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6.3 Reactions of arenes

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6.3 Reactions of arenes Powered By Docstoc
					        Reactions of arenes
L.O.:

 Outline the mechanism of nitration.
 Outline the mechanism of of acylation.
 Identify the reactive intermediates involved
  in nitration and acylation.
 Name the mechanisms of both reactions.
            STRUCTURE OF BENZENE


    H               H
        C       C

                        C   H
H   C

            C       C
        H               H
STRUCTURE OF BENZENE
STRUCTURE OF BENZENE
                 NITRATION

                                   NO2


         +   HNO 3                          +   H 2O


                             nitrobenzene

Conditions   conc HNO3
             conc H2SO4 catalyst
             50ºC
        NITRATION – ELECTROPHILIC SUBSTITUTION

Formation of electrophile
                                    +
HNO3 + 2 H2SO4                     NO2      + 2 HSO4- + H3O+
                                nitronium ion




Reaction of electrophile with aromatic compound

            +
           NO2                    NO2            +
                                                -H     NO2
                                   H
                            +
      NITRATION


CH3               CH3
                           NO2




 Equation (name product)
 Conditions
 Mechanism
                       NITRATION

 CH3                                CH3
                                           NO2

        +    HNO   3                               +   H 2O


                            2-methylnitrobenzene

Conditions    conc HNO3
              conc H2SO4 catalyst
              50ºC
                         NITRATION

Uses of nitro compounds:

  1) as explosives
  2) to make aromatic amines (used to make dyes)

          CH3

O2N              NO2




          NO2

 1,3,5-trinitrotoluene
          TNT
Name the mechanism for this reaction.



Electrophilic substitution
Draw the electron arrangement (dot-cross
 diagram) of aluminium chloride.
      FRIEDEL-CRAFTS ACYLATION
                                  R       O
                                      C
                 O

       +     R   C   Cl                       +   HCl




                                  R       O
                                      C
                 O        O                             O
       +     R   C   O    C   R               +   R     C   OH



                                  aromatic
                                   ketone

Conditions       AlCl3 catalyst
       FRIEDEL-CRAFTS ACYLATION

WARNING! - do not mix
Friedel-Crafts acylation   &   other acylations
    (needs AlCl3)
                                    H

           H                    H   N     R


                                H   O     R


Swap H on benzene ring         Swap H on O/N
    for acyl group             for acyl group
     FRIEDEL-CRAFTS ACYLATION

WARNING! - Classic question to test this


       NH2                             NHCOCH3

                   CH3COCl




      H replaced is on N not benzene ring.
      This is NOT Friedel-Crafts acylation!
FRIEDEL-CRAFTS ACYLATION – ELECTROPHILIC SUBSTITUTION



Formation of electrophile
                                             O
AlCl3   + RCOCl             AlCl4–   +   R   C
                                               +
                                         acylium ion




 OR


                                     O                         O
             O     O
                                              –
AlCl3 + R-C-O-C-R               R-C-O-AlCl3            +   R   C
                                                                 +
                                                           acylium ion
FRIEDEL-CRAFTS ACYLATION – ELECTROPHILIC SUBSTITUTION

Reaction of electrophile with aromatic compound

            O                     O
                                                           O
            C   R                 C       R       +
            +                                 -H           C   R
                                      H
                              +



  Regeneration of catalyst


   AlCl4–       +   H+                AlCl3 + HCl
    O                                         O       or
                –
  R-C-O-AlCl3       +    H+               R-C-OH + AlCl3
FRIEDEL-CRAFTS ACYLATION

    CH3              CH3




                     C
                 O       CH2CH3

    Equation
    Conditions
    Mechanism
       FRIEDEL-CRAFTS ACYLATION

 CH3                                 CH3
                      O
                                            +     HCl
       +     CH3CH2   C   Cl

                                     C
                                 O       CH2CH3


Conditions      AlCl3 catalyst

				
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