Aromatic compounds and amines

• Benzene features

  • Clyclic, planar molecule
  • Carbon has 4 valent electrons, each carbon is bonded to 2 other carbons and 1 hydrogen, the final lone electron is in a P-orbital which sticks out above and below the planar ring
  • Due to the delocalised ring of electrons structure, all C-C bonds in the molecule are the same bond length
  • Bond length lies between a single and double bond
• Benzene V kekules benzene stability

  • Benzene is 152 Kj mol-1 more stable (3x-120 - -208)
  • From enthalpy of hydrogenation data
  • Due to the delocalised electron structure and equal bond lengths
• Uses of benzene

  • Pharmaceuticals
  • Dyes
• Friedel-Crafts Acylation, electrophile generation

  AlCl3 + RCOCl -> AlCl4- + ROC+
• Friedel-Crafts Acylation mechanism

  • Delocalised ring to the positive carbon
  • H bond to the positively charged ring
  • H that has dropped off reacts with AlCl4- to create AlCl3 + HCl

  
• Why do we nitrate benzene

  • To produce dyes
  • explosives
  • Pharmaceuticals
• Nitration of benzene electrophile generation

  HNO3 + H2SO4 -> NO2+ + HSO4- + H2O
• Nitration of benzene mechanism

  • Electrons from the delocalised ring to the electrophile
  • H bond to the positive ring
  • H+ drops off and refoms H2SO4

  
• How to reduce multiple nitrations of benzene

  • Low temperature of below 55
• Use of quaternary ammonium salts

  • Cationic surfactants used to make cleaning products such as shampoo, laundry detergents and washing up liquids
  • Creates a micelle with dirt/oil
  • Hydrophilic tails point towards hydrophilic oil and hydrophobic head is attracted to the water
  • Also removes static from hair as it is attracted to the negative charge
• Amines as a base

  • A proton bonds to an amine via a coordinate bond, both electrons in the bond originate from the lone pair of nitrogen
• Base strength of amines

  • Tertiary amine > Secondary amine > Primary amine > Ammonia > Aromatic amines
  • Benzene is a withdrawing group so it pulls electrons away from nitrogen into the ring, reducing lone pair availability
  • Alkyl groups perform the positive inductive effect onto the nitrogen, increasing the density of the lone pair on the nitrogen so availability is increased
• Making aliphatic amines

  • Reacting with excess ammonia; impure product as reaction keeps going to make secondary and tertiary amines alongside quaternary ammonium salts
  • Reduction of nitriles
• Reducing nitriles reaction with catalyst

  • Nickle catalyst and hydrogen gas with high temperature and pressure
  • Catalytic hydrogenation reaction
  • RCH2CN + 2H2 -> RCH2CH2NH2
• Reducing nitriles with a strong reducing agent

  • LiAlH4 and dilute acid (More expensive than Ni & H2)
  • RCH2CN + 4[H] -> RCH2CH2NH2
• Making aromatic amines

  • Nitrobenzene with concentrated HCl and tin catalyst
  • Salt produced is reacted with NaOH to produce aromatic amine
  • H

  
• Amide features

  • -CONH2
  • N-Substituted amine = amide with a H group replaced with an alkyl group