シルバー触媒のスタイレンエポキシデーションにおけるセシウム促進
Ling Zhou1, Craig F Gorin, Robert J Madix
1School of Engineering and Applied Sciences, Harvard University, 29 Oxford Street, Cambridge, Massachusetts 02138, USA.
Journal of the American Chemical Society
|December 22, 2009
まとめ
シルバー触媒にセシウムを加えると,スタイレン酸化をスタイレン酸化物へと誘導する. セシウムは主要な中間物質を安定させ,表面構造を変更し,選択的エポキシデーションの触媒性能を向上させます.
科学分野:
- 表面科学とは,地表科学である.
- 異質なカタリシス
- 酸化化学 オキシデーション化学
背景:
- スタイレン酸化は,重要な産業プロセスである.
- シルバー触媒は,スタイレンエポキシデーションに広く使用されています.
- 酸化反応における選択性を制御することは依然として課題です.
研究 の 目的:
- ステルエンの酸化選択性に対するセシウム吸収の効果を調査する (Ag110).
- 反応中間物質の安定化と表面構造の変更におけるセシウムの役割を明らかにする.
- 銀の触媒性能に対するセシウムの影響の顕微鏡的起源を理解するために.
主な方法:
- 表面構造分析のための低エネルギー電子 difraktion (LEED) について.
- 吸附と反応経路を研究するために,温度プログラム脱吸収 (TPD)
- 電子構造の決定のためのX線光電子スペクトロスコーピー (XPS) (暗示).
主要な成果:
- セシウム添加は,ステレン酸化をフェニルアセタルデヒド/フェニルケテンからステレン酸化物へと誘導する.
- セシウムは,オックスメタラサイクル中間物質を安定させ,望ましくない製品への変換を防止します.
- 低セシウムの覆いは,Agの欠落した列の再構築 (1 x 2) と表面酸化物 (3 x 5) を誘導する.
- Ag(111) マイクロファセットの表面酸化物構造は,拡張されたAg(111) 表面の反応性を模倣しています.
結論:
- セシウムは,電子プロモーターではなく,構造指向剤として,スタイレンエポキシデーションでAg110で作用する.
- 表面の再構築と特定の表面酸化物相の形成は,セシウムの選択性への影響の鍵です.
- これらの発見は,酸化反応のための選択銀触媒の設計に関する洞察を提供します.
さらに関連する動画
09:45Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene
Published on: March 20, 2017
06:46Facile Preparation of (2Z,4E)-Dienamides by the Olefination of Electron-deficient Alkenes with Allyl Acetate
Published on: June 21, 2017
関連する概念動画
02:57Sharpless Epoxidation
The conversion of allylic alcohols into epoxides using the chiral catalyst was discovered by K. Barry Sharpless and is known as Sharpless epoxidation. The use of a chiral catalyst enables the formation of one enantiomer of the product in excess. This chiral catalyst is mainly a chiral complex of titanium tetraisopropoxide and tartrate ester (specific stereoisomer). The stereoisomer used in the chiral catalyst dictates the formation of the enantiomer of the product. In other words, the use of...
01:17Thermal Electrocyclic Reactions: Stereochemistry
The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
02:24Acid-Catalyzed Ring-Opening of Epoxides
Epoxides that are three-membered ring systems are more reactive than other cyclic and acyclic ethers. The high reactivity of epoxides originates from the strain present in the ring. This ring strain acts as a driving force for epoxides to undergo ring-opening reactions either with halogen acids or weak nucleophiles in the presence of mild acid. The acid catalyst converts the epoxide oxygen, a poor leaving group, into an oxonium ion, a better leaving group, making the reaction feasible. The...
03:00Preparation of Epoxides
Overview
Epoxides result from alkene oxidation, which can be achieved by a) air, b) peroxy acids, c) hypochlorous acids, and d) halohydrin cyclization.
Epoxidation with Peroxy Acids
Epoxidation of alkenes via oxidation with peroxy acids involves the conversion of a carbon–carbon double bond to an epoxide using the oxidizing agent meta-chloroperoxybenzoic acid, commonly known as MCPBA. Since the O–O bond of peroxy acids is very weak, the addition of electrophilic oxygen of peroxy acids to...
Epoxides result from alkene oxidation, which can be achieved by a) air, b) peroxy acids, c) hypochlorous acids, and d) halohydrin cyclization.
Epoxidation with Peroxy Acids
Epoxidation of alkenes via oxidation with peroxy acids involves the conversion of a carbon–carbon double bond to an epoxide using the oxidizing agent meta-chloroperoxybenzoic acid, commonly known as MCPBA. Since the O–O bond of peroxy acids is very weak, the addition of electrophilic oxygen of peroxy acids to...
02:43E2 Reaction: Stereochemistry and Regiochemistry
Elimination reactions of alkyl halides can yield one or more alkenes depending on the specific regiochemical and stereochemical considerations. While the regiochemistry of the reaction governs the location of the double bond in the product, the stereochemical requirements often influence the geometry.
When a substrate with two different β hydrogens undergoes an E2 elimination, the presence of a strong base can yield two regioisomeric alkenes. The more-substituted alkene is the major product and...
When a substrate with two different β hydrogens undergoes an E2 elimination, the presence of a strong base can yield two regioisomeric alkenes. The more-substituted alkene is the major product and...
02:17Reduction of Alkenes: Asymmetric Catalytic Hydrogenation
Catalytic hydrogenation of alkenes is a transition-metal catalyzed reduction of the double bond using molecular hydrogen to give alkanes. The mode of hydrogen addition follows syn stereochemistry.
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...