Experiment 93

Objective

To prepare salicylic acid from phenol through the Kolbe-Schmitt reaction, using carbon dioxide and sodium hydroxide.

Introduction

In the Kolbe-Schmitt reaction, phenol reacts with carbon dioxide under controlled conditions of temperature (125°C) and pressure (4-5 atm) to produce sodium salicylate. This compound is then hydrolyzed to yield salicylic acid.

Reaction Steps

1.    Formation of Sodium Salicylate

C6​H5​Ona + CO2 ​→ C6​H4​(OH)COONa

2.    Hydrolysis to Salicylic Acid

C6​H4​(OH)COONa + HCl → C6​H4​(OH)COOH + NaCl

Materials

Chemicals

·       Phenol

·       Carbon dioxide (CO₂)

·       Hydrochloric acid (HCl)

·       Distilled water

·       Sodium hydroxide (NaOH)

Apparatus

·       Test tube

·       Test tube holder

·       Thermometer

·       Bunsen burner

Reagents

·       Mix phenol with NaOH in a test tube and introduce CO₂.

Procedure

1.    Preparation of Sodium Phenate Solution

o   In a test tube, combine phenol and NaOH.

2.    Heating and CO₂ Flow

o   Heat the mixture to 125°C, ensuring the mouth of the test tube is closed.

o   Introduce a steady flow of CO₂ into the mixture to form sodium salicylate.

3.    Hydrolysis

o   After sodium salicylate forms, add HCl to the mixture to hydrolyze it, producing salicylic acid.

Observation

A colorless solution of salicylic acid is produced.

Questions

1.    What is salicylic acid?

2.    What is the Kolbe-Schmitt (Kolbe) reaction?

3.    Why is CO₂ necessary in the production of salicylic acid?