Experiment 165

Objective

To systematically identify the unknown organic sample, hypothesized as o-nitro phenol, through melting point determination and functional group tests.

Introduction

Sample Characteristics

●      Color: Yellow

●      Physical State: Solid

●      Odor: Powerful

●      Melting Point: 45°C

This organic compound is identified through elementary analysis and functional group tests. Determining the melting point, along with chemical tests, enables accurate identification of the sample's structure and functional groups.

Solubility Tests

Materials

Chemicals

●      Sample (suspected o-nitro phenol)

●      Distilled water, 5% HCl, 5% NaOH, 5% NaHCO₃

●      Ferrous sulfate, Nitric acid, Silver nitrate, Ferric chloride

●      10% Sodium nitrite (NaNO₂), 2% Bromine solution, 20% NaOH

Apparatus

●      Test tubes, test tube holder, Bunsen burner, thermometer

●      500 ml flask, test tube stand, pipette, fusion tube, mortar, pestle

Reagents Preparation:

●      Prepare 5% solutions of HCl, NaOH, and NaHCO₃ in 500 ml flasks.

●      Prepare 5% Ferrous sulfate and 10% NaNO₂ solutions.

●      Take HNO₃ and AgNO₃ in beakers.

●      Prepare 20% NaOH solution.

Procedure

1.    Elementary Analysis

●      Preparation of Stock Solution: Place a clean, dry piece of sodium in a fusion tube, heat until it melts, add a small amount of sample, and heat until dull-red. Drop the fusion tube into a mortar with 3-5 ml distilled water, break the tube, and filter for use as stock solution.

●      Nitrogen Test: Add 1 ml of freshly prepared ferrous sulfate to 1-2 ml of stock solution, boil, cool, then add H₂SO₄. Prussian blue color formation confirms nitrogen presence.

●      Halogen Test: Acidify 1 ml of stock solution with nitric acid, boil for 6-7 minutes, cool, then add silver nitrate. No precipitate confirms halogens (chlorine, bromine, iodine) are absent.

●      Sulfur Test: Acidify 1 ml of stock solution with dilute acetic acid, then add lead acetate. Absence of black precipitate indicates sulfur is absent.

2. Functional Group Tests

●      Unsaturation Test:

▪        Dissolve 0.2 g of sample in CCl₄, add 2% bromine in CCl₄ dropwise. Bromine color discharge indicates unsaturation.

▪        Dissolve 0.2 g of sample in acetone or water, add 2% KMnO₄. KMnO₄ color discharge confirms unsaturation.

●      Nitro (-NO₃) Group Test: Boil sample with tin and HCl, cool, dilute, add NaNO₂, and test with alkaline α-naphthol. Formation of orange-red color confirms the presence of the -NO₃ group.

●      Carbonyl (=C=O) Group Test: Dissolve sample in rectified spirit, add 2,4-DNPH, and observe. No orange-red precipitate indicates absence of =C=O.

●      Primary Amine (-NH₂) Test: No reaction with HCl and NaNO₂ confirms -NH₂ is absent.

●      Secondary Amine (-NH-) Test: No oily liquids or solids form with NaNO₂, suggesting the absence of secondary amine.

●      Tertiary Amine (=N-) Test: No green crystal formation with NaOH indicates =N- is absent.

●      Substituted Amide (-NHCOR) Test: Boil with 20% HCl, cool, and test with α-naphthol. No color change confirms -NHCOR is absent.

●      Carboxylic Acid (-COOH) Test: Add sample to NaHCO₃ solution. Absence of reaction confirms -COOH is absent.

●      Phenol (Ar-OH) Test: Dissolve sample in rectified spirit, add FeCl₃. Intense coloration (purple, blue, red, violet, green) confirms the presence of an -OH group.

●      Aromatic Hydrocarbon Test: Dissolve sample in alcohol, add picric acid solution. Formation of orange-red needle-shaped crystals confirms aromatic hydrocarbon.

Observations

The sample contains nitrogen (N) and -OH, -NO₃ groups as its functional groups. The melting point of 45°C and chemical properties confirm the sample as o-nitro phenol.

Questions

1.    What is nitro phenol?

2.    How are o-nitro phenol and p-nitro phenol identified?

3.    What color forms in the phenol test?

4.    What reagent is used in the phenol group test?

5.    What is phenate?