WM1

Alcohols

Physical Properties of Alcohols

• Polar due to \(O\)-\(H\) bond

• Able to hydrogen bond

  • Explains why alcohols have higher MBP’s than corresponding alkanes

  • Also explains why alcohol and water mix

• \(O\)-\(H\) bond becomes less influential in longer chains

  • Solubility in water decreases

  • Other properties more similar to those of corresponding alkanes

Reactions of Alcohols

Types of alcohols

Primary alcohols:

• -\(O\)-\(H\) carbon bonded to one other

Secondary alcohols:

• -\(O\)-\(H\) carbon bonded to two others

Tertiary alcohols:

• -\(O\)-\(H\) carbon bonded to three others

Oxidation

• The \(O\)-\(H\) group is oxidised by strong oxidising agents

  • Acidified Potassium Dichromate(VI), \(K_2Cr_2O_7\)

    • Orange dichromate ion reduced to green chromate(III) ion

    • \(Cr_2O_7^{2-}\Rightarrow Cr^{3+}\)

• \(O\)-\(H\) group converted to carbonyl \(C\)=\(O\) group

• Will not take place if there is no hydrogen attached to the carbon

• Carbonyl formed depends on reacting alcohol and conditions

  • Aldehyde or ketone

Heating under Reflux

• Safer when using volatile compounds

• Prevents loss of solvent, reagent, or product

Oxidation of Primary alcohols

• Initially oxidised to an Aldehyde

• Can be further oxidised to a Carboxylic Acid

  • Excess oxidising agent

  • Under reflux

• If the Aldehyde is required:

  • Distilled in situ

    • Prevents further oxidation

  • Excess Alcohol

  • No reflux