Borane

Definition

Borane is a chemical compound with the formula BH3, consisting of a boron atom bonded to three hydrogen atoms. It is a highly reactive and flammable gas that serves as a key intermediate in organic chemistry, particularly in reactions involving alkenes, alkynes, and carboxylic acids.

5 Must Know Facts For Your Next Test

1. Borane is a key reagent in the hydroboration-oxidation reaction, which is used to add water (H2O) to alkenes to form alcohols.
2. Borane can also be used in the hydration of alkynes, where it adds to the triple bond to form an organoborane intermediate that can be further converted to an alcohol.
3. In the preparation of alcohols, borane is used to reduce carbonyl compounds (aldehydes and ketones) to the corresponding alcohols.
4. Borane plays a role in the reactions of carboxylic acids, where it can be used to reduce the carboxyl group to an alcohol.
5. Borane is a Lewis acid and can participate in electrophilic addition reactions with alkenes, adding to the carbon-carbon double bond to form an organoborane intermediate.

Review Questions

• Explain the role of borane in the hydroboration-oxidation reaction of alkenes.
  • In the hydroboration-oxidation reaction, borane (BH3) adds to the carbon-carbon double bond of an alkene in a Markovnikov-selective manner, forming an organoborane intermediate. This intermediate is then oxidized, typically using hydrogen peroxide and sodium hydroxide, to convert the organoborane into an alcohol. The hydroboration-oxidation reaction is a key method for the anti-Markovnikov addition of water to alkenes, allowing for the synthesis of alcohols.
• Describe how borane can be used in the hydration of alkynes.
  • Borane can be used to hydrate alkynes, where it adds to the carbon-carbon triple bond to form an organoborane intermediate. This intermediate can then be converted to an alcohol through further reactions, such as oxidation. The hydration of alkynes using borane is a useful method for the synthesis of alcohols from alkyne starting materials.
• Analyze the role of borane in the preparation of alcohols from carbonyl compounds.
  • Borane can be used as a reducing agent to convert carbonyl compounds, such as aldehydes and ketones, into the corresponding alcohols. In this reaction, the borane reduces the carbonyl group, forming an organoborane intermediate that is subsequently hydrolyzed to yield the desired alcohol product. This reduction of carbonyl compounds to alcohols using borane is an important method in the preparation of alcohols from other organic functional groups.

Related terms

Hydroboration: A reaction in which a borane compound, such as borane (BH3), is added to an alkene to form an organoborane intermediate, which can then be converted to other functional groups.

Organoborane: A class of compounds containing a carbon-boron bond, formed as intermediates in hydroboration reactions.

Diborane: A diborane (B2H6) is a compound consisting of two boron atoms and six hydrogen atoms, used as a reducing agent and in the synthesis of other borane compounds.