Reduction Of Bromide Research Articles

Cathodic Behaviour of Dicationic Imidazolium Bromides: The Role of the Spacer

AbstractThe cathodic reduction of dicationic imidazolium bromides, whose spacer is either an aliphatic chain or a xylyl group, leads to the formation of the corresponding N‐heterocyclic carbenes (NHCs), which were isolated as the corresponding thiones, after reaction with elemental sulfur. The behaviour of the dications was compared with the corresponding monocations. The behaviour of dicarbenes depends on the nature of the spacer. This study evidenced that dicarbenes deriving from xylyl dications are less stable than the corresponding aliphatic ones (giving lower yields in thiones), due to a debenzylation reaction. On the other hand, the yields in thiones starting from aliphatic dications are higher than the corresponding monocations, suggesting a cooperative reduction at the electrode of the two imidazolium moieties. The cathodic process was confirmed using the co‐electrogenerated hydrogen to reduce 2,2,2‐trifluoroacetophenone to the corresponding alcohol.

Ag x Cu y Ni z Trimetallic Alloy Catalysts for the Electrocatalytic Reduction of Benzyl Bromide in the Presence of Carbon Dioxide.

Different compositions of trimetallic alloy containing silver, copper, and nickel (AgxCuyNiz) were electrodecorated in a protic ionic liquid medium on glassy carbon electrodes in order to investigate the suitability of the materials as catalysts for electrochemical reduction of carbon dioxide (CO2). Surface characteristic morphology obtained by scanning electron microscopy shows cauliflower crystallites for the deposit of Ag, whereas materials of Cu and Ni exhibit cubic grains and fine particles, respectively. Deposits of trimetallic alloy containing Ag, Cu, and Ni exhibit the mixture of the three characteristic features. Further, trimetallic alloy containing a large amount of Ag provides high crystallinity, whereas predominance of Cu as well as Ni results in porous structures, as revealed by X-ray diffraction analysis. Atomic absorption spectroscopy () was used to determine the compositions of different alloy materials. The suitability of nanomaterials as cathodes for electroreduction of benzyl bromide in CO2 containing 0.1 M tetra-n-butylammonium tetrafluoroborate (DMF/TBABF4)/N,N-dimethylformamide medium was explored. The linear sweep voltammogram reveals that Ag46Cu40Ni14 shows higher cathodic peak current and lower cathodic peak potential than those of other deposited nanomaterials as well as alloys, indicating its higher catalytic activity for such an electroreduction process, whereas potentiostatic electrolysis confirms the abovementioned results.

Direct Synthesis of Heavy Grignard Reagents: Challenges, Limitations, and Derivatization

The direct synthesis of organocalcium compounds (heavy Grignard reagents) by the reduction of organyl halides with activated calcium powder succeeded in a straightforward manner for organic bromides and iodides that are bound at sp2 -hybridized carbon atoms. Extension of this strategy to alkyl halides was very limited, and only the reduction of trialkylsilylmethyl bromides and iodides with activated calcium allowed the isolation of the corresponding heavy Grignard reagents. Substitution of only one hydrogen atom of the methylene moiety by a phenyl or methyl group directed this reduction toward the Wurtz-type coupling and the formation of calcium halide and the corresponding C-C coupling product. The stability of the methylcalcium and benzylcalcium derivatives in ethereal solvents suggests an unexpected reaction behavior of the intermediate organyl halide radical anions. Quantum chemical calculations verify a dependency between the ease of preparative access to organocalcium complexes and the C-I bond lengths of the organyl iodides. The bulkiness of the trialkylsilyl group is of minor importance. Chloromethyltrimethylsilane did not react with activated calcium; however, halogen-exchange reactions allowed the isolation of [Ca(CH2 SiMe3 )(thf)3 (μ-Cl)]2 . Furthermore, the metathetical approach of reacting [Ca(CH2 SiMe3 )I(thf)4 ] with KN(SiMe3 )2 and the addition of N,N,N',N'',N''-pentamethyldiethylenetriamine (pmdeta) allowed the isolation of heteroleptic [CaCH2 SiMe3 {N(SiMe3 )2 }(pmdeta)]. In the reaction of this derivative with phenylsilane, the trimethylsilylmethyl group proved to be more reactive than the bis(trimethylsilyl)amido substituent.

Reprint of “Electrochemical reduction of organic bromides in 1-butyl-3-methylimidazolium tetrafluoroborate”

The electrochemical reduction of a series of aliphatic and aromatic bromides on glassy carbon, silver and copper electrodes has been investigated by cyclic voltammetry in 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm]BF4). As in polar aprotic solvents, reductive cleavage of aromatic bromides occurs by a stepwise mechanism with the formation of a transient radical anion. In contrast, concerted electron transfer/bond rupture is the preferred reaction pathway for aliphatic bromides. Both Ag and Cu show remarkable electrocatalytic activities for the activation of the carbon-bromine bond, but the catalytic effect depends on reaction mechanism and molecular structure of RBr. Catalysis is high when reduction occurs by a concerted dissociative electron transfer pathway, which is the case of alkyl bromides. When instead a stepwise mechanism is preferred, i.e., the case of all aromatic bromides, catalysis strongly decreases with the ability of the molecule to delocalize the incoming negative charge. For example, the high positive shift of peak potential (>0.7V) observed for bromobenzene on Ag decreases to <0.1V for 4-bromobenzonitrile and <0.02V for 9-bromoanthracene.Overall, [BMIm]BF4 behaves like molecular solvents such as acetonitrile and dimethylformamide but, in general, both Ag and Cu are less active in the ionic liquid than in polar aprotic solvents.

Catalytic Reduction of Alkyl and Aryl Bromides Using Propan‐2‐ol

AbstractMilstein's complex, (PNN)RuHCl(CO), catalyzes the efficient reduction of aryl and alkyl halides under relatively mild conditions by using propan‐2‐ol and a base. Sterically hindered tertiary and neopentyl substrates are reduced efficiently, as well as more functionalized aryl and alkyl bromides. The reduction process is proposed to occur by radical abstraction/hydrodehalogenation steps at ruthenium. Our research represents a safer and more sustainable alternative to typical silane, lithium aluminium hydride, and tin‐based conditions for these reductions.

Catalytic Reduction of Alkyl and Aryl Bromides Using Propan-2-ol.

Milstein's complex, (PNN)RuHCl(CO), catalyzes the efficient reduction of aryl and alkyl halides under relatively mild conditions by using propan-2-ol and a base. Sterically hindered tertiary and neopentyl substrates are reduced efficiently, as well as more functionalized aryl and alkyl bromides. The reduction process is proposed to occur by radical abstraction/hydrodehalogenation steps at ruthenium. Our research represents a safer and more sustainable alternative to typical silane, lithium aluminium hydride, and tin-based conditions for these reductions.

Radical Hydrodehalogenation of Aryl Bromides and Chlorides with Sodium Hydride and 1,4-Dioxane.

A practical method for radical chain reduction of various aryl bromides and chlorides is introduced. The thermal process uses NaH and 1,4‐dioxane as reagents and 1,10‐phenanthroline as an initiator. Hydrodehalogenation can be combined with typical cyclization reactions, proving the nature of the radical mechanism. These chain reactions proceed by electron catalysis. DFT calculations and mechanistic studies support the suggested mechanism.

Electrochemical reduction of organic bromides in 1-butyl-3-methylimidazolium tetrafluoroborate

The electrochemical reduction of a series of aliphatic and aromatic bromides on glassy carbon, silver and copper electrodes has been investigated by cyclic voltammetry in 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm]BF4). As in polar aprotic solvents, reductive cleavage of aromatic bromides occurs by a stepwise mechanism with the formation of a transient radical anion. In contrast, concerted electron transfer/bond rupture is the preferred reaction pathway for aliphatic bromides. Both Ag and Cu show remarkable electrocatalytic activities for the activation of the carbon-bromine bond, but the catalytic effect depends on reaction mechanism and molecular structure of RBr. Catalysis is high when reduction occurs by a concerted dissociative electron transfer pathway, which is the case of alkyl bromides. When instead a stepwise mechanism is preferred, i.e., the case of all aromatic bromides, catalysis strongly decreases with the ability of the molecule to delocalize the incoming negative charge. For example, the high positive shift of peak potential (>0.7V) observed for bromobenzene on Ag decreases to <0.1V for 4-bromobenzonitrile and <0.02V for 9-bromoanthracene.Overall, [BMIm]BF4 behaves like molecular solvents such as acetonitrile and dimethylformamide but, in general, both Ag and Cu are less active in the ionic liquid than in polar aprotic solvents.

Cyclohexyl Bromide and Iodide: Direct Reduction at Vitreous Carbon Cathodes together with Nickel(I) Salen‐ and Cobalt(I) Salen‐Catalyzed Reductions in Dimethylformamide

AbstractCyclic voltammetry and controlled‐potential (bulk) electrolysis have been used to study the direct electrochemical reduction of cyclohexyl bromide (1) and cyclohexyl iodide (2) at glassy carbon cathodes in dimethylformamide (DMF) containing 0.10 M tetramethylammonium tetrafluoroborate (TMABF4). Direct reduction of 1 is a one‐step process that affords a carbanion intermediate, whereas 2 undergoes stepwise reduction to a radical and then a carbanion intermediate. Mixtures of cyclohexane, cyclohexene, and bicyclohexyl arise from bulk electrolyses of both 1 and 2. Catalytic reduction of 1 and 2 by nickel(I) salen and cobalt(I) salen electrogenerated at glassy carbon cathodes in DMF‐TMABF4 has been investigated with the aid of both cyclic voltammetry and bulk electrolysis. Products arising from these catalytic reductions are cyclohexane, cyclohexene, and bicyclohexyl, although significant amounts of unreduced 1 are found when cobalt(I) salen is utilized as the catalyst. Mechanistic aspects of the direct and catalyzed reductions of 1 and 2 are discussed.

Sequential Vinyl Radical Cyclization/Fixation of Carbon Dioxide through Electrochemical Reduction of Vinyl Bromide in the Presence of an Electron‐Transfer Mediator

AbstractConstant‐current electrolysis of vinyl bromide in DMF containing 0.1 m Bu4NBF4 by using an undivided cell equipped with a platinum plate cathode and a magnesium rod anode in the presence of an electron‐transfer mediator, methyl 4‐tert‐butylbenzoate, and carbon dioxide resulted in selective generation of a vinyl radical, for which cyclization followed by fixation of carbon dioxide with a carbon–carbon bond formation gave γ,δ‐unsaturated carbo‐ and heterocycle carboxylic acids in moderate to good yields. The vinyl radical could be selectively generated under the electrolysis conditions, and the following reaction of the anion species, generated by one‐electron reduction of the resulting cyclized radical, with carbon dioxide took place efficiently. These results and cyclic voltammetry indicate that methyl 4‐tert‐butylbenzoate plays an important role in the generation of vinyl radicals from vinyl bromides. The resulting cyclized γ,δ‐unsaturated carboxylic acid was successfully applied to stepwise and direct iodo‐lactonization to give the corresponding bicycle γ‐lactones in good yields.

Increase in the nitric oxide release without changes in cell viability of macrophages after laser therapy with 660 and 808nm lasers.

The aim of this study was to evaluate the influence of low-level laser therapy (LLLT) with different parameters and wavelengths on nitric oxide (NO) release and cell viability. Irradiation was performed with Ga-Al-As laser, continuous mode and wavelengths of 660 and 808nm at different energy and power densities. For each wavelength, powers of 30, 50, and 100mW and times of 10, 30, and 60s were used. NO release was measured using Griess reaction, and cell viability was evaluated by mitochondrial reduction of bromide 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) to formazan. LLLT promoted statistically significant changes in NO release and MTT value only at the wavelength of 660nm (p < 0.05). LLLT also promoted an increase in the NO release and cell viability when the energy densities 64 (p = 0.04) and 214J/cm2 (p = 0.012), respectively, were used. LLLT has a significant impact on NO release without affecting cell viability, but the significance of these findings in the inflammatory response needs to be further studied.

Base-Promoted Vinyl Carbon–Bromine Bond Cleavage by Group 9 Metalloporphyrin Complexes

Base-promoted vinyl carbon–bromine bond cleavage of styryl bromide by group 9 metalloporphyrin complexes was achieved to give the metal(III) porphyrin styryls M(ttp)(styryl) (ttp = 5,10,15,20-tetra-p-tolylporphyrinato dianion). Mechanistic studies suggest that [MII(ttp)]2 (M = Rh, Ir) cleaves the vinyl C–Br bond via an addition–elimination mechanism. The much less reactive CoII(ttp) undergoes a radical recombination with styryl radical which is generated by the hydroxide reduction of styryl bromide to give a radical anion with subsequent C–Br cleavage.

Radical Hydrodeiodination of Aryl, Alkenyl, Alkynyl, and Alkyl Iodides with an Alcoholate as Organic Chain Reductant through Electron Catalysis.

A simple and efficient method for radical hydrodeiodination is reported. The novel approach uses electron catalysis. In situ generated Na-alcoholates are introduced as radical chain reducing reagents and reactions work with O2 as cheap initiator. Hydrodeiodination works on aryl, alkenyl, alkynyl iodides and a tert-alkyl iodide also gets reduced applying the method. Albeit less general, the method is also applicable to the reduction of aryl bromides. The novel reagent is successfully used to conduct typical reductive radical cyclization reactions and mechanistic studies are reported.

Analysis of interaction between reactants and substrate materials during the growth of tantalum coatings

We have analyzed interaction between reactants and substrate materials during the reduction of tantalum bromide with cadmium in the course of tantalum deposition on Cu, Fe, Mo, and Ni metallic substrates and the 25Kh3M3NBTsA, Ni3Al, VKNA, and ZhS32 alloys. The results indicate that molybdenum and nickel substrates are the most stable to the reactants used in this study; copper and iron experience etching; and aluminum, chromium, and titanium are capable of competing with cadmium as a reducing agent. The presence of carbon in the substrate material leads to the formation of tantalum carbide in the metal–coating interfacial layer. In the absence of aluminum, oxygen impurities are likely to be removed as oxybromides. Optimal materials for the fabrication of reaction chambers for tantalum deposition are nickel-coated high-temperature steels.

Composition Control Synthesis and Catalytic Properties in the Suzuki Reaction of Bimetallic PdSn Nanoparticles

We have successfully prepared 6.5 nm palladium tin (PdSn) alloy nanoparticles (NPs) with tunable compositions by high-temperature reduction of tin acetate and palladium bromide in the presence of oleylamine and trioctylphosphine. The catalytic activities of PdSn NPs with different compositions were evaluated through Suzuki reactions. The PdSn nanocatalysts show better catalytic activity on Suzuki reactions than an equal amount of pure Pd NPs, and their catalytic activities are highly composition dependent. Among these NPs, Pd63Sn37/C NPs exhibited the highest catalytic performance with higher reaction activity, lower Pd leaching properties, and higher stability even after eight recycle reactions.

Surface engineered gold nanoparticles through highly stable metal–surfactant complexes

Monodispersed Au nanoparticles were synthesized by the reduction of Au-decyltrimethylammonium bromide (Au-DTAB), which was easily prepared via the reaction of HAuCl4 and DTAB. This Au-DTAB complex is highly stable in air and moisture, and suitable for large-scale synthesis of uniform-sized Au nanoparticles. The nanoparticles were characterized by transmission electron microscopy, optical absorption spectrometry, X-ray diffraction, and Fourier Transform infrared spectroscopy. The size of Au nanoparticles was controlled in the range of 5–10nm by changing the concentrations of reducing agent and Au precursor. The resulting Au nanoparticles were transferred to the aqueous phase after surface engineering using multidentate polymeric ligands with multiple imidazole functional groups. Polymeric imidazole ligands (PILs) demonstrated enhanced binding stability with the Au surface, and overcame the disadvantage of multidentate thiol ligand systems which have oxidative cross-linking and the formation of disulfide bonding. The colloidal stability of surface engineered Au nanoparticles with PILs was investigated by dynamic light scattering (DLS) characterization.

ChemInform Abstract: Reductions of Aryl Bromides in Water at Room Temperature.

AbstractSurfactant (NOK) generates nanoreactors in water in which the reduction of aryl bromides with NaBH4 proceeds efficiently.

Controlled synthesis of monodisperse PdxSn100−x nanoparticles and their catalytic activity for hydrogen generation from the hydrolysis of ammonia-borane

Composition controllable monodisperse palladium tin nanoparticles (PdxSn100−x NPs, x = 77, 69, 63, 52, 49) were prepared by the thermal reduction of palladium bromide and tin acetate in the presence of trioctylphosphine and oleylamine. The NPs were investigated for their catalytic abilities of hydrogen generation from hydrolysis of ammonia borane complex. Deposited on a carbon support without any further treatment, these NPs were active nanocatalysts for hydrolysis of ammonia borane complex, and their catalytic activities were highly composition dependent. Among these NPs studied, Pd69Sn31 NPs exhibited the highest catalytic activity and stability under mild reaction conditions. Kinetic investigations showed that the catalytic hydrolysis of ammonia borane was first-order with respect to catalyst concentration and zero-order with respect to ammonia borane concentration. The activation energy for the hydrolysis of ammonia borane complex in the presence of Pd69Sn31 NPs was calculated to be 27.22 kJ mol−1. The PdxSn100−x NPs are promising candidates toward the practical development of the ammonia borane complex as a feasible hydrogen storage medium for fuel cell applications under ambient conditions.

Thermodynamic analysis of Ta chemical vapor deposition via the reduction of tantalum halides with cadmium and zinc

This paper presents thermodynamic analysis of the gas-phase reduction of tantalum chlorides, bromides, and iodides by zinc and cadmium. We consider in detail the reduction process and optimize low-temperature tantalum deposition parameters.

Pseudomonas gessardii growing cells as a new biocatalyst for asymmetric synthesis of α-bromohydrins

Abstract The growing whole cells of bacterial strain, Pseudomonas gessardii provides a highly selective biocatalyst for reduction of phenacyl bromides to generate ( S )-2-bromo-1-phenylethan-1-ol derivatives in high enantioselectivity (up to 96% ee). The chiral alcohols were isolated with complete conversion (>99%) employing DMSO as the co-solvent. Effect of various physiochemical parameters on the reduction has been studied. The other α -substitued acetophenones (chloro-, cyano-, and azide-) were reduced their corresponding alcohols with lower enantioselectivity.