Alcohols Phenols And Ethers

Let's analyze the options to find out which one is not a characteristic of alcohols.

Option 1: Alcohols are polar molecules due to the presence of -OH group.

This statement is true. Alcohols are indeed polar molecules. The presence of the -OH group (hydroxyl group) creates a partial positive charge on the hydrogen atom and a partial negative charge on the oxygen atom, making the molecule polar. This polarity allows alcohols to dissolve in water and interact with other polar substances.

Option 2: Lower members of alcohols are insoluble in water as well as in organic solvents.

This statement is incorrect. Lower members (such as methanol, ethanol, and propanol) are very soluble in water because of their small size and the ability to form hydrogen bonds with water molecules. Higher alcohols, however, tend to become less soluble in water as the non-polar hydrocarbon tail increases in size. Thus, the lower members are soluble in both water and organic solvents, making this option not a characteristic of alcohols.

Option 3: Boiling point of alcohols increases with an increase in their molecular mass.

This statement is true. As the molecular mass of alcohols increases, the boiling point tends to increase as well. This is because larger alcohol molecules have more electrons and stronger London dispersion forces, which require more energy to break during boiling. Additionally, larger alcohols can form more hydrogen bonds, further increasing the boiling point.

Option 4: Methanol is a toxic liquid.

This statement is true. Methanol (CH₃OH) is indeed toxic. It can cause serious harm if ingested, inhaled, or absorbed through the skin. Methanol is metabolized in the liver to formaldehyde, which is highly toxic and can cause permanent damage to organs or even death.

Conclusion:

The correct answer is Option 2: Lower members of alcohols are insoluble in water as well as in organic solvents. This is not a characteristic of alcohols, as the lower members of alcohols are actually soluble in water, contradicting this statement.

Benzene itself is not a method of preparing phenol. Phenol is typically produced from benzene through various chemical processes such as the cumene process or the Raschig process, but benzene alone is not a method for directly preparing phenol.
To summarize:
(A) Chlorobenzene: While not a direct method, chlorobenzene can be used as a starting material for the synthesis of phenol.
(B) Benzene: Benzene is not a method of preparation for phenol.
(C) Aniline: Aniline can undergo certain chemical reactions to produce phenol, such as in the Raschig process.
(D) Cumene: The cumene process is a well-known method for the industrial production of phenol.
Therefore, the correct answer is (B) Benzene, as it is not a method of preparation for phenol.

Correct Answer: Option 2 - Benzene diazonium chloride
The preparation of phenol from aniline involves a two-step chemical process, and the key intermediate formed during this reaction is benzene diazonium chloride.

Step 1: Diazotization of Aniline
• In the first step, aniline (C₆H₅NH₂) is reacted with nitrous acid (HNO₂) in the presence of hydrochloric acid (HCl) at low temperatures (0–5°C).
• Nitrous acid is usually generated in situ by reacting sodium nitrite (NaNO₂) with dilute HCl.

The reaction is:
C₆H₅NH₂ + HNO₂ + HCl → C₆H₅N₂Cl + 2H₂O

• The compound formed here is benzene diazonium chloride, which is a stable intermediate only at low temperatures.

Step 2: Hydrolysis to form Phenol
• In the second step, this intermediate benzene diazonium chloride is heated with water (hydrolysis), often in the presence of dilute acids.
• This decomposes the diazonium salt and releases nitrogen gas (N₂), forming phenol (C₆H₅OH) as the final product.

The reaction is:
C₆H₅N₂Cl + H₂O → C₆H₅OH + N₂ + HCl

Conclusion:
The intermediate product formed during the conversion of aniline to phenol is benzene diazonium chloride. This compound plays a critical role in many substitution reactions in aromatic chemistry and is an essential intermediate in organic synthesis.