Name: alkyl halide reduction with tributyltin hydride
Uploaded: 2023-04-30T11:22:27.000Z
Duration: 1 min 26 s
Channel: JoVE

라디칼 치환 반응은 알칸과 알켄의 할로겐화에 유용합니다.
유사하게, 근본적인 치환은 알킬 할로겐화물의 수소 분해로 알려진 트리부틸틴 수소화물을 사용하여 알킬 할라이드에서 할로겐을 제거할 수 있습니다.
특히, 주석 수소화물은 Sn-H 결합이 약하고 할로겐화 알킬과 반응하여 할로겐을 수소로 대체하여 알칸과 할로겐화 주석을 형성 할 수 있습니다.
형성된 새로운 결합이 끊어진 결합보다 강하기 때문에 반응이 정력적으로 선호됩니다.
수소 분해의 메커니즘은 연쇄 반응을 따릅니다.
초기에 주석 수소화물은 빛의 존재 하에서 트리부틸틴 라디칼을 생성하고, 이는 유기 할로겐화물에서 할로겐을 추출하여 라디칼 중간체를 생성합니다.
다음으로, 라디칼 중간체는 주석 수소화물에서 수소를 추출하여 최종적으로 알칸과 트리부틸틴 라디칼을 형성하여 반응을 전파합니다. 
수소 분해에 대한 할로겐화 알킬의 반응성은 요오드화물에서 불소로 감소하며, 여기서 불화 알킬은 반응성이 없습니다.
특히, 염화알킬의 환원은 더 높은 농도의 트리부틸틴 라디칼을 필요로 하며, 이는 AIBN과 같은 개시제를 반응에 첨가함으로써 달성됩니다.

라디칼 치환: 트리부틸주석 수소화물을 사용한 알킬 할로겐화물의 수소화분해

Radical Substitution: Hydrogenolysis of Alkyl Halides with Tributyltin Hydride

라디칼 치환 반응은 분자에서 작용기를 제거하는 데 사용될 수 있습니다. 할로겐화 알킬의 수소화분해는 트리부틸주석 수소화물의 약한 Sn-H 결합이 할로겐화 알킬과 반응하여 알칸을 형성하는 반응 중 하나입니다. 여기서 Bu_3SnH 시약은 트리부틸틴 할라이드를 부산물로 생성합니다.

이 반응에서 형성된 결합은 끊어진 결합보다 강하여 에너지 측면에서 유리합니다. 이 반응은 Bu_3SnH가 빛이 있을 때 균일 분해를 거쳐 트리부틸틴 라디칼을 형성하는 라디칼 할로겐화 반응과 유사한 라디칼 사슬 메커니즘을 따릅니다. 이 라디칼은 할로겐화 알킬에서 할로겐을 추출하여 알킬 라디칼 중간체와 트리부틸주석 할로겐화물을 형성합니다. 라디칼 중간체는 트리부틸주석 수소화물에서 수소를 추가로 추출하고 알칸과 트리부틸주석 라디칼을 생성하여 반응을 전파합니다.

C-Br과 C-I 결합은 C-Cl 결합보다 약하기 때문에 일광은 브롬화 알킬과 요오드화물의 수소화 분해를 시작하기에 충분합니다. 대조적으로, 알킬 플루오라이드는 강한 C-F 결합으로 인해 반응성이 없습니다. Bu_3SnH를 사용한 알킬 염화물의 수소분해에는 반응 혼합물에 개시제를 첨가하여 얻어진 고농도의 트리부틸틴 라디칼이 필요합니다. AIBN은 60°C 이상에서 열적 균질분해를 거쳐 니트릴 안정화 라디칼을 형성하기 때문에 가장 널리 사용되는 개시제입니다. 이들 라디칼은 트리부틸주석 수소화물에서 수소를 추출하여 트리부틸주석 라디칼을 형성하고, 이것이 반응을 전파합니다.

<img alt="Figure1" src="/files/ftp_upload/12901/PT_12901_Figure%201.svg" style="text-align: center; height: 190px;">

 과산화물 라디칼은 반응성이 높고 유기 할로겐화물에서 수소를 추출하여 원치 않는 부반응을 일으킬 수 있기 때문에 과산화물은 개시제로 사용되지 않습니다.

라디칼 치환 반응은 분자에서 작용기를 제거하는 데 사용할 수 있습니다. 할로겐화 알킬의 수소 분해는 그러한 반응 중 하나이며, 여기서 ...

radical-substitution-hydrogenolysis-alkyl-halides-with-tributyltin

Education

교육

JoVE Core

Organic Chemistry

유기 화학

Unit 1

제1단원

Radical Chemistry

라디컬 화학

KEY TERMS AND CONCEPTS

주요 용어 및 개념

alkyl halide reduction with tributyltin hydride

Alkyl halide reduction with tributyltin hydride removes a halogen and replaces it with hydrogen. This reaction turns alkyl halides into alkanes. The reagent Bu3SnH has a weak Sn–H bond, and the reaction forms tributyltin halide as a byproduct. Because the new bonds are stronger than the bonds that are broken, the reaction is energetically favorable.

The reaction proceeds by a radical chain mechanism, which is similar to radical halogenation. Light causes Bu3SnH to split homolytically, meaning the bond breaks evenly to form a tributyltin radical. That radical removes the halogen from the alkyl halide. This step creates an alkyl radical intermediate and tributyltin halide.

Next, the alkyl radical takes hydrogen from tributyltin hydride. This forms the alkane product and a new tributyltin radical. The new radical then continues the chain reaction.

Bond strength affects how easily the reaction starts. C–Br and C–I bonds are weaker than C–Cl bonds, so daylight can start the hydrogenolysis of alkyl bromides and iodides. Alkyl fluorides do not react because C–F bonds are very strong.

Alkyl chlorides need more tributyltin radicals, so an initiator is added to the reaction mixture. AIBN is the most common initiator. Above 60 °C, it undergoes thermal homolysis and forms nitrile-stabilized radicals. These radicals remove hydrogen from tributyltin hydride and create the tributyltin radical that keeps the reaction going.

Peroxides are not used as initiators in this reaction. Their radicals are very reactive and can remove hydrogen from organic halides. That can lead to unwanted side reactions.

Alkyl Halide Reduction with Tributyltin Hydride

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key terms and concepts

Learn how tributyltin hydride removes halogens from alkyl halides through a radical chain reaction, and why light, AIBN, and bond strength matter.

Alkyl Halide Reduction with Tributyltin Hydride | JoVE K12

organic chemistry

JoVE Core Organic Chemistry explains basic concepts of stereochemistry, reactions, and mechanisms using concise and easy-to-understand animated video lessons. Additionally, the scientist-in-action videos demonstrate the application of related concepts in classical and original research experiments performed in today's laboratories worldwide.

Alkyl Halide Reduction with Tributyltin Hydride

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