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03:08Hydroboration-Oxidation of Alkenes
In addition to the oxymercuration–demercuration method, which converts the alkenes to alcohols with Markovnikov orientation, a complementary hydroboration-oxidation method yields the anti-Markovnikov product. The hydroboration reaction, discovered in 1959 by H.C. Brown, involves the addition of a B–H bond of borane to an alkene giving an organoborane intermediate. The oxidation of this intermediate with basic hydrogen peroxide forms an alcohol.
01:04Hydrogen Bonds
A hydrogen bond is formed when a weakly positive hydrogen atom already bonded to one electronegative atom (for example, the oxygen in the water molecule) is attracted to another electronegative atom from another polar molecule, such as water (H2O), hydrogen fluoride (HF), or ammonia (NH3). The huge electronegativity difference between the H atom (2.1) and the atom to which it is bonded (4.0 for an F atom, 3.5 for an O atom, or 3.0 for an N atom), combined with the very small size of an H atom...
00:26Hydrogen Bonds
Hydrogen BondsHydrogen bonds are weak attractions between atoms that have formed other chemical bonds. One of these atoms is electronegative, like oxygen, and has a partial negative charge. The other is a hydrogen atom that has bonded with another electronegative atom and has a partial positive charge.Hydrogen Bonds Control the World!Because hydrogen has very weak electronegativity when it binds with a strongly electronegative atom, such as oxygen or nitrogen, electrons in the bond are...
02:47Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation
Introduction
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
01:32Aldehydes and Ketones with HCN: Cyanohydrin Formation Overview
Cyanohydrins are compounds that contain –CN and –OH groups on the same carbon atom. They are formed by the nucleophilic addition of the cyanide ions to the carbonyl group. Cyanide ions are highly basic and nucleophilic and can be generated from HCN under aqueous conditions. However, since HCN is a weak acid, the number of cyanide ions generated is very small. Hence, a small amount of base or KCN/NaCN is added to HCN to increase the concentration of the cyanide ions in the reaction mixture.
02:36Regioselectivity and Stereochemistry of Hydroboration
A significant aspect of hydroboration–oxidation is the regio- and stereochemical outcome of the reaction.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
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Supercritical Nitrogen Processing for the Purification of Reactive Porous Materials
Published on: May 15, 2015
ヒドラジンボラン:有望な水素貯蔵材料である.
Thomas Hügle1, Moritz F Kühnel, Dieter Lentz
1Institut für Chemie und Biochemie, Anorganische Chemie, Freie Universität Berlin, Fabeckstrasse 34-36, 14195 Berlin, Germany.
Journal of the American Chemical Society
|May 13, 2009
まとめ
研究者は,ヒドラジンボランを強化した.
科学分野:
- マテリアルサイエンス 材料科学
- 化学工学化学工学とは
背景:
- ハイドラジンボランは,水素貯蔵のための有望な材料です.
- 水素の放出運動と容量の改善は,実用的なアプリケーションにとって極めて重要です.
研究 の 目的:
- ヒドラジンボランの水素貯蔵能力を高めるために.
- 水素の放出に対するリチウム水化物添加の効果を調査する.
主な方法:
- ヒドラジンボランに等分量リチウム水素を添加する.
- 質量 % H を用いて水素含有量の分析.
- 様々な温度で水素の放出行動を研究する.
主要な成果:
- この混合物により,貯蔵容量は14.8 wt % H ((2)) 達成された.
- 優れた水素放出率が観察されました.
- 最適な水素の放出は100~150°Cの間に発生する.
結論:
- リチウム水素の等分添加は,ヒドラジンボランの水素貯蔵性能を大幅に改善します.
- 改造された材料は,適度な温度で効率的な水素放出を提供し,実用的な用途に適しています.
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