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http://phs244.wikispaces.com/. Lab 1. Electrophilic substitution. Electrophilic substitution. chemical reactions in which an electrophile displaces a group in a compound, typically but not always hydrogen. Electrophilic substitution. Electrophilic aromatic substitution

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  1. http://phs244.wikispaces.com/

  2. Lab 1 Electrophilic substitution

  3. Electrophilic substitution chemical reactions in which an electrophile displaces a group in a compound, typically but not always hydrogen.

  4. Electrophilic substitution • Electrophilic aromatic substitution • Electrophilic aliphatic substitution

  5. electrophilic aliphatic substitution • chemical reactions in which an electrophile displaces a functional group in aliphatic compounds. • Mechanism of reaction: two electrophilic reaction mechanisms SE1 and SE2

  6. electrophilic aliphatic substitution • SE1 course of action the substrate first ionizes into a carbanion and a positively charged organic residue. The carbanion then quickly recombines with the electrophile. • SE2 single transition state in which the old bond and the newly formed bond are both present.

  7. electrophilic aliphatic substitution • Nitrosation • Ketone halogenation • Keto-enol tautomerism • aliphatic diazonium coupling • carbene insertion into C-H bonds

  8. Electrophilic aromatic substitution atom appended to the aromatic ring, usually hydrogen, is replaced by an electrophile. Type • Nitration • halogenation • sulfonation • acylation and alkylating Friedel-Crafts reactions.

  9. Halogination Nitration sulfonation Friedel-Crafts alkylation Friedel-Crafts acylation

  10. Mechaniism of EAS: arenium ions Arenium ions (nonaromatic cyclohexadienyl cation) Step 1

  11. Mechaniism of EAS: arenium ions Step 2 The proton is removed by any of the bases, for example by the anion derived from the electrophile

  12. Halogenation of benzene • Benzene does not react with Br2 or CL2 unless a Lewis acid is present in mixture • Lewis acid is an electron-pair acceptor • Lewis acids most commonly used to effect bromination and chlorination reactions are FeCl3,FeBr3 and AlCl3

  13. Bromonation of benzene

  14. Electrophilic Aromatic Bromination Step 1 Bromine combines with FeBr3 to form acomplex that dissocates to form apostive bromine ion and FeBr4- Step 2 Arenium ions Postive bromine ion is attacked by benzen to form an arenium ion

  15. Electrophilic Aromatic Bromination Step 3 Proton is removed from the arenium ion to become bromobenzene

  16. Nitration of Benzene

  17. Nitration of Benzene Step 1 Step 2

  18. Nitration of Benzene Step 3 Arenium ions The nitronium ion is the actual electrophile in nitration ; it reacts with benzene to form a resonance-stabilized arenium ion Step 4 The arenium ion then loses a proton to a Lewis base and becomes nitrobenzene

  19. Sulfonation of benzene Benzenesulfonic acid

  20. Sulfonation of benzene • Benzene react with fuming sulfuric acid at room temperature to produce benzensulphonic acid • Fuming sulfuric acid is sulfuric acid that contain added sulfur trioxide (SO3) • Sulfonation can takes place in conc sulfuric acid, alone but more slowly

  21. Sulfonation of benzene

  22. Sulfonation of benzene Step 1 Step 2 SO3,is the actual electrophile that reacts with benzene to form an arenium ion

  23. Sulfonation of benzene Step 3 Step 4

  24. Friedel-Crafts Alkylation

  25. Friedel-Crafts Alkylation • Mechanism for reaction start with formation of carbocation (step 1 ) • The carbocation then act as an electrophile and attack benzene ring to form an arenium ion (step 2) • The arenium ion then loses a proton to generate alkylbenzene (step 3)

  26. Friedel-Crafts Alkylation Step 1 + Step 2

  27. Friedel-Crafts Acylation • Friedel-Crafts Acylation reaction is mean introducting an acyl group into aromatic ring • Two common acyl groups are acetyl group and benzoyl group benzoyl group acetyl group

  28. Friedel-Crafts Acylation • The reaction is carried out by treating the aromatic compound with acyl halide( often an acyl chloride) • The reaction requires the addition of a Lewis acid (such as AlCl3 ) • The product of reaction is an aryl ketone.

  29. Friedel-Crafts Acylation Step 1 Acyl halide Step 2 Acylium ion

  30. Friedel-Crafts Acylation Step 3 The acylium ion, acting as an electrophile, reacts with benzene to form the arenium ion Step 4 A proton is removed from the arenium ion, forming the aryl ketone

  31. Friedel-Crafts Acylation Step 5 The ketone acting as lewis base ,reacts with alaminum chloride (Lewis acid) to form a complex Step 6 Treating the complex with water liberates the ketone and hydrolyzes the Lewis acid

  32. Preparation of nitrobenzene • By nitration of benzene in pesent of sulphoric acid replace hydrogen atom by (NO2) groups nitrobenzene benzene

  33. Preparation of nitrobenzene • Nitrations are usually carried out at comparatively low temperatures • At high temp may loss of material b/c of oxidaising action of nitric acid

  34. Preparation of nitrobenzene • Suphoric acid furnish astrong acid. medium to convert nitric acid into highly reactive nitronium ion NO2+

  35. Procedure: • Add 9ml of nitric acid and add, in portion,with shaking conc. Sulphuric acid(10ml) to round-bottemed flask • Place the mixture in cold water and keep the temp between 50◦-55◦ use thermometer • Add slowly (1-2ml) pure benzene 7ml shake after each addition • When addition is complete warm the flask in water bath 60° for 10-15 min with continued shaking.

  36. Thank you

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