歪んだオックスメタラサイクルによって阻害されるエチンのエポキシデーション選択性:Ag表面酸化物に関するDFT研究
Marie-Laure Bocquet1, David Loffreda
1Laboratoire de chimie, UMR CNRS 5182, Ecole Normale Supérieure de Lyon, 46 Allée d'Italie, F-69364 Lyon, Cedex 07, France. mbocquet@ens-lyon.fr
Journal of the American Chemical Society
|December 8, 2005
まとめ
この研究では,銀酸化物表面でのエチンの酸化において,エチンエポキシドよりもアセタルデヒドが優れていることが明らかになりました. この選択性は,重要な中間物質のユニークな形状の柔軟性に関連しており,効率的なアセタルデヒド生産を可能にします.
科学分野:
- 表面化学について
- カタリシス カタリシス カタリシス
- コンピューティング・ケミストリー
背景:
- エチンの酸化は,貴重な化学物質の生産に不可欠です.
- 金属酸化物表面の反応経路を理解することは,触媒設計の鍵です.
- 以前の研究は,銀の低カバー酸素アダトムに焦点を当てていた.
研究 の 目的:
- Ag111の表面酸化フェーズp{\displaystyle p{\displaystyle p}4x4}上で競合するエチンの酸化経路を調査する.
- アセトアルデヒドとエチネエポキシドの選択性を左右する要因を解明する.
- 現実的な条件下で選択性を予測するための運動モデルを開発する.
主な方法:
- 反応経路をモデル化するための密度関数理論 (DFT) 計算.
- 中間構造とエネルギーバリアの分析.
- DFTの結果を組み込む運動モデルの開発.
主要な成果:
- アセタルデヒド (AcH) 形成は,一般的なオックスメタラサイクル中間体 (OMME) を介して2kcal/molでエチンエポキシド (EO) よりも好ましい.
- 酸化物の再生経路は,速度を制御しない.
- 運動モデルは,シミュレートされた触媒条件下でのAcHの96%の選択性を予測しています (600 K, 1 atm エチネ, 1 atm 酸素).
結論:
- 超薄な酸化物添加層の弾力性は,歪んだOMME構造を可能にし,AcH形成を好む.
- 低エステンエポキシドの選択性は,OMME中間物質の形状障壁に起因する.
- EOに対するセレクティブ・リング・クローゼーションには,より高いエネルギーのコンフォメーション・インバーションが必要です.
関連する概念動画
02:44Oxidation of Alkenes: Syn Dihydroxylation with Osmium Tetraoxide
Alkenes are converted to 1,2-diols or glycols through a process called dihydroxylation. It involves the addition of two hydroxyl groups across the double bond with two different stereochemical approaches, namely anti and syn. Dihydroxylation using osmium tetroxide progresses with syn stereochemistry.
02:04Oxidation of Alkenes: Anti Dihydroxylation with Peroxy Acids
Diols are compounds with two hydroxyl groups. In addition to syn dihydroxylation, diols can also be synthesized through the process of anti dihydroxylation. The process involves treating an alkene with a peroxycarboxylic acid to form an epoxide. Epoxides are highly strained three-membered rings with oxygen and two carbons occupying the corners of an equilateral triangle. This step is followed by ring-opening of the epoxide in the presence of an aqueous acid to give a trans diol.
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...
02:57Sharpless 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...
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...
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.