LABORATORY 5
DETECTION OF FUNCTIONAL GROUPS IN ORGANIC COMPOUNDS
I. Characteristic reactions differentiating saturated aliphatic hydrocarbons from
unsaturated aliphatic hydrocarbons
1. The test of bromine addition.
Unsaturated hydrocarbons and other compounds with unsaturated bonds decolorize bromine solution in
consequence of addition reaction.
⎢ ⎢
⎯ C = C ⎯ + Br2 → ⎯ C − C ⎯
⏐ ⏐ ⏐ ⏐
Br Br
Procedure: Add dropwise 1 % acetic acid solution of bromine to about 0.5 ml of sample dissolved in acetic acid
or other organic solvent. Mix carefully the contents of the test tube. The pink color of bromine quickly
disappears to the moment, when total multiple bonds are saturated.
2. The test with potassium permanganate by Lehman.
The solution of KMnO4 submits decolorization in the presence of compounds with unsaturated bonds. This is
the consequence of manganese reduction from +7 to +2. During reaction, the solution becomes alkaline (KOH
is formed) and the brown precipitate of manganese dioxide can appear in the reaction mixture.
Procedure: Add dropwise 0.1 % acetone solution of KMnO4 to about 1 ml of examined sample. Mix the solution
carefully after addition of each drop and wait for disappearance of KMnO4 pink color. The quantity of
decolorized solution and the speed of its decolorizing depend on the amount of multiple bonds in the molecule
of examined compound.
II. Characteristic reactions of alcohols
1. The Lucas test (1 test per group).
Primary, secondary and tertiary alcohols react in different way with Lucas’ reagent (the solution of anhydrous
zinc chloride in concentrated hydrochloric acid). Primary alcohols, containing less than six carbon atoms, do not
react with the reagent, and give clear, slightly dark solution. With secondary alcohols, turbidity of the solution
1
, appears, forming two phase solution after 1-1.5 hours. In the presence of tertiary alcohols, the solution turbidity
and solution separation for two phases form very quickly. Tertiary alcohols react with concentrated HCl even in
the absence of ZnCl2.
R R
⏐ ZnCl2 ⏐
(R)H-C-OH + HCl ⎯⎯⎯⎯⎯→ (R)H-C-Cl + H2O
⏐ ⏐
R R
Procedure: Add 5 ml of Lucas’ reagent to three dry test tubes with ground-in stoppers, containing respectively
primary, secondary and tertiary alcohols (0.5 ml). Mix the content for a while, put them away to the laboratory
rack, and check the time difference, necessary in each case for turbidity and two phase solution formation.
2. The test with mercury sulfate (HgSO4) for tertiary alcohols by Deniges.
Only tertiary alcohols submit to this reaction. After dehydration, they form unsaturated hydrocarbons. In these
conditions, secondary alcohols form only turbid solution and primary ones only opalescence, because of very
low speed of alkenes formation.
Procedure: Add 1-2 drops of tertiary alcohol solution to about 1 ml of Deniges reagent (the solution of mercury
sulfate in diluted sulfuric acid). Heat the sample in the boiling water bath until a yellow sediment appears.
3. The esterification test – detection of methanol.
Salicylic acid methyl ester (methyl salicylate) is formed by heating of methyl alcohol with salicylic acid in the
presence of concentrated sulfuric acid, acting both as a catalyst and a water bonding agent.
OH +
OH
H
+ HO CH3 H2O +
C OH C O CH3
O
O
salicylic acid methyl salicylate
Procedure: Add a pinch of salicylic acid and about 1 ml of concentrated H2SO4 to 1 ml of methanol. After
mixing, heat the sample in the boiling water bath. After a few minutes, specific resinous aroma of methyl
salicylate will appear.
4. The iodoformic test by Lieben – detection of ethanol.
Among primary alcohols, only ethanol undergoes iodination reaction. This is the summarized notation of the
reaction:
2
DETECTION OF FUNCTIONAL GROUPS IN ORGANIC COMPOUNDS
I. Characteristic reactions differentiating saturated aliphatic hydrocarbons from
unsaturated aliphatic hydrocarbons
1. The test of bromine addition.
Unsaturated hydrocarbons and other compounds with unsaturated bonds decolorize bromine solution in
consequence of addition reaction.
⎢ ⎢
⎯ C = C ⎯ + Br2 → ⎯ C − C ⎯
⏐ ⏐ ⏐ ⏐
Br Br
Procedure: Add dropwise 1 % acetic acid solution of bromine to about 0.5 ml of sample dissolved in acetic acid
or other organic solvent. Mix carefully the contents of the test tube. The pink color of bromine quickly
disappears to the moment, when total multiple bonds are saturated.
2. The test with potassium permanganate by Lehman.
The solution of KMnO4 submits decolorization in the presence of compounds with unsaturated bonds. This is
the consequence of manganese reduction from +7 to +2. During reaction, the solution becomes alkaline (KOH
is formed) and the brown precipitate of manganese dioxide can appear in the reaction mixture.
Procedure: Add dropwise 0.1 % acetone solution of KMnO4 to about 1 ml of examined sample. Mix the solution
carefully after addition of each drop and wait for disappearance of KMnO4 pink color. The quantity of
decolorized solution and the speed of its decolorizing depend on the amount of multiple bonds in the molecule
of examined compound.
II. Characteristic reactions of alcohols
1. The Lucas test (1 test per group).
Primary, secondary and tertiary alcohols react in different way with Lucas’ reagent (the solution of anhydrous
zinc chloride in concentrated hydrochloric acid). Primary alcohols, containing less than six carbon atoms, do not
react with the reagent, and give clear, slightly dark solution. With secondary alcohols, turbidity of the solution
1
, appears, forming two phase solution after 1-1.5 hours. In the presence of tertiary alcohols, the solution turbidity
and solution separation for two phases form very quickly. Tertiary alcohols react with concentrated HCl even in
the absence of ZnCl2.
R R
⏐ ZnCl2 ⏐
(R)H-C-OH + HCl ⎯⎯⎯⎯⎯→ (R)H-C-Cl + H2O
⏐ ⏐
R R
Procedure: Add 5 ml of Lucas’ reagent to three dry test tubes with ground-in stoppers, containing respectively
primary, secondary and tertiary alcohols (0.5 ml). Mix the content for a while, put them away to the laboratory
rack, and check the time difference, necessary in each case for turbidity and two phase solution formation.
2. The test with mercury sulfate (HgSO4) for tertiary alcohols by Deniges.
Only tertiary alcohols submit to this reaction. After dehydration, they form unsaturated hydrocarbons. In these
conditions, secondary alcohols form only turbid solution and primary ones only opalescence, because of very
low speed of alkenes formation.
Procedure: Add 1-2 drops of tertiary alcohol solution to about 1 ml of Deniges reagent (the solution of mercury
sulfate in diluted sulfuric acid). Heat the sample in the boiling water bath until a yellow sediment appears.
3. The esterification test – detection of methanol.
Salicylic acid methyl ester (methyl salicylate) is formed by heating of methyl alcohol with salicylic acid in the
presence of concentrated sulfuric acid, acting both as a catalyst and a water bonding agent.
OH +
OH
H
+ HO CH3 H2O +
C OH C O CH3
O
O
salicylic acid methyl salicylate
Procedure: Add a pinch of salicylic acid and about 1 ml of concentrated H2SO4 to 1 ml of methanol. After
mixing, heat the sample in the boiling water bath. After a few minutes, specific resinous aroma of methyl
salicylate will appear.
4. The iodoformic test by Lieben – detection of ethanol.
Among primary alcohols, only ethanol undergoes iodination reaction. This is the summarized notation of the
reaction:
2
