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Hydroboration Oxidation - Hydroboration, Oxidation Reaction of Alkenes and Alkynes, Mechanism, Hydroboration Step, Oxidation step, Practice Problems and Frequently Asked Questions

Hydroboration Oxidation - Hydroboration, Oxidation Reaction of Alkenes and Alkynes, Mechanism, Hydroboration Step, Oxidation step, Practice Problems and Frequently Asked Questions

Girls, in general, enjoy experimenting with different nail paint hues and changing their nail polish frequently. What kind of nail polish remover do they use?

Nail polish remover is the answer, and it's readily available on the market. Nail polish remover is an organic solvent that may contain pigment, fragrances, oils, and solvents. Acetone is the most frequent ingredient in nail polish removers, and it aids in the removal of polish. So, let's look at how we may use Hydroboration oxidation to make various ketones, aldehydes, and alcohols.

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Table of Contents

Hydroboration Oxidation reaction for Alkynes

The hydroboration oxidation reaction is a type of organic chemical reaction that converts alkynes to ketones or aldehydes. This is done in 2 steps, including a hydroboration step and an oxidation step. This is completed through a net water addition (across the entire triple bond).

Mechanism

The conversion of alkynes into neutral aldehydes or ketones takes place here. The mechanism of hydroboration oxidation is similar to an anti-Markovnikov reaction in which a hydroxyl group attaches to the less substituted carbon. The entire reaction can be broken down into two steps, as explained below.

Step-1 Hydroboration Process

In an anti-Markovnikov way, the alkynes can undergo hydroboration. The less substituted carbon, which is also the least hindered, becomes a priority target for the boron atom's attack. A bulky reagent of borane must be used to stop the reaction at the alkenyl group attached to the borane stage. If borane is used alone, it will result in the hydroboration of both the alkyne's pi bonds.

Step-2: The Oxidation Process

The second step in the hydroboration process can now begin, as the trialkyl borane has been produced. In this step, the boron atom is attacked by the nucleophilic hydroperoxide ion. The R group has been rearranged, along with its electron bond pair to the adjacent oxygen atom.

The hydroxide ion has now been eliminated. This process is repeated three times to yield trialkyl borate as the product. This trialkyl borate is now treated with water to generate the necessary neutral alcohol. The mechanism's step is depicted below.

Non-Terminal Alkyne (Pent-2-yne)

Hyboration-Oxidation Reaction for Alkenes:

An organic chemical reaction used to convert alkenes into primary alcohols is the hydroboration oxidation reaction. This is accomplished in two steps, including a hydroboration step and an oxidation step. Using an anti-Markovnikov Rule, a net addition of water (across the entire double bond) is achieved.

Consider the hydroboration oxidation of alkene hex-1-ene.

Mechanism of Alkene Hydroboration-Oxidation

The mechanism of hydroboration oxidation can be thought of as an anti-Markovnikov reaction in which a hydroxyl group attaches itself to the less substituted carbon. Herbert Charles Brown, an English-born American chemist, reported the hydroboration oxidation reaction for the first time in the second half of the 1950s.

For this work, he was awarded the Nobel Prize in Chemistry in 1979.

Characteristics of Hydroboration of terminal alkenes

  1. Stereospecific -syn addition
  2. Anti Markovnikov mechanism
  3. Primary alcohol formation

The conversion of alkenes into primary alcohols takes place here. As explained below, the entire reaction can be broken down into two steps.

Step-1: The Hydroboration Process

The first step is the addition of borane in the form of BH3 to the given double bond. This results in the transfer of a hydrogen atom to the carbon atom next to the carbon atom bonded with the boron atom. The hydroboration step is now repeated further twice, yielding three alkenes attached to the boron atom from the starting BH3.

Step-2: The Oxidation Process

Now that the trialkyl borane has been produced, the second step in the hydroboration process can begin. The boron atom is attacked in this step by the hydroperoxide ion, which is nucleophilic in nature. The R group, along with its electron bond pair to the adjacent oxygen atom, is now rearranged.

The ion of hydroxide has now been removed. This process is repeated three times to produce trialkyl borate as the product. This trialkyl borate is now treated with water to produce the required primary alcohol. The steps of the mechanism are illustrated below.

Practice Problems

Q1. When 3-methyl cyclohexyne undergoes a hydroboration-oxidation reaction, the expected product would be

A. 3-Methyl Cyclohexan-1-one
B. 3-Methyl Cyclohexan-2-one
C. 2-Methyl Cyclohexan-2-one
C. 3-Methyl Cyclohexan-3-one

Solution: The hydroboration oxidation reaction converts alkynes to aldehydes and ketones by an organic chemical reaction. A two-stage technique, which involves a hydroboration step and an oxidation step, is used to produce this. Using an anti-Markovnikov Rule, a net addition of water is achieved.

When methyl cyclohexyne is reacted with BH3 followed by H2O2OH-, the expected product according to the Anti Markovnikov rule is 3-Methyl cyclohexan-1-one. Hence, the correct answer is an option (A).

Q2. When Pent-2-yne undergoes a hydroboration-oxidation reaction, the expected product would be

A. Pentan-2-one
B. Pentan-3-one
C. Pentan-4-one
D. Pentanal

Solution: The hydroboration oxidation reaction converts alkynes to aldehydes and ketones by an organic chemical reaction. A two-stage technique, which involves a hydroboration step and an oxidation step, is used to produce this. Using an anti-Markovnikov Rule, a net addition of water is achieved.

When Pent-2-yne is reacted with BH3 followed by H2O2OH-, the expected product according to the Anti Markovnikov rule is Pentan-2-one. Hence, the correct answer is an option (A).

Q3. In which case will hydroboration oxidation and acid hydration produce different products?

(A)

(B)

(C) CH= CH2

(D) CH3-CH=CH-CH3

Solution: The hydroboration oxidation reaction converts alkenes into alcohol by an organic chemical reaction. A two-stage technique, which involves a hydroboration step and an oxidation step, is used to produce this. Using an anti-Markovnikov Rule, a net addition of water is achieved.

Acid catalysed hydration is a chemical reaction in which water is added to an unsaturated substrate while an acid catalyst is present. The hydration of ethene is one example.

Cyclohexene (option B), CH2=CH2 (option C) and CH3-CH=CH-CH3 (option D) all are symmetrical alkene. Hence, the Markovnikov Rule is not applicable in this case. As products formed from Markovnikov or anti-Markovnikov are the same compound.

In option (A), the unsymmetrical alkene will yield a different product concerning the reagent and can be shown as

Hence, the correct answer is option (A).

4.

Q4. The nature of Product A is

A. Optically Active primary alcohol
B. Optically Active secondary alcohol
C. Optically Inactive primary alcohol
D. Optically Inactive secondary alcohol

Solution: The hydroboration oxidation reaction, which employs an anti-Markovnikov Rule, converts alkenes into alcohol via an organic chemical reaction. This is made using a two-stage technique that includes a hydroboration step and an oxidation step.

Because carbon contains two hydrogens and one alkyl group, the alcohol produced by this reaction is a primary alcohol. Because carbon-containing two identical groups (2 hydrogens) is achiral, a compound is optically inactive if it lacks chiral carbon.

Hence, product A is the primary optically inactive alcohol. Hence, the correct answer is (C).

Frequently Asked Questions-FAQs

Q1. What does the alkynes hydroboration product do?
Answer:
Alkynes hydroboration product ketones and aldehydes are the most widely used solvents, particularly in the explosives, lacquers, paints, and textiles industries. Ketones are also used as preservatives, tanning agents, and in hydraulic fluids. The most important ketone is acetone, a liquid with a sweetish odour.

Q2. What applications does the Hydroboration reaction have?
Answer: In contrast to other oxidation reactions used in the formation of alcohol, the main application of the Hydroboration Oxidation Reaction is stereospecific and regioselective alcohols.

Q3. What are the applications of alkene?
Answer: They contribute to the production of plastics such as polystyrene, which is used to make refrigerator parts and automobile battery boxes, and polythene, which is used to make buckets, bowls, and bags.

Q4. What do you mean by "hydroboration" exactly?
Answer:  Hydroboration is the addition of the hydrogen boron bond to a double bond between carbon and carbon or carbon and nitrogen. It is also possible to do it on a triple carbon bond. Hydroboration can be used to synthesise some organic compounds.

Q5. What is a stereospecific reaction in organic chemistry?
Answer: Stereospecific: A reaction in which the outcome is determined by the stereochemistry of the reactants. In general, one stereoisomer of a given reactant produces one stereoisomer of the same product, whereas another stereoisomer of the same reactant produces a different stereoisomer of the same product.

 

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