Halogenoalkanes

• General formula of Halogenoalkanes?

  CnH2n+1 X
• Uses of halogenoalkanes

  Refrigerants

  Solvents

  Pharmaceutical
• Nucleophile

  Electron pair donor
• Halogenoalkanes take part in nucleophilic substitution because the carbon-halogen bond is polar
• Halogenoalkanes react with aqueous hydroxides to form alcohols
• Hydrolysis?

  breaking of bonds using water
• Hydrolysis:

  Reagent - sodium hydroxide solutions

  Conditions-warm and aqueous
• Halogenoalkanes react with potassium cyanide to form nitriles
• Reaction with potassium cyanide

  Reagent - KCN

  Conditions - warm ethanol
• reacting a halogenoalkane with cyanide increases length of the carbon chain
• Halogenoalkanes react with excess ammonia to form amines
• reaction with excess ammonia?

  Reagent - excess ammonia

  Conditions - warm in a sealed tube, ethanol solvent
• The rate of reaction can be measured by timing how long it takes for a precipitate of silver halide to form
• to ensure it is a fair test:

  • use equal amounts in mol of each halogenoalkanes
  • use halogenoalkanes with the same chain length
  • use a water bath to ensure a constant temperature
• Elimination?

  reaction in which an atom or group of atoms is removed from a reactant
• in an elimination reaction halogenoalkanes reacts to form an alkene
• Elimination

  Reagent: sodium (or potassium) hydroxide

  Conditions: reflux in ethanol
• in an elimination reaction

  • the halogen atom is always removed
  • A H atom from an adjacent C atom is also removed
  • A double bond forms between the two C atoms
• Ozone forms in the upper atmosphere from the reaction of oxygen atoms with oxygen molecules.

  O2 + O. ->O3

  The ozone layer is beneficial because it absorbs the UV radiation that can cause skin cancer
• Waste CFCs do not break down easily and would rise up to the upper atmosphere and break down to form chlorine radicals.

  CCl3F -> .CCl2F + Cl.

  chlorine radicals catalyse the breakdown of ozone and have led to a hole in the ozone layer.

  Cl.+O3 -> O2 + ClO

  ClO. +O3 -> 2O2 + Cl.

  Overall equation is

  2O3 -> 3O2
• Chemist have developed an alternative organohalogen compounds that do not contain chlorine
• Halogenoalkanes react with excess ammonia to form amines
• Reaction with amines

  Reagent: NH3

  Conditions: excess ammonia, warm ethanol

  General equation:

  RX + 2NH3 --> RNH2 + NH4X
• 1-chlorobutane forms a white precipitate of AgCl
• 1-bromobutane forms a cream precipitate of AgBr
• 1-iodobutane forms a yellow precipitate of AgI
• 1-chlorobutane takes the longest for a precipitate to appear while 1-iodobutane takes the fastest for a precipitate to appear