Alkanes and Alkenes - PowerPoint PPT Presentation

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Alkanes and Alkenes

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  1. Alkanes and Alkenes

  2. Processing AlkanesCRACKING, REFORMING, ISOMERISATION How is it carried out? C – Al2O3 and heat R – Pt/Rh and heat I – Pt separated by zeolyte catalyst and heat What are the products? C – Smaller Alkanes AND alkenes R – Cyclic alkanes and hydrogen I – Branched alkane isomers of original Why is it carried out? C – Smaller Alkanes used as fuels, alkenes used to make polymers R – Lowers bp of alkane so more vapour at same temp so better ignition (Weaker VDW as smaller molecule) I – Lowers bp of alkane so more vapour at same temp so better ignition (Weaker VDW as molecules pack together less well)

  3. Free radical substitution chlorination of methane i.e. homolytic breaking of covalent bonds Overall reaction equation CH4 + Cl2 CH3Cl + HCl Conditions ultra violet light excess methane to reduce further substitution

  4. Free radical substitution mechanism Cl + Cl CH4 + Cl CH3 + HCl CH3 + Cl2 CH3Cl + Cl CH3 + Cl CH3 + CH3 ultra-violet Cl2 initiation step two propagation steps termination step CH3Cl minor termination step CH3CH3

  5. Further free radical substitutions Overall reaction equations CH3Cl + Cl2 CH2Cl2 + HCl CH2Cl2 + Cl2 CHCl3 + HCl CHCl3 + Cl2 CCl4 + HCl Conditions ultra-violet light excess chlorine

  6. Electrophilic addition bromine with ethene Overall reaction equation CH2=CH2 + Br2 CH2BrCH2Br 1,2-dibromoethane mechanism

  7. bromine with ethene H H C C H H H H C C H H + Br - Br Br Br δ+ Br Br H H δ- C C H H Br Br Electrophilic addition mechanism carbocation 1,2-dibromoethane reaction equation

  8. Electrophilic addition 2 Hydrogen bromide with propene Overall reaction equation CH3CH2CH2Br CH3CH=CH2 + HBr 1-bromopropane or CH3CHBrCH3 Conditions DRY HBr in Ethanol 2-bromopropane mechanism

  9. Hydrogen bromide with Propene CH3 H C C CH3 H H H C C H H + H - H H Br δ+ δ+ Br Br CH3 H δ- δ- C C H H Br H Electrophilic addition mechanism 1-bromopropane reaction equation

  10. Hydrogen bromide with Propene CH3 H C C H CH3 H H C C H H + H - H H Br δ+ δ+ Br Br H CH3 δ- δ- C C H H Br H Electrophilic addition mechanism 2-bromopropane reaction equation