固体NMR光譜を用いたゼオライトH-BEAにおけるフェノールアルキレーションのメカニズム
Zhenchao Zhao1, Hui Shi1, Chuan Wan1
1Institute for Integrated Catalysis, Pacific Northwest National Laboratory , P.O. Box 999, Richland, Washington 99352, United States.
Journal of the American Chemical Society
|June 20, 2017
まとめ
固体酸の触媒はフェノールアルキル化を促進する. サイクロヘクサノールによるフェノールアルキル化は,サイクロヘクサノールジマーが反応性電粒子の形成を阻害するので,サイクロヘクサノールへの脱水が必要である.
科学分野:
- カタリシス
- 有機化学
- 物理化学
背景:
- フェノールアルキレーションは有機合成における重要な反応である.
- 反応メカニズムの理解は,触媒の開発に不可欠です.
- 固体酸の触媒は環境と分離の利点を提供します.
研究 の 目的:
- 固体酸触媒によるフェノールアルキル化反応の仕組みを解明する.
- 反応経路におけるサイクロヘクサノール脱水の役割を調査する.
- 反応性電気フィルムとその形成メカニズムを特定する.
主な方法:
- 反応を研究するために,in situ 13C MAS NMRスペクトロシーを使用した.
- 13C同位体ラベリングは,反応中間物質の追跡に使用された.
- 反応はアポラー溶剤 (デカリン) で行われた.
主要な成果:
- サイクロヘクサノールによるフェノールのアルキレーションは,サイクロヘクサノールからサイクロヘクセンへの脱水後にのみ行われます.
- サイクロヘキシルカルベニウムイオンは,反応性電気フィルムであり,サイクロヘキセンのプロトネーションによって形成されます.
- ブロンステッド酸部位のプロトン化されたサイクロヘクサノールジメは,サイクロヘクセンの吸収とカルベニウムイオン形成を阻害する.
- 陽子化されたサイクロヘクサノール二酸化物は,カルベニウムイオン形成なしに脱水する.
結論:
- 反応配列は反応性電粒子の形成によって決定される.
- サイクロヘクサノールの存在は,アルキル化に必要なカルベニウムイオン形成を阻害する.
- サイクロヘキシルフェニルエーテルの分子内再配置は有意なアルキル化経路ではない.
関連する概念動画
¹H NMR: Long-Range Coupling
2.8K
The coupling interactions of nuclei across four or more bonds are usually weak, with J values less than 1 Hz. While these are usually not observed in spectra, the presence of multiple bonds along the coupling pathway can result in observable long-range coupling.
In alkenes, spin information is communicated via σ–π overlap, as seen in allylic (four-bond) and homoallylic (five-bond) couplings. These coupling interactions are stronger when the σ bond is parallel to the alkene...
In alkenes, spin information is communicated via σ–π overlap, as seen in allylic (four-bond) and homoallylic (five-bond) couplings. These coupling interactions are stronger when the σ bond is parallel to the alkene...
2.8K
Nucleophilic Aromatic Substitution: Elimination–Addition
5.2K
Simple aryl halides do not react with nucleophiles. However, nucleophilic aromatic substitutions can be forced under certain conditions, such as high temperatures or strong bases. The mechanism of substitution under such conditions involves the highly unstable and reactive benzyne intermediate. Benzyne contains equivalent carbon centers at both ends of the triple bond, each of which is equally susceptible to nucleophilic attack. This 50–50 distribution of products is...
5.2K
¹H NMR of Conformationally Flexible Molecules: Temporal Resolution
1.3K
At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the...
1.3K
¹H NMR of Labile Protons: Temporal Resolution
1.8K
Protons bonded to heteroatoms such as nitrogen and oxygen exhibit a range of chemical shift values. This is due to the varying degree of hydrogen bonding between the proton and the heteroatom in other molecules. The extent of hydrogen bonding affects the electron density around the proton, thereby giving different chemical shift values for the protons in the proton NMR spectrum.
The –OH proton in alcohols typically appears in the range of δ 2 to 5 ppm but can vary depending on the specific...
The –OH proton in alcohols typically appears in the range of δ 2 to 5 ppm but can vary depending on the specific...
1.8K
NMR Spectroscopy of Benzene Derivatives
11.7K
Simple unsubstituted benzene has six aromatic protons, all chemically equivalent. Therefore, benzene exhibits only a singlet peak at δ 7.3 ppm in the 1H NMR spectrum. The observed shift is far downfield because the aromatic ring current strongly deshields the protons. Any substitution on the benzene ring makes the aromatic protons nonequivalent, and the protons split each other. The peak is, therefore, no longer a singlet and the splitting pattern and their associated coupling...
11.7K
¹H NMR: Complex Splitting
2.0K
A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied...
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied...
2.0K


