Reduction carbonyl and Nitrobenzene

• Formation of nitronium ion, NO2+ (electrophile) at 50°C
• NO2+ nitronium ion is attracted to the delocalized π bond in benzene and attaches to one of the carbon atoms
• High activation energy (Ea) is required as the delocalized π bond in benzene is partially broken
• Positive charge is distributed over the remains of the π bond in the intermediate
• Intermediate loses a proton to HSO4- ion and forms back sulfuric acid as a catalyst
• Energy is evolved as the delocalized π bond is reformed and the benzene ring is reformed again
• Formation of nitrobenzene
• Reduction of Nitrobenzene with excess NaOH in reflux
• Phenylammonium chloride is protonated because of acidic conditions
• Phenylammonium chloride is deprotonated because of basic conditions
• Reduction with Sn/Zn/Fe and Conc. HCl
• Phenylammonium ion is protonated because of acidic conditions
• Phenylammonium ion is deprotonated because of basic conditions
• Reduction Reactions
• Reduction of carbonyl compounds
• Reduction of aldehydes and ketones using LiAlH4 or NaBH4
• Reduction of nitrobenzene to phenylamine
• Reduction with Sn/Zn/Fe, conc HCl and NaOH
• Oxidation of Aldehydes and Ketones
• Oxidation conditions: K2Cr2O7 & H2SO4
• Nucleophilic Addition of Hydride ion: Alcohol Formation
• Addition of hydride reagents produce alcohols by reduction of a carbonyl
• Occurs by basic nucleophilic addition mechanism
• Protonation after addition yields the alcohol
• Hydride ions act as reducing agents
• Reduction agents include lithium aluminium hydride (LiAlH4) and sodium borohydride (NaBH4)
• LiAlH4 and NaBH4 act as donors of hydride ion
• Reduction of Carbonyl and Reducing Agents
• NaBH4 (weaker RA) - Sodium borohydride/Sodium tertrahydridoborate
• LiAlH4 (stronger RA) - Lithium aluminium hydride/Lithium tetrahydridoaluminate/Hydrogen in the presence of catalyst (Ni, Pd, Pt)
• Protic solvent: alcohol (reacts with water & acidic)
• Condition:

  • NaBH4, ethanol/water
  • H+ (aq) 1st solvent: aprotic solvent Ether or THF (reacts with water & acidic) Tetrahydrofuran (THF)
• Condition:

  • LiAlH4, ether or THF
  • H+ (aq) Condition: H2 presence of catalyst (Ni, Pd, Pt)
• Reduction: aldehyde to 1° RRRRRR
• Reduction: ketone to 2° RRRRRR
• Unable to reduce RCOOH or ester to alcohol
• Nucleophilic Addition of Hydride ion:

  • Aldehyde reduction by NaBH4/LiAlH4 yields 1o alcohols
  • Ketone reduction by NaBH4/LiAlH4 yields 2° alcohols
• Structure of carbonyl group

  • Carbonyl carbon: sp2 hybridized
  • Trigonal Planar structure
  • Electron deficient carbon atom of carbonyl group
• Reduction of Carbonyl Compounds with Nucleophiles

  • Nucleophilic addition reaction to the electron deficient carbon atom of the carbonyl group
• Nucleophilic Addition

  • Aldehydes are more reactive than ketones
  • Aldehydes are more polarized than ketones
  • More alkyl groups stabilize the carbocation inductively