Experiment 147

Objective

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

Introduction

This experiment combines physical observation, solubility testing, and functional group analysis to identify the unknown compound. A melting point comparison aids in confirming the compound’s identity.

Physical Characteristics of Sample:

●      Color: Colorless

●      State: Liquid

●      Odor: Ammoniacal

●      Melting Point: 185°C

Solubility Test Results

Materials

Chemicals

●      Unknown organic sample (presumed benzylamine)

●      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, 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: Orange-red precipitate confirms the presence of -NH₂.

●       Secondary Amine (-NH-): Dissolve in dilute HCl, add excess NaNO₂.

●      Observation: No reaction, indicating absence of secondary amine.

●       Tertiary Amine (=N-): Dissolve sample in dilute HCl, add 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 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: 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: Nitrogen (N)

●       Functional Groups: Primary amine (-NH₂), methylene (-CH₂-)

Based on the melting point of 185°C and the presence of these functional groups, the sample is identified as benzylamine.

Questions

1.    What is benzylamine?

2.    How is a tertiary amine identified?

3.    What is the Lassaigne test?

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