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271.
Photochemical Synthesis of Ultrafine Cubic Boron Nitride Nanoparticles under Ambient Conditions
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Hui Liu Peng Jin Yan‐Ming Xue Cunku Dong Xiang Li Cheng‐Chun Tang Xi‐Wen Du 《Angewandte Chemie (International ed. in English)》2015,54(24):7051-7054
Cubic boron nitride (c‐BN) is a super‐hard material whose hardness increases dramatically with decreasing size. However, c‐BN nanoparticles (NPs) with sizes less than 10 nm have never been obtained. Herein we report a simple strategy towards the synthesis of ultrafine c‐BN NPs with an average size of 3.5 nm. The method, under ambient conditions, exploits a laser‐induced photochemical effect and employs dioxane solution of ammonia borane (AB) as a liquid target. Meanwhile, total dehydrogenation of AB is realized by laser irradiation. Therefore, this approach shows great potential for the preparation of super‐hard NPs as well as controllable dehydrogenation. 相似文献
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273.
William K. Holley George E. Ryschkewitsch 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):271-284
Abstract The first borane adducts of N-alkyl and N-aminotriphenylphosphoranimines, Ph3P[dbnd]N—R, were prepared by two different general synthetic methods. The first method involved displacement of THF (tetrahydofuran) from THF-borane by the free imines, and the second employed the reaction of LiBH4 with iminium bromides, Ph3P[dbnd]N(R)HBr, in diethyl ether. Imine boranes, Ph3P[dbnd]N(R)BH3, were synthesized where R [dbnd] methyl, ethyl, n-propyl, isopropyl, isobutyl, t-butyl. dimethylamino, phenylamino, and methyl, phenylamino as the nitrogen attached groups. Symmetrical boron cations, (Ph3P[dbnd]NR)2, BH2 +, where R = methyl, ethyl, and n-propyl, were synthesized by displacement of iodide from in-situ generated iodoborane adducts, Ph3P[dbnd]N(R)BH2I, by the free imines. An attempt to form an unsymmetrical boron cation from (CH3)3 NBH2I and Ph, P[dbnd]N(n-C3H7) resulted only in a mixture of the corresponding symmetrical boron cations. Physical, chemical and spectral properties of the borane adducts and boron cations, namely thermal and hydrolytic stabilities, infrared and NMR data are presented. Oxidative and reductive stabilities of the boron cations were studied. The borane adducts can be chlorinated with either HCI or Ph3CCI. Relative base strengths of some imines were determined by following the exchange of BH3 between borane adducts of (CH3)3 N or 4- (CH3)C5H4 N and the imines via NMR. 相似文献
274.
新型手性膦-硼烷配合物的合成及其在不对称催化氢化反应中的应用 总被引:2,自引:0,他引:2
以苯乙烯为原料,通过Sharpless不对称二羟基化反应合成高对映体纯的苯基乙二醇,经酯化、亲核取代反应转化为手性膦-硼烷配合物.后者克服了有机膦配体易氧化的缺点,其制备过程简单,易于提纯,在空气中可长期保存.该手性膦-硼烷配合物在四氟硼酸-甲醚的存在下解络,生成的自由膦不经分离直接与[Rh(COD)Cl]2作用生成手性膦-铑原位催化剂.在α-乙酰氨基肉桂酸甲酯的不对称氢化反应中,转化率为100%,对映选择性88%e.e. 相似文献
275.
S.D. MoreM.N. Meshram S.P. WankhedeP.L. Muthal S.M. DhopteS.V. Moharil 《Physica B: Condensed Matter》2011,406(5):1178-1181
Phase pure LiCaPO4 was prepared by following a specific procedure involving several annealing steps, not exceeding the temperature 800 °C at any stage. Luminescence of Cu+ and Eu2+ activators is studied. A single emission band is observed for both the activators in contrast to two bands reported in earlier literature. It is argued that in the earlier work the samples were contaminated by alpha Ca3(PO4)2 phase, which could be responsible for these differences. Thermoluminescence of LiCaPO4:Eu2+ was found to be four times more than the commercial phosphor LiF-TLD 100. Phase pure LiCaPO4 shows interesting luminescence properties different than those reported in the literature and hence it should prove fruitful to probe this material in future. 相似文献
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278.
《Analytical letters》2012,45(10):2115-2126
ABSTRACT A flow injection catalytic method is proposed for determination of trace vanadium based on its catalytic action on a new indicator reaction between Victoria blue B (VBB) and potassium bromate in the presence of citric acid as an activator and in dilute sulfuric acid medium. The reaction is monitored spectrophotometrically by measuring the decrease in absorbance of VBB injected at the maximum absorption wavelength of 618 nm. The detection limit is 0.5 ng ml?1 and is independent of the initial valence state of vanadium. The relative standard deviation is 1.5% obtained from 11 standard solutions each containing 40 ng ml?1 of vanadium. The sampling rate is about 15 samples per hour. This method is very simple and has been applied to the determination of trace vanadium in some natural waters with recoveries of 93-103%. 相似文献
279.
Ana Martín‐Sómer Dr. Al Mokhtar Lamsabhi Prof. Manuel Yáñez Dr. Juan Z. Dávalos Javier González Rocío Ramos Dr. Jean‐Claude Guillemin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(49):15699-15705
The gas‐phase acidity of a series of amine–borane complexes has been investigated through the use of electrospray mass spectrometry (ESI‐MS), with the application of the extended Cooks kinetic method, and high‐level G4 ab initio calculations. The most significant finding is that typical nitrogen bases, such as aniline, react with BH3 to give amine–borane complexes, which, in the gas phase, have acidities as high as those of either phosphoric, oxalic, or salicylic acid; their acidity is higher than many carboxylic acids, such as formic, acetic, and propanoic acid. Indeed the complexation of different amines with BH3 leads to a substantial increase (from 167 to 195 kJ mol?1) in the intrinsic acidity of the system; in terms of ionization constants, this increase implies an increase as large as fifteen orders of magnitude. Interestingly, this increase in acidity is almost twice as large as that observed for the corresponding phosphine–borane analogues. The agreement between the experimental and the G4‐based calculated values is excellent. The analysis of the electron‐density rearrangements of the amine and the borane moieties indicates that the dative bond is significantly stronger in the N‐deprotonated anion than in the corresponding neutral amine–borane complex, because the deprotonated amine is a much better electron donor than the neutral amine. On the top of that, the newly created lone pair on the nitrogen atom in the deprotonated species, conjugates with the BN bonding pair. The dispersion of the extra electron density into the BH3 group also contributes to the increased stability of the deprotonated species. 相似文献
280.
Silicone surfactants are widely used in commerce because of the unusual surface activity when compared with fluorocarbon or hydrocarbon surfactants. However, most silicone surfactants are comprised of ill-defined mixtures, which preclude the development of an understanding of structure-surface activity relationships. Herein, we report a synthetic strategy that permits exquisite control over silicone structure by using the B(C(6)F(5))(3)-catalyzed condensation of hydro- and alkoxysilanes. Six different, precise hydrophobes were then mated to hydrophilic poly(oxyethylene)s of three different molecular weights by a metal-free click cyclization to generate a library of explicit silicone surfactants. These compounds were calculated to have a relatively linear value range of the hydrophilic-lipophilic balance, ranging from about 8 to about 15. The solubility of some of the compounds was too low to measure a critical micelle concentration (CMC). The others exhibited a broad range of surface tension values at the CMC that depend both on the length of the hydrophilic tail and, more importantly, the nature of the hydrophobic head group. Subtle distinctions in surfactant-related properties, which can be attributed to the three-dimensional structures, can be seen for compounds with comparable numbers of hydrocarbons and silicon groups. 相似文献