Experiment 88

Objective

To prepare iodoform (triiodomethane) in the laboratory from ethanol using iodine and a strong base.

Introduction

Iodoform can be synthesized by reacting ethanol with iodine in the presence of a base (NaOH or KOH). The process involves several steps, beginning with the oxidation of ethanol to acetaldehyde, followed by substitution reactions with iodine, resulting in the formation of triiodomethane (iodoform), which precipitates as a yellow solid.

Reaction Steps

1.    Oxidation of Ethanol

CH3​CH2​OH + I2 ​→ CH3​CHO + 2HI

2.    Formation of Triiodo Compound

CH3​CHO + 3I2​ → CCl3​CHO + 3HI

3.    Formation of Iodoform

CCl3​CHO + NaOH → CH3​I + CH3​COONa

Materials

Chemicals

●      Ethanol (CH₃CH₂OH)

●      Iodine solution

●      Potassium hydroxide (KOH)

Apparatus

●      Flask

●      Bunsen burner

●      Stand and sand bath

●      Beaker for iodoform collection

●      Thermometer

●      Pipette

Reagents

●      Mix 3.695 g of KOH with iodine in a flask, and use 10 mL of ethanol in a pipette.

Procedure

1.    Preparation of Reaction Mixture

o   Combine iodine and KOH in a flask.

2.    Heating

o   Heat the mixture to 60-70°C.

3.    Cooling

o   Allow the mixture to cool in an ice bath.

4.    Addition of Ethanol

o   Gradually add ethanol dropwise until the color of iodine disappears completely.

5.    Formation of Iodoform Precipitate

o   Iodoform precipitates as a yellow solid.

6.    Purification of Iodoform

o   Add dilute ethanol to the mixture to further separate iodoform crystals from the solution.

Observation

As ethanol is added, the color of iodine gradually fades, and yellow crystals of iodoform form in the solution.

Questions

1.    What is an iodoform, and what is its structure?

2.    Why are KOH and NaOH used in the preparation of iodoform?

3.    How can you confirm that iodoform has been produced?

4.    What are the uses of iodoform?