Reduction of aldehydes and ketones with tetraalkylammonium borohydrides

Misinterpretations regarding the selectivity of tetraalkylaminonium borohydride reductions in dichloromethane are resolved. Tetrabutyl ammonium borohydride offers several advantages, but both it and tetraethyl ammoniumborohydride are highly useful synthetic reagents.     

Reinvestigation of the Reaction of Sodium Borohydrate with Benzhydryl Halides under Solvolytic Conditions

Solvolysis of benzhydryl halides in aqueous diglyme containing sodium borohydride was studied. Contrary to the literature, sodium borohydride was found not to be a convenient trap for benzhydryl carbocations, especially for those containing electron-withdrawing substituent, and it decomposed appreciably in 80% aqueous diglyme at 45 °C. In addition, significant acceleration of reactions due to the presence of sodium borohydride was realized in the solvolysis of 3-chloro- and 3-trifluoromethyl-benzhydryl chlorides.     

Reduction of 2,3,4-substituted quinolines with sodium borohydride

1,2-Dihydroquinolines were obtained by the reduction of 3-substituted 2-methyl-4-phenylquinolines with sodium borohydride in aliphatic carboxylic acids; N-alkyl derivatives are also formed. The corresponding 1,4-dihydroquinoline was obtained in the reaction of 2-methyl-3-nitroquinolinium perchlorate with sodium borohydride.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1680–1686, December, 1991.     

Observations on the reduction of aryl nitro groups with palladium-sodium borohydride

The reduction of aryl nitro groups by the palladium-sodium borohydride system can be controlled in some instances to give products differing from those of catalytic hydrogenation. With six equivalents of borohydride added to the catalyst 2,2′-dinitrobiphenyl formed only 2,2′-diaminobiphenyl. With added sodium hydroxide and varying amounts of borohydride and catalyst, the reduction can be controlled to give benzo[c]cinnoline, benzo[c]cinnoline 5-oxide or benzo[c]cinnoline 5,6-dioxide. In a closed system, the reagents reduce both the nitro and olefin functional groups in 6-nitro-5,8-dimethoxy-1,4-dihydro-1,4-ethano-naphthalene. In an open flask flushed with argon, the reduction is confirmed to the nitro group. Reduction of 2-chloro and 4-chloronitrobenzene with palladium-borohydride gives substantial yields of the appropriate chloroanilines. In contrast, hydrogen and palladium give aniline as the major product from each of these. These results suggest that the addition of sodium borohydride to palladium on carbon produces a reductive entity differing from that of catalytic hydrogenation.     

A membrane electrode assembly with high fuel coulombic efficiency for passive direct borohydride fuel cells

Here, we report the development of a new membrane electrode assembly (MEA) structure for passive direct borohydride fuel cells (DBFCs). The anode of this type of MEA includes upper and lower parts for the electro-oxidation of borohydride and hydrogen, respectively. In comparison to conventional MEAs, the maximum power of this MEA is increased by 28.1%, and the anode polarization is decreased due to the current contribution of hydrogen electro-oxidation. The hydrogen generated from borohydride hydrolysis can be oxidized inside the cell, and the fuel coulombic efficiency reaches 100%. Therefore, high fuel utilization and cell safety can be obtained by employing this novel MEA in DBFCs.     

Microdetermination of carbonyl compounds by reduction with alkaline sodium borohydride

Summary Alkaline sodium borohydride has been employed as a reducing reagent for the titrimetric determination of compounds containing the carbonyl function. The sample is dissolved in methanol and is then reduced with alkaline sodium borohydride. After completion of the reaction, the excess sodium borohydride is back titrated against standardized hydrochloric acid solution using methyl red as indicator. The stoichiometry between the carbonyl function and sodium borohydride is 41.

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Zusammenfassung Natriumborhydrid dient als Reduktionsmittel zur Titration von Carbonylverbindungen. Die Probe wird in Methanol gelöst und dann mit alkalischem Natriumborhydrid reduziert. Nach Ablauf der Reaktion wird der Überschuß mit Salzsäure gegen Methylrot zurücktitriert. Carbonylverbindung und Natriumborhydrid reagieren im Verhältnis 41.

     

Reactions of 4-oxo-1,3-benzoxazinium perchlorates with sodium borohydride

Reduction of 4-oxo-1,3-benzoxazinium perchlorates with sodium borohydride depending on the structure of starting salt and the reaction conditions leads to different products. 2-Alkyl- and 2-phenylsubstituted salts react with sodium borohydride to give 2,3-dihydro-4-oxo-1,3-benzoxazines. 2-Arylvinyl- and 2-heterylvinyl-substituted perchlorates either form 4-oxo-1,3-benzoxazines or undergo hydrogenation to arylor heterylethyldihydrobenzoxazinones.     

Complexes of sodium and lithium borohydrides with macrocyclic polyethers

A method for the synthesis of complexes of sodium and lithium borohydrides with crown ethers is proposed. The complexes of sodium borohydride with benzo-15-crown-5, 4′-aminobenzo-15-crown-5, dibenzo-18-crown-6, and diaza-18-crown-6 and the complexes of lithium borohydride with benzo-15-crown-5 and dibenzo-18-crown-6 are synthesized. These complexes can be used for the preparation of hydrogen in their reactions with methanol. The complex formation does not affect the purity of hydrogen formed.     

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.     

Selective Reductions with Sodium Borohydride in Dimethyl Sulphoxide with Added Metal Salts

Sodium borohydride in Dimethyl Sulphoxide in the presence of added metal salts selectively reduces aldehydes in the presence of ketones and converts α,β -unsaturated ketones to the corresponding unsaturated alcohols.     

New catalysts for borohydride electro-oxidation using Rh porphyrins

New borohydride electro-oxidation catalysts for direct borohydride fuel cells were developed. These catalysts use rhodium porphyrins on carbon black. The overpotential for borohydride electro-oxidation is much lower than that for a gold electrode. Hydrogen generation by the hydrolysis of borohydride is suppressed much more with rhodium porphyrin catalysts than with a platinum catalyst. Rh porphyrins oxidized borohydride below 0 V vs. a reversible hydrogen electrode. The measurement of hydrogen generation after electrolysis indicates that the apparent number of electrons transferred in rhodium octaethylporphyrin exceeds 7.     

双核双金属酞菁(FeCoPc_2)阴极催化直接硼氢化物燃料电池

研制一种无膜型直接硼氢化物燃料电池(DBFC).循环伏安测试发现FeCoPc2在碱性溶液中对氧还原具有催化作用.稳态极化曲线表明,由于FeCoPc2结构具有较强的共轭效应以及Fe、Co在催化中的协同作用使它比FePc、CoPc具有更强的氧还原能力,并获得了110mW/cm2的功率密度.恒电流放电测试表明该燃料电池性能具有良好的稳定性.     

Stability of aqueous-alkaline sodium borohydride formulations

Stability of sodium borohydride in the form of concentrated solutions and suspensions and solids corresponding to a crystal hydrate in composition was studied. The effects of temperature, concentrations of sodium borohydride and alkali, and nature of alkali metal cation on the rate of sodium borohydride hydrolysis were studied.     

Thiol Esters in Organic Synthesis. XV. Reduction with Tetrabutylammonium Borohydride

Treatment of thiol esters with tetrabutylammonium borohydride in refluxing chloroform gave rise to the corresponding alcohols.     

脂肪族酯基选择性还原模型的建立

以不同烷基取代的酯作为模型, 对其进行NaBH4还原研究. 不同取代基酯的起始反应温度和半衰期显示出了明显的差别和一定的选择性; 用B3LYP/6-31++G(d,p)//HF/6-31G(d,p)方法计算得到的过渡态能量与实验得到的活化能变化趋势一致; 实验中观察到了奇偶碳效应; 对NaBH4还原酯基的溶剂影响进行了初步研究.     

Selective Reduction Among Carboxylic Acids with Sodium Borohydride

The selective reduction among carboxylic acids via acyloxyborohydrides derived from sodium borohydride and carboxylic acid mixture is demonstrated.     

Selective Reduction of Thiol Esters with Sodium Borohydride

A couple of years ago, Fujita and co-workers¹ reported the reduction of 2-thiazoline-2-thiol esters to alcohols with sodium borohydride in aqueous tetrahydrofuran. In connection with an ongoing synthetic project which requires the selective reduction of a stable acid derivative to the alcohol level in the presence of nitrile and ester groups, we examined the reaction of a variety of thiol esters with sodium borohydride. Our results show that the highly reactive (and thus unstable) 2-thiazoline-2-thiol ester derivatives are unnecessary and in fact various types of thiol esters are readily convertible to alcohols under mild conditions which do not effect the reduction of common acid derivatives such as nitrile, ester, and amide.     

Chemoselective reduction of aldehydes with zinc borohydride in tetrahydrofuran

A variety of structurally different aldehydes undergo chemoselectire reduction over ketones with zinc borohydride in tetrahydrofuran at −10°C to the corresponding alcohols.     

A Mild,Efficient Reduction of Sulfoxides with Ferric Chloride/Sodium Borohydride

Under mild conditions various sulfoxides were reduced to sulfides by combined reagent ferric chloride/ sodium borohydride in excellent yields.     

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.