Experiment 95

Objectives:

To perform a nucleophilic substitution test (SN1 reaction) on the alpha-methyl carbonyl group, using the iodoform test as a diagnostic tool.

Introduction:

The SN1 (Substitution Nucleophilic Unimolecular) reaction is a common substitution reaction in organic chemistry, characterized by a two-step mechanism. The first step involves the formation of a carbocation intermediate, which determines the reaction rate. This reaction often occurs with secondary or tertiary alkyl halides under strong acidic or basic conditions, or with secondary or tertiary alcohols.

Chemicals:

0.2 M Iodine Solution:Dissolve 37.35 g of potassium iodide in 375 mL of distilled water in an Erlenmeyer flask.Add 19.05 g of iodine and stir until homogeneous.

Apparatus:

Hot plate2 thermometers3 conical measures (500 mL graduated)3 glass stirring rodsErlenmeyer flask (500 mL)Beaker (100 mL)3 beakers (200 mL)2 pipettes (5 mL graduated in 0.1 mL)2 measuring cylinders (200 mL)2 pipette bulbs2 snap-cap vials (20 mL)

Experimental Procedure:

1.    Conical Measure 1:

o   Warm 200 mL of 0.2 M iodine solution to 40°C.

o   Add 60 mL of ethanol, then add 50 mL of 2 N NaOH (warmed to 40°C) while stirring. This is the iodoform test on ethanol.

2.    Conical Measure 2:

o   Add 3.8 mL of 2-propanol to 200 mL of 0.1 M iodine solution.

o   Add 150 mL of 2 N NaOH at room temperature while stirring. This is the iodoform test on 2-propanol.

3.    Conical Measure 3:

o   Add 3.7 mL of acetone to 200 mL of 0.1 M iodine solution.

o   Add 150 mL of 2 N NaOH at room temperature. This is the iodoform test on acetone.

Observations:

A yellow crystalline precipitate (iodoform) is formed in each of the three conical measures, confirming the presence of the methyl carbonyl group in the compounds tested.

Questions:

1.    What is the name of your experiment?

2.    At what temperature must the samples be heated?

3.    Why is it important to maintain the correct temperature during the experiment?