Experiment 164

Objective

To identify the presence of o-aminobenzoic acid (anthranilic acid) in an unknown organic sample.

Introduction

This experiment involves a combination of physical observations, solubility testing, and functional group analyses to systematically identify the unknown compound. The melting point is compared with known values to confirm its identity.

Physical Characteristics of Sample:

●      Color: White

●      Physical State: Solid

●      Odor: Sweet

●      Melting Point: 145°C

Solubility Test Results

Materials

Chemicals

●      Unknown organic sample (presumed o-aminobenzoic acid)

●      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)

●      Heat a piece of sodium in a fusion tube until molten.

●      Add a small amount of the sample, heat to a dull red, then drop the tube into a mortar with 3-5 mL of distilled water.

●      Crush the tube, filter the solution, and use it for further testing.

●      Test for Nitrogen: Add 1-2 mL of the stock solution to freshly prepared ferrous sulfate, boil, cool, and add a few drops of H₂SO₄.

●      Observation: Prussian blue indicates nitrogen is present.

●      Test for Halogens: Acidify 1 mL of boiling solution with nitric acid, boil, cool, and add silver nitrate.

●      Observation: No white, pale yellow, or yellow precipitate indicates no halogens (Cl, Br, I).

●      Test for Sulfur: Acidify 1 mL of solution with acetic acid and add lead acetate.

●      Observation: No black precipitate indicates sulfur is absent.

2.    Functional Group Tests

●      Primary Amine (-NH₂): Dissolve sample in dilute HCl, add NaNO₂, and transfer to an alkaline α-naphthol solution.

●      Observation: Orange-red precipitate confirms -NH₂.

●      Secondary Amine (-NH-): Add excess NaNO₂ to a sample in dilute HCl.

●      Observation: No reaction, indicating secondary amine is absent.

●      Tertiary Amine (=N-): Add NaNO₂ to a sample in dilute HCl, heat with NaOH.

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

●      Substituted Amide (-NHCOR): Boil with HCl, cool, and add to an alkaline α-naphthol solution.

●      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 -NO₃ group is absent.

●      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: Effervescence of CO₂, turning limewater milky, confirms -COOH.

●      Phenol Group (Ar-OH): Dissolve in rectified spirit, add FeCl₃.

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

●      Aromatic Hydrocarbon: Dissolve in absolute alcohol, add picric acid solution.

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

Observation

Identified Functional Groups:

●      Elements: Nitrogen (N)

●      Functional Groups: Primary amine (-NH₂), Carboxylic acid (-COOH)

Based on the melting point of 145°C and the presence of these functional groups, the sample is identified as o-aminobenzoic acid (anthranilic acid).

Questions

1.    What is anthranilic acid?

2.    How are primary, secondary, and tertiary amines identified?

3.    What is the Lassaigne test?

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

5.    What color appears in the nitrogen test?