Question

all reduction reactions in jee advanced syllabus

Answer 1

The JEE Advanced syllabus covers numerous reduction reactions in Chemistry, predominantly in Organic Chemistry. These reactions are essential for transforming functional groups and are achieved using various reagents, including metal hydrides (LiAlH₄, NaBH₄), catalytic hydrogenation (H₂/catalyst), dissolving metals (Na/NH₃), and named reactions (Clemmensen, Wolff-Kishner). The solution lists these reactions, categorized by the functional group being reduced, along with their specific reagents and products, providing a comprehensive overview.

Answer 2

The JEE Advanced syllabus covers numerous reduction reactions in Chemistry, predominantly in Organic Chemistry. These reactions are essential for transforming functional groups and are achieved using various reagents, including metal hydrides (LiAlH₄, NaBH₄), catalytic hydrogenation (H₂/catalyst), dissolving metals (Na/NH₃), and named reactions (Clemmensen, Wolff-Kishner). The solution lists these reactions, categorized by the functional group being reduced, along with their specific reagents and products, providing a comprehensive overview.

I. Reduction of Carbonyl Compounds (Aldehydes and Ketones)

1. Reduction to Alcohols:

   • Catalytic Hydrogenation:
     • Reagents: H₂, Pd/C (or Pt, Ni, Rh)
     • Product: Primary alcohols (from aldehydes), Secondary alcohols (from ketones)
     • Example: $\text{RCHO} + \text{H}_2 \xrightarrow{\text{Pd/C}} \text{RCH}_2\text{OH}$ $\text{R}_2\text{CO} + \text{H}_2 \xrightarrow{\text{Pd/C}} \text{R}_2\text{CHOH}$
   • Metal Hydride Reduction:
     • Reagents:
       • Sodium Borohydride (NaBH₄): Milder, selective for aldehydes and ketones.
       • Lithium Aluminium Hydride (LiAlH₄): Stronger, reduces aldehydes, ketones, esters, amides, etc.
     • Product: Primary alcohols (from aldehydes), Secondary alcohols (from ketones)
     • Example: $\text{R}_2\text{CO} + \text{NaBH}_4 \xrightarrow{\text{H}_2\text{O}} \text{R}_2\text{CHOH}$
   • Meerwein-Ponndorf-Verley (MPV) Reduction:
     • Reagents: Aluminium isopropoxide (Al(OiPr)₃) in isopropyl alcohol.
     • Product: Secondary alcohols (selective for ketones over aldehydes).

2. Reduction to Alkanes (Deoxygenation):

   • Clemmensen Reduction:
     • Reagents: Zinc amalgam (Zn(Hg)) in concentrated HCl.
     • Product: Alkanes.
     • Example: $\text{R}_2\text{CO} \xrightarrow{\text{Zn(Hg), conc. HCl}} \text{R}_2\text{CH}_2$
   • Wolff-Kishner Reduction:
     • Reagents: Hydrazine (N₂H₄) followed by a strong base (e.g., KOH) at high temperature.
     • Product: Alkanes.
     • Example: $\text{R}_2\text{CO} \xrightarrow{\text{N}_2\text{H}_4, \text{KOH}, \Delta} \text{R}_2\text{CH}_2$
   • HI/Red P:
     • Reagents: Concentrated HI and Red Phosphorus at high temperature.
     • Product: Alkanes.

II. Reduction of Carboxylic Acids

1. Reduction to Primary Alcohols:
   • Lithium Aluminium Hydride (LiAlH₄):
     • Reagents: LiAlH₄ in dry ether, followed by aqueous workup.
     • Product: Primary alcohols.
     • Example: $\text{RCOOH} \xrightarrow{\text{LiAlH}_4} \text{RCH}_2\text{OH}$
   • Borane (BH₃):
     • Reagents: BH₃ (e.g., BH₃·THF complex) in dry ether.
     • Product: Primary alcohols.

III. Reduction of Esters

1. Reduction to Primary Alcohols:

   • Lithium Aluminium Hydride (LiAlH₄):
     • Reagents: LiAlH₄ in dry ether, followed by aqueous workup.
     • Product: Two molecules of primary alcohol.
     • Example: $\text{RCOOR'} \xrightarrow{\text{LiAlH}_4} \text{RCH}_2\text{OH} + \text{R'OH}$
   • Catalytic Hydrogenation:
     • Reagents: H₂, high pressure, copper chromite catalyst.
     • Product: Primary alcohols.

2. Reduction to Aldehydes:

   • Diisobutylaluminium Hydride (DIBAL-H):
     • Reagents: DIBAL-H at low temperature (-78°C), followed by hydrolysis.
     • Product: Aldehydes.
     • Example: $\text{RCOOR'} \xrightarrow{\text{DIBAL-H, } -78^\circ\text{C; H}_3\text{O}^+} \text{RCHO}$

IV. Reduction of Amides

1. Reduction to Amines:
   • Lithium Aluminium Hydride (LiAlH₄):
     • Reagents: LiAlH₄ in dry ether, followed by aqueous workup.
     • Product: Amines.
     • Example: $\text{RCONH}_2 \xrightarrow{\text{LiAlH}_4} \text{RCH}_2\text{NH}_2$

V. Reduction of Nitriles

1. Reduction to Primary Amines:

   • Lithium Aluminium Hydride (LiAlH₄):
     • Reagents: LiAlH₄ in dry ether, followed by aqueous workup.
     • Product: Primary amines.
     • Example: $\text{RCN} \xrightarrow{\text{LiAlH}_4} \text{RCH}_2\text{NH}_2$
   • Catalytic Hydrogenation:
     • Reagents: H₂, Ni or Pd/C.
     • Product: Primary amines.

2. Reduction to Aldehydes:

   • DIBAL-H:
     • Reagents: DIBAL-H at low temperature (-78°C), followed by hydrolysis.
     • Product: Aldehydes.
     • Example: $\text{RCN} \xrightarrow{\text{DIBAL-H, } -78^\circ\text{C; H}_3\text{O}^+} \text{RCHO}$
   • Stephen Reduction:
     • Reagents: Stannous chloride (SnCl₂) in HCl, followed by hydrolysis.
     • Product: Aldehydes.

VI. Reduction of Alkenes and Alkynes

1. Reduction to Alkanes:

   • Catalytic Hydrogenation:
     • Reagents: H₂, Pd/C, Pt, Ni.
     • Product: Alkanes.
     • Example: $\text{RCH}=\text{CHR'} + \text{H}_2 \xrightarrow{\text{Pd/C}} \text{RCH}_2\text{CH}_2\text{R'}$ $\text{RC}\equiv\text{CR'} + 2\text{H}_2 \xrightarrow{\text{Pd/C}} \text{RCH}_2\text{CH}_2\text{R'}$

2. Partial Reduction of Alkynes:

   • To cis-Alkenes:
     • Lindlar's Catalyst: H₂, Pd/CaCO₃/Pb(OAc)₂, in the presence of quinoline.
     • Product: cis-Alkenes.
     • Example: $\text{RC}\equiv\text{CR'} \xrightarrow{\text{Lindlar's catalyst}} \text{cis-RCH}=\text{CHR'}$
   • To trans-Alkenes:
     • Dissolving Metal Reduction: Na or Li in liquid ammonia (NH₃) with an alcohol.
     • Product: trans-Alkenes.
     • Example: $\text{RC}\equiv\text{CR'} \xrightarrow{\text{Na/NH}_3, \text{EtOH}} \text{trans-RCH}=\text{CHR'}$

VII. Reduction of Nitro Compounds

1. Reduction to Amines:
   • Catalytic Hydrogenation: H₂, Pd/C or Pt.
   • Metal/Acid: Fe/HCl, Sn/HCl, Zn/HCl.
   • Other Reducing Agents: Na₂S, (NH₄)₂S, NaHS, SO₂/H₂O.
   • Example: $\text{RNO}_2 \xrightarrow{\text{Fe/HCl}} \text{RNH}_2$

VIII. Reduction of Halides (Dehalogenation)

1. Reduction to Alkanes:
   • Catalytic Hydrogenation: H₂, Pd/C (especially for aryl, allylic, benzylic halides).
   • Metal Hydrides: LiAlH₄ (effective for alkyl halides).
   • Zinc/Acid: Zn/HCl.

IX. Reduction of Epoxides

1. Reduction to Alcohols:
   • Lithium Aluminium Hydride (LiAlH₄): Reduces epoxides to alcohols.
   • Catalytic Hydrogenation: Can also reduce epoxides.

X. Reduction of Aromatic Rings

1. Reduction to Cyclohexanes:

   • Catalytic Hydrogenation: H₂, Ni, Pt, Rh under high pressure and temperature.
   • Example: $\text{Benzene} + 3\text{H}_2 \xrightarrow{\text{Ni}, \Delta, P} \text{Cyclohexane}$

2. Birch Reduction:

   • Reagents: Alkali metal (Na or Li) in liquid ammonia with an alcohol.
   • Product: 1,4-Cyclohexadienes (from benzene).

XI. Other Reductions

• Ozonolysis of Alkenes/Alkynes (with reducing workup):

  • Reagents: O₃ followed by Zn/H₂O or Me₂S.
  • Product: Aldehydes and/or ketones (reductive cleavage).
  • Example: $\text{RCH}=\text{CHR'} \xrightarrow{\text{O}_3; \text{Zn/H}_2\text{O}} \text{RCHO} + \text{R'CHO}$

• Reduction of Sulfoxides to Sulfides:

  • Reagents: LiAlH₄.

• Reduction of Disulfides to Thiols:

  • Reagents: Zn/Acid, LiAlH₄.