ハロアニリンの光化学におけるホモリチス対ヘテロリチス経路
Mauro Freccero1, Maurizio Fagnoni, Angelo Albini
1Department of Organic Chemistry, University of Pavia, via Taramelli 10, 27100 Pavia, Italy.
Journal of the American Chemical Society
|October 23, 2003
まとめ
ハロアニリンの光化学は,溶媒とハロゲン型に依存する. 極性溶媒はC-ClおよびC-Br結合の効率的な異解性分裂を可能にし,プロティック溶媒は光生成されたフェニルカチオンによるC-F結合の分裂を容易にする.
科学分野:
- フォトケミストリー フォトケミストリー
- 有機化学 オーガニック・ケミストリー
- 物理化学 物理化学
背景:
- 4-ハロアニリンと4-ハロ-N,N-ジメチラニリンの光化学は,様々な溶媒の極性において研究されています.
- 反応はトリプレート状態から開始され,ハロゲンと溶媒の環境によって異なる反応性が観察されます.
研究 の 目的:
- ハロアニリンの光化学の溶剤およびハロゲン依存メカニズムを解明する.
- ホモリティックおよびヘテロリティック解離経路の興奮トリプレート状態とエネルギープロフィールを特徴付ける.
- 合成および環境アプリケーションのための光生成フェニルカチオンによる効率的な脱ハロゲン化の条件を定義する.
主な方法:
- 光物理実験とフラッシュ光分解を用いて,反応動力学と量子産量を研究した.
- UB3LYP/6-31G ((d) レベルでの計算研究で,トリプル状態とエネルギー景観が特徴付けられました.
- アリルトリメチルシランを用いた選択捕獲実験では,フェニルカチオンの形成をモニターした.
主要な成果:
- 非極性溶媒の反応性は低く,極性媒介では塩素およびフッ素誘導体の量子収量が大幅に増加しています.
- ホモリティックなC-X結合の割れ方はエンドサーミックであり,C-ClとC-Brのヘテロリティックな割れ方はアセトニトリルではエクソサーミックである.
- 極性溶剤で効率的な異解性脱塩化 (Phi = 0.77 in MeCN) が起こり,プロティック溶剤 (Phi = 0.48 in MeOH) のみで効率的な脱フッ素化があった.
結論:
- 溶媒の極性とハロゲン同一性は,脱ハロゲン化の効率とメカニズム (ホモリチス対ヘテロリチス) を決定的に決定します.
- 光生成されたフェニルカチオンは,合成方法論で効果的に利用できます.
- これらの光化学的経路の理解は,ハロゲン化芳香質汚染物質の分解とフッ素化薬物の光毒性に対処するために重要である.
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