Reactions of benzene

Electrophilic substitution of benzene

  • A+ = any electrophile

  • be really careful not to draw the delocalised ring too long

    • do not extend past the two neighbouring carbons (correct shown in step 2)

general mechanism for all electrophilic substitution reactions of benzene

Nitration of benzene

  • mechanism

nitration of benzene mechanism

  • Formation of the electrophile

    • sulphuric acid is acting as acid

    • nitric acid is acting as base

    • also means sulphuric acid acts as a catalyst

      • regains H+ ion from reaction so never used up

      • hence sits above arrow in full equation

    • done at 50C

      • monosubstitution

forming NO2+

  • overall equation

nitrification of benzene

Nitration summarised

  • electron ring attracts electrophiles

  • a bond forms using delocalised electrons

  • the aromatic ring is lost briefly before electrons from the hydrogen bond restore the delocalised system

  • sulphuric acid acts as a catalyst and is restored by the addition of the hydrogen ion formed

Halogenation of benzene

  • formation of the electrophile uses a halogen carrier

  • induces polarisation and produces a halogen electrophile

  • FeBr3 is regenerated in step 3 thus acts as a catalyst

    • Cl2 and AlCl3 can also be used in the same way

      formation of the electrophile using a halogen carrier

halogenation of benzene

Alkylation

  • reagents and conditions

    • alkyl chloride, RCl

    • halogen carrier catalyst eg. AlCl3

    • anhydrous conditions

alkylation

Acylation

  • reagents and conditions

    • acyl chloride, RCOCl

    • halogen carrier catalyst eg. AlCl3

    • anhydrous conditions

acylation