Alcohols: Preparation & Properties

The acidity of a compound depends on the stability of the conjugate base. An acetic acid conjugate base is resonance stabilized hence it is the most acidic. 

The phenol is more stable than alcohol and water because the phenol conjugate base is resonance stabilized. 

The structure is as follows:
 

The conjugate base of water is more stable than ethanol because CH₃CH₂ group destabilized the negative charge on the oxygen atom. 

The stability of the conjugate base is as follows: 

The acidity order is as follows:
e 
 

In the Lucas test, primary, secondary, and tertiary alcohols are distinguished on the basis of their reactivity with conc. $HCl + ZnCl_2$ , known as Lucas Reagent. 

Tertiary alcohol gives immediate white turbidity with Lucas reagent, secondary alcohol gives white turbidity in 5 minutes, and primary alcohol does not react with Lucas reagent at room temperature. 

The general reaction is as follows:

Hence,  Statement I is correct but statement II is incorrect. 

NaBH₄ is a mild reducing agent and reduces. Aldehyde into the primary alcohol and ketone into the secondary alcohol. In the given compound ketone group is present, thus, NaBH₄ reduces the ketone group into an alcohol group. 

In the second step, the molecule undergoes a dehydration reaction, and an alkene is obtained as a product. 

The reactions are as follows:

Thus, option first is the correct answer. 
 

When primary alcohol reacts with a strong oxidizing agent then an acid is formed as a product. When primary alcohol reacts with the mild oxidizing agent then aldehyde is formed as a product. 

Here, CrO₃ – H₂SO₄, K₂Cr₂O₇ + H₂SO₄, and KMnO₄ + KOH/H₃O⁺ are strong oxidizing agents thus, converts alcohol into acid. 

But Cu, 573 K, and CrO₃₊ (CH₃CO)₂O are the weak oxidizing agent and reduce primary alcohol to aldehyde. 

Thus, option third is the correct answer. 
 

Explanation:
The first reaction is a reduction reaction. When acid reacts with a reducing agent then alcohol is obtained as a product. 
Here, B₂H₆ and LiAlH₄ can be used as reducing agents. 

The second reaction is also known as the hydroboration-oxidation reaction. In this reaction, alkene reacts with diborane gives trialkyl boranes as addition product. This is oxidized to alcohol by hydrogen peroxide in the presence of aqueous sodium hydroxide. 

Thus, in both reactions X is B₂H₆. 

Thus, an option first is the correct answer. 
 

When alcohol reacts with HBr then substitution reaction takes place and the OH group is substituted by the Br atom. In the first step, the OH group is converted into an H₂O group, and a secondary carbocation is formed as a product. Then rearrangement of carbocation takes place and more stable tertiary carbocation is obtained. 
In the first step, tertiary carbocation reacts with bromide ion, and an alkyl halide is obtained as a product. 

The reaction with mechanism is as follows:

Thus, option second is the correct answer.

Explanation:

(1) “Lucas’ reagent” is a solution of anhydrous zinc chloride in concentrated hydrochloric acid. This solution is used to classify alcohols of low molecular weight. The reaction is a substitution in which the chloride replaces a hydroxyl group.

(2) Lucas reagent converts alcohols to alkyl chlorides: tertiary alcohols give an immediate reaction, indicated when the alcohol solution turns cloudy; secondary alcohols usually show evidence of reacting within five minutes; primary alcohols do not react to any significant extent. The order of reactivity of alcohols is: $3^{\circ}\ \ 2^{\circ}\ 1^{\circ}$

Among the given alcohols,  is a tertiary alcohol. So, it will react instantaneously with Lucas reagent. 

Thus, option 3 is the correct answer.

Regioselective

 Anti-Markovnikov 

A. H₃C-CH₃OH (ethanol) → C₆H₆ (benzene):

• Reaction Name: Dehydration of ethanol (or Decarboxylation in some cases).
• This transformation involves the removal of water (dehydration) from ethanol to form ethene (C₂H₄), followed by further dehydration to form benzene (C₆H₆).
• Intermediate: Ethene (C₂H₄), which then undergoes a second step to form benzene.
• Reagent/Condition: The reaction is typically carried out with conc. H₂SO₄ (sulfuric acid) and heat (Δ).

Correct Match: A → IV (Conc. H₂SO₄, Δ)

B. CH₃COOH (acetic acid) → CH₃CH₂OH (ethanol):

• Reaction Name: Reduction of acetic acid to ethanol.
• The reduction of acetic acid (CH₃COOH) to ethanol (CH₃CH₂OH) typically involves the addition of hydrogen (H₂).
• Intermediate: Acetyl radical (CH₃CO·) or Hydride transfer.
• Reagent/Condition: This is typically achieved by the use of NaOH (base) and heat (Δ), which assists in the reduction.

Correct Match: B → II (NaOH, Δ)

C. CH₃CH₂OH (ethanol) → C₃H₇OH (propanol):

• Reaction Name: Hydrogenation of ethanol to propanol.
• This involves the hydrogenation of ethanol (C₂H₅OH) to form propanol (C₃H₇OH).
• Intermediate: Ethanol as the starting material, and hydrogen is added to the system.
• Reagent/Condition: The reaction is carried out using H₂ (hydrogen) and a catalyst.

Correct Match: C → III (H₂, catalyst)

D. C₆H₆OH (phenol) → C₆H₆ (benzene):

• Reaction Name: Dehydration of phenol.
• Phenol (C₆H₆OH) is converted to benzene (C₆H₆) by the elimination of water (dehydration).
• Intermediate: Phenoxide ion (C₆H₅O⁻), which is formed when phenol loses a proton.
• Reagent/Condition: Conc. H₂SO₄ (sulfuric acid) and heat.

Correct Match: D → I (Oleum)