progress kinetic analysis suggested that monomeric cesium alkoxides be the key reactive species for alkylation with electrophiles. DFT calculations supported that oxygen atoms at C2, C3, and C6 of mannose promote the deprotonation of the anomeric hydroxyl group by Cs2CO3 and chelating interactions between Cs and these oxygen atoms favour the formation of equatorial anomeric alkoxides, leading to the highly β-selective anomeric O-alkylation. Based on experimental data and computational results, a revised mechanism for this β-mannosylation is proposed. The utilization of this β-mannosylation was demonstrated by an efficient synthesis of the hexasaccharide core of complex fucosylated N-linked glycans.

Microporous Metal-Organic Framework (MOF)-Based Composite Polymer Electrolyte (CPE) Mitigating Lithium Dendrite Formation in All-Solid-State-Lithium Batteries.

Poly(ethylene oxide) (PEO)-based composite polymer electrolytes (CPEs) containing the amine-functionalized, zirconium-based metal–organic framework @silica (UiO-66-NH2@SiO2) and lithium, LiN(CF3SO2)2 salt (LiTFSI) are prepared using a simple hot press method. The electrochemical properties such as compatibility of the electrolyte with the Li metal anode, Li transference number, and ionic conductivity are investigated for the different systems containing different relative concentrations of the additives. The incorporation of UiO-66-NH2@SiO2 in the PEO-LiTFSI matrix not only enhanced ionic conductivity by one order of magnitude but also offered better compatibility and suppressed the formation of lithium dendrites appreciably. X-ray photoelectron spectroscopy studies on post-cycled materials revealed the formation of lithium alkoxide (RO–Li) on the cathode and Li2O on the anode. The coin cell (2032-type) consisting of LiFePO4/CPE/Li with UiO-66-NH2@SiO2 as filler provided a discharge capacity of 151 mA h g–1 at 0.1 C-rate at 60 °C, measurably higher than control experiments utilizing SiO2 and UiO-66-NH2. The notable enhancement of electrochemical properties when incorporating the UiO-66-NH2@SiO2 at the CPE was attributed to formation of more uniform ion conduction pockets and channels within the PEO matrix, facilitated by the presence of the microporous UiO-66-NH2@SiO2. The enhanced distribution of microporous channels, where Li ions are assumed to percolate through within the matrix, is assumed to desirably reduce formation of Li dendrites by increasing diffusion channels and therefore reducing crystallization and growth of dendrites at the electrode surface.

The reaction of potassium xanthates with five-membered cyclic carbonates: selectivity of the underlying cascade reactions and mechanistic insights.

In this paper we describe the reaction between various potassium xanthates (potassium O-methyl xanthate, potassium O-isobutyl xanthate, xanthate functionalized MPEGs, etc.) and common five-membered cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC). The reaction was carried out under catalyst-free conditions. Intensive evolution of both CO2 and COS and the simultaneous formation of a rich precipitate were found to be the characteristic features of the studied reaction. It was determined that the precipitate consists of various alkoxides, including potassium ethane-1,2-bis(olate) (EC-based reaction) and potassium propane-1,2-bis(olate) (PC-based reaction) and alkoxide-terminated sulfides. It was also demonstrated that the resulting liquid phase (the mother liquor) contains polyalkylene sulfides whose number average molecular weight (Mn) was found to be in the range 400–550 Da and 300–400 Da for EC- and PC-based oligomers, respectively. Further studies revealed that the distribution between major products varies considerably with variation in the parameters of the reaction. Thus, by applying reduced pressure conditions and a temperature equal to 90 °C, up to 95% selectivity towards the formation of alkoxide-terminated sulfide (e.g., potassium 1,1′-thiobis(propan-2-olate)) was achieved. On the other hand, selectivity towards alkoxide formation equal to 98% was achieved for the reactions carried out in the presence of water. As a general trend, it was also established that a shift in balance between products towards the formation of sulfur-containing products (sulfides) occurs with an appropriate increase in the temperature of the reaction. Based on the obtained experimental data supplemented with quantum-chemical calculations (NBO analysis and scanning of the potential energy surface), the mechanisms of the cascade reactions underlying the formation of key intermediates and final products were also proposed.

Reductive conversion of 5-hydroxymethylfurfural to 1,2,6-hexanetriol in water solvent using supported Pt catalysts

Abstract One-pot conversion of biomass derived 5-hydroxymethylfurfural (HMF) to 1,2,6-hexanetriol (1,2,6-HT) in water solvent was performed using Pt catalysts supported on various acid-base metal oxides. Pt catalysts supported on hydrotalcite, MgO, and CeO2 showed better yield of 1,2,6-HT and 2,5-bis(hydroxymethyl)-tetrahydrofuran (BHF), while ring-rearranged cyclopentanol derivatives were predominant products on the other Pt catalysts. The product distribution with time course on Pt/hydrotalcite revealed that HMF is at first hydrogenated to BHF, then the following parallel reactions proceed; ring-rearrangement to cyclopentanol derivatives, ring-hydrogenation to BHF, and hydrogenolysis to 1,2,6-HT. When pure hydrotalcite, MgO and CeO2 were physically mixed with Pt/SiO2, the selectivity to 1,2,6-HT was almost zero or less than 10 %. It was suggested that the formation of 1,2,6-HT proceeds at metal-support interface. The effect of metal-support interface was examined by means of IR spectra of adsorbed methanol. It was indicated that both basic property of supports and surface monodentate alkoxide formation are essential for the production of 1,2,6-HT. The maximum yield of 1,2,6-HT (42 %) was obtained using Co-promoted Pt/CeO2 catalysts pre-reduced at 200 °C.

Zinc Oxide-Catalyzed Dehydrogenation of Primary Alcohols into Carboxylic Acids.

Zinc oxide has been developed as a catalyst for the dehydrogenation of primary alcohols into carboxylic acids and hydrogen gas. The reaction is performed in mesitylene solution in the presence of potassium hydroxide, followed by workup with hydrochloric acid. The transformation can be applied to both benzylic and aliphatic primary alcohols and the catalytically active species was shown to be a homogeneous compound by a hot filtration test. Dialkylzinc and strongly basic zinc salts also catalyze the dehydrogenation with similar results. The mechanism is believed to involve the formation of a zinc alkoxide which degrades into the aldehyde and a zinc hydride. The latter reacts with the alcohol to form hydrogen gas and regenerate the zinc alkoxide. The degradation of a zinc alkoxide into the aldehyde upon heating was confirmed experimentally. The aldehyde can then undergo a Cannizzaro reaction or a Tishchenko reaction, which in the presence of hydroxide leads to the carboxylic acid.

Influence of Metal Fragment Mobility and Solution Dynamics on Cationic Rearrangements in Multimetallic Alkoxide Frameworks

AbstractMultimetallic alkoxides show manifold dynamics in solution comprising ligand switching among different sites (terminal, doubly or triply bridging), coordination lability of alkoxometallate units ({M(OR)x−}) and rearrangement of metal centers. Solution behavior and structural investigations of heterobimetallic iodide isopropoxides [IM{Ce2(OPri)9}]2 (M=Cd (1), Ba (2)) and corresponding potassium alkoxometallates of Sr and Al revealed equilibrium of several interconverting species that rearrange to form stable monomeric or dimeric trimetallic frameworks. Quantitative formation of dimeric heterotrimetallic alkoxides [{Cd(OPri)3}Sr{Ce2(OPri)9}]2 (3), [{Cd(OPri)3}Ba{Ce2(OPri)9}]2 (4) and monomeric [{Al(OPri)4}(HOPri)Ba{Ce2(OPri)9}] (5) confirmed the tendency of metallo‐fragments to rearrange themselves for achieving the maximum possible coordination number for constituent metals. Multinuclear NMR spectroscopy, elemental analysis, mass spectrometry and X‐ray diffraction analyses verified the potential of electronically and sterically unsaturated alkoxometallate units in initiating the redistribution of metal centers.

DFT-based calculations of the adsorptions of acetic acid, triacetin, methanol and the alkoxide formation on the surfaces of zinc acetate

DFT calculations with periodic boundary conditions were performed in order to study the esterification/transesterification mechanisms involved in the biodiesel production. The simulation of the adsorptions of acetic acid, methanol and triacetin was carried out on zinc acetate as the catalyst. The adsorption energies of these processes could be obtained and PDOS of the zinc sites and the carboxylate group carbons of the acetic acid and the triacetin were explored for the evaluation of their acidity. The adsorption energies and the reaction barrier of the alkoxide formation showed that the triglyceride adsorption is very likely to occur first in transesterification processes. The barriers also denote that an alkoxide formation from the methanol is not favored and, consequently, a nucleophilic attack from the methanol molecule occurs.

A review on performance and emission characteristics of biodiesel produced from animal fat

DFT calculations with periodic boundary conditions were performed in order to study the esterification/transesterification mechanisms involved in the biodiesel production. The simulation of the adsorptions of acetic acid, methanol and triacetin was carried out on zinc acetate as the catalyst. The adsorption energies of these processes could be obtained and PDOS of the zinc sites and the carboxylate group carbons of the acetic acid and the triacetin were explored for the evaluation of their acidity. The adsorption energies and the reaction barrier of the alkoxide formation showed that the triglyceride adsorption is very likely to occur first in transesterification processes. The barriers also denote that an alkoxide formation from the methanol is not favored and, consequently, a nucleophilic attack from the methanol molecule occurs.

Construction of bicyclic systems containing an oxygen bridge by isomerization of cyclic epoxy alcohols

A novel method for constructing a 7-oxabicyclo[2.2.1]heptane skeleton was developed. The substrates, namely cis-3,4-epoxy-1-cyclohexanol derivatives, were prepared from the corresponding 3-cyclohexen-1-ol derivatives via a stereoselective epoxidation reaction using a vanadium catalyst. Upon heating with lithium iodide in propionitrile, the cis-epoxy alcohol was transformed into the 7-oxabicyclo[2.2.1]heptane derivative in high yield. The reaction proceeds through formation of a lithium alkoxide bearing an iodohydrin moiety, followed by an intramolecular SN2 reaction.

Retinol initiated poly(lactide)s: stability upon polymerization and nanoparticle preparation

The synthesis of retinol initiated polylactide (PLA) by ring opening polymerization (ROP) of l-lactide via in situ calcium alkoxide formation with all-trans-retinol and Ca[N(SiMe3)2]2(THF)2 is described.

Mechanism of the carbonate-based-electrolyte degradation and its effects on the electrochemical performance of Li 1+x (Ni a Co b Mn 1-a-b ) 1-x O 2 cells

In lithium-ion batteries with carbonate electrolytes, the formation of lithium alkoxides at the anode impairs the electrochemical performance and the cycle life of the cells through destabilisation of the cathode–electrolyte interface. To fully understand the effect of electrolyte composition on the stability of the cathode–electrolyte interface, and therefore to minimise alkoxide formation and improve cycling stability, we study different carbonate solvents and mixtures thereof. Electrolytes that promote the formation of ethoxide are found to be more detrimental to the cell performance than those forming methoxide. The presence of cyclic carbonates in the electrolyte-solvent mixture alleviates the detrimental effects of ethoxide-forming solvents on the electrochemical performance of Li1.05(Ni0.33Co0.33Mn0.33)0.95O2 by reducing the solubility of the ethoxide.

Proton proximity – New key parameter controlling adsorption, desorption and activity in propene oligomerization over H-ZSM-5 zeolites

The proximity of protons (∼5Å) derived from the distribution of Al atoms in the H-ZSM-5 framework has been shown to substantially affect the rate of propene oligomerization. Two sets of H-ZSM-5 zeolites (Si/Al 13–30) greatly differing in the occurrence of Al pairs (AlSiSiAl sequences in 6MRs) or distant Al atoms in the framework (both located prevailingly at the channel intersections) were synthesized to analyze the effect of the proton proximity. Propene adsorption and formation of oligomeric alkoxides is faster over distant isolated protons, while the close (5Å) positive charges of proximate protons result in faster olefin(s) release from H-bonded propene and oligomeric alkoxides. As the steady-state TOF of propene oligomerization to C4–C9 olefins at 473–533K over close protons exceeds 2–10 fold (with increasing Si/Al) those over isolated protons, the release of olefins from alkoxides is suggested to be an important reaction step. The distribution of framework Al atoms determining the mutual distances of protons represents a new parameter for evaluating rates of acid-catalyzed reactions and individual steps over H-zeolites.

ChemInform Abstract: On the Configurational Stability and Reactivity of Tertiary Silyloxy Carbanions Derived from Stereoselective Brook Rearrangement.

Here we report a stereospecific Brook rearrangement/trapping sequence, initiated by the formation of a zinc alkoxide from an enantioenriched (hydroxyallyl)silane. The chiral carbanion resulting from the Brook rearrangement is trapped intermolecularly by carbonyl electrophiles with complete transfer of chirality. A concerted mechanism is proposed to rationalize the stereospecificity observed in the reaction sequence.

Reactivity of 3-carbon-atom chain alcohols on gold electrode: A comparison to understand the glycerol electro-oxidation

In this work, the electro-oxidation of glycerol was compared with those of similar 3-carbon-atom chain alcohols, namely 1-propanol, 2-propanol, propane-1,2-diol and propane-1,3-diol, in order to further understand the reactivity of glycerol on gold in alkaline environment. The corresponding products formation was monitored by in situ FTIR spectroscopy. The reactivity of the investigated alcohols on gold in alkaline medium decreased in the following order: glycerol>propane-1,2-diol≫propane-1,3-diol>2-propanol≈1-propanol. For glycerol and propane-1,2-diol, the products distribution provided by in situ FTIR spectroscopy showed indications of high CC bond breaking rates, as evidenced by the presence of products with 1 and 2 carbon-atom chain. On the other hand, the electrochemical oxidation of propane-1,3-diol, 2-propanol and 1-propanol led only to products with 3-carbon-atom chain. Based on these evidences, it was stated that the presence of vicinal OH groups in the alcohol molecule may be a key feature for the CC bond breaking in alkaline medium, leading to the generation of further oxidized products that, in turns, yield more electrons per alcohol molecule and consequently higher current densities. Additionally, electrochemical measurements were also performed in acidic and neutral media for comparison. Under these conditions, the alcohols exhibited much lower current densities compared to those in alkaline medium. This was explained by the lack of alkoxide formation (active species in alkaline medium) and the blockage of the surface by ClO4− anions.

On the Configurational Stability and Reactivity of Tertiary Silyloxy Carbanions Derived from Stereoselective Brook Rearrangement

Here we report a stereospecific Brook rearrangement/trapping sequence, initiated by the formation of a zinc alkoxide from an enantioenriched (hydroxyallyl)silane. The chiral carbanion resulting from the Brook rearrangement is trapped intermolecularly by carbonyl electrophiles with complete transfer of chirality. A concerted mechanism is proposed to rationalize the stereospecificity observed in the reaction sequence.

Dehydration of 1-Octadecanol over H-BEA: A Combined Experimental and Computational Study

Liquid-phase dehydration of 1-octadecanol, which is intermediately formed during the hydrodeoxygenation of microalgae oil on zeolite H-BEA, has been studied, combining experiment and theory. Both the OH group and the alkyl chain of 1-octadecanol interact with zeolite Bronsted acid sites, inducing inefficient utilization in the presence of high acid-site concentrations. The parallel intramolecular and intermolecular dehydration pathways, leading to octadecene and dioctadecyl ether, have different activation energies and pass through different reaction intermediates. The formation of surface alkoxides is the rate-limiting step in the intramolecular dehydration, whereas the intermolecular dehydration proceeds via a bulky dimer intermediate, occurring preferentially at the pore mouth or outer surface of zeolite crystallites. Despite the main contribution of Bronsted acid sites toward both dehydration pathways, Lewis acid sites are also active to form dioctadecyl ether.