Topic 10C: Alcohols in Organic Chemistry

Overview

• Focus on alcohols as part of haloalkanes, alcohols, and spectra topic
• Learning outcomes:
  • Nomenclature and drawing of alcohols
  • Classification of alcohols: primary, secondary, tertiary
  • Specific reactions: halogenation and oxidation
  • Techniques for preparation and purification of liquid organic compounds
  • Practice with past paper questions

Alcohols

• Alcohols are part of a homologous series with the general formula CnH2n+1OH
• Not hydrocarbons due to the hydroxyl (OH) group
• Formula can be simplified to ROH (R = alkyl group, e.g., ethyl, propyl)

Nomenclature

• Similar naming as branched alkanes, alkenes, halogenoalkanes
• Important to identify the location of the hydroxyl group due to structural isomers
• Prefixes used for multiple alcohol groups: diol (2), triol (3)

Classification

• Based on number of alkyl groups attached to the carbon with OH:
  • Primary: 1 alkyl group
  • Secondary: 2 alkyl groups
  • Tertiary: 3 alkyl groups
• Classification affects reactivity

Reactions of Alcohols

1. Combustion

   • Alcohols are very flammable
   • Complete combustion forms CO2 and H2O

2. Conversion to Halogenoalkanes (Halogenation)

   • Replaces OH with a halogen (Cl, Br, I)
   • Different methods and reagents for Cl, Br, and I
     • Chlorination: PCl5 for primary/secondary, concentrated HCl for tertiary
     • Bromination: Potassium bromide and 50% concentrated sulfuric acid
     • Iodination: Red phosphorus and iodine, heated under reflux

3. Dehydration to Alkenes

   • Heating with concentrated phosphoric acid (H3PO4)
   • Forms alkenes by removing OH and adjacent H, forming a double bond

4. Oxidation

   • Involves loss of hydrogen from carbon and OH group, forming carbonyl group
   • Primary alcohols: Oxidized to aldehydes then to carboxylic acids
   • Secondary alcohols: Oxidized to ketones (no further oxidation)
   • Tertiary alcohols: Cannot be oxidized

Oxidation Tests

• Tests to distinguish between alcohols and identify oxidation:
  • Acidified potassium dichromate: color change from orange to green for primary/secondary alcohols or aldehydes
  • Fehling's/Benedict's solutions: red precipitate for aldehydes
  • Tollen's reagent: silver mirror for aldehydes

Preparation and Purification

• Reflux: For complete oxidation to carboxylic acids
  • Vapors condense and return to flask
• Distillation: For partial oxidation to aldehydes
  • Separates substances based on boiling points
• Solvent Extraction: Using separating funnel to isolate products
• Drying: Removing water using drying agent like anhydrous metal salts
• Purity Testing: Melting/boiling points compared to known values

Exam Practice

• Multiple choice and structured questions on alcohol properties, structures, and reactions
• Example questions:
  • Identify tertiary alcohols
  • Explain solubility differences in alcohols
  • Describe chemical tests for oxidation products

Additional Resources

• Check past paper questions for practice
• Videos and tutorials on reactions and preparation techniques

Conclusion

• Understanding alcohol chemistry is crucial for further organic chemistry studies
• Practice with questions and experiments to reinforce learning

Feel free to revisit this topic and use these notes for exam preparation and further studies.