Experiment 3: Classification Tests for Hydrocarbons, Organic Halides, and Amines

Hydrocarbons

one of the two general classification of organic compounds. These compounds are composed entirely of C and H atoms that are arranged and bonded in specific ways.

Factors Affecting the Physical and Chemical Properties of Organic Compounds

• Molecular Geometry

• Presence of Functional Groups

• Number of Carbon Atoms and Branching

• Intermolecular Force of Attraction (IMF)

Physical States of Hydrocarbons

• Physical states and proper are influenced by IMFs

• Higher IMF (stronger) = Higher MP and BP

• Higher Presence of polar function groups = Higher MP and BP

• Higher number of Carbons = Higher MP and BP

• Higher branching (more) = Lower MP and BP

Hydrocarbons can be classified as:

• Aliphatic or Aromatic

• Acyclic or Cyclic

• Saturated, Unsaturated, or Actively Unsaturated

Solubility Test in H2SO4

1. Place 1 mL of H2SO4 in test tube

2. Add 1-2 drops of the sample to their assigned test tube

3. Determine which sample is MISCIBLE or IMMISCIBLE

Solubility Test

Generalities:

• Solubility is inversely related to melting point (Higher MP = Lower solubility)

• In isomers, cis- isomeric forms are more soluble than trans'-

• Higher Molecular Weight = High IMF = Low solubility

• Branched-chain is more soluble than straight-chain. The position of a functional group can also affect solubility (similar to the concept of branched-chain).

Ignition Test

1. Place 3-5 drops of sample in a small evaporating dish.

2. Light the sample with a match. Observe the results.

3. Observe for samples: Flammability Color of flame Burning Time

Ignition Test

• Combustibility

• Flammability

Combustibility

a measure of how easily a substance bursts into flame through fire or combustion.

Flammability

is the ease with which a combustible substance can be ignited causing fire, combustion, or even explosion.

Test of Unsaturation

• Baeyer’s Test

• Bromine Test

• Iodine Test

Test of Unsaturation: Baeyer’s Test

1. Place 5 drops of the sample in a clean and dry test tube.

2. Add 2 drops of 2% KMnO4. Observe for decolorization.

3. Observe as for the formation of brown sludge or suspension.

• In a separate test tube, place water and use is as your standard for decolorization.

• Solution decolorizes immediately if it happens within 1 minute.

Test of Unsaturation: Bromine Test

1. Place 5 drops of the sample in a clean and dry test tube.

2. Add 10 drops of 0.5% Br2 in CCl4 reagent. Shake. Observe for decolorization.

3. Observe as for the formation of bromine discharge (brownish red).

• In addition, place a moistened blue litmus paper on a glass rod and place it across the mouth of the test tube. Note the color change.

Baeyer’s Test

uses KMnO4 and is a form of oxidation reaction which forms a brown suspension/sludge. It detects the presence of active unsaturation like in alkenes and alkynes.

Bromine Test

uses Br2 in CCl4 to confirm the presence of double/triple bonds. It is an addition reaction in which the Br2 solution is decolorized when mixed with unsaturated compounds.

Iodine Test

used I2 solution and is also an addition reaction used to confirm the presence of alkene/alkynes. The positive results for this test is the formation of a tan-colored solid while retaining the color of the I2 solution.

Test for Aromaticity via Nitration Reaction

1. Place 5 drops of sample in a clean and dry test tube

2. Add 8 drops of the nitrating mixture

3. Shake vigorously for complete mixing. Observe for yellow oily layer or droplet.

4. Dilute the resulting solution with 2 drops of water. Observe for reaction.

5. If no observed reaction. Place the test tube in water bath for 10 minutes.

6. Dilute with 20 drops of water. Observe for results.

Test for Aromaticity via Nitration Reaction

• Nitration is a common substitution reaction for aromatic molecules. It is used to detect the presence of benzene rings in a compound.

• The formation of a yellow oily layer confirms the presence of a benzene ring.

• NOTE: The presence of electron-donating groups (e.g. -
  CH3 ) on the benzene ring will result into faster reaction.

Basic Oxidation

1. Place 4 drops of sample in a clean and dry test tube.

2. Add 8 drops of 2% KMnO4 and 3 drops of 10% NaOH.

3. Place the test tubes in a water bath for 20 minutes. Observe for color change or brown precipitate.

Basic Oxidation

• This test uses KMnO 4 in NaOH solution and is often referred to as mild oxidation.

• It can be used to detect the presence of alkene and benzylic carbon (must have benzylic hydrogen) that are both susceptible to oxidation.

• A brown precipitation or suspension confirm the presence of the target organic compounds.

Organic Halides

• or haloalkanes (RX) are organic compounds that contains a halogen moiety (-X = F, Cl, Br and I).

• They can be categorized based on the type of alpha carbon they posses in the structure.

General Properties

• Organic halides (RX) are mostly synthetic.

• RX is soluble in organic solvent but are insoluble in water despite being polar.

• RX can exhibit dipole-dipole interactions because of the C-X bond where the polarity is shifted -X causing it to be polar.

• The bond strength of C-X decreases as the size of the halogen increases. Iodine is a better leaving group during reactions compared to fluorine.

• RX reacts via substitution and elimination reactions.

Beilstein Test / Copper Halide Test

1. Using a copper wire, create a small loop in one end.

2. Heat the copper wire until the green color it produces disappears. Cool the loop.

3. Dip the loop in a sample and heat the sample in the loop. Observe for resulting colors.

• Note: You can use the same copper wire for all the sample. Just rinse it and reheat before dipping into another sample.

• A blue-green flam indicates the presence of Br, Cl, and I.

Beilstein Test / Copper Halide Test

• This is a flame test that detects the presence of halogens from samples.

• It uses CuO that reacts with the halogen forming copper-halide compounds which is visible via formation of blue-green flame.

Nucleophilic Substitution Reactions (Sn1 and Sn2)

• Sn1 - Reaction with Alcoholic AgNO3

  • The Ag in AgNO3 acts as a Lewis acid and promotes the formation of the carbocation. AgX is formed as a by-product together with the R+.

Nucleophilic Substitution Reactions (Sn1 and Sn2)

• Sn2 - Reaction with Nal in Acetone

  • Before starting, make sure the reagent is not turbid.

1. Place 5 drops of sample in a clean and dry test tube.

2. Add 2 drops of 15% Nal in anhydrous Acetone.

3. Shake and record the time to form the NaX precipitate. Note the color of precipitate.

Nucleophilic Substitution Reactions (Sn1 and Sn2)

• Sn2 - Reaction with Nal in Acetone

  • The I- in Nal in acetone displaces the X in not sterically hindered RX (primary or secondary RX) resulting in R-I (alkyl iodide) and a NaX (Br or Cl) salt.

  • Nal is soluble in acetone but NaBr/NaCl are not and will form a precipitate indicating the occurrence of an Sn2 reaction.

Amines

are nitrogen-containing organic compounds which can be classified as primary, secondary, or tertiary based on the number of alkyl (R-) groups attached to the nitrogen atom.

• Aniline (primary amine)

• N-methylaniline (secondary amine)

• N,N - dimethylaniline (tertiary amine)

General Properties

• RNH2 are basic and have a characteristic fishy odor and can exist as liquid (low carbon) or solids (higher carbon) depending on the number of carbons.

• The presence of H atoms results into hydrogen bonding which cause higher boiling for primary amines (BP primary > secondary > tertiary).

• Amines are soluble in water due to its ability to undergo H- bonding. However, as the size of the alkyl group increases, water solubility decreases.

• Aromatic amines (ex. Aniline) readily undergoes atmospheric oxidation can gets colored as a result.

Hinsberg Test

1. In a test tube, place approximately 0.3 ml of the sample.

2. Add 5 ml 10% NaOH and 0.4 ml benzene sulfonyl chloride.

3. Cover the test tube. Shake vigorously for 5 minutes. Observe for results.

Solubility with HCl and NaOH

1. Test the resulting solution from Hinsberg test for alkalinity using a litmus paper.

2. If solution is not alkaline, add 4M KOH drowse until alkalinity is achieved.

3. Place test tube in a rack and stand the alkaline solution for 10 minutes.

4. After standing, add 6M HCl dropwise, until solution is acidic. Note for results.

5. If a precipitate forms, collect the precipitate in a test tube with 3 mL of 2.5M NaOH.

6. Heat the solution in a water bath. Shake for 2 minutes. Note for results.

Hinsberg Test

• This uses benzene sulfonyl chloride to differentiate between primary, secondary, and tertiary amines.

  • Primary amines forms alkali soluble sulfonamide product.

  • Secondary amines forms alkali insoluble sulfonamide product.

  • Tertiary amines do not react.