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-Experiment 8A –
Angela Ray T. Abala
Kurt Roland A. Asperas
University of the Philippines – Manila
College of Arts and Sciences
Department of Physical Sciences and Mathematics
CHEM 31.1 Organic Chemistry
1.1. Physical Properties of compoundsPhysical Properties of compounds2.2. Classification by solubilityClassification by solubility3.3. Elemental analysisElemental analysis4.4. Classification test for functional groupsClassification test for functional groups
This experiment focuses on the fourth area of inquiry.
1.1. Test for UnsaturationTest for Unsaturation2.2. Test for AromaticityTest for Aromaticity3.3. Test for Acidity and BasicityTest for Acidity and Basicity4.4. Test for AlkylhalidesTest for Alkylhalides
The carbon atom has the capability to bond with four other atoms. However, this ability to bond to several atoms (especially to H atoms) becomes reduced because of the presence of multiple bonds. The presence of double or triple bonds is an indication of the unsaturation of the compound.
Alkenes and Alkynes
Test for Unsaturation – Bromine in Methylene Chloride Test
How to prepare Acetylene?
Test for Unsaturation – Bromine in Methylene Chloride Test
Preparation of Acetylene
Test for Unsaturation – Bromine in Methylene Chloride Test
- electrophilic addition or halogenation
Test for Unsaturation – Bromine in Methylene Chloride Test
• Addition reaction of Bromine (Br2), a red liquid, to a compound containing a double or triple bond produces a colorless Dibromide. (A positive Test!)
• The double (or triple bond) must be sufficiently electron-rich to initiate the reaction. Therefore, minimal electron withdrawing groups (Deactivators), such as Carboxyl Groups attached to molecule, would hinder the reaction.
•Unsubstituted Aromatic compounds (Benzene) do not react with the Bromine reagent.
•Even if the ring has substituted activating groups (donate electrons to the ring) the reaction would be a substitution and not an addition.
Test for Unsaturation – Bromine in Methylene Chloride Test
Test Samples Visible ResultStructure/Formula of
Compound Responsible for the visible result
Acetylene Unpleasant odor, produced smoke, pale yellow-clear solution
Benzene Red solution No visible resultStyrene Presence of smoke,
cloudy-clear solution
Hexane Negative testNo visible result
POSITIVE TEST: clear solution
Test for Unsaturation – Baeyer Test
Test for Unsaturation – Baeyer Test
- Redox reaction
Test for Unsaturation – Baeyer Test
Potassium Permanganate (KMNO4) is an oxidizing agent.
It has a Purple color
Following the oxidation of an unsaturated compound, the Permanganate ion is reduced to Manganese Dioxide (MnO4), a brown precipitate.
The reaction is important because it doesn’t work on alkanes (compounds with carbon-carbon single bonds) or aromatic compounds.
Test for Unsaturation – Baeyer Test
Drawbacks:
Easily oxidized compounds give a positive test: a) Most aldehydes give a positive test. b) Formic acid and its esters give a positive test.
Often, the brown precipitate fails to form and the solution turns reddish-brown.
Alcohols with trace impurities give a positive test.
Phenols and aryl amines give a positive test.
Test for Unsaturation – Ignition Test
POSITIVE TEST: The disappearance of the KMnO4's purple color and the appearance of a brown suspension of MnO2 is a positive test.
Test Samples Visible ResultStructure/Formula of
Compound Responsible for the visible result
Acetylene Brown solution, chocolate brown precipitate
MnO2 for the brown precipitate
Benzene Dark purple solution
No visible result
Styrene Dark brown precipitate in clear solution
MnO2 for the brown precipitate
Hexane Violet precipitate No visible result
Test for Unsaturation – Ignition Test
Test for Unsaturation – Ignition Test
• Ignition test is used for High Degrees of Unsaturation.
•The ignition test is used to differentiate aliphatic substances from aromatic unsaturated hydrocarbons.
•Multiple bonds of carbon cause the deposition of carbon in the ignition medium → soot → positive test!
Test for Unsaturation – Ignition Test
•Highly unsaturated compounds such as aromatic compounds, give off a yellow sooty flame.
•The yellow color is due to the presence of carbon and the soot is credited to the deposition of carbon.
•Positive test is indicative of a high degree of Unsaturation and is probably Aromatic
Test for Unsaturation – Ignition Test
POSITIVE TEST: Positive test is a sooty yellow flame.
Test Samples
Visible ResultStructure/Formula of
Compound Responsible for the visible result
**Acetylene Orange-blue flame
C
Toluene Yellow flame, soot
C
Styrene Yellow flame, soot
C
Hexane Yellow flame No visible result for carbon deposition
Test for Aromaticity – Nitration
Test for Aromaticity – Nitration
- electrophilic aromatic substitution
Test for Aromaticity – Nitration
• Benzene derivatives in a general sense react in the same way that benzene does, although there are some interesting differences.
•Nitration of toluene generates a mixture of products. The major products are those with substitution at the ortho and para positions.
•In the case of toluene, ortho (and para) attack result in the positive charge being spread over two secondary carbons and one tertiary carbon atom (the one bearing the CH3 group).
•When reaction of toluene occurs at the meta position, then the resonance forms of the sigma complex put positive charge over 3 secondary carbons - the same as for benzene.
Test for Aromaticity – Nitration
• Appearance of the product (Nitration of toluene) : light yellow to darker yellow-green liquid
Test for Aromaticity – Nitration
Test Samples
Visible Result
Structure/formula of compound
responsible for the visible result
Toluene Yellow color on top of solution; similar to oil-water mixture; smoky; smells like rugby
POSITIVE TEST: Yellow solution
Test for Aromaticity – Le Rosen Test
Test for Aromaticity – Le Rosen Test
Test for Aromaticity – Le Rosen Test
•In the Le Rosen test, same processes in nitration take place. However, instead of HNO3, formaldehyde is used.
Test for Aromaticity – Le Rosen Test
Test Samples
Visible Result
Structure/formula of compound
responsible for the visible result
Toluene Exhibited two layers
Rose pink solution
p - aquinone
Test for Acidity and Basicity – pH of an Aqueous Solution
Test for Acidity and Basicity – pH of an Aqueous Solution
Test for Acidity and Basicity – pH of an Aqueous Solution
•pH is a measure of the acidity or alkalinity of a solution.
•Aqueous solutions with a pH less than seven are considered acidic, while those with a pH greater than seven are considered basic.
•When a pH level is 7.0, it is defined as 'neutral' because at this pH the concentration of H3O equals the concentration of OH− in pure water.
•pH is formally dependent upon the activity of hydronium ions (H3O+).
Test for Acidity and Basicity – pH of an Aqueous Solution
Solution pH
Acetic Acid 2
Phenol 4
Aniline 7
Benzoic Acid 2
*water 5
Test for Acidity and Basicity – NaHCO3 Test
Test for Acidity and Basicity – NaHCO3 Test
Test for Acidity and Basicity – NaHCO3 Test
•Solubility will be indicated by the formation of a homogeneous solution, a color change, or the evolution of gas or heat.
•If soluble, then it is a strong organic acid. If not, then it is a weak organic acid.
• The most common weak organic acid are phenols. Typically, only a carboxylic acid will react with NaHCO3.
•Negatively substituted phenols such as nitrophenols, aldehydrophenols, and polyhalophenols are sufficiently acidic to dissolve in 5% sodium bicarbonate.
Test for Acidity and Basicity – NaHCO3 Test
Sample Observation
Acetic Acid Evolution of gas
Phenol Brown solution
Aniline Distinct 2 layers
Benzoic Acid Dissolved
POSITIVE TEST: Evolution of a carbon dioxide gas is a positive test for the presence of the carboxylic acid
Test for Acidity and Basicity – AgNO3 Test
Test for Acidity and Basicity – AgNO3 Test
Test for Acidity and Basicity – AgNO3 Test
•The silver nitrate test is designed to detect strong acids especially carboxylic acids.
•The presence of an acid is detected by the presence of replaceable H+ atoms and the formation of precipitates.
•The essence of this test is the reaction between carboxylic acids and silver nitrate. Silver nitrate reacts with carboxylic acids to form salts of the carboxylic acid.
•To verify the presence of the silver salt, dilute nitric acid should be added. Silver salts are soluble in the aforesaid acid.
Test for Acidity and Basicity – AgNO3 Test
Sample Observation
Acetic Acid Cloudy solution
Phenol Precipitate appeared
Aniline Brown-yellow precipitate
Benzoic Acid White precipitate
POSITIVE TEST: Appearance of precipitate and dissolution of the precipitate in Nitric acid
Test for Acidity and Basicity – Silver Acetylide Test
Test for Acidity and Basicity – Silver Acetylide Test
- Silver acetylide is formed when acetylene is passed into an ammoniacal solution of silver nitrate.
Test for Acidity and Basicity – Silver Acetylide Test
• These substitution reactions which ethynes undergo to form compounds with metals are not occur with the alkenes. •These reactions can be used as tests to distinguish between acetylene and ethylene.
•When acetylene is passed through an ammonical solution of silver nitrate or cuprous chloride, at room temperature, precipitates of silver acetylide (white) or cuprous acetylide (red) are formed.
Test for Acidity and Basicity – Silver Acetylide Test
Sample Observation
Acetylene Pale yellow precipitate → gray-silver precipitate
Test for Alkylhalides – Beilstein Test
Test for Alkylhalides – Beilstein Test
• The Beilstein test is a simple chemical test used in chemistry as a qualitative test for halides.
•In Beilstein test, a green flash is indicative of chlorine, bromine, and iodine.
•Fluorine is not detected because copper fluoride is not volatile.
•This test is very sensitive, thus halogen-containing impurities may give misleading results.
Test for Alkylhalides – Beilstein Test
Test SamplesVisible Result
Structure / Formula of Compound
Responsible for the visible
result
Tert-butylchlorideBlue-green
flameCuCl2
Sec-butylchloride Green flame CuCl2
BenzylchlorideRed flame;
sootCuCl2
cholorobenzeneRed-orange flame; soot
CuCl2
ethylchloride Green flame CuCl2ethylbromide Green flame CuBr2
Ethyliodie Green flame CuI2
Test for Alkylhalides – Alcoholic AgNO3 Test
Test for Alkylhalides – Alcoholic AgNO3 Test
Test for Alkylhalides – Alcoholic AgNO3 Test
• this test can be used to differentiate aromatic halides from aliphatic halides.
•The reaction of an alkyl halide with silver nitrate in ethanol will result in the formation of a white or yellow silver halide precipitate that is insoluble in nitric acid.
•This reaction quite often proceeds slowly, and occasionally slight warming is necessary.
•Different rate if silver halide precipitation would be expected from halogen in each of these environments, namely, primary<secondary<tertiary.
•Alkyl bromides and iodides react more rapidly than chlorides
•Aryl Halides are unreactive toward the test reagent.
Test for Alkylhalides – Alcoholic AgNO3 Test
Test Samples Visible Result
Structure / Formula of Compound
Responsible for the visible result
Tert-butylchlorideWhite
precipitateAgCl
Sec-butylchlorideWhite-silver precipitate
AgCl
Benzylchloride Distinct 2 layers AgCl
cholorobenzeneWhite
precipitateAgCl
Ethylchloride White precipitate
AgCl
Ethylbromide White precipitate
AgBr
Ethyliodide White precipitate
AgI