Organic Chemistry: Alcohols

Organic Chemistry: Alcohols

Introduction to Alcohols

  • Alcohols are a group of organic compounds characterised by the presence of one or more hydroxyl (–OH) groups.
  • The simplest alcohol is methanol (CH3OH), with one carbon atom.
  • Other examples include ethanol (C2H5OH) and propanol (C3H7OH) which have two and three carbon atoms respectively.
  • The general formula for alcohols is CnH2n+1OH where n is the number of carbon atoms.
  • They are typically less dense than water, have a distinctive odour, and are colourless.

Physical Properties of Alcohols

  • Alcohols have higher boiling points than similar sized alkanes due to the ability of alcohols to form hydrogen bonds.
  • Alcohols are generally soluble in water because they can form hydrogen bonds with water molecules. However, the solubility decreases as the length of the hydrocarbon chain increases.
  • Being neutral substances, the pH of an alcohol solution is typically around 7.

Reactions of Alcohols

  • Alcohols undergo combustion, reacting with oxygen to produce carbon dioxide and water while also releasing energy.
  • Alcohols can be oxidised to produce aldehydes and carboxylic acids.
  • Dehydration of alcohols using an acid catalyst forms alkenes and water.
  • Alcohols can react with carboxylic acids in a process called esterification to form esters - used in making perfumes and flavourings.

Uses of Alcohols

  • Methanol is used as a solvent, antifreeze, and in making formaldehyde.
  • Ethanol is the alcohol present in alcoholic drinks, and is also used as a solvent in the manufacture of medicines and cosmetics, and as an alternative fuel source.
  • Alcohols are used as intermediates in the manufacture of other chemicals and as disinfectants.

Environmental Impact and Responsibility

  • While burning ethanol produces carbon dioxide, it is often considered a cleaner fuel than gasoline due to a lower production of soot and nitrogen oxides.
  • Ethanol for fuel can be obtained from fermentation of sugarcane or corn, which absorbs CO2 while growing, potentially making it a carbon-neutral energy source.
  • However, the farming practices associated have their own environmental impacts - deforestation, use of pesticides, and competition with food crops.