Triiodomethane or Iodoform Test

In this video we want to discuss the triiodomethane test or iodoform test.

The reagents and conditions to administer the test is I2 in NaOH(aq), warm.

The observation for a positive test is the formation of a yellow precipitate.

triiodomethane test reagents conditions observation

This test is used to identify certain types of alcohols and carbonyl compounds which contain these specific structures:

triiodomethane test structures that give positive test

If we study the 2 structures closely the common groups that are required are:

1. Methyl CH3 group (yellow)
2. Carbon that carrys an oxygen, either an alcohol carbon CH(OH) or a carbonyl carbon C=O (blue)
3. Hydrogen or alkyl group (green)

triiodomethane test important parts of structure

On reaction with iodine in alkaline conditions, the methyl group will be converted to triiodomethane or iodoform which gives us the observation of yellow precipitate.

The carbon which carries the oxygen will be converted to salt of carboxylic acid or conjugate base of carboxylic acid, H/R-COO-

triiodomethane test deduce products

Students will need to identify compounds which have the required structures to give a positive triiodomethane test.

Here are 3 examples for students to try out. Which of these compounds will give a positive triiodomethane test?

triiodomethane test examples

To find out the answers, check out this video now!

Topic: Alcohols, Organic Chemistry, A Level Chemistry, Singapore

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