Formation Of Alkyl Research Articles

Ether Degradation Thermodynamics in Li-O2 Redox Environments: A Computational Study

The reaction thermodynamics of the 1,2-dimethoxi-ethane (DME) in a highly oxidizing environment has been studied by first principles methods to predict the spontaneous degradation processes of this model solvent molecule commonly used in electrolytes for Li-O2 rechargeable batteries. The potential energy surfaces of the reactivity of DME towards the O2 - superoxide radical anion in oxygen-poor or oxygen rich environments have been calculated by quantum chemistry techniques. A large set of density functional theory (DFT) methods has been used and compared to post-Hartree-Fock predictions to evaluate their predictive relative performances and select the best for the calculation of the full reactivity. Solvation effects have been considered by employing self-consistent reaction field in a continuum solvation model. The onset reaction of the degradation of the DME model molecule is the H-extraction by the O2 - superoxide anion to form an ether radical with an unpaired electron on a carbon atom. The subsequent reactivity of this radical molecule differs depending on the availability of molecular oxygen molecules. In oxygen rich environment this radical species follow multistep paths to give formaldehyde and alkyl carbonates whereas in oxygen poor environment the final products are alkyl oxalates or alkyl formates.

Organic photoredox catalysis for the oxidation of silicates: applications in radical synthesis and dual catalysis.

Metal free photooxidation of alkyl bis(catecholato)silicates with the organic dye 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyano-benzene (4CzIPN) allows the smooth formation of alkyl radicals. The latter can be efficiently engaged either with radical acceptors to provide homolytic addition products or in photoredox/nickel dual catalysis reactions to obtain cross-coupling products.

Synthesis of methyl 7-aryl-6-cinnamoyl-4,7-dihydrotetrazolo-[1,5-a]pyrimidine-5-carboxylates

Reactions of alkyl aroylpyruvates with a mixture of aromatic aldehyde and 5-aminotetrazole led to the formation of alkyl 7-aryl-6-aroyl-4,7-dihydrotetrazolo [1,5-а] pyrimidine-5-carboxylates.

Experimental and theoretical studies on the tautomerism and reactivity of isoxazolo[3,4-b]quinolin-3(1H)-ones

A variety of substituted isoxazolo[3,4-b]quinolin-3(1H)-ones incorporating an ambident amidine functionality was synthesized by a two-step procedure starting from the corresponding 2-chloroquinoline-3-carboxylic acids. Alkylation and acylation reactions carried out in DMF solution in the presence of Et3N occurred preferentially on the available σ lone pair of the pyridine-type N1 nitrogen atom of the most stable 9H-oxo tautomer. The use of sodium hydroxide in place of Et3N led to isoxazolone ring cleavage with the formation of alkyl 2-(alkoxy(alkyl)amino)quinoline-3-carboxylates. The electronic structure of the three possible N1-oxo, N9-oxo and 3-hydroxy tautomeric forms, and the NaOH-induced cleavage of the isoxazolone ring were studied theoretically with use of the B3LYP/6-31+G* density functional method and SM8 (DMF) solvation model. The synthesized N1-alkyl and N1-acyl derivatives of isoxazolo[3,4-b]quinolin-3(1H)-one were evaluated for their in vitro antifungal activity against 19 pathogenic yeast-like fungal strains.

Outer-Sphere Electrophilic Fluorination of Organometallic Complexes.

Organofluorine chemistry plays a key role in materials science, pharmaceuticals, agrochemicals, and medical imaging. However, the formation of new carbon-fluorine bonds with controlled regiochemistry and functional group tolerance is synthetically challenging. The use of metal complexes to promote fluorination reactions is of great current interest, but even state-of-the-art approaches are limited in their substrate scope, often require activated substrates, or do not allow access to desirable functionality, such as alkenyl C(sp(2))-F or chiral C(sp(3))-F centers. Here, we report the formation of new alkenyl and alkyl C-F bonds in the coordination sphere of ruthenium via an unprecedented outer-sphere electrophilic fluorination mechanism. The organometallic species involved are derived from nonactivated substrates (pyridine and terminal alkynes), and C-F bond formation occurs with full regio- and diastereoselectivity. The fluorinated ligands that are formed are retained at the metal, which allows subsequent metal-mediated reactivity.

Flow reactor studies of non-equilibrium plasma-assisted oxidation of n-alkanes.

The oxidation of n-alkanes (C1-C7) has been studied with and without the effects of a nanosecond, non-equilibrium plasma discharge at 1 atm pressure from 420 to 1250 K. Experiments have been performed under nearly isothermal conditions in a flow reactor, where reactive mixtures are diluted in Ar to minimize temperature changes from chemical reactions. Sample extraction performed at the exit of the reactor captures product and intermediate species and stores them in a multi-position valve for subsequent identification and quantification using gas chromatography. By fixing the flow rate in the reactor and varying the temperature, reactivity maps for the oxidation of fuels are achieved. Considering all the fuels studied, fuel consumption under the effects of the plasma is shown to have been enhanced significantly, particularly for the low-temperature regime (T<800 K). In fact, multiple transitions in the rates of fuel consumption are observed depending on fuel with the emergence of a negative-temperature-coefficient regime. For all fuels, the temperature for the transition into the high-temperature chemistry is lowered as a consequence of the plasma being able to increase the rate of fuel consumption. Using a phenomenological interpretation of the intermediate species formed, it can be shown that the active particles produced from the plasma enhance alkyl radical formation at all temperatures and enable low-temperature chain branching for fuels C3 and greater. The significance of this result demonstrates that the plasma provides an opportunity for low-temperature chain branching to occur at reduced pressures, which is typically observed at elevated pressures in thermal induced systems.

Practical Ligand‐Free Copper‐Catalysed Short‐Chain Alkoxylation of Unactivated Aryl Bromides

AbstractAn efficient and practical short‐chain alkoxylation of unactivated aryl bromides has been developed with special attention focussed on the applicability of the reaction. Sodium alkoxide is used as the nucleophile, and the corresponding alcohol as the solvent. The reaction requires neither precious metals nor organic ligands. It uses a catalytic system consisting of copper(I) bromide as a catalyst, the corresponding alkyl formate as a noncontaminating cocatalyst, and lithium chloride as an additive. A wide range of substrates and test cases highlight the synthetic utility of the approach. Considering the commercial accessibility and affordability of the feedstocks, this protocol shows promise as a new alternative for the sustainable preparation of aryl alkyl ethers.

One-step formation of bifunctionnal aryl/alkyl grafted films on conducting surfaces by the reduction of diazonium salts in the presence of alkyl iodides.

The formation of partial perfluoroalkyl or alkyl radicals from partial perfluoroalkyl or alkyl iodides (ICH2CH2C6F13 and IC6H13) and their reaction with surfaces takes place at low driving force (∼-0.5 V/SCE) when the electrochemical reaction is performed in acetonitrile in the presence of diazonium salts (ArN2(+)), at a potential where the latter is reduced. By comparison to the direct grafting of ICH2CH2C6F13, this corresponds to a gain of ∼2.1 V in the case of 4-nitrobenzenediazonium. Such electrochemical reaction permits the modification of gold surfaces (and also carbon, iron, and copper) with mixed aryl-alkyl groups (Ar = 3-CH3-C6H4, 4-NO2-C6H4, and 4-Br-C6H4, R = C6H13 or (CH2)2-C6F13). These strongly bonded mixed layers are characterized by IRRAS, XPS, ToF-SIMS, ellipsometry, water contact angles, and cyclic voltammetry. The relative proportions of grafted aryl and alkyl groups can be varied along with the relative concentrations of diazonium and iodide components in the grafting solution. The formation of the films is assigned to the reaction of aryl and alkyl radicals on the surface and on the first grafted layer. The former is obtained from the electrochemical reduction of the diazonium salt; the latter results from the abstraction of an iodine atom by the aryl radical. The mechanism involved in the growth of the film provides an example of complex surface radical chemistry.

Alkylation of Nitrogen-Containing Heterocycles via In Situ Sulfonyl Transfer

Correction to: Alkylation of Nitrogen-Containing Heterocycles via In Situ Sulfonyl TransferSynlett 2015; 26(07): 953-959DOI: 10.1055/s-0034-1379961

Boron sulfonic acid (BSA) catalyzed selective synthesis of aryl-bis(2-hydroxynaphth-1-yl)methanes and 14-alkyl- and 14-aryl-14H-dibenzoxanthenes under solvent-free condition

Article history: Received January 21, 2015 Received in revised form March 29, 2015 Accepted 9 April 2015 Available online 9 April 2015 This study investigated the selective synthesis of aryl-bis(2-hydroxy-1-naphthyl)methane for the first time under microwave irradiation in solvent-free medium within 5 min using 10 mol % of B(HSO4)3 (BSA) as reusable solid acid catalyst. The same reaction could also be conducted at 90-100 °C in neat for the formation of alkyl or aryl 14H-dibenzoxanthenes in presence of BSA catalyst with excellent yields. © 2015 Growing Science Ltd. All rights reserved.

Borane-catalyzed room-temperature hydrosilylation of alkenes/alkynes on silicon nanocrystal surfaces.

Room-temperature borane-catalyzed functionalization of hydride-terminated silicon nanocrystals (H-SiNCs) with alkenes/alkynes is reported. This new methodology affords formation of alkyl and alkynyl surface monolayers of varied chain lengths (i.e., C5-C12). The present study also indicates alkynes react more readily with H-SiNC surfaces than equivalent alkenes. Unlike other toxic transition-metal catalysts, borane or related byproducts can be readily removed from the functionalized SiNCs. The new method affords stable luminescent alkyl/alkenyl-functionalized SiNCs.

Complex formation of sodium alkyl sulfates with chitosan in aqueous-ethanol solutions

The influence of the length of the hydrocarbon radical in sodium alkyl sulfates and of the solvent composition on the formation of polymer-colloid complexes with chitosan in aqueous-ethanol solution was studied. The critical association constants, binding cooperativity parameters, and dissociation constants of the complexes were determined. An increase in the length of the alkyl radical leads to enhancement of the association of sodium alkyl sulfates with chitosan at an ethanol concentration in solution of up to 30 vol %. In solutions with higher ethanol concentrations, the solvent composition becomes the decisive factor of the complex formation of chitosan with sodium alkyl sulfate.

Enthalpies of formation of alkyl radicals

The data on the enthalpies of formation (ΔfH°) for alkyl radicals (R·) were examined. Taking into account the values of enthalpies of C-X bond dissociation (X = H, Cl) in alkanes and their monochlorosubstituted derivatives, ΔfH° of fifteen R· were determined for the first time. The values of ΔfH°(R·) were analyzed on the basis of quantitative structure—property relationships in terms of the additive groups model with the new extended set of fragments introduced according to the quantum theory “Atoms in Molecule.” The parameters for prediction of ΔfH° of radicals for of the considered class were determined. The renewed and extended by more than 25% database on ΔfH° of alkyl radicals was proposed.

Efficient Hydrogenation of Alkyl Formate to Methanol over Nanocomposite Copper/Alumina Catalysts

The production of methanol, an important fuel and chemical feedstock, from carbon dioxide is an important process for CO2 utilization. We describe herein a mild and efficient method for the indirect hydrogenation of carbon dioxide to methanol via a CO2-derived formate ester intermediate by using a simple heterogeneous catalyst system comprising Cu highly dispersed in an alumina matrix under solvent-free conditions. This catalyst is also effective for the hydrogenation of other formate esters, such as ethyl formate, propyl formate, and butyl formate.

Mechanism and kinetics of the atmospheric degradation of perfluoropolymethylisopropyl ether by OH radical: a theoretical study

In the present work, the mechanism and kinetics of the reaction of perfluoropolymethylisopropyl ether (PFPMIE) with OH radical are studied. The reaction between PFPMIE and OH radical is initiated through breaking of C–C or C–O bond of PFPMIE. These reactions lead to the formation of COF2 molecules and alkyl radical. The pathways corresponding to the reaction between PFPMIE and OH radical have been modelled using density functional theory methods M06-2X and MPW1K with 6-31G(d,p) basis set. It is found that the C–C bond breaking reaction is most favourable than the C–O bond breaking reaction. The subsequent reactions of the alkyl radicals, formed from the C–C bond breaking reactions, are studied in detail. The rate constant for the initial oxidation reactions is calculated using canonical variational transition state theory with small curvature tunnelling corrections over the temperature range of 278–350 K. From the calculated reaction, potential energy surface and rate constant, the lifetime and global warming potential of PFPMIE are studied.

Chemical Control of Hydrodynamic Instabilities in Partially Miscible Two-Layer Systems.

Hydrodynamic instabilities at the interface between two partially miscible liquids impact numerous applications, including CO2 sequestration in saline aquifers. We introduce here a new laboratory-scale model system on which buoyancy- and Marangoni-driven convective instabilities of such partially miscible two-layer systems can easily be studied. This system consists of the stratification of a pure alkyl formate on top of a denser aqueous solution in the gravitational field. A rich spectrum of convective dynamics is obtained upon partial dissolution of the ester into the water followed by its hydrolysis. The properties of the convective patterns are controlled by the miscibility of the ester in water, the feedback of the dissolved species on its own miscibility, as well as the reactivity of given chemicals in the aqueous solution with the solubilized ester.

Formation of new alkyl functionalized poly(ethylene terephthalate) oligomers through exchange reactions with titanium alkoxides in melt conditions

A new and original method to recycle the PET into low molar masses di-alkyl functionalized oligomers is proposed. Ti(OnBu)4 and Ti(OnPr)4 used through alkoxide ligand exchange reactions, with a vertical twin-screw micro-extruder laboratory process, allow in a very short range of time around 10 min at high temperature to shorten the PET chains length. In homogeneous-like considered conditions fast decreases of molecular chains length and melting temperatures were observed. The structures of these oligomers were identified by 1H NMR, MALDI-ToF and SEC methods, and then correlated with physical properties determined by DSC and TGA analyses. Very useful tools are proposed to control the chemical reaction in order to scale up this process to reactive extrusion at relatively low temperatures.

Electro-catalytic scission of carbon–iodine bonds. Building of SAMs at gold surfaces through long chain primary radical adsorption

Primary alkyl iodides (RI) are reduced at smooth gold electrodes in polar organic solvents such as N,N-dimethylformamide (DMF) in the presence of tetraalkylammonium salts (TAAX). Beside a main two-electron step currently observed at potential>−2.0V vs. Ag/AgCl, a bell-shaped step appears with all organic iodides within a potential range between −0.6V and −1.2V. This peak does not depend on the organic substrate concentration, its current is proportional to the scan rate in voltammetry; it disappears at the second scan. These features arise from slow adsorption of the RI at gold, followed by an electro-catalytic reduction induced by the metal. It is expected that this (simple) process allows the formation of alkyl radicals readily adsorbed at the metal surface and thus produced layer strongly inhibits the main cathodic step at more negative potentials. With linear chains in C10, C12, C16 and C18, the coverage of gold leads to self-assembled monolayers (SAMs). The compactness of this coverage was found to be about 10−10molcm−2.

Nickel-Catalyzed Hydrosilylation of CO2 in the Presence of Et3B for the Synthesis of Formic Acid and Related Formates

The reaction of CO2 with Et3SiH catalyzed by the nickel complex [(dippe)Ni(μ-H)]2 (1) afforded the reduction products Et3SiOCH2OSiEt3 (12%), Et3SiOCH3 (3%), and CO, which were characterized by standard spectroscopic methods. Part of the generated CO was found as the complex [(dippe)Ni(CO)]2 (2), which was characterized by single-crystal X-ray diffraction. When the same reaction was carried out in the presence of a Lewis acid, such as Et3B, the hydrosilylation of CO2 efficiently proceeded to give the silyl formate (Et3SiOC(O)H) in high yields (85–89%), at 80 °C for 1 h. Further reactivity of the silyl formate to yield formic acid, formamides, and alkyl formates was also investigated.

Characterization and oxidative addition reactions of rhodium(I) carbonyl cupferrate diphenyl-2-pyridylphoshine complexes

The oxidative addition of CH3I to the [Rh(cupf)(CO)(DPP)] complex (DPP = diphenyl-2-pyridylphoshine and cupf = N-nitroso-N-phenylhydroxylaminen) was kinetically investigated using UV/vis and infrared spectroscopy. The kinetics followed in chloroform, acetonitrile and acetone as solvents, indicated three different consecutive reactions. Firstly, a very fast reaction (intermediate formation, IM), secondly, a slower reaction with the formation of the Rh(III) alkyl complex (5.0(1) × 10−3 M−1 s−1 for acetonitrile at 20 °C) and thirdly a very slow formation of the Rh(III) acyl complex as final product with a rate constant of 2.9(6) × 10−4 s−1. The same oxidative addition reaction in ethyl acetate as solvent exhibited only two reactions. Firstly the Rh(III) alkyl formation (1.03(3) × 10−3 M−1 s−1), which was five times slower than in the other solvents. Secondly, the Rh(III) acyl formation, which was masked by solvent IR stretching frequencies in the detection area. Rh(III) acyl, however, was isolated from ethyl acetate. There was no indication of intermediate formation with ethyl acetate. This apparent discrepancy between the rate and the mechanism for the same reaction prompted a DFT study to gain more insight into the reactants and products of the reaction, as well as to try and determine the geometry of the transition state. The DFT study predicted the formation of a linear transition state (TS), followed by the formation of the cationic five-coordinate [Rh(cupf)(CO)(DPP)(CH3)]+ intermediate with the CH3 group in the apical position and with the iodide ion drifting away into the solvent sphere. This was in agreement with the experimental very fast first reaction. The experimentally observed difference in the rates and mechanisms of the [Rh(cupf)(CO)(DPP)] + CH3I reaction in ethyl acetate relative to the other solvents can be attributed to the rate of the formation and/or the build-up and conversion of the I.M.