Laboratory Preparation of Methyl Iodide (Iodomethane) from Methyl Alcohol
22nd Nov 2024
Experiment 89
Objective
To prepare methyl iodide (CH₃I) in the laboratory from methyl alcohol using red phosphorus and iodine.
Introduction
Methyl iodide is synthesized through a two-step reaction in which red phosphorus reacts with iodine to form phosphorus triiodide (PI₃), which then reacts with methanol to produce methyl iodide.
Reaction Steps
1. Formation of Phosphorus Triiodide 2P + 3I2→ 2PI3
2. Reaction with Methanol to Form Methyl Iodide 2PI3 + 6CH3OH → 6CH3I + 2H3PO3
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The resulting product is then purified to obtain nearly pure methyl iodide.
Materials
Chemicals
● Red phosphorus
● Methanol
● Iodine
● Sodium hydroxide (NaOH)
● Calcium chloride (CaCl₂)
Apparatus
● Flask
● Bunsen burner
● Stand
● Beaker for methyl iodide collection
● Thermometer
Reagents
● A mixture of red phosphorus and methanol with iodine added gradually.
Procedure
1. Preparation of Reaction Mixture
o Combine methyl alcohol and red phosphorus in a flask.
2. Setting Up the Reaction Flask
o Secure the flask on a stand with a thermometer and a dropper in place at the flask’s opening.
3. Addition of Iodine
o Add iodine solution dropwise to the flask while monitoring the temperature to keep it constant. If the reaction heats up, cool the flask with water.
4. Reaction Continuation
o Maintain the reaction for approximately one hour to allow complete formation of methyl iodide.
5. Purification of Methyl Iodide
o The mixture contains HI, I₂, and CH₃OH along with CH₃I. Treat this mixture with NaOH to remove HI and I₂ as NaI.
o Distill the CH₃I with CaCl₂ to obtain 99.98% pure and dry methyl iodide.
Observation
The reaction results in a final mixture containing CH₃I, and upon adding NaOH, the desired CH₃I is separated as a liquid. The iodine color fades, confirming completion of the reaction.
Questions for Reflection
1. What are the uses of iodomethane?
2. Why is red phosphorus used in this reaction?
3. How can CH₃I be purified from the mixture?