Chemistry: Alcohols, Carboxylic Acids and Esters

Alcohols
1. Alcohols are a homologous series of organic compounds that contain the functional group -OH.
  1. Homologous series: A family of compounds that share a functional group and therefore have similar chemical reactions and have trends in physical properties.
  2. The first three are methanol, ethanol and propanol.
    1. They are highly flammable, making them good to use as fuels.
    2. Also used as solvents in marker pens, medicines and cosmetics
  3. Ethanol is the alcohol found in alcoholic drinks such as wine and beer and is usually mixed with petrol for use as fuel
  4. They follow the rule C(n)H(n+2)OH
  5. They are colourless liquids that dissolve in water to form neutral solutions (pH7)
  6. React with sodium to produce hydrogen and a salt
    1. E.g.: ethanol + sodium --> hydrogen + sodium ethoxide
  7. Burn in air, releasing energy and producing CO2 and water.
    1. E.g.: methanol + oxygen --> carbon dioxide + water 2CH3OH + 3O2 --> 2CO2 + 4H2O
      1. Ethanol + oxygen --> carbon dioxide + water 2C2H5OH + 6O2 --> 4CO2 + 6H2O
        Propanol + oxygen --> carbon dioxide + water 2C3H7OH + 9O2 --> 6CO2 + 8H2O
Carboxylic Acids
1. Carboxylic acids are a homologous series of organic compounds with the functional group -COOH
  1. Names end with '-oic acid', ie ethanoic acid
  2. Vinegar is an aqueous solution containing ethanoic acid formed through the oxidation of ethanol.
    1. This can be done through either adding oxidising agents, such as acidified potassium dichromate, or the action of microbes in aerobic conditions.
      1. This is noticed on small scales when a bottle of wine is left open and exposed to air- on a commercial scale it is achieved in a fermenter using acetic acid bacteria
  3. Dissolve in water to produce acidic solutions (pH below 7)
  4. React with carbonates to produce carbon dioxide, a salt and water.
    1. E.g.: Calcium carbonate + ethanoic acid --> calcium ethanoate + water + carbon dioxide
  5. All react with alcohols to form esters when in the presence of an acid catalyst.
    1. E.g.: ethanol + ethanoic acid --> ethyl ethanoate + water
  6. Ionisation of weak acids
    1. Strong acids such as hydrochloric acid ionise fully in water
      1. HCl --> H+ + CL-
      2. Their aqueous solutions have a high concentration of hydrogen ions, H+, giving them a low pH.
    2. Carboxylic acids are weak acids. They do not completely ionise when they are dissolved in water. Instead, only some of the molecules ionise to form H+ ions
      1. Ch3COOH <---> CH3COO- + H+
      2. This means an aqueous solution of a weak acid will have a higher pH compared to the same concentration of an solution of a strong acid.
      3. Weak acids still have a pH below 7.
Esters
1. A group of organic compounds with the functional group -COO-
2. They are volatile- liquids that can become vapours easily
3. They have distinctive 'fruity' smells
4. Used as food flavourings and perfumes due to their properties
5. Ethyl Ethanoate
  1. Ethyl ethanoate is the ester made from ethanol and ethanoic acid, with sulphuric acid used as a catalyst
    1. http://www.bbc.co.uk/schools/gcsebitesize/science/triple_aqa/alcohols_carboxylic_acids_esters/esters/revision/1/
      1. Diagram of reaction
    2. Ethanol + ethanoic acid <---> ethyl ethanoate + water
      1. CH3CH2OH + CH3COOH <---> CH3CH2OOCCH3 + H2O
6. Alcohol makes the first part of the name, carboxylic acid makes the second
  1. E.g.: Ethanol + Proanoic acid = Ethyl propanoate, Butanol + methanoic acid = Butyl methanoate

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