Organic reactions: SAQ 2

Addition Reactions

• Addition reactions occur only in organic compounds with double or triple bonds
• Ethene (C₂H₄) is a commonly used example in addition reactions
• The general equation for addition reactions involving ethene is:
  • C₂H₄ + X₂ → C₂H₄X₂
• Examples of addition reactions involving ethene:
  • Reaction with chlorine (Cl₂): C₂H₄ + Cl₂ → C₂H₄Cl₂
  • Reaction with bromine (Br₂): C₂H₄ + Br₂ → C₂H₄Br₂
  • Reaction with hydrogen chloride (HCl): C₂H₄ + HCl → C₂H₅Cl
  • Reaction with hydrogen (H₂): C₂H₄ + H₂ → C₂H₆
  • Reaction with water (H₂O): C₂H₄ + H₂O → C₂H₅OH

Polymerisation Reactions

• Polymerisation reactions involve the addition of molecules to form a large chain
• Ethene is used to produce polyethene, a common plastic
• The reaction involves the combination of many ethene molecules:
  • nC₂H₄ → [C₂H₄]ₙ
• Polyethene is used in various products, such as plastic bags, ropes, and wrapping material

Substitution Reactions

• Substitution reactions involve the replacement of an atom or group of atoms with another atom or group of atoms
• These reactions occur in saturated molecules (i.e., molecules with only single bonds)
• The general equation for substitution reactions is:
  • R-X + Y-Z → R-Y + X-Z
• Example of substitution reaction: chlorination of methane (CH₄):
  • CH₄ + Cl₂ → CH₃Cl + HCl

Esterification

• Esterification is a substitution reaction between a carboxylic acid and an alcohol to form an ester
• The general equation for esterification is:
  • RCOOH + R'OH → RCOOR' + H₂O
• Example of esterification: reaction between ethanoic acid (CH₃COOH) and methanol (CH₃OH):
  • CH₃COOH + CH₃OH → CH₃COOCH₃ + H₂O

Base Hydrolysis and Soap Manufacture

• Base hydrolysis is the reaction of an ester with a base to form a carboxylic acid and an alcohol
• The general equation for base hydrolysis is:
  • RCOOR' + OH⁻ → RCOO⁻ + R'OH
• Example of base hydrolysis: reaction between ethylethanoate (CH₃COOC₂H₅) and sodium hydroxide (NaOH):
  • CH₃COOC₂H₅ + NaOH → CH₃COONa + C₂H₅OH
• Soap manufacture involves the base hydrolysis of esters to form carboxylic acid salts (soaps)

Elimination Reactions

• Elimination reactions involve the removal of a small molecule from a larger molecule, leaving a double bond
• The general equation for elimination reactions is:
  • R-X → R-X + H₂O
• Example of elimination reaction: dehydration of ethanol (C₂H₅OH) to form ethene (C₂H₄):
  • C₂H₅OH → C₂H₄ + H₂O

Oxidation and Reduction Reactions

• Oxidation reactions involve the gain of oxygen or loss of hydrogen
• Reduction reactions involve the loss of oxygen or gain of hydrogen
• Examples of oxidation and reduction reactions:
  • Oxidation of primary alcohols to aldehydes: RCH₂OH → RCHO + H₂O
  • Reduction of aldehydes to primary alcohols: RCHO + H₂ → RCH₂OH
  • Oxidation of aldehydes to carboxylic acids: RCHO → RCOOH

Breath Tests

• Breath tests involve the oxidation of primary alcohols to carboxylic acids using acidified sodium dichromate (Cr₂O₇²⁻)
• The reaction is detected by a colour change from orange to green

Oxidation of Alcohols to Carboxylic Acids

• The reaction involves the oxidation of primary alcohols to carboxylic acids using potassium permanganate (KMnO₄)
• The reaction is detected by a colour change from purple to brown

Reduction of Carboxylic Acids

• The reaction involves the reduction of carboxylic acids to primary alcohols using hydrogen gas (H₂) and a nickel catalyst (Ni)

• The reaction is detected by a colour change from brown to colourless### Carboxylic Acids Reactions

• Carboxylic acids react by losing a H+ ion due to the inductive effect of the oxygen atom, which polarizes the O-H bond.

Reaction as Acids

• Carboxylic acids react with:
  • Mg metal to form a salt and hydrogen gas
    • 2CH₃COOH + Mg → (CH₃COO)₂Mg + H₂
  • Sodium hydroxide to form a salt and water
    • CH₃COOH + NaOH → CH₃COONa + H₂O
  • Sodium carbonate to form a salt, water, and carbon dioxide
    • 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂

Organic Synthesis

• Synthesis is the formation of a chemical compound from simpler compounds.
• Example: Aspirin is synthesized from simpler products in the lab, rather than extracted from natural sources.
• Synthesis involves breaking and making of bonds, and may involve up to 3 conversions in a synthesis pathway diagram.