活化硼氢化钠在有机合成中的应用

介绍了有机合成反应中NaBH4与添加剂共同作用的反应,其中包括烯烃和炔烃的还原,羧酸的还原,氨基酸及其衍生物的还原,羧酸酯的还原,酰胺的还原,腈基的还原,酰氯的还原,硝基化合物的还原,醛酮的还原等。与LiAIH4的还原相比较,其反应条件更温和,反应过程更安全、易操控、易放大。     

硼氢化钠在羧酸及其衍生物还原中的应用

硼氢化钠可以很容易的将醛和酮还原为相应的醇,甚至可以在水介质中等当量的反应,但在温和条件下却很难将羧酸、羧酸酯、酰胺、酰氯和氨基酸及其衍生物还原,往往需要大大过量而且长时间回流,即使这样收率也很低.通过加入甲醇、路易斯酸、碘等修饰剂可以显著的提高硼氢化钠的活性,从而将羧酸及其衍生物还原为相应的醇.介绍了硼氢化钠还原羧酸及其衍生物的机理,综述了硼氢化钠在羧酸、羧酸酯、酰胺、酰氯和氨基酸及其衍生物还原中的应用.     

硼氢化钠在有机合成中的新应用

NaBH_4是一种高选择性和异常温和的亲核还原试剂。在一般情况下,它只能还原醛、酮和酰氯,而对其他宫能团不起作用。因而它的应用范围在某种程度上受到了限制。但NaBH_4价廉,易于处理,使用方便,故已成为有机合成用的重要试剂,受到了有机化学家的普遍重视。为了进一步扩大这一试剂的应用范围,许多化学家一直在致力于其还原性能的改善。研究结果表明,影响NaBH_4还原性能的因素主要有:反应温度、反应体系的pH值、溶剂、其他金属离子的作用、催化剂的作用、NaBH_4在介质中的分散程度以及底物分子中活性基团的影响。综合这些因素,已发展了许多提高NaBH_4还原能力的方法。     

芳香羧酸甲酯的硼氢化钠还原

采用NaBH_4-THF-甲醇体系将芳香羧酸甲酯进行还原反应2～5h得到相应的醇,收率为70%～90%。实验证明,NaBH_4-THF-甲醇体系对于芳香羧酸甲酯的还原具有很好的选择性。     

硼氢化钠的合成工艺及应用

论述了国内外硼氢化钠的合成工艺及该产品的应用。     

硼氢化钠固相还原反应的研究

通过硼氢化钠在固相条件下还原羰基化合物的研究,探索出硼氢化钠在固相条件下还原反应的规律：硼氢化钠在固相条件下,对孤立的羰基还原几乎是定量的,而对共轭的羰基化合物不起反应.     

环己基甲胺的硼氢化钠催化合成

采用硼氢化钠还原体系,考察了3种不同原料的合成路线,实现了标题化合物的制备。建立了以环己酮为原料,经Knoevenagel反应、还原制备的路线。通过对不同的催化剂、催化剂用量、反应温度、还原试剂等对反应产率影响的研究与考察,确定了标题化合物的最佳合成工艺,总收率83.6%,结构经核磁、质谱确证。该方法具有原料廉价易得、操作简单、条件温和、收率好的优点。     

硼氢化钠在氢氧化钠溶液中的密度和黏度

在291、298、303 K下,将不同质量的硼氢化钠固体分别加入到质量分数为13.35%的氢氧化钠溶液中,用密度瓶法和Ubbelohde黏度管分别测量溶液密度和黏度。根据溶液的密度计算硼氢化钠溶液的表观摩尔体积,讨论浓度的变化对混合溶液密度的影响,可知随着硼氢化钠浓度的加大,密度逐渐减小。根据溶液黏度数据和BH4- 半径计算了不同温度下硼氢化钠和BH4- 的黏度系数B,结果表明,BH4- 是结构促进型离子,且随着温度升高,黏度系数B逐渐减小。     

Pd-Ag/C在硼氢化钠电氧化反应中的电化学行为

采用化学还原法制备了不同原子比的Pd-Ag/C催化剂。通过X射线衍射（XRD）表征了催化剂的晶体结构,并运用循环伏安、计时电流等电化学方法研究了其对硼氢化钠电氧化反应的催化活性。结果表明：适量Ag的掺杂不仅可以提高催化剂的催化活性,而且使得硼氢化钠电氧化反应过程中的转移电子数增加,其中Pd₇₅Ag₂₅/C的催化活性和转移电子数均为最高。     

Preparation of porous PVDF-NiB capsules as catalytic adsorbents for hydrogen generation from sodium borohydride

Porous poly(vinylidene fluoride) (PVDF)-NiB capsules were prepared by phase inversion of PVDF, nickel salt and sodium borohydride (NaBH₄) mixtures in water. During the process, nickel salt was reduced to NiB particles by NaBH₄, and the excess NaBH₄ was hydrolyzed to produce hydrogen gas bubbles which aided the formation of the large holes inside the porous capsules. It was proved that the porous capsules can adsorb about 33 wt.% NaBH₄ in THF/NaBH₄ solution for about 4 h. Most of NiB particles were attached on the surface of the porous capsules with inside holes according to the observation of scanning electron microscopy (SEM) and EDS. The special structure of the capsules was successfully used as catalysts and container simultaneously for hydrogen production via catalytic hydrolysis of NaBH₄ in aqueous solution.     

LiCoO2-based catalysts for generation of hydrogen gas from sodium borohydride solutions

The catalytic performance of lithium cobaltite, LiCoO₂, in sodium borohydride hydrolysis has been studied and compared with catalytic properties of Co₃O₄, CoCl₂ and Co(NO₃)₂. Activation times and observed H₂ generation rates were found dependent on the chemical nature and dispersion of the catalysts, as well as on the reaction temperature. The magnetic susceptibility method was used to demonstrate that all studied cobalt compounds, including cobalt oxides and soluble salts, are being reduced under catalytic conditions to form catalytically active cobalt boride phases. Impregnating LiCoO₂ with Pt and Rh chlorides increases only the initial catalytic activity, which then quickly declines during cyclic stability tests and in just a few cycles approaches that of the starting LiCoO₂ material.     

高效、高选择性还原剂硼氢化锌在有机合成研究中的应用

介绍了硼氢化锌的制备及其对醛、酮、羧酸及其衍生物、亚胺、腈、叠氮化合物、环氧化合物、烯 (炔 )等的高效、高选择性还原。     

硼氢化钠水解制氢技术研究进展

随着石化能源的日益枯竭,氢能成为解决当前能源危机的一种新能源。制氢的方式多种多样,由于金属氢化物在储氢容量上具有其他材料无法比拟的优势,因此,金属氢化物制氢技术得到了迅速发展。硼氢化钠就是一种典型的金属氢化物,硼氢化钠水解制氢技术作为一种安全、方便的新型制氢技术,已成为当前燃料电池氢源研究中的热点之一。介绍了硼氢化钠制氢原理;综述了硼氢化钠水解制氢技术的优点、影响产氢速率的因素;对硼氢化钠制氢技术的装置进行了举例说明;指出了目前此技术所存在的问题;概述了此技术的应用与发展前景。     

Cr掺杂的Co-B非晶态合金的制备及催化硼氢化钠水解制氢

采用化学还原法制备了三元非晶态Co-Cr-B纳米催化剂。采用透射电镜（TEM）、扫描电镜（SEM）、X射线衍射仪（XRD）等测试方法对催化剂的形貌、结构、成分做了表征。通过排水法进行NaBH₄溶液水解产氢反应,测量了催化剂的催化性能。结果表明,当掺杂少量的Cr时,催化剂的粒径明显减小,比表面积明显增大,催化剂的性能提高。过量的Cr会导致出现过多的氧化物和Cr ³⁺,覆盖了催化剂表面活性位点,降低催化剂的性能。当Cr与Co物质的量比为0.005时,催化剂性能最佳。与纯Co-B相比,其对硼氢化钠水解产氢速率提高了2倍。此外,研究了催化剂用量、NaBH₄浓度、反应温度、NaOH浓度等因素对NaBH₄溶液水解产氢反应的影响。     

Cyclic voltammetry investigation of borohydride oxidation at a gold electrode

Sodium borohydride (NaBH₄) is receiving increasing attention during the last decade regarding its possible application in energy systems. NaBH₄ has the dual potential of generating hydrogen on demand or being directly oxidised in a direct borohydride fuel cell (DBFC). Progress on DBFCs relies on the development of systematic studies to allow a more comprehensive characterisation of the borohydride (BH₄⁻) oxidation process. In this paper, cyclic voltammetry (CV) is applied to study systematically the BH₄⁻ electrooxidation on a gold (Au) disc macroelectrode in 2 mol l⁻¹ NaOH solutions. Voltammograms are obtained for various NaBH₄ concentrations [0.03-0.12 mol l⁻¹], working temperatures [25-65 °C], and potential scan rates [0.02-20 V s⁻¹], over a wide potential range [−1.0-0.8 V vs. SCE]. Modelling of CV data indicates that BH₄⁻ oxidation on Au electrode follows a first irreversible electrochemical pathway via the direct BH₄⁻ oxidation reaction, involving nearly 8 mol of exchanged electrons per mole of BH₄⁻. A second pathway, at higher potentials, concerns a yet undetermined oxidation mechanism in the partially oxidised Au surface which, in a third pathway, is reactivated, allowing an electrochemical-adsorption mechanism to take place. Relevant parameters such as transfer coefficient, kinetic rate constant, standard rate constant, charge transfer activation energy, and number of exchanged electrons are estimated. The BH₄⁻ oxidation reaction on Au is found to be first order with respect to BH₄⁻.     

NaBH4溶液催化制氢的阴离子效应研究

研究了Cl-和NO3-阴离子对NaBH4溶液现场制氢反应的影响,发现在制氢反应过程中存在着生成金属硼化物和生成金属氢氧化物的竞争反应.当溶液中阴离子为Cl-时,金属离子在催化NaBH4溶液制氢反应时将与硼结合,促使其活化为高活性金属硼化物,能有效促进制氢反应;当溶液中的阴离子为NO3-时,将诱导金属离子生成没有催化活性的金属氢氧化物,抑制制氢反应.     

Schlesinger法合成硼氢化钠工艺条件及优化途径

目前工业化合成硼氢化钠的工艺有Schlesinger法和Bayer法,而Schlesinger法是工业化合成硼氢化钠应用最广的工艺,其关键步骤为氢化钠和硼酸三甲酯的合成。本文一方面从氢化钠的合成、硼酸三甲酯的合成及硼氢化钠的合成3个方面详细论述了Schlesinger法合成工艺进展情况;并指出目前方法存在的问题,如采用油液分散金属钠法合成的氢化钠活性差,制约了氢化钠的应用,硼酸三甲酯工业合成过程中过多使用浓硫酸造成环境严重污染。另一方面对Schlesinger法工艺改进提出了几点设想,如企业全流程合成硼氢化钠可节约外购成本和仓储成本;硼酸三甲酯的合成取代浓硫酸的应用,提纯采用盐析的方法均可以减轻环境污染;硼氢化钠水解过程中采用稀液碱溶液代替淡水,可避免硼氢化钠水解,提高产品收率。     

Electrooxidation of borohydride on platinum and gold electrodes: implications for direct borohydride fuel cells

The electrochemical oxidation of BH₄⁻ in 2 M NaOH on Pt and Au (i.e. catalytic and non-catalytic electrodes, respectively, for BH₄⁻ hydrolysis accompanied by H₂ evolution) has been studied by cyclic voltammetry, chrono-techniques (i.e., potentiometry, amperometry, coulometry) and electrochemical impedance spectroscopy. In the case of Pt the cyclic voltammetry behaviour of BH₄⁻ is influenced by both, the catalytic hydrolysis of BH₄⁻ yielding H₂ (followed by electrooxidation of the latter at peak potentials between −0.7 and −0.9 V versus Ag/AgCl, KCl_std) and direct oxidation of BH₄⁻ at more positive potentials, i.e., between −0.15 and −0.05 V. Thiourea (TU, 1.5×10⁻³ M) was an effective inhibitor of the catalytic hydrolysis associated with BH₄⁻ electrooxidation on Pt. Therefore, in the presence of TU, only the direct oxidation of BH₄⁻ has been detected, with peak potentials between −0.2 and 0 V. It is proposed that TU could improve the BH₄⁻ utilization efficiency and the coulombic efficiency of direct borohydride fuel cells using catalytic anodes. The electrooxidation of BH₄⁻ on Pt/TU is an overall four-electron process, instead of the maximum eight electrons reported for Au, and it is affected by adsorbed species such as BH₄⁻ (fractional surface coverage ∼0.3), TU and possibly reaction intermediates.