Experiment 163

Objective

To identify the presence of benzonitrile in an unknown organic sample.

Introduction

This experiment involves analysis of physical characteristics, solubility testing, and functional group analysis to systematically identify the unknown compound. The melting point comparison helps confirm the compound's identity.

Physical Characteristics of Sample:

●      Color: Colorless

●      State: Oily liquid

●      Odor: Bitter almond smell

●      Melting Point: 191°C

Solubility Test Results

Materials

Chemicals

●      Unknown organic sample (presumed benzonitrile)

●      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: No Prussian blue indicates nitrogen is absent.

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

●      Observation: Absence of 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, indicating 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: No orange-red precipitate, indicating absence of primary amine.

●      Tertiary Amine (=N-): Dissolve in dilute HCl, add NaNO₂, and heat with NaOH.

●      Observation: Green crystals confirm the presence of a tertiary amine group.

●      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.

●      Carboxylic Acid (-COOH): Add sample to NaHCO₃ solution.

●      Observation: No reaction, indicating -COOH group is absent.

●      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: None (N, X, S absent)

●       Functional Groups: Tertiary amine (=N-)

Based on the melting point of 191°C and the presence of these functional groups, the sample is identified as benzonitrile.

Questions

1.    What is benzonitrile?

2.    Which group is contained in benzonitrile?

3.    How is unsaturation tested?

4.    What happens when bromine reacts with an unsaturated organic compound?

5.    What is a nitrile group?