Question

Propan-1-ol can be prepared from propene by treating it with (A) ${\mathrm{H}}_2\mathrm{O}$ in presence of ${\mathrm{H}}_2{\mathrm{SO}}_4$ (B) $\mathrm{Hg}(\mathrm{OAc}{)}_2$ and water, and subsequently with ${\mathrm{NaBH}}_4$ (C) ${\mathrm{H}}_2\mathrm{O}$ in presence of ${\mathrm{HgSO}}_4$ and ${\mathrm{H}}_2{\mathrm{SO}}_4$ (D) ${\mathrm{B}}_2{\mathrm{H}}_6$ in THF and subsequently with ${\mathrm{H}}_2{\mathrm{O}}_2$ and $\mathrm{NaOH}$

Short answer

The correct reagents and conditions to prepare propan-1-ol from propene are H₂O in the presence of HgSO₄ and H₂SO₄ (Option C). This reaction proceeds via an anti-Markovnikov addition of water, resulting in the formation of propan-1-ol (1-propanol).

Step-by-step solution

Option A: H2O in presence of H2SO4

This option involves the hydration of propene using water in the presence of sulfuric acid. This reaction would occur by the addition of the water molecule across the double bond of propene, forming a secondary alcohol, propan-2-ol (2-propanol). Therefore, this option does not yield propan-1-ol.

Option B: Hg(OAc)2 and water, subsequently with NaBH4

In this option, the reaction is an oxymercuration-reduction involving the use of mercuric acetate (Hg(OAc)2) and water followed by sodium borohydride (NaBH4). This reaction proceeds with Markovnikov addition, which leads to the formation of a secondary alcohol, propan-2-ol (2-propanol). Therefore, this option does not yield propan-1-ol.

Option C: H2O in presence of HgSO4 and H2SO4

This option involves the oxymercuration of propene using a combination of mercuric sulfate (HgSO4) and sulfuric acid (H2SO4). This reaction proceeds via an anti-Markovnikov addition of water, resulting in the formation of propan-1-ol (1-propanol). This is the correct option to convert propene into propan-1-ol.

Option D: B2H6 in THF, subsequently with H2O2 and NaOH

This option uses diborane (B2H6) in tetrahydrofuran (THF) followed by hydrogen peroxide (H2O2) and sodium hydroxide (NaOH) in a hydroboration-oxidation reaction. This reaction results in anti-Markovnikov addition of water to the propene molecule, forming propan-1-ol. However, the use of HgSO4 and H2SO4 (Option C) is more commonly associated with propan-1-ol synthesis from propene. In conclusion, the correct answer is: (C) H₂O in the presence of HgSO₄ and H₂SO₄

Key concepts

Anti-Markovnikov Addition

Anti-Markovnikov addition is a fascinating concept in chemistry that describes how certain reagents add across a double bond in alkenes. Unlike the Markovnikov addition, where the hydrogen atom attaches to the carbon with more hydrogen atoms, in anti-Markovnikov addition, the hydrogen atom attaches to the carbon atom with fewer hydrogen atoms.
This unusual addition pattern is primarily facilitated by reactions like hydroboration-oxidation and is crucial in synthesizing certain alcohols from alkenes. For example, converting propene to propan-1-ol requires an anti-Markovnikov addition of water across the double bond in propene.

• Allows selective formation of certain alcohols.
• Reagents like boranes are typical facilitators of this reaction.
• Results in primary alcohols often desired in synthetic organic chemistry.

Understanding anti-Markovnikov addition is essential for controlling product formation in chemical synthesis and for achieving specific chemical transformations.

Hydroboration-Oxidation

Hydroboration-oxidation is a two-step chemical process that transforms alkenes into alcohols. It's pretty smart and efficient. To picture it, let's break it down into simple steps.
In the first step—hydroboration—a boron compound, such as diborane ($B_2{H}_6$), adds across the alkene double bond in an anti-Markovnikov fashion. This step is selective for less substituted carbon atoms, leading to an organoborane intermediate.
In the second step—oxidation—the reaction mixture is treated with hydrogen peroxide ($H_2{O}_2$) and a base like sodium hydroxide ($NaOH$). The boron atom is replaced by a hydroxyl group, completing the conversion to a primary alcohol.

• Useful for synthesizing primary alcohols.
• Proceeds without rearrangement of the carbon skeleton.
• Simple and relatively safe to conduct under mild conditions.

This method is particularly valued for its specificity and gentle reaction conditions.

Oxymercuration-Reduction

Oxymercuration-reduction is an elegant method for hydrating alkenes to form alcohols without carbocation rearrangements. The process has a few distinct stages.
First, in the oxymercuration step, mercuric acetate ($Hg(OAc{)}_2$) reacts with an alkene and water to form a mercurinium ion intermediate. This is followed by the attack of water, adding an OH group in a Markovnikov fashion, typically on the more substituted carbon.
This step does not involve the formation of an actual carbon cation, which makes it free of rearrangement issues, leading to a more predictable product.
The subsequent reduction stage involves sodium borohydride ($NaB{H}_4$), which reduces the organomercury compound to yield an alcohol.

• Yields secondary alcohols in most cases.
• Favored for its predictability and reliability.
• Suitable for complex molecule synthesis due to non-rearranging reaction.

This method is essential in organic synthesis, offering a robust way to convert alkenes to alcohols under controlled conditions.

Hydration Reaction

A hydration reaction involves the addition of water ($H_{2}O$) to a substrate, such as an alkene, resulting in an alcohol. It's one of the most fundamental types of reactions in organic chemistry.
The acid-catalyzed hydration is a common method for adding water across an alkene's double bond, turning it into alcohol, often following the Markovnikov rule. This happens with the use of acids like sulfuric acid ($H_{2}S{O}_4$), where the double bond reacts to form a carbocation intermediate, which then captures a water molecule.
While convenient, direct hydration often results in secondary alcohols due to Markovnikov addition and can be prone to carbocation rearrangements.

• Involves simple reagents, typically acids and water.
• Often leads to secondary alcohols due to predictable carbocation intermediate formation.
• Not suitable for producing certain primary alcohols like propan-1-ol from propene.

Understanding hydration reactions provides insight into the dynamics of alcohol formation and is pivotal in synthetic strategies where alcohols are desired end products.