Hydrogenation

 What is Hydrogenation?

Hydrogenation is a chemical reaction in which hydrogen (H₂) is added to another substance, usually in the presence of a catalyst.

In simple terms:
It converts unsaturated compounds → saturated compounds by adding hydrogen.

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Basic Reaction

$R-CH=CH-R' + H_2 \xrightarrow{\text{Ni/Pt/Pd}} R-CH_2-CH_2-R'$

• Double bond (C=C) breaks
• Hydrogen atoms attach to carbon atoms

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Types of Hydrogenation

1. Catalytic Hydrogenation

• Uses catalysts like:
  • Nickel (Ni)
  • Platinum (Pt)
  • Palladium (Pd)
• Most common type

Example:

• Ethene → Ethane

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2. Partial Hydrogenation

• Only some double bonds are hydrogenated
• Used in food industry

Can form harmful trans fats

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3. Complete Hydrogenation

• All double/triple bonds are saturated
• Produces fully saturated compounds

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Conditions Required

• Hydrogen gas (H₂)
• Catalyst (Ni/Pt/Pd)
• Temperature: ~150–300°C
• Pressure: Moderate to high

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Mechanism (Simplified Steps)

1. Hydrogen molecules attach to catalyst surface
2. Unsaturated compound binds to catalyst
3. Hydrogen atoms transfer to compound
4. Saturated product is released

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Examples

1. Alkene Hydrogenation

• Ethene → Ethane

2. Alkyne Hydrogenation

• Ethyne → Ethene → Ethane

3. Vegetable Oil Hydrogenation

• Liquid oil → Solid fat (vanaspati ghee)

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Industrial Applications

1. Food Industry

• Converts vegetable oils into:
  • Margarine
  • Vanaspati ghee

2. Petroleum Industry

• Used in refining fuels

3. Chemical Industry

• Production of:
  • Alcohols
  • Alkanes
  • Pharmaceuticals

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Advantages

•  Increases shelf life of food
•  Improves stability
• Converts liquid → solid

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Disadvantages

Formation of trans fats (harmful)
Increases risk of:

• Heart disease
• Obesity

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Difference: Hydrogenation vs Reduction

Feature	Hydrogenation	Reduction
Definition	Addition of H₂	Gain of electrons / loss of oxygen
Specificity	Specific type of reduction	General process

Hydrogenation is a type of reduction reaction

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Important Points for Exams (NEET)

• Catalyst: Ni, Pt, Pd
• Reaction type: Addition reaction
• Converts unsaturated → saturated
• Used in oils → fats
• Can produce trans fats

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Quick Summary

• Hydrogenation = Addition of H₂
• Needs catalyst
• Used in industries
• Important for organic chemistry