substitution reactions

• method 1: hydrogen halides: R-OH + H-X -> R-X + H2O

  heat under reflux

  strongly acid
• conditions for substitution reaction of hydrogen halide:

  aqueous (acidic) - so H+ ion is separate and not covalent structure

  vigorous - heat under reflux
• method 2: NaX and H2SO4

  alcohols do not react with non-acidic NaCl, NaBr and NaI

  alcohols can be converted to haloalkanes by reacting them with an acid catalyst (generates hydrogen halide which will react)
• generation of HBr:

  NaBr(s) + H2SO4(aq) --> NaH2SO4(aq) + HBr (aq)
• substitution:

  CH3CH2OH + HBr -> CH3CH2Br + H2O

  for iodine, use phosphoric acid (H3PO4) instead of sulfuric acid, still heat under reflux
• order of reactivity:

  • the OH groups in alcohols are substituted with halide ions in the presence of acid to form haloalkanes
  • tertiary > secondary > primary
  • in hydrogen halides: HI > HBr > HCl
  • acid catalyst needed