Creating one hydrocarbon from another

Hydrocarbons can be converted from one type to another using:

✅ Addition Reactions

✅ Elimination Reactions

✅ Substitution Reactions

The process depends on the functional group present and the desired product.

1. Conversion Pathways

1.1 From Alkanes to Alkenes (Elimination)

• Reaction: Dehydrohalogenation (removal of $HX$) or Dehydration (removal of $H₂O$).
• Reagents & Conditions:
  • $Haloalkane + NaOH (ethanol), heat → Alkene + HX$
  • $Alcohol + H₂SO₄ (conc.), heat → Alkene + H₂O$ 💡 Example:

$C_2H_5Br + NaOH \rightarrow C_2H_4 + HBr$

(Bromoethane → Ethene)

1.2 From Alkenes to Alkanes (Addition: Hydrogenation)

• Reaction: Hydrogenation (addition of $H₂$).
• Reagents & Conditions: $Pt, Pd, or$ $Ni$ catalyst.
• Converts alkenes into alkanes by breaking the double bond. 💡 Example:

$C_2H_4 + H_2 \xrightarrow{\text{Ni}} C_2H_6$

(Ethene → Ethane)

1.3 From Alkenes to Haloalkanes (Addition: Hydrohalogenation & Halogenation)

• Reaction: Addition of $HX$ (Hydrohalogenation) or $X₂$ (Halogenation).
• Reagents & Conditions: No catalyst needed.
• Markovnikov's Rule: The $H$ from $HX$ bonds to the carbon with more hydrogen atoms. 💡 Example:

$C_2H_4 + HBr \rightarrow C_2H_5Br$

(Ethene → Bromoethane)

$C_2H_4 + Br_2 \rightarrow C_2H_4Br_2$

(Ethene → 1,2-Dibromoethane)

1.4 From Haloalkanes to Alkenes (Elimination: Dehydrohalogenation)

• Reaction: Removal of $HX$ to form alkenes.
• Reagents & Conditions: $NaOH$ (ethanol), heat. 💡 Example:

$C_3H_7Cl + NaOH \xrightarrow{\text{heat}} C_3H_6 + HCl$

(Chloropropane → Propene)

1.5 From Haloalkanes to Alcohols (Substitution: Hydrolysis)

• Reaction: Hydrolysis of haloalkanes to form alcohols.
• Reagents & Conditions: $NaOH$ (diluted), heat. 💡 Example:

$C_2H_5Br + H_2O \rightarrow C_2H_5OH + HBr$

(Bromoethane → Ethanol)

1.6 From Alcohols to Alkenes (Elimination: Dehydration)

• Reaction: Dehydration (removal of $H₂O$) to form alkenes.
• Reagents & Conditions: $H₂SO₄$ (conc.), heat. 💡 Example:

$C_2H_5OH \xrightarrow{H_2SO_4} C_2H_4 + H_2O$

(Ethanol → Ethene)

2. Summary of Hydrocarbon Conversions

Starting Compound	Reaction Type	Product	Conditions
Alkane → Alkene	Elimination	Alkene	Heat, $NaOH$ (ethanol)
Alkene → Alkane	Addition	Alkane	$H₂,$ $Pt/Pd/Ni$ catalyst
Alkene → Haloalkane	Addition	Haloalkane	$HX$ or $X₂$
Haloalkane → Alkene	Elimination	Alkene	$NaOH$ (ethanol), heat
Haloalkane → Alcohol	Substitution	Alcohol	$NaOH$ (diluted), heat
Alcohol → Alkene	Elimination	Alkene	$H₂SO₄$ (conc.), heat

3. Key Takeaways

✅ Addition reactions occur in unsaturated compounds (alkenes).

✅ Elimination reactions occur in saturated compounds to form unsaturated compounds.

✅ Substitution reactions replace one atom/group with another.

✅ Reaction conditions determine the type of product formed.