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Borohydride
Borohydride refers to the anion , which is also called tetrahydroborate, and its salts. Borohydride or hydroborate is also the term used for compounds containing , where ''n'' is an integer from 0 to 3, for example cyanoborohydride or cyanotrihydroborate and triethylborohydride or triethylhydroborate . Borohydrides find wide use as reducing agents in organic synthesis. The most important borohydrides are lithium borohydride and sodium borohydride, but other salts are well known (see Table). Tetrahydroborates are also of academic and industrial interest in inorganic chemistry. History Alkali metal borohydrides were first described in 1940 by Hermann Irving Schlesinger and Herbert C. Brown. They synthesized lithium borohydride from diborane : :, where M = Li, Na, K, Rb, Cs, etc. Current methods involve reduction of trimethyl borate with sodium hydride. Structure In the borohydride anion and most of its modifications, boron has a tetrahedral structure. The reactivity of the B−H ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sodium Borohydride
Sodium borohydride, also known as sodium tetrahydridoborate and sodium tetrahydroborate, is an inorganic compound with the formula Na BH4. This white solid, usually encountered as an aqueous basic solution, is a reducing agent that finds application in papermaking and dye industries. It is also used as a reagent in organic synthesis. The compound was discovered in the 1940s by H. I. Schlesinger, who led a team seeking volatile uranium compounds.Hermann I Schlesinger and Herbert C Brown (1945)Preparation of alkali metal compounds. US Patent 2461661. Granted on 1949-02-15; expired on 1966-02-15. Results of this wartime research were declassified and published in 1953. Properties The compound is soluble in alcohols, certain ethers, and water, although it slowly hydrolyzes. Sodium borohydride is an odorless white to gray-white microcrystalline powder that often forms lumps. It can be purified by recrystallization from warm (50 °C) diglyme. Sodium borohydride is soluble ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lithium Borohydride
Lithium borohydride (LiBH4) is a borohydride and known in organic synthesis as a reducing agent for esters. Although less common than the related sodium borohydride, the lithium salt offers some advantages, being a stronger reducing agent and highly soluble in ethers, whilst remaining safer to handle than lithium aluminium hydride.Luca Banfi, Enrica Narisano, Renata Riva, Ellen W. Baxter, "Lithium Borohydride" e-EROS Encyclopedia of Reagents for Organic Synthesis, 2001, John Wiley & Sons. . Preparation Lithium borohydride may be prepared by the metathesis reaction, which occurs upon ball-milling the more commonly available sodium borohydride and lithium bromide: : NaBH4 + LiBr → NaBr + LiBH4 Alternatively, it may be synthesized by treating boron trifluoride with lithium hydride in diethyl ether: : BF3 + 4 LiH → LiBH4 + 3 LiF Reactions Lithium borohydride is a stronger reducing agent than sodium borohydride. In mixtures of methanol and diethyl ether, lithium borohydride is a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lithium Triethylborohydride
Lithium triethylborohydride is the organoboron compound with the formula Li Et3 BH. Commonly referred to as LiTEBH or Superhydride, it is a powerful reducing agent used in organometallic and organic chemistry. It is a colorless or white liquid but is typically marketed and used as a THF solution. The related reducing agent sodium triethylborohydride is commercially available as toluene solutions. LiBHEt3 is a stronger reducing agent than lithium borohydride and lithium aluminium hydride. Preparation LiBHEt3 is prepared by the reaction of lithium hydride (LiH) and triethylborane (Et3B) in tetrahydrofuran (THF): :LiH + Et3B → LiEt3BH Its THF solutions are stable indefinitely in the absence of moisture and air. Reactions Alkyl halides are reduced to the alkanes by LiBHEt3. LiBHEt3 reduces a wide range of functional groups, but so do many other hydride reagents. Instead, LiBHEt3 is reserved for difficult substrates, such as sterically hindered carbonyls, as illustrated by reduc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sodium Cyanoborohydride
Sodium cyanoborohydride is the chemical compound with the formula Sodium, NaBoron, BHydrogen, H3cyanide, CN. It is a colourless salt, but commercial samples can appear tan. It is widely used in organic synthesis for the reduction of imines. The salt tolerates aqueous conditions. Use Owing to the presence of the electron-withdrawing cyanide substituent, [B(CN)H3]− is less reducing than is sodium borohydride, [BH4]−. As a mild reducing agent, it is used to convert imines to amines. It is especially favored for reductive aminations, wherein aldehydes or ketones are treated with an amine in the presence of this reagent: : R2CO + R'NH2 + NaBH3CN + CH3OH → R2CH-NHR' + "NaCH3OBH2CN" The reagent is typically used in excess. Selectivity is achieved at mildly basic solutions (pH 7–10). The reagent is ideal for reductive aminations ("Borch Reaction"). In conjunction with tosylhydrazine, sodium cyanoborohydride is used in the reductive deoxygenation of ketones. Structure and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cyanoborohydride
Sodium cyanoborohydride is the chemical compound with the formula Sodium, NaBoron, BHydrogen, H3cyanide, CN. It is a colourless salt, but commercial samples can appear tan. It is widely used in organic synthesis for the reduction of imines. The salt tolerates aqueous conditions. Use Owing to the presence of the electron-withdrawing cyanide substituent, [B(CN)H3]− is less reducing than is sodium borohydride, [BH4]−. As a mild reducing agent, it is used to convert imines to amines. It is especially favored for reductive aminations, wherein aldehydes or ketones are treated with an amine in the presence of this reagent: : R2CO + R'NH2 + NaBH3CN + CH3OH → R2CH-NHR' + "NaCH3OBH2CN" The reagent is typically used in excess. Selectivity is achieved at mildly basic solutions (pH 7–10). The reagent is ideal for reductive aminations ("Borch Reaction"). In conjunction with tosylhydrazine, sodium cyanoborohydride is used in the reductive deoxygenation of ketones. Structure and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hydrogen Storage
Hydrogen storage can be accomplished by several existing methods of holding hydrogen for later use. These include mechanical approaches such as using high pressures and low temperatures, or employing chemical compounds that release H2 upon demand. While large amounts of hydrogen are produced by various industries, it is mostly consumed at the site of production, notably for the synthesis of ammonia. For many years hydrogen has been stored as compressed gas or cryogenic liquid, and transported as such in cylinders, tubes, and cryogenic tanks for use in industry or as propellant in space programs. Interest in using hydrogen for on-board storage of energy in zero-emissions vehicles is motivating the development of new methods of storage, more adapted to this new application. The overarching challenge is the very low boiling point of H2: it boils around 20.268 K (−252.882 °C or −423.188 °F). Achieving such low temperatures requires expending significant energy. Es ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diborane
Diborane(6), generally known as diborane, is the chemical compound with the formula B2H6. It is a toxic, colorless, and pyrophoric gas with a repulsively sweet odor. Diborane is a key boron compound with a variety of applications. It has attracted wide attention for its electronic structure. Several of its derivatives are useful reagents. Structure and bonding The structure of diborane has D2h symmetry. Four hydrides are terminal, while two bridge between the boron centers. The lengths of the B–Hbridge bonds and the B–Hterminal bonds are 1.33 and 1.19 Å respectively. This difference in bond lengths reflects the difference in their strengths, the B–Hbridge bonds being relatively weaker. The weakness of the B–Hbridge compared to B–Hterminal bonds is indicated by their vibrational signatures in the infrared spectrum, being ≈2100 and 2500 cm−1 respectively. The model determined by molecular orbital theory describes the bonds between boron and the termina ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hermann Irving Schlesinger
Hermann Irving Schlesinger (October 11, 1882 – October 3, 1960) was an American inorganic chemist, working in boron chemistry. He and Herbert C. Brown discovered sodium borohydride in 1940 and both were involved in the further development of borohydride chemistry. Schlesinger studied chemistry at the University of Chicago from 1900 till 1905, where he received his Ph.D. for work with Julius Stieglitz. In the following two years, he worked with Walther Nernst at the University of Berlin; with Johannes Thiele at the University of Strasbourg; and with John Jacob Abel at Johns Hopkins University. From 1907 to 1960, he taught in the Department of Chemistry at the University of Chicago, rising through the ranks from instructor to full professor in 1922. He administered the department from 1922-1946, and retired in 1949. Schlesinger was honored by membership in the National Academy of Sciences and received the Priestley Medal, the highest honor of the American Chemical Society ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ammonia Borane
Ammonia borane (also systematically named amminetrihydridoboron), also called borazane, is the chemical compound with the formula H3NBH3. The colourless or white solid is the simplest molecular boron-nitrogen-hydride compound. It has attracted attention as a source of hydrogen fuel, but is otherwise primarily of academic interest. Synthesis Reaction of diborane with ammonia mainly gives the diammoniate salt 2B(NH3)2sup>+ (BH4)−. Ammonia borane is the main product when an adduct of borane is employed in place of diborane: :BH3(THF) + NH3 → BH3NH3 + THF Properties and structure The molecule adopts a structure similar to that of ethane, with which it is isoelectronic. The B−N distance is 1.58(2) Å. The B−H and N−H distances are 1.15 and 0.96 Å, respectively. Its similarity to ethane is tenuous since ammonia borane is a solid and ethane is a gas: their melting points differing by 284 °C. This difference is consistent with the highly polar natur ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Trimethyl Borate
Trimethyl borate is the organoboron compound with the formula B(OCH3)3. It is a colourless liquid that burns with a green flame. It is an intermediate in the preparation of sodium borohydride and is a popular reagent in organic chemistry. It is a weak Lewis acid (AN = 23, Gutmann-Beckett method). M.A. Beckett, G.C. Strickland, J.R. Holland, and K.S. Varma, "A convenient NMR method for the measurement of Lewis acidity at boron centres: correlation of reaction rates of Lewis acid initiated epoxide polymerizations with Lewis acidity", ''Polymer,'' 1996, 37, 4629–4631. doi: 10.1016/0032-3861(96)00323-0 Borate esters are prepared by heating boric acid or related boron oxides with alcohols under conditions where water is removed. Applications Trimethyl borate is the main precursor to sodium borohydride by its reaction with sodium hydride: :4 NaH + B(OCH3)3 → NaBH4 + 3 NaOCH3 It is a gaseous anti-oxidant in brazing and solder flux. Otherwise, trimethyl borate has no announced ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Boron
Boron is a chemical element with the symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the ''boron group'' it has three valence electrons for forming covalent bonds, resulting in many compounds such as boric acid, the mineral borax, sodium borate, and the ultra-hard crystals of boron carbide and boron nitride. Boron is synthesized entirely by cosmic ray spallation and supernovae and not by stellar nucleosynthesis, so it is a low-abundance element in the Solar System and in the Crust (geology), Earth's crust. It constitutes about 0.001 percent by weight of Earth's crust. It is concentrated on Earth by the water-solubility of its more common naturally occurring compounds, the borate minerals. These are mined industrially as evaporites, such as borax and kernite. The largest known deposits are in Turkey, the largest producer of boron minerals. Elemental b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sodium Dithionite
Sodium dithionite (also known as sodium hydrosulfite) is a white crystalline powder with a sulfurous odor. Although it is stable in dry air, it decomposes in hot water and in acid solutions. Structure The structure has been examined by Raman spectroscopy and single-crystal X-ray diffraction. The dithionite dianion has C symmetry, with almost eclipsed with a 16° O-S-S-O torsional angle. In the dihydrated form (), the dithionite anion has gauche 56° O-S-S-O torsional angle. A weak S-S bond is indicated by the S-S distance of 239 pm, which is elongated by ca. 30 pm relative to a typical S-S bond. Because this bond is fragile, the dithionite anion dissociates in solution into the O2sup>− radicals, as has been confirmed by EPR spectroscopy. It is also observed that 35S undergoes rapid exchange between S2O42− and SO2 in neutral or acidic solution, consistent with the weak S-S bond in the anion. Preparation Sodium dithionite is produced industrially by reduction of sulfur d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
