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Electrophilic Substitution

Electrophilic Substitution. Nitration of benzene. Where an H atom attached to an aromatic ring is replaced by an NO 2 group of atoms. C 6 H 6. + HNO 3. C 6 H 5 NO 2. + H 2 O. Conditions / Reagents. concentrated HNO 3. and concentrated H 2 SO 4. 50 o C. mechanism.

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Electrophilic Substitution

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  1. Electrophilic Substitution Nitration of benzene Where an H atom attached to an aromatic ring is replaced by an NO2 group of atoms C6H6 + HNO3 C6H5NO2 + H2O Conditions / Reagents concentrated HNO3 and concentrated H2SO4 50oC mechanism

  2. electrophilic substitution mechanism (nitration) NO2 + 1. Formation of NO2 H + + NO2 O SO3H- + NO2 NO2 H O SO3H the nitronium ion HNO3 + 2H2SO4 + H3O+ + 2HSO4- 2. Electrophilic attack on benzene 3. Forming the product and re-forming the catalyst reaction equation

  3. Bromination of benzene Where an H atom attached to an aromatic ring is replaced by a Br atom electrophilic substitution C6H6 + Br2 C6H5Br + HBr R = alkyl group Conditions / Reagents Br2 and anhydrous AlBr3 25oC

  4. Electrophilic substitution mechanism - - Br AlBr3 Br AlBr3 + + Br Br Br H Br H + BrBr Br 1. Formation of the electrophile AlBr3 2. Electrophilic attack on benzene 3. Forming the products and re-forming the catalyst AlBr3 bromobenzene

  5. Alkylation of benzene Where an H atom attached to an aromatic ring is replaced by a C atom electrophilic substitution C6H6 + RCl C6H5R + HCl R = alkyl group Conditions / Reagents RCl (haloakane) and anhydrous AlCl3 0 - 25oC to prevent further substitution

  6. Alkylation example - Cl AlCl3 + CH3CH2 Cl CH3CH2 With chloroethane overall reaction equation C6H6 + CH3CH2Cl C6H5CH2CH3 + HCl Three steps in electrophilic substitution mechanism 1. Formation of the electrophile (a carbocation) AlCl3

  7. Alkylation electrophilic substitution mechanism 2 - Cl AlCl3 + CH3CH2 H Cl H + CH3CH2 CH3CH2 2. Electrophilic attack on benzene 3. Forming the product and re-forming the catalyst AlCl3 ethylbenzene

  8. Acylation of benzene An H atom attached to an aromatic ring is replaced by a C atom where C is part of C=O electrophilic substitution C6H6 + RCOCl C6H5COR + HCl Conditions / Reagents RCOCl (acyl chloride) and anhydrous AlCl3 50 oC

  9. Acylation example - Cl AlCl3 O + CH3C O CH3C Cl With ethanoyl chloride overall reaction equation C6H6 + CH3COCl C6H5COCH3 + HCl Three steps in electrophilic substitution mechanism 1. Formation of the electrophile (an acylium ion) AlCl3

  10. Acylation electrophilic substitution mechanism 2 - Cl AlCl3 O CH3C H Cl O + CH3C O H CH3C + 2. Electrophilic attack on benzene 3. Forming the products and re-forming the catalyst AlCl3 phenylethanone

  11. Nucleophilic Addition addition of hydrogen cyanide to carbonyls to form hydroxynitriles + HCN RCOR RC(OH)(CN)R RCH(OH)CN + HCN RCHO Conditions / Reagents NaCN (aq) andH2SO4(aq) supplies H+ supplies the CN- nucleophile Room temperature and pressure

  12. Nucleophilic Addition Mechanism C N - O + O H O C CH3 C CN CH3 CH3 C CN CH3 CH3 CH3 CN hydrogen cyanide with propanone + HCN CH3COCH3 CH3C(OH)(CN)CH3 NaCN (aq) is a source of cyanide ions fromH2SO4 (aq) H+ H+ 2-hydroxy-2-methylpropanenitrile

  13. Advice To get back to the mechanism links page from anywhere in the presentation, click the button at the top right corner of the screen. This version provides the organic mechanisms specified (2002/3) by the Edexcel exam board. Each stage of a reaction equation, its conditions and mechanism are revealed in turn on a mouse click or keyboard stroke. Note that there is another version available where each reaction and mechanism play automatically after an initiating click or key stroke. The number of ways of navigating through this presentation may depend on the version of PowerPoint being used and how it is configured. Some possible ways of advancing: left mouse click or return key or right arrow key or up arrow key. Some possible ways of reversing: backspace key or left arrow key or down arrow key.

  14. References Steve Lewis for the Royal Society of Chemistry

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