Benzene

Benzene：phenol、side chain、reaction、structure、arene……

benzene

• arene
  • aryl compound
    • definition: compound of benzene
  • arene
    • definition: compound that contain at least one benzene ring
• structure
  • delocalised π bonding system
    • sideways overlap of carbon's p orbital, from each of the six carbon atoms
• reaction
  • electrophilic substitution
    • alkylation
      • benzene+halogenalkene→alkylbenzene+HX
      • catalyst
        • AlX3 only (where X is halogen ion)
      • mechanism
        • step1: make alkyl group from halogenalkene
          • halogenalkene+AlX3→alkyl group + [AlX4]+
        • step2: replace H with alkyl group
          • do remember the half circle
    • acylation
      • benzene+acychloride/bromide→acylbenzene+HX
      • catalyst
        • AlX3 only (where X is halogen ion)
      • mechanism
        • same as alkylation
    • nitration
      • NO2++benzene→nitrobenzene+H+
      • reagent
        • HNO3+H2SO4
      • condition
        • temperature：25℃~60℃
      • mechanism
        • step1: HNO3+H2SO4→NO2＋+2HSO4-+H3O+
        • step2: replace H with NO2+
  • free-radical substitution
    • alkylbenzene+halogen
    • replaced H is on alkyl group
  • oxidation
    • oxidasing agent: KMnO4
    • acidified with dilute H2SO4
    • alkylbenzene+[O]→C6H5COOH+H2O
      • carbon in alkyl group must bonded to at leat one hydrogen (i.e,tertiary carbotation cannot be oxidised)
      • one alkyl group can only produce one carboxyl group
  • hydrogenation
    • benzene+H2→cyclohexene
    • reaction condition
      • heating
      • catalysed by Ni/Pt (same as electrophilic addition)
    • side-chain is not change in this reaction
• side chain
  • electron-donating group
    • COOH/CHO/COR/NO2
    • activate position 1,3,5
      • it makes postion 1,3,5 becom partially negative, which is easier to attract electrophile
  • electron-withdrawing group
    • OH/R/NH2
    • activate position 2,4,6
      • make postion2,4,6 become partially negative, which is easier to attract electrophile
• phenol
  • feature
    • melting point:43℃ (relatively high)
    • state
      • solid (a few of them are liquid)
  • reaction
    • electronphilic substitution
      • similar as benzene
      • electrophile(s) is(are) connected at position 2,4,6
    • preparation
      • reagent: NaNo2,HCl,phenylamine
      • condition：temperature＜10℃
      • reaction
        • step1:NaNO2+HCl→NaCl+HNO2
        • step2:C6H5NH2+HNO2+HCl→C6H5N+≡NCl-(diazonmium salt)+2H2O
        • C6H5N+≡NCl- +2H2O→C6H5OH+HCl+N2
          • condition:warming
    • with Na metal
      • 2C6H5OH(l)+2Na→2C6H5ONa+H2
    • with alkaline
      • C6H5OH(l)+NaOH→C6H5ONa+H2O
  • acidity (compare with alcohol)
    • phenol＞alcohol
      • reason
        • the negative charge of C6H5O-spread over the benzene ring, overlapping with the π system, so electron density is low, which attract H+less readily.
        • electron spread densely on C2H5O-due to the inductive effect of alkyl group,so it's easier to accept H+
        • the stronger the conjegate base, the weaker the acid
  • solubility
    • water
      • slightly soluble
        • benzene ring is non-polar, which disrupt the interation between C6H5OH and the OH- in water
    • alkaline solution
      • soluble
        • phenol is acidic, so it will react with alkaline to form soluble salt and water
  • reactivity (compare with benzene)
    • more reactive than bezene
  • naphthol