Hydrophilic polymer-immobilized lipoamides-iron(II) system as a new reducing catalyst for the reduction of O-benzylhydroxylamine by sodium borohydride

Based on a redox function of 1,2-dithiolane ? 1,3-dithiol, lipoamide immobilized on hydrophilic polymers such as polyacrylamide, polyethyleneimine, and chitosan was found to work as polymeric reducing catalysts for the reduction of O-benzylhydroxylamine to benzyl alcohol and ammonia with sodium borohydride in the presence of ferrous ion. These polymers were easily separable and maintained high reactivities even after repeated uses.     

Polymer-immobilized lipoamides—iron(II) system as a reducing catalyst for the reduction of nitrobenzenes to anilines by sodium borohydride

Based on a redox function of 1,2-dithiolane ? 1,3-dithiol, lipoamide (LAm), and polymers having lipoamide structure were found to work as reducing catalysts for the reduction of p-substituted nitrobenzenes to corresponding anilines with sodium borohydride in the presence of ferrous chloride in ethanol. Polyallylamine having lipoamide structure (PAA—LAm) showed a good reactivity for the reduction and was easily separated from the reaction mixture.     

Photo-enhanced reduction of carbonyl compounds by sodium borohydride

The reduction of ketones and some esters by sodium borohydride is dramatically accelerated by uv irradiation. The reaction seems to proceed from the (n, π) excited state of the carbonyl compound. The photocatalytic effect is dependent on the solvent polarity and substituents on aromatic carboxylic acids and alcohols of esters.     

Selective reduction of vinylhydroxyphenyl azomethines by sodium borohydride

Conclusions Vinylhydroxyphenyl azomethines are reduced by sodium borohydride at room temperature only at the azomethine group.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2076–2078, September, 1978.     

Comparative study of sodium borohydride tablet and tin(II) chloride reducing systems in the determination of mercury by atomic-absorption spectrophotometry

Summary An atomic-absorption spectrophotometric method for the rapid and precise determination of mercury has been studied by using the sodium borohydride tablet reduction and cold-vapour atomicabsorption procedure coupled with amalgamation on gold. The comparison of the sodium borohydride tablet and tin(II) chloride solution reducing systems are described in detail. The use of the sodium borohydride tablet wrapped in a wafer sheet is very simple and gives more precise results. From the comparison of the effect of diverse ions, it is obvious that both reducing systems have their merits and demerits.

---

AAS-Bestimmung von Quecksilber. Vergleichende Untersuchung der Reduktion mit Natriumborhydrid oder Zinn(II)-Chlorid

Zusammenfassung Ein atomabsorptions-spektralphotometrisches Kaltdampf-Verfahren zur schnellen Quecksilberbestimmung wird beschrieben, das auf der Reduktion mit Hilfe der Natriumborhydridtablette und der Amalgamierung mit Gold beruht. Der Vergleich mit der Zinn(II)-Chloridmethode wird diskutiert. Genaue Ergebnisse werden durch einfaches Einhüllen der Reduktionstablette in ein Waffelblatt erzielt, wodurch der Reaktionsbeginn verzögert wird. In bezug auf Störelemente ergeben sich für beide Verfahren Vor- und Nachteile.

     

Poly(1,4-butyl-bis-vinylpyridinium) borohydride as a new stable and efficient reducing agent in organic synthesis

The unstable sodium borohydride is stabilized on modified poly(4-vinylpyridinium), and it is used as an efficient and regenerable polymer-supported borohydride reagent for the reduction of a variety of carbonyl compounds, such as aldehydes, ketones, α,β-unsaturated carbonyl compounds, α-diketones and acyloins, in good to excellent yields.     

Dichloro bis(η5) molybdenum catalysed reduction of organic halides by sodium borohydride

Summary Dichloro bis(⁵) molybdenum catalyses the reduction of organic halides by sodium borohydride smoothly and selectively. The reactions with representative organic monohalides and polyhalides are investigated. The ease of reduction depends on the structure of the halide and the solvent used. alkoxycarbonyl and cyano groups are unattacked in the reaction. An oxidative addition-reductive elimination mechanism is tentatively suggested.     

Poly(n-butyl-4-vinylpyridinium) borohydride as a new stable and efficient reducing agent in organic synthesis

Sodium borohydride is stabilized on poly(n-butyl-4-vinylpyridinium) chloride, and it is used as an efficient and regenerable polymer-supported borohydride reagent for the reduction of a variety of carbonyl compounds, such as aldehydes, ketones, α,β-unsaturated carbonyl compounds, α-diketones, and acyloins.     

Investigations of polyaniline-platinum composites prepared by sodium borohydride reduction

Two procedures were applied for the preparation of polyaniline (PANI)-Pt composites in aqueous solutions using sodium borohydride as the reducing agent. The first one involved reduction of Pt ions originating from PtCl₄ conducted in the presence of PANI. The second was a two-step method in which doping of PANI with Pt-containing anions was followed by their reduction. The composites containing various amounts of Pt were obtained. They were characterized by X-ray diffraction, X-ray photoelectron and IR spectroscopies. This allowed to establish differences in the efficiency of both methods of composite preparation. It was also found that the composites show mainly redox activity in catalytic isopropyl alcohol conversion.     

Ruthenium(III) acetylacetonate: A homogeneous catalyst in the hydrolysis of sodium borohydride

Ruthenium(III) acetylacetonate was employed for the first time as homogeneous catalyst in the hydrolysis of sodium borohydride. Ruthenium(III) acetylacetonate was not reduced by sodium borohydride under the experimental conditions and remains unchanged after the catalysis. Poisoning experiments with mercury and trimethylphosphite provide compelling evidence for the fact that ruthenium(III) acetylacetonate is indeed a homogenous catalyst in the hydrolysis of sodium borohydride. Kinetics of the ruthenium(III) acetylacetonate catalyzed hydrolysis of sodium borohydride was studied depending on the catalyst concentration, substrate concentration, and temperature. The hydrogen generation was found to be first order with respect to both the substrate concentration and catalyst concentration. The activation parameters of this reaction were also determined from the evaluation of the kinetic data: activation energy; E_a = 58.2 ± 2.6 kJ mol⁻¹, the enthalpy of activation; ΔH^# = 55.7 ± 2.5 kJ mol⁻¹ and the entropy of activation ΔS^# = 118 ± 5 J mol⁻¹ K⁻¹. Ruthenium(III) acetylacetonate was found to be highly active catalyst providing 1200 turnovers over 180 min in hydrogen generation from the hydrolysis of sodium borohydride before deactivation.     

Electrospun nickel nanoparticles@poly(vinylidene fluoride-hexafluoropropylene) nanofibers as effective and reusable catalyst for H2 generation from sodium borohydride

Nickel nanoparticles (Ni NPs) supported on Poly(vinylidene fluoride-co-hexafluoropropylene) nanofibers (PVDF-HFP NFs) were successfully synthesized through electrospinning and in-situ reduction of Ni²⁺ salts into the surface of PVDF-HFP NFs to form metallic Ni NPs@PVDF-HFP NFs. Different percentages of nickel acetate tetrahydrate (NiAc) (10 %, 20 %, 30 %, 40 % wt.) based PVDF-HFP. The formation of tiny metallic Ni NPs @PVDF-HFP membrane NFs was demonstrated using standard physiochemical techniques. Nanofibers membranes have demonstrated good catalytic activity in H₂ production from sodium borohydride (NaBH₄). The sample composed of 40 %wt Ni showed the highest catalytic activity compared to the other formulations. Whereas 103 mL of H₂, from the hydrolysis of 1.34 mmol NaBH₄, was produced using 40 wt% NiAc compared to 68 mL, 81 mL, and 93 mL for 10 wt%, 20 wt%, and 30 wt% NiAc, respectively, in 60 min at 25 °C. The hydrogen generation has been enhanced with an increase in the Nanofibers membrane amount and reaction temperature. The latter results in a low activation energy (23.52 kJ mol^?1). The kinetics study revealed that the reaction was pseudo-first-order in sodium borohydride concentration and catalyst amount. Furthermore, the catalyst exhibits satisfactory stability in the hydrolysis process for ten cycles. Because of its easy recyclability, the introduced catalyst has a wide range of potential applications in the generation of H₂ from sodium borohydride hydrolysis.     

Intrazeolite ruthenium(0) nanoclusters: a superb catalyst for the hydrogenation of benzene and the hydrolysis of sodium borohydride

The use of microporous materials with ordered porous structures as the hosts to encapsulate metal nanoclusters has attracted particular interest in catalysis because the pore size restriction could limit the growth of nanoclusters and lead to an increase in the percentage of the catalytically active surface atoms. This letter reports the preparation of ruthenium(0) nanoclusters stabilized by the framework of Zeolite-Y by using a simple, easy, efficient method and their superb catalytic activities in two important reactions: the hydrogenation of arenes (benzene, toluene, o-xylene, mesitylene) and the hydrolysis of sodium borohydride, all at room temperature. Particularly, the intrazeolite ruthenium(0) nanoclusters exhibit unprecedented catalytic activity in the hydrogenation of neat benzene at 22.0 +/- 0.1 degrees C and 40 +/- 1 psig H2 with a record TOF of 1040 mol benzene/mol Ru . h.     

Theoretical investigation of the reducing capacity of sodium borohydride and sodium acetoxyborohydride derivatives

The reducing capacity of sodium borohydride and its acetoxy derivatives was studied. Density functional theory using four different functionals were used to investigate the enthalpies, charges and molecular structures of four distinct reactions associated with hydride release. The theoretical results in the gas phase reinforce the experimental observations that the acetoxyborohydride derivative reducing capacities are a consequence of both the inductive electron-withdrawing ability of the acetoxy group and the steric bulk surrounding the BH bond. The electron acceptor effect of the acetoxy group provided a linear relation between the boron GAPT charges and the enthalpy necessary to remove the hydride from sodium borohydride, justifying the smaller or even nonexistent reductor capacity of more substituted borohydrides.     

Kinetics of reduction of copper(II) by sodium tetrahydroborate

Summary The kinetics of reduction of copper(II) ion by sodium tetrahydroborate in buffered aqueous solution have been investigated. The rate of the reaction is first order in the concentrations of each of the reactants. The activation parameters were evaluated and a plausible mechanism for the reduction of copper(II) ion is proposed.     

Evolution of copper(II) as a new alkene amination promoter and catalyst

Copper(II) carboxylates and chiral copper(II) triflate·bis(oxazoline) complexes promote and catalyze intramolecular alkene carboamination, diamination and aminooxygenation reactions, creating an array of nitrogen heterocycles. High diastereoselectivity and enantioselectivity can be achieved in these transformations. This account reviews the discovery and development of these useful and interesting reactions.