Experiment 160

Objective

To systematically identify the presence of aniline in an unknown organic sample.

Introduction

Aniline is a colorless, liquid organic compound with a faint odor. This compound can be identified by elementary analysis and functional group tests. The melting point, along with chemical tests, helps determine the structure and functional groups present in the sample.

Physical Characteristics of Sample:

●      Color: Colorless

●      Physical State: Liquid

●      Odor: Faint

●      Melting Point: -6°C

Solubility Test Results

Materials

Chemicals

●       Supplied sample (presumed aniline)

●       Distilled water

●       5% HCl, 5% NaOH, 5% NaHCO₃

●       Ferrous sulfate, Nitric acid

●       Silver nitrate, Ferric chloride

●       10% NaNO₂, 2% bromine solution

Apparatus

●       Test tubes and holder

●       Bunsen burner

●       Thermometer

●       500 mL flask, test tube stand

●       Pipette

●       Fusion tube

●       Mortar and pestle

Preparation of Reagents

●       Prepare solutions of 5% HCl, 5% NaOH, 5% NaHCO₃, and 5% ferrous sulfate in a 500 mL flask.

●       Prepare a 10% NaNO₂ solution and a 20% NaOH solution for specific tests.

Procedure

1.    Elementary Analysis (Stock Solution Preparation)

●       Place a clean piece of sodium in a fusion tube and heat it until molten.

●       Add a small amount of the sample and heat again until the tube reaches a dull red.

●       Drop the hot tube into a mortar containing 3-5 mL of distilled water, break it up, and filter. Use the filtrate as the stock solution for the tests.

●       Test for Nitrogen:

●      Add 1-2 mL of the stock solution to 1 mL of freshly prepared ferrous sulfate solution.

●      Boil, cool, and add 1-2 drops of H₂SO₄.

●      Observation: A Prussian blue color indicates nitrogen is present.

●       Test for Halogens:

●      Acidify 1 mL of boiling stock solution with nitric acid, continue boiling, then cool and add silver nitrate.

●      Observation: No precipitation, indicating absence of Cl, Br, and I.

●       Test for Sulfur:

●      Take 1 mL of the stock solution, acidify with acetic acid, and add lead acetate.

●      Observation: No black precipitate indicates sulfur is absent.

    2. Functional Group Tests

●       Primary Amine (-NH₂):

●      Dissolve the sample in dilute HCl, add 10% NaNO₂, and transfer a few drops to alkaline α-naphthol.

●      Observation: An orange-red precipitate confirms the presence of -NH₂.

●       Secondary Amine (-NH-):

●      Add excess 10% NaNO₂ to the sample in dilute HCl.

●      Observation: No oily layer confirms the absence of secondary amine.

●       Tertiary Amine (=N-):

●      Dissolve in dilute HCl, add 10% NaNO₂, and heat with NaOH.

●      Observation: No green crystals form, indicating tertiary amine is absent.

●       Substituted Amide (-NHCOR):

●      Boil the sample with 20% HCl, cool, and add to alkaline α-naphthol.

●      Observation: No orange-red precipitate, indicating -NHCOR is absent.

●       Nitro Group (-NO₃):

●      Boil with tin and HCl, cool, dilute with water, and add NaNO₂.

●      Observation: No orange-red precipitate, indicating absence of nitro group.

●       Carbonyl Group (=C=O):

●      Dissolve in rectified spirit, add 2,4-DNPH.

●      Observation: No orange-red precipitate, indicating carbonyl group is absent.

●       Carboxylic Acid (-COOH):

●      Add sample to NaHCO₃ solution.

●      Observation: No reaction, indicating carboxylic acid is absent.

●       Phenol Group (Ar-OH):

●      Dissolve in rectified spirit, add 5% FeCl₃.

●      Observation: No intense color change, indicating phenol group is absent.

●       Aromatic Hydrocarbon:

●      Dissolve in absolute alcohol, add picric acid.

●      Observation: Orange-red needle-shaped crystals confirm aromatic hydrocarbon.

Observation

Identified Functional Groups:

●       Elements: Nitrogen (N)

●       Functional Groups: Primary amine (-NH₂)

Based on the melting point of -6°C and the presence of these functional groups, the sample is identified as aniline.

Questions

1.    What is aniline?

2.    How is a primary amine identified?

3.    What is the Lassaigne test?

4.    What happens when bromine solution is added to unsaturated carbon?

5.    What color appears in the nitrogen test?