Oxidation of food, fragrances and skin care

• The partial oxidation of an alcohol can be brought about by using an oxidising agent.
• Some typical oxidising agents are:

  • acidified potassium dichromate solution
  • acidified potassium permanganate solution
  • hot copper (II) oxide (black solid)
  • Benedict’s reagent
  • Tollen’s reagent (silver-mirror)
• Oxidation of primary alcohols forms two products in a two stage reaction.
• alkanes general formula = CnH2n+2
• alkenes general formula= CnH2n
• Isomers are compounds with the same molecular formula but different structural formulae. Isomers may belong to a different homologous series and usually have different physical properties.
• The chemical test for unsaturation – a double bond (e.g. an alkene) is it decolourises bromine water Alkenes undergo addition reactions: the addition of a small molecule across a double bond
• Molecules with more carbons have stronger forces of attraction between the molecules therefore it takes more energy to separate these molecules. These molecules have stronger intermolecular forces.
• alcohols functional group is hydroxyl
• alcohol general formula= CnH2n+1 OH
• Alcohols can be divided into 3 types depending on the position of the –OH. The three types are primary, secondary and tertiary
• As the number of hydroxyl groups increases the boiling points tend to increase. This is because hydroxyl groups are polar, and this leads to more hydrogen bonding hence more energy is needed to break them.
• stronger intermolecular forces mean higher melting points, increased viscosity (thickness) and increased solubility in water.
• carboxylic acid Functional group = Carboxyl group (-COOH group)
• carboxylic acid General formula: CnH2nO2
• When naming the -COOH carbon MUST be counted as one of the carbons When numbering the -COOH carbon is always carbon 1
• Metal oxide + carboxylic acid → salt + water

  eg Sodium oxide + ethanoic acid → sodium ethanoate + water
• Metal hydroxide + carboxylic acid → salt + water

  e.g. Sodium hydroxide + methanoic acid → sodium methanoate + water
• Metal carbonate + carboxylic acid → salt + water + carbon dioxide

  e.g. Calcium carbonate + propanoic acid → calcium propanoate + water + carbon dioxide
• Esters are formed by reacting an alcohol with a carboxylic acid. This is known as an esterification reaction which is an example of a condensation reaction (two molecules are joined with the elimination of a small molecule - water)
• Alcohol + Carboxylic acid → Ester + Water
• Alcohols contain the functional group -OH (hydroxyl group) and are characterised by the name ending in -ol
• Carboxylic acids contain the functional group –COOH (carboxyl group) and are characterised by the name ending in –anoic acid.
• Esters contain the functional group –COO- (ester link).
• Esters are made in a lab by the condensation reaction between and alcohol and carboxylic acid.
• The tube is placed in a beaker of hot water/water bath (not heated with a Bunsen since alcohols are flammable.
• A wet paper towel is put around the top of the test tube to act as a condenser.
• Concentrated sulphuric acid is added as a catalyst.
• Equal quantities of the reactants (alcohol and carboxylic acid) are added to a test tube.
• Reaction mixture is poured onto sodium hydrogen carbonate solution to neutralise the conc. sulphuric acid and any unreacted carboxylic acid.
• Evidence the ester has formed: 1) distinct smell 2) two layers are formed
• Esters are used as flavourings and fragrances as many have pleasant, fruity smells.
• Esters are also used as solvents for non-polar compounds that do not dissolve water
• Why does dichromate need to be acidified

  to provide H+ ions
• What’s the formula of an isoprene

  C5H10
• Propanone and propanal both contains the same functional group, what’s the group?

  Carbonyl