Identification of Unknown Organic Compound

Introduction

This aim of this coursework is to plan and outline a sequence of
simple chemical tests that can be used to identify unknown organic
compound.

These unknown compounds contain one of the following functional
groups: Alkenes, Tertiary Alcohol, Aldehyde, Ketone, carboxylic acid,
Primary Alcohol, Ester and Phenol.

The tests, observations, and inferences will be tabulated and then the
risk analysis/safety precautions will be tabulated as well, followed
by a flow chart.. the flow chart will be drawn separately from the
test, because drawing a flowchart that includes,, tests, observation
and inferences will be too rough.

Reagents and Apparatus

Bromine Water

Test tubes/Test tube racks

Acidified Potassium Dichromate (VI) (K2Cr2O7)

2,4-Dinitrophenylhydrazine (2,4-DNP)

5% Aqueous Sodium hydrogen carbonate (NaHCO3)

Water Cooled condenser

Clamp and stand

20ml - 400ml Beakers

Measuring Cylinder

Bunsen burner

Phosphorous Pentachloride (PCl5)

Ethanoic acid

Iron(III)Chloride (FeCl3)

Sodium metal (Na)

Tollens Reagent

Sulphuric Acid

Jones’s reagent (CrO3-H2SO4 in H2O)

Water bath

Bunsen burner/heating Mantle

1 ml of 0.5 mols hydroxylamine hydrochloride

Sodium Hydroxide (NaOH)

Hydrochloric Acid (HCl)

Ethanol

Lucas reagent [ZnCl2 - conc. HCl]


S/No

Test

Method

Observation

Inference

1

PCl5 Test

For Hydroxyl groups, OH in Alcohols, Phenols and Carboxylic acid

Pour 1cm3 of sample into test tube in fume cupboard (making sure that
the test tube is in a rack).

Carefully add a spatula of PCl5 bit by bit.

Keep product Dry

If positive, steamy white fumes will be given off.

Hydroxyl group present, could be Primary alcohol, Tertiary Alchohol,
Phenol or Carboxylic acid

2

Ethanoic acid test

Test for all Alcohols

Pour 2cm3 of H into test tube; add equal volume of ethanoic acid. Add
10 drops of H2SO4 and the warm gently.

Pour mixture into 400ml beaker containing 200ml water.

A Sweet smell is given off

Alcohols present, could be primary or Tertiary. The Alchohol was
oxidised to and ester.

3

Test for Primary Alchohols using Jones’s reagent

(CrO3-H2SO4 in H2O)

In a test tube, place 1 ml of acetone in a test tube and dissolve one
drop of the unknown compound

Add one drop of Jones’s reagent and then shake the test tube to mix
contents

Primary and secondary alcohols react within two seconds. There is
colour change form orange to green or blue-green, product is a
precipitate.

Primary alcohol is fully oxidised to acid,

No reaction for Tertiary Alchohol.

Primary Alchohol Present and Confirmed.

Label Test tube “Alchohols”

4

Test for Tertiary Alchohol using Lucas reagent

[ZnCl2 - conc. HCl]

To 1 ml of the unknown compound in a test tube add 6 mls of Lucas'
reagent at room temperature. Close the tube with a cork, shake
properly and then allow to stand.

Very fast reaction and droplets of alkyl chloride formed almost
immediately

For Primary alcohols there is no reaction (except allyl alcohol -
droplets which are formed after 7 minutes).

Therefore tertiary Alcohol is present and Confirmed.

Label test tube Tertiary Alchohol

5

Acid Test

pH of aqueous solution

Test the pH of the unknown compound using universal indicator

Carboxylic acid around pH 3-4

Phenol around pH 5-6

Phenol and carboxylic acids again confirmed present.

6

NaHCO3 Test

Acid test for carboxylic groups

Add a spatula of NaHCO3 to aqueous unknown compound

A gas is given off. Gas turns lime water milky, ( Gas given off is
CO2)

Carboxylic acid present and confirmed as this test is negative for
Phenols and Alchohols.

Label Test tube Carboxylic Acid

7

FeCl3 Test

This is the test for Phenols

Dissolve 0.50g of unknown compound in water, add aqueous solution of
iron(III) chloride drop-wise

There is colour change.

Violet colour for phenol,

Red colour for carboxylic acids

Phenol present and confirmed

Label Test tube Phenol

8

2,4-DNP test

This is a test for carbonyls ( Aldehydes and Ketones)

Add a few drops of a solution of 2,4-DNP t o the unknown compound

Label product Carbonyl

A yellow or orange precipitate is produced.

No Precipitate is produced with Carboxylic acid, phenol or esters.

Therefore carbonyls(Aldehyde and Ketone) present

9

Confirmation of Aldehyde using Tollens Reagent

Add 2 - 3 drops of the unknown compound in methanol to 2 - 3 mL of
Tollen's reagent contained in a very clean test tube. Warm gently in a
water bath.

A silver mirror forms on the side of the test tube from the colourless
solution

Silver Ion is reduced to silver metal.

Reaction is negative with Ketone

Therefore Aldehyde Present and Confirmed.

Label test tube Aldehyde.

10

Confirmation of Presence of Ketone

Recrystallise the product labelled Carbonyl (from Test No. 8 ).

Determine its melting point, and then compare against a known ketone
melting point

Positive Result,

Melting point matches that of a known ketone

Ketone present and Confirmed.

Label test tube as Ketone

11

Bromine Test

For Alkenes

To the unknown compound add bromine water drop-wise until the bromine
colour remains

Bromine water is decolourised from brown to colourless

Phenol will form a white ppt with bromine water, but a colourless
solution depicts presence of Alkenes.

Alkenes present and confirmed.

Label test tube as Alkenes

12

Hydroxamic acid test for Identifying esters

In a test tube, mix 1 drop of unknown compound with 1 ml of 0.5 mols
hydroxylamine hydrochloride in 95% ethanol and add 0.2 ml of 6 mols
aqueous sodium hydroxide. Heat the mixture until it boils. On cooling,
add 2 ml of hydrochloric acid. If the solution is cloudy, add 2 mL of
95% ethanol. Add I drop of 5% iron (III) chloride. Observe colour
change

A positive test will be a distinct burgundy or magenta colour

Esters react with hydroxylamine in the presence of sodium hydroxide to
form the sodium salt of the corresponding hydroxamic acid. On
acidification and addition of ferric chloride the magenta-coloured
iron (III) complex of the hydroxamic acid is formed.

Therefore Ester is present and confirmed.

Flow Chart

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Risk Analysis

Safety precautions

Alchohols – (Ethanol)

Causes skin and eye irritation

Highly flammable

Harmful by Inhalation

Avoid contact with skin and eyes. Wear eye protection; wash with cold
water in the event of contact.

Avoid contact with open fire, take car while heating/refluxing, if
possible use heating mantle instead of Bunsen burner.

Avoid Inhaling gas

Ester

May act as Irritant

Wear safety glasses

Ensure there is adequate ventilation

H2SO4

Corrosive

Liquid can cause damage to skin and eyes

See safety precautions on alchohols

Use gloves

PCl5

Corrosive

Always use the fume cupboard

Tollens Reagent

Highly explosive

After the test with Tollens reagent, pour the contents of the test
tube into a sink and wash the test tube with dilute nitric acid. Any
silver fulminate present, which is highly explosive when dry, will be
destroyed

* Proper care should be taken when handling glass wares


References

Here are some resources that I used for this coursework.

Make the Grades Chemistry

By George Facer

ISBN 0-7487-7281-2

Page 37

OCR Chemistry 2

ISBN 0-521-79882-5

Pages 7,16,21-31 &50

http://www.chem.missouri.edu/Chem2140/Identification%20of%20Unknown%20Organic%20Compounds.doc

http://www.wellesley.edu/Chemistry/chem211lab/Orgo_Lab_Manual/Appendix/ClassificationTests/alcohol.html

www.mrsvillegas.com/labs/identifying_organic_compounds.pdf

http://www.chemguide.co.uk/organicprops/alcohols/oxidation.html

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