Qualitative tests in Organic Chemistry

Question 1

Classification tests FOR UNSATURATION

Answer 1

• Bromine Test for Multiple Bonds
• Baeyer Test
• Ignition Test for High Degrees of Unsaturation

Question 2

• Reagent: solution of bromine in methylene chloride
• Test for: Alkenes and Alkynes
• Positive Result: Discharging of the bromine color without the evolution of hydrogen bromide gas

NOTE: Should be employed in conjunction with Baeyer test (dilute KMnO4).

Answer 2

Bromine Test for Multiple Bonds

Question 3

• Reagent: solution of potassium permanganate + acetone
• Test for: Alkenes and Alkynes
• Positive Result: disappearance of the KMnO4’s purple color ; appearance of a brown suspension of MnO2

Answer 3

Baeyer Test for Multiple Bonds

Question 4

• Reagent: Heat a small sample on a spatula.
• Test for: Aromatic rings
• Positive Result: sooty yellow flame (aromatic ring or other centers of unsaturation)

Answer 4

Ignition Test for High Degrees of Unsaturation

Question 5

Classification tests FOR ALDEHYDES AND KETONES

Answer 5

• Brady’s Test
• Tollen’s Test
• Jones Oxidation Test
• Iodoform Test

Question 6

• Reagent: 2,4-dinitrophenylhydrazine reagent
• Test for: Aldehydes and Ketones
• Positive Result: Formation of a precipitate

Answer 6

Brady’s Test

Question 7

• Reagent: Silver Nitrate + Sodium Hydroxide + Ammonia
• Test for: Aldehydes
• Positive Result: Formation of silver mirror or a black precipitate

Answer 7

Tollen’s Test

Question 8

• Reagent: Chromic acid + Sulfuric Acid
• Test for: Aldehydes
• Positive Result:
  > production of an opaque suspension with a green to blue color (aldehydes and primary or secondary alcohols)
  > no visible reaction within 2 seconds, the solution remaining orange in color. (tertiary alcohols)

Disregard any changes after 15 seconds.

Answer 8

Jones Oxidation Test

Question 9

• Reagent: Iodine solution + Sodium Hydroxide + Water
• Test for: Methyl ketones
• Positive Result: Formation of solid iodoform (yellow) is a positive test.

(Iodoform can be recognized by its odor and yellow color and, more securely, from the melting point 119o-123oC).

Answer 9

Iodoform Test

Question 10

Classification tests FOR ALCOHOLS

Answer 10

• Jones Oxidation Test
• Lucas Test

Question 11

• Reagent: Chromic acid + Sulfuric Acid
• Test for: Primary and Secondary Alcohols
• Positive Result:
  > production of an opaque suspension with a green to blue color (aldehydes and primary or secondary alcohols)
  > Tertiary alcohols give no visible reaction within 2 seconds, the solution remaining orange in color

Answer 11

Jones Oxidation Test

Question 12

• Reagent: Lucas Reagent (HCl + ZnCl2)
• Test for: Secondary and Tertiary Alcohols
• Positive Result: Appearance of a cloudy second layer or emulsion

> 3o alcohols: immediate to 2-3 minutes
2o alcohols: 5 -10 minutes
1o alcohols: no reaction

test applies only to those alcohols soluble in the reagent (monofunctional alcohols lower than hexyl and some polyfunctional alcohols.) This often means that alcohols with more than six carbon atoms cannot be tested.

Answer 12

Lucas Test

Question 13

Classification tests FOR ALKYL OR ACYL HALIDES

Answer 13

• Silver Nitrate in Ethanol Test
• Sodium Iodide in Acetone Test
• Beilstein’s Test

Question 14

• Reagent: 1% ethanolic silver nitrate solution
• Test for: Alkyl or acyl halides
• Positive Result: Formation of a precipitate

NOTE: Carboxylic acids have been known to react in this test, giving false positives.

Answer 14

Silver Nitrate in Ethanol Test

Question 15

• Reagent: 15% solution of sodium iodide in acetone
• Test for: Alkyl or acyl halides
• Positive Result: white precipitate indicates the presence of halides

Answer 15

Sodium Iodide in Acetone Test

Question 16

• Reagent: Heat the tip of a copper wire
• Test for: Alkyl or acyl halides
• Positive Result: green flash is indicative of chlorine, bromine, and iodine

fluorine is not detected because copper fluoride is not volatile.

Answer 16

Beilstein’s Test

Question 17

Classification tests FOR CARBOXYLIC ACIDS

Answer 17

• Sodium Bicarbonate Test

Question 18

• Reagent: methanol + saturated solution of sodium bicarbonate
• Test for: carboxylic acids
• Positive Result: Evolution of a carbon dioxide gas

Answer 18

Sodium Bicarbonate Test

Question 19

Classification tests FOR PHENOLS AND NITRO GROUPS

Answer 19

• Ferric Chloride Test
• Ferric Chloride - Pyridine Test
• Ferrous Hydroxide Test

Question 20

• Reagent: water or water-alcohol mixture + 1% aqueous ferric chloride solution
• Test for: Water-soluble phenols
• Positive Result: red, blue, green, or purple color is a positive test.

This is a less sensitive test for phenols.

Answer 20

Ferric Chloride Test

Question 21

• Reagent: 1% solution ferric chloride in methylene chloride + a drop of pyridine
• Test for: Water-insoluble phenols (or less-reactive phenols)
• Positive Result: Addition of pyridine and stirring will produce a color if phenols or enols are present.

This is a more sensitive test for phenols.

Answer 21

Ferric Chloride - Pyridine Test

Question 22

• Reagent: ferrous ammonium sulfate + alcoholic potassium hydroxide
• Test for: Nitro (–NO2) group
• Positive Result: formation of the red-brown precipitate of ferric hydroxide

Answer 22

Ferrous Hydroxide Test

Question 23

Classification tests FOR AMINES

Answer 23

• Carbylamine Test
• Azo-Dye Test
• Nitrous Acid Test
• Hinsberg Test

Question 24

• Reagent: alcoholic KOH + chloroform
• Test for: primary amines
• Positive Result: confirmed by the release of a foul smell

aliphatic and aromatic primary amines respond to this test. However, secondary and tertiary amines do not give this test

Answer 24

Carbylamine Test

Question 25

- Reagent: sodium nitrite + nitrous acid + HCl followed by Beta-naphthol + Diluted NaOH - Test for: aromatic amines - Positive Result: red-orange dye confirms the presence of aromatic amines

Answer 25

Azo-Dye Test

Question 26

- Reagent: benzene sulfonyl chloride - Test for: distinguishing a primary, secondary, and tertiary amine - Positive Result: * Primary amine: No reaction or precipitation occurs in the case of primary amines. On adding concentrated hydrochloric acid insoluble substance is visible. * Secondary amines: Precipitate in the test tube but do not dissolve in concentrated hydrochloric acid. * Tertiary amines: Precipitate in the test tube but dissolve in concentrated HCl.

Answer 26

Hinsberg Test

Question 26

- Reagent: sodium nitrite + nitrous acid + HCl - Test for: distinguishing aliphatic and aromatic primary, secondary, and tertiary amines - Positive Result: * Primary aliphatic amines - result into evolution of nitrogen gas, which is seen as bubbles. * Secondary amines - result into formation of a yellow, oily nitrosamine. * Tertiary amines - form soluble nitrite salts.

Answer 26

Nitrous Acid Test