• Alcohols?are reactive molecules which undergo a wide range of reactions

Combustion of alcohols

• Alcohols react with oxygen in the air when ignited and undergo?complete combustion?to form carbon dioxide and water

Alcohol + oxygen → carbon dioxide + water

Complete combustion of alcohols to produce carbon dioxide and water

Substitution of alcohols

• In the?substitution?of alcohols, a hydroxy group (-OH) is replaced by a halogen to form an?halogenoalkane
• The substitution of the alcohol group for a halogen can be achieved by reacting the alcohol with:
  • HX (rather than using HBr, KBr is reacted with H₂SO₄?or H₃PO₄?to make HBr that will then react with the alcohol)
  • PCl₃?and heat
  • PCl₅?at room temperature
  • SOCl₂

Substitution of alcohols to produce halogenoalkanes

Reaction with Na

• When an alcohol reacts with a?reactive metal?such as sodium (Na), the oxygen-hydrogen bond in the hydroxy group?breaks
• Though the reaction is less vigorous than sodium reacting with water,?hydrogen gas?is given off and a?basic?compound (alkoxide) is formed
  • If the excess ethanol is evaporated off after the reaction a white crystalline solid of?sodium?alkoxide?is left

Alcohol + sodium → sodium alkoxide + hydrogen

• The longer the hydrocarbon chain in the alcohol, the less?vigorous?the reaction becomes

Alcohols react with Na to form a basic sodium alkoxide salt and hydrogen gas

Oxidation of alcohols

• Primary alcohols can be oxidised to form?aldehydes?which can undergo further oxidation to form?carboxylic?acids
• Secondary alcohols can be oxidised to form?ketones?only
• Tertiary alcohols do not undergo oxidation
• The oxidising agents of alcohols include?acidified K₂Cr₂O₇?or?acidified KMnO₄
• Acidified potassium dichromate(VI), K₂Cr₂O₇, is an orange oxidising agent
  • Acidified means that that the potassium dichromate(VI) is in a solution of?dilute?acid?(such as dilute sulfuric acid)
  • For potassium dichromate(VI) to act as an oxidising agent, it itself needs to be reduced
  • This reduction requires hydrogen (H⁺) ions which are provided by the acidic medium
    • When alcohols are?oxidised?the orange dichromate ions (Cr₂O₇^2-) are reduced to green Cr³⁺?ions
• Acidified potassium manganate(VII), KMnO₄, is a purple oxidising agent
  • As with acidified K₂Cr₂O₇?the potassium manganate(VII) is in an acidic medium to allow reduction of potassium manganate(VII) to take place
    • When alcohols are?oxidised,?the purple manganate ions (MnO₄^-) are reduced to colourless Mn²⁺?ions
• Warm primary alcohol is added to the oxidising agent
• The formed aldehyde has a lower boiling point than the alcohol reactant so it can be?distilled off?as soon as it forms
• If the aldehyde is not distilled off, further?refluxing?with excess oxidising agent will oxidise it to a carboxylic acid
• Since ketones cannot be further oxidised, the ketone product does not need to be?distilled off?straight away after it has been formed

Oxidation of ethanol by acidified K₂Cr₂O₇ to form an aldehyde by distillation and carboxylic acid by refluxing

Oxidation of propan-2-ol by acidified K₂Cr₂O₇?to form a ketone by distillation

Dehydration of alcohols

• Alcohols can also undergo?dehydration?to form alkenes
  • Dehydration is a reaction in which a water molecule is removed from a larger molecule
  • A dehydration reaction is a type of?elimination?reaction
• Alcohol vapour is passed over a?hot catalyst?of aluminium oxide (Al₂O₃) powder OR pieces of porous pot or pumice as well as concentrated acid can be used as catalysts

Dehydration of ethanol using aluminium oxide as a catalyst forms ethene gas, which can be collected over water

Esterification of Alcohols

• Esterification is a?condensation?reaction between a carboxylic acid and an alcohol to form an?ester?and a water molecule
• For esterification to take place, the carboxylic acid and alcohol are?heated under reflux?with a?strong acid catalyst?(such as H₂SO₄?or H₃PO₄)

Carboxylic acid + alcohol → ester + water

• The reaction is reversible so an equilibrium mixture can be established with all the reactants and products
• Esters have?sweet,?fruity smells

Esterification of ethanol and ethanoic acid using a strong acid catalyst to form ethyl ethanoate and water