Reduction d'alcools allyliques fluores par le borohydrure de sodium

Reduction of 1,1-difluoro 1-alken 3-ols with sodium borohydride in diglyme gives 1,1-difluoro 2-alkenes by SN2' substitution of the hydroxy moiety.     

Microscale gas generator of methane for the dead time determination of capillary columns

Methane produced by the reduction of iodomethane by sodium borohydride in diglyme can be used to determine the dead time in capillary gas chromatography. Best results were achieved using standard non-polar capillary columns, hydrogen, helium and nitrogen carrier gases and flame ionization detection.     

Stereoelective Conversion of Ethyl Pipecolinate into (±)-α- and (±)-β-Conhydrins

Reaction of ethyl N-benzhydrylpipecolinate with ethylmagnesium bromide in the presence of catalytic amount of titanium(IV) isopropoxide furnished in a high yield the corresponding hydroxypropyl-substituted piperidine that by treating with alcoholic alkali was quantitatively converted into 1-benzhydryl-2-propionylpiperidine. The reduction in the latter of carbonyl group with lithium aluminum hydride or sodium borohydride in methanol gave rise prevailingly to threo-aminoalcohol. With sodium borohydride in the presence of cerium chloride an erythro-aminoalcohol was the main product. Deprotection of the nitrogen atom from the benzhydryl group of the aminoalcohols obtained provided racemic - and -conhydrines.     

PTSA–catalyzed functionalization of hydroquinones with benzhydryl alcohols in water

An intriguing and operationally simple direct benzylation of hydroquinones with benzhydryl alcohols has been developed using PTSA in water, affording functionalized hydroquinones in good to excellent yields. The advantages of being environmentally benign, metal-free, base-free, easy workup and having a wide substrate scope make it a promising process for the synthesis of symmetrically and unsymmetrically benzylated hydroquinones as well as for industrial applications.     

Microscale gas generator of methane for the dead time determination of capillary columns

Methane produced by the reduction of iodomethane by sodium borohydride in diglyme can be used to determine the dead time in capillary gas chromatography. Best results were achieved using standard non-polar capillary columns, hydrogen, helium and nitrogen carrier gases and flame ionization detection. Received: 7 February 2000 / Revised: 29 May 2000 / Accepted: 31 May 2000     

Solid-State Hydrogen-Generating Composites Based on Sodium Borohydride: Effect of the Heat Treatment of Boron–Cobalt Catalysts on the Hydrogen Generation Rate

Calcined boron–cobalt catalysts prepared by reduction of cobalt chloride in an aqueous sodium borohydride solution can be successfully used as components of pelletized solid-state hydrogen-generating composites based on sodium borohydride. Morphological changes and phase and chemical transformations occurring in the catalysts with an increase in the calcination temperature were studied. The catalyst performance in hydrolysis of sodium borohydride was determined. The hydrogen generation rate depends on the specific surface area of the calcined sample.     

Controversial influence of aqueous treatments on historic textiles

Different historic textiles were subject to aqueous treatments with and without sodium borohydride as a reducing agent. As the action of borohydride generates an alkaline environment that is potentially harmful for oxidized cellulose in historic textiles, two less alkaline treatment options using buffer systems were additionally tested.In order to track the impact of the treatments on the samples, the development of oxidized cellulose functionalities and of the molecular weight was analyzed by selective labelling of carbonyl and carboxyl groups combined with gel permeation chromatography and multi-detector set-up. The crystallinity index of the samples was analyzed by CP-MAS NMR to elucidate the impact of age and treatment on the historic material.Already pure aqueous treatment changed the molecular weight distribution of historic textiles in some cases. These changes are discussed in the context of oxidized cellulose functionalities and crystallinity index. Furthermore the chosen historic samples reacted best towards a reduction treatment with sodium borohydride that had not been buffered, whereas the two buffered systems caused more damage and failed to reduce carbonyl groups along the cellulose chain.     

Electronic structure of aqueous borohydride: a potential hydrogen storage medium

Borohydride salts have been considered as good prospects for transportable hydrogen storage materials, with molecular hydrogen released via hydrolysis. We examine details of the hydration of sodium borohydride by the combination of X-ray absorption spectroscopy and first principles' theory. Compared to solid sodium borohydride, the aqueous sample exhibits an uncharacteristically narrow absorption feature that is shifted to lower energy, and ascribed to the formation of dihydrogen bonds between borohydride and water that weaken the boron-hydrogen covalent bonds. Water also acts to localize the highly excited molecular orbitals of borohydride, causing transitions to excited states with p character to become more intense and a sharp feature, uncharacteristic of tetrahedral molecules, to emerge. The simulations indicate that water preferentially associates with borohydride on the tetrahedral corners and edges.     

Determination of inorganic arsenic and organic arsenic compounds in marine organisms by hydride generation/cold trap/gas chromatography— mass spectrometry

The behavior of arsenite, methylarsonic acid, dimethylarsinic acid, trimethylarsine oxide, dimethyl-R-arsine oxides, and trimethyl-R-arsonium compounds (R = carboxymethyl, 2-carboxyethyl, 2-hydroxyethyl) toward sodium borohydride and hot aqueous sodium hydroxide was investigated. The arsines obtained by sodium borohydride reduction of the undigested and digested solutions were collected in a liquid-nitrogen cooled trap, separated with a gas chromatograph, and detected with a mass spectrometer in the selected-ion-monitoring mode. The investigated arsenic compounds were stable in hot 2 mol dm^?3 sodium hydroxide except arsenobetaine [trimethyl(carboxymethyl)arsonium zwitterion] that was converted to trimethylarsine oxide, and dimethyl(ribosyl)arsine oxides that were decomposed to dimethylarsinic acid. Hydride generation before and after digestion of extracts from marine organisms allowed inorganic arsenic, methylated arsenic, arsenobetaine, and ribosyl arsenic compounds to be identified and quantified. This method was applied to extracts from shellfish, fish, crustaceans, and seaweeds.     

Aromatic Nucleophilic Substitution Polymerization of Dichloro-1,3,5-Triazines with Alkanedithiols

Reaction of 2,4-dichloro-6-phenyl-1,3,5-triazine with alkane-dithiols in the presence of a base in THF afforded the corresponding condensation polymers containing triazinylthio group in moderate yields. This polymerization reaction also proceeded in the o-dichlorobenzene-water two-phase system by using phase transfer catalysts. The resulting polymers consisted of THF-soluble and insoluble fractions. When the reaction was carried out at a higher temperature or for a longer reaction time, the yield of the insoluble polymer was increased. The THF-soluble polymers were also soluble in toluene, and they had the ability to extract sodium and potassium ions from aqueous picrates. The polymers functioned as catalysts for substitution reactions of an alkyl bromide and the reduction of a ketone with sodium borohydride under liquid-liquid phase transfer conditions with a reactivity superior to that of the monomeric analog.     

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.     

Direct Reductive Amination of Aldehydes and Ketones with 2,4-Ionene-Based Borohydride Exchange Resin as a Novel Polymer-Supported Reducing Agent

Direct reductive amination of aldehydes and ketones were accomplished efficiently using high-capacity, ionene-based, polymer-supported borohydride reagent in isopropyl alcohol at reflux under neutral conditions. The reagent is easily prepared by mixing aqueous solution of 2,4-ionene bromide with an alkaline solution of sodium borohydride at room temperature. The generality of reaction was established using both aliphatic and aromatic aldehydes, ketones, and amines.     

Environmentally benign oxidation reaction of aldehydes to their corresponding carboxylic acids using Pd/C with NaBH4 and KOH

Pd/C catalyst in aqueous methanol with sodium borohydride and potassium hydroxide under the air efficiently oxidized aldehydes to their corresponding carboxylic acids at room temperature. The utilization of room temperature reaction, aqueous methanol solvent, and the open-air conditions make this manipulation very interesting for economic and environmental perspectives.     

Reaction of N-vinylindazolium and N-vinylbenzotriazolium salts with nucleophiles

Reaction of N-vinylindazolium tetrafluoroborates with aqueous potassium carbonate or sodium borohydride affords 2,3-dihydroquinazolines which evolve to 1,2,3,4-tetrahydroquinazolines by intra or intermolecular nucleophilic attack. The X-ray structure of one tetrahydroquinazoline, the tricyclic compound 17a, was determined (C₁₄H₁₆N₂O₅, P2₁/n, a=6.001(4)Å, b=13.601(8)Å, c=17.452(6)Å, β=94.93(3)°, V=1419(1)ų, Z=4, R=0.078 for 1541 observed reflexions). Only open-chain compounds are obtained when these salts react with methanol. 2-Vinylindazolium and 3-vinylbenzotriazolium tetrafluoroborates react with aqueous potassium carbonate and with sodium borohydride yielding the corresponding neutral benzazoles by cleavage of the azole-vinyl bond. They add methanol to the exocyclic double bond and, in the case of indazole derivative, an expansion to a 1,2-dihydroquinazoline is observed in basic medium.A general mechanism is proposed for the reaction of vinylpyrazolium and indazolium salts with nucleophiles.     

Synthesis, characterization, and electrocatalytic activity of PtPb nanoparticles prepared by two synthetic approaches

Intermetallic PtPb nanoparticles have been synthesized by two solution-phase reduction methods. In the first (PtPb-B), Pt and Pb salts were reduced by sodium borohydride in methanol at room temperature. In the second (PtPb-N), metal-organic Pt and Pb precursors were reduced by sodium naphthalide in diglyme at 135 degrees C. Both methods produced small agglomerated nanoparticles of the ordered intermetallic PtPb (mean crystal domain size <15 nm) which were characterized by pXRD, SEM, UHV-STEM, BET, EDX, and electron diffraction. The electrocatalytic activity of PtPb nanoparticles produced by both methods toward formic acid and methanol oxidation was investigated and compared to Pt and PtRu. Both PtPb-B and PtPb-N nanoparticles exhibited enhanced electrocatalytic activity compared to commercially available Pt black and PtRu nanoparticles. For formic acid oxidation, the PtPb nanoparticles exhibited considerably lower onset potentials and higher current densities than Pt or PtRu. For methanol oxidation, the PtPb nanoparticles had onset potentials slightly positive of PtRu but exhibited higher current densities at potentials about 100 mV positive of onset. The general applicability of these methods for the synthesis of nanoparticles of ordered intermetallic phases is discussed.     

Sodium Borohydride–Mediated Transesterification

In the presence of sodium borohydride, esters react with alcohols with formation of the corresponding esters. The reaction is sensitive to the solvent, structure of the ester, and is often concurrent with reduction. Thioesters containing an ester group can be selectively cleaved by the reagent. Both esters and thioesters attached to solid support are resistant toward sodium borohydride. The in situ prepared sodium tetraalkoxyborate is introduced as an efficient reagent and catalyst for transesterification.     

Gas-chromatographic determination of the product distribution in the synthesis of sodium borohydride

A gas-chromatographic method has been developed for determination of the sodium borohydride and methanol content of alkaline aqueous solutions of NaBH(4). From the ratio between NaBH(4) and CH(3)OH the product distribution in NaBH(4) synthesis from NaH and B(OCH(3))(3) in mineral oil can be calculated and the amount of the by-product NaBH(OCH(3))(3) formed can be estimated. A separation and extraction procedure for the mineral oil dispersion must precede the gas-chromatographic analysis. Sodium borohydride is determined by measurement of the 2-propanol formed after treatment of the solution with acetone, whereas methanol can be determined directly by gas chromatography, with 1-propanol as internal standard. The analysis of the synthesis products is thus the separation and detection of simple alcohols.     

Kinetics of the Catalytic Hydrolysis of Concentrated Aqueous Solutions of NaBH4 on Co/TiO2 Powder

Kinetics and Catalysis - The results of experimental studies on the hydrolysis of concentrated aqueous solutions of sodium borohydride in a concentration range of 1.05–6.3 mol/kg at...     

Crystal structure of sodium iodide·(diglyme): An unprecedented bridging role for diglyme

The diglyme adduct of sodium iodide, NaI·(CH₃OCH₂CH₂)₂O, has been structurally characterized by X-ray diffraction. It forms infinite zig-zag chains which, unlike most complexes of the salt, retain Na---I bonds. In addition, diglyme molecules bridge pairs of Na atoms through four-co-ordinate O atoms, so representing a new role for this neutral oxygen donor.     

Inexpensive, in-situ monitoring of borohydride concentrations

Non-destructive, in-situ detection of 10(-3) to 10(-4) M borohydride ions in aqueous alkaline solutions containing borates can be easily and rapidly accomplished by simply measuring open circuit potentials of selected metals (relative to a suitable reference) immersed in these solutions.