Question

Write Dow process for preparation of Phenol. What is the action of bromine water on phenol? Give reason: Group 16th elements have lower ionization enthalpy compared to group 15th elements. Write two uses of dioxygen. 
 

Hint:

The Dow process is one of the main industrial methods for preparing phenol, and bromine water reacts with phenol to form a tribromophenol due to electrophilic aromatic substitution.

Answer 1

Step 1: Dow Process for Preparation of Phenol.
The Dow process involves the chlorination of benzene to form benzene hexachloride (also known as "Lindane") which is then treated with sodium hydroxide to produce phenol: \[ \text{C}_6\text{H}_6 + \text{Cl}_2 \xrightarrow{\text{FeCl}_3} \text{C}_6\text{H}_5\text{Cl}_6 \] \[ \text{C}_6\text{H}_5\text{Cl}_6 + 6NaOH \rightarrow \text{C}_6\text{H}_5\text{OH} + 6NaCl \] This yields phenol (\(C_6H_5OH\)). Step 2: Action of Bromine Water on Phenol.
When phenol reacts with bromine water, it undergoes electrophilic substitution to form 2,4,6-tribromophenol: \[ C_6H_5OH + 3Br_2 \rightarrow C_6H_2Br_3OH + 3HBr \] The bromine atoms are added to the ortho and para positions of the phenol ring. Step 3: Ionization Enthalpy Comparison.
Group 16 elements have lower ionization enthalpy compared to group 15 elements because: - Group 16 elements have a lower effective nuclear charge due to the additional electron in the p-orbital, making the outer electrons easier to remove. - Group 15 elements, being nitrogen, phosphorus, arsenic, etc., have a half-filled p-orbital which is more stable, resulting in higher ionization enthalpy. Step 4: Uses of Dioxygen.
- Respiration: Dioxygen is essential for respiration in most aerobic organisms. - Combustion: Dioxygen supports combustion and is used in various industrial processes like steelmaking.