Slide 1

• Topic: Nitrogen Containing Organic Compounds - Catalytic Hydrogenation of Nitroaromatics
• Introduction
  • Definition of Nitroaromatics
  • Importance of Nitroaromatics in organic synthesis
• Objectives of the lecture
  • Understanding the process of catalytic hydrogenation
  • Examining the mechanism of hydrogenation of Nitroaromatics
• Let’s get started!

Slide 2

• Nitroaromatics
  • Definition: Aromatic compounds containing a nitro group (-NO2) attached to the aromatic ring
  • Common examples: Nitrobenzene, Nitrotoluene, Nitroanisole, Nitrophenol, etc.
• Importance of Nitroaromatics:
  • Used as intermediates in the synthesis of various compounds
  • Solvents, pharmaceuticals, dyes, explosives, fungicides, and pesticides

Slide 3

• What is Catalytic Hydrogenation?
  • Definition: A chemical reaction where hydrogen gas (H2) is added to an unsaturated compound in the presence of a catalyst
  • Catalyst: Substance that increases the rate of a chemical reaction without being consumed itself

Slide 4

• Mechanism of Catalytic Hydrogenation
  • Step 1: Activation of the catalyst
    • Catalysts like Nickel (Ni) or Platinum (Pt) are used
    • The catalyst adsorbs the reactants on its surface, weakening the double bond
  • Step 2: Adsorption of hydrogen
    • Hydrogen gas (H2) is adsorbed on the catalyst surface
    • The hydrogen molecule dissociates into two hydrogen atoms (H•)
  • Step 3: Reaction with the adsorbed reactants
    • The adsorbed reactants (Nitroaromatics) react with the adsorbed hydrogen atoms (H•)
    • Hydrogen atom adds to the carbon atom of the nitro group, breaking the double bond
  • Step 4: Desorption and regeneration of the catalyst
    • The product is desorbed from the catalyst surface
    • The catalyst is regenerated and is ready for the next cycle

Slide 5

• Conditions for Catalytic Hydrogenation
  • Suitable temperature: Typically 100-150°C
  • Controlled pressure: Usually 1-5 atmospheres
  • Stirring: Aids in the uniform distribution of the reactants
  • Catalyst: Transition metals like Nickel or Platinum supported on a solid substrate (e.g., alumina)
  • Solvent: Non-reactive solvent is used to dissolve the reactants and facilitate the reaction

Slide 6

• Advantages of Catalytic Hydrogenation
  • High selectivity: It allows specific reduction of nitro groups without affecting other functional groups
  • Mild reaction conditions: Relatively low temperature and pressure requirements
  • Versatile: Can be applied to a wide range of substrates containing nitro groups
  • Cost-effective: Catalysts can be reused multiple times, reducing the overall cost of the reaction

Slide 7

• Examples of Catalytic Hydrogenation
  • Nitrobenzene (C6H5NO2) to Aniline (C6H5NH2)
  • Nitrotoluene (C7H7NO2) to Toluene (C7H8)
• Reactions:
  • C6H5NO2 + 3H2 → C6H5NH2 + 2H2O
  • C7H7NO2 + 3H2 → C7H8 + 2H2O

Slide 8

• Aniline
  • Definition: An aromatic amine with the chemical formula C6H5NH2
  • Importance of Aniline:
    • Used in the synthesis of dyes, pharmaceuticals, plastics, and rubber products
    • Intermediates in the production of herbicides, antioxidants, and other chemicals

Slide 9

• Toluene
  • Definition: An aromatic hydrocarbon with the chemical formula C7H8
  • Importance of Toluene:
    • Widely used as an industrial solvent
    • Used as a feedstock in the production of benzene, xylene, and other chemicals
    • Found in gasoline, paints, coatings, and cleaning agents

Slide 10

• Summary
  • Nitroaromatics are aromatic compounds containing a nitro group (-NO2) attached to the aromatic ring
  • Catalytic hydrogenation is a process where hydrogen gas (H2) is added to unsaturated compounds in the presence of a catalyst
  • The mechanism involves catalyst activation, adsorption of hydrogen, reaction with the adsorbed reactants, and catalyst regeneration
  • Catalytic hydrogenation of nitroaromatics can yield products like aniline and toluene
  • Aniline and toluene have significant industrial applications

Slide 11

• Reductive Hydrogenation of Nitro Groups
  • Nitro group (-NO2) reduction to amino group (-NH2)
  • An important step in the synthesis of many organic compounds
• Catalytic Hydrogenation vs. Other Reduction Methods
  • Catalytic hydrogenation: Selectively reduces nitro groups
  • Alternative methods like metal/hydride reducing agents can cause over-reduction

Slide 12

• Reaction Conditions and Reactivity
  • pH: Basic conditions enhance the reactivity of the nitro group
  • Temperature and pressure: Higher temperature and pressure can increase the reaction rate
  • Substrate structure: Electron-withdrawing groups in the aromatic ring hinder reaction

Slide 13

• Selectivity in Nitro Group Reduction
  • Nitro group reduction is generally selective and occurs in the presence of other functional groups
  • Examples:
    • Nitrobenzene with an aldehyde group: Nitro group is reduced without affecting the aldehyde group
    • Nitrobenzene with a ketone group: Neither the nitro nor ketone group is reduced

Slide 14

• Mechanism: Protonation of the Nitro Group
  • Step 1: Protonation of the nitro group
    • The catalyst is acidic and donates a proton to the nitro group
    • This increases the electrophilicity of the nitro group

Slide 15

• Mechanism: Formation of the Nitroso Compound
  • Step 2: Formation of the nitroso compound
    • Electrons from the pi bond attack the electrophilic nitro group
    • A new sigma bond forms between the nitro group and one of the oxygen atoms
    • The other oxygen atom picks up a proton from the solvent, forming water

Slide 16

• Mechanism: Reduction of the Nitroso Compound
  • Step 3: Reduction of the nitroso compound
    • Electrons from the metal catalyst reduce the nitroso compound
    • A new sigma bond forms between the nitrogen and the hydrogen atom, resulting in the formation of the amino group

Slide 17

• Applications of Catalytic Hydrogenation in Organic Synthesis
  • Pharmaceutical industry: Synthesis of drugs, like antibiotics, analgesics, and antihypertensives
  • Agrochemical industry: Synthesis of herbicides, pesticides, and fungicides
  • Polymer industry: Production of polymers like polyamides and polyurethanes

Slide 18

• Example: Catalytic Hydrogenation of Nitrobenzene to Aniline
  • Nitrobenzene (C6H5NO2) to Aniline (C6H5NH2)
  • Reactants:
    • Nitrobenzene
    • Hydrogen gas (H2)
    • Catalyst (e.g., Nickel or Platinum)
  • Products:
    • Aniline
    • Water (byproduct)

Slide 19

• Example: Catalytic Hydrogenation of Nitrophenol to Aminophenol
  • Nitrophenol (C6H5NO3) to Aminophenol (C6H5NH2)
  • Reactants:
    • Nitrophenol
    • Hydrogen gas (H2)
    • Catalyst (e.g., Nickel or Platinum)
  • Products:
    • Aminophenol
    • Water (byproduct)

Slide 20

• Summary
  • Catalytic hydrogenation is an important process for the reduction of nitro groups in organic compounds.
  • The mechanism involves protonation of the nitro group, formation of the nitroso compound, and reduction of the nitroso compound.
  • The reaction conditions, substrate structure, and catalyst selectivity determine the outcome of the reaction.
  • Catalytic hydrogenation finds applications in the pharmaceutical, agrochemical, and polymer industries.
  • Examples include the reduction of nitrobenzene and nitrophenol to form aniline and aminophenol, respectively.

Slide 21

• Nitroaromatics:
  • Aromatic compounds containing a nitro group (-NO2) attached to the aromatic ring
  • Examples: Nitrobenzene, Nitrotoluene, Nitroanisole, Nitrophenol
• Catalytic Hydrogenation:
  • Introduction to the process of catalytic hydrogenation
  • Definition: Addition of hydrogen gas (H2) to unsaturated compounds in the presence of a catalyst
• Importance of the Topic:
  • Understanding the mechanism of catalytic hydrogenation of nitroaromatics
  • Applications of catalytic hydrogenation in organic synthesis

Slide 22

• Mechanism of Catalytic Hydrogenation:
  • Activation of the catalyst
  • Adsorption of hydrogen
  • Reaction with the adsorbed reactants
  • Desorption and regeneration of the catalyst
• Conditions for Catalytic Hydrogenation:
  • Suitable temperature and pressure
  • Stirring for uniform distribution of reactants
  • Catalytic materials: Nickel (Ni), Platinum (Pt) supported on a solid substrate
  • Non-reactive solvent to dissolve reactants

Slide 23

• Advantages of Catalytic Hydrogenation:
  • High selectivity for the reduction of nitro groups
  • Mild reaction conditions compared to other reduction methods
  • Versatility in application to various substrates containing nitro groups
  • Cost-effectiveness due to catalyst reusability
• Examples of Catalytic Hydrogenation:
  • Nitrobenzene (C6H5NO2) to Aniline (C6H5NH2)
  • Nitrotoluene (C7H7NO2) to Toluene (C7H8)

Slide 24

• Aniline:
  • Definition: An aromatic amine (C6H5NH2)
  • Uses: Dyes, pharmaceuticals, plastics, rubber products
• Toluene:
  • Definition: An aromatic hydrocarbon (C7H8)
  • Uses: Industrial solvent, feedstock for chemicals like benzene and xylene

Slide 25

• Reductive Hydrogenation of Nitro Groups:
  • Importance in organic compound synthesis
  • Contrast between catalytic hydrogenation and other reduction methods
• Reaction Conditions and Reactivity:
  • Basic pH enhances nitro group reactivity
  • Higher temperature and pressure increase reaction rate
  • Electron-withdrawing groups hinder reaction

Slide 26

• Selectivity in Nitro Group Reduction:
  • Nitro group reduction occurs selectively in the presence of other functional groups
  • Example 1: Reduction of nitrobenzene without affecting aldehyde groups
  • Example 2: Nitrobenzene with a ketone group, where neither group is reduced

Slide 27

• Mechanism: Protonation of the Nitro Group:
  • Step 1: Nitro group is protonated by the catalyst
  • Nitro group becomes more electrophilic
• Mechanism: Formation of the Nitroso Compound:
  • Step 2: Electrons from the pi bond attack the electrophilic nitro group
  • Sigma bond forms between nitro group and one oxygen atom
  • The other oxygen atom gains a proton, forming water

Slide 28

• Mechanism: Reduction of the Nitroso Compound:
  • Step 3: Electrons from the metal catalyst reduce the nitroso compound
  • Sigma bond forms between nitrogen and hydrogen atom, forming an amino group
• Applications of Catalytic Hydrogenation:
  • Pharmaceutical industry: Synthesis of antibiotics, analgesics, antihypertensives
  • Agrochemical industry: Herbicides, pesticides, fungicides
  • Polymer industry: Polyamides, polyurethanes

Slide 29

• Example: Catalytic Hydrogenation of Nitrobenzene to Aniline:
  • Nitrobenzene (C6H5NO2) + H2 → Aniline (C6H5NH2) + H2O
• Example: Catalytic Hydrogenation of Nitrophenol to Aminophenol:
  • Nitrophenol (C6H5NO3) + H2 → Aminophenol (C6H5NH2) + H2O

Slide 30

• Summary:
  • Nitroaromatics are aromatic compounds with a nitro group (-NO2) attached to the aromatic ring
  • Catalytic hydrogenation is the addition of hydrogen gas (H2) to unsaturated compounds in the presence of a catalyst
  • Selective reduction of nitro groups is achieved through specific reaction conditions and catalytic activity
  • Catalytic hydrogenation finds applications in pharmaceutical, agrochemical, and polymer industries
  • Examples of catalytic hydrogenation include conversion of nitrobenzene to aniline and nitrophenol to aminophenol