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Carbonyl Compounds (PowerPoint)

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									Carbonyl Compounds
Carbonyl compounds –
Preparation

1. Ozonolysis
                                     O O
                 O3
     C   C                       C        C
                ice-cold
                                     O
                chloroform

                                         H2O / H +
                                         Zn dust


                             C   O       O    C
Carbonyl compounds –
Preparation

2. Oxidation of alcohol
         H
                    MnO4- / H +      R
    R    C   OH                          C    O


If primary alcohol is oxidized, distill out the aldehyde
immediately. But normally aldehyde is difficult to
synthesize.
Carbonyl compounds –
Preparation

3. Acylation of benzene

                                     R
          R            Anhy. AlCl3
                                         C   O
      +        C   O
                                                 + HCl
          Cl
Carbonyl compounds –
Preparation

4. Hydration of Alkyne
                                  H   OH
                     dil. H2SO4
  C   C      + H2O                C   C
                      HgSO4
                                          Tautomerisation
                                  H   O

                                  C   C

                                  H
 Normally, ketone is formed.
Carbonyl compounds –
Preparation

5. Decarboxylation

                             R
   (RCOO)2Ca         O   C       + CaCO3
                             R
Carbonyl compounds –
Preparation

6. From Acid Chloride (Good method)
  R                             R
                   Pd / BaSO4
      C   O + H2                    C   O + HCl
 Cl                             H

  It is a good method to prepare aldehyde.
Carbonyl compounds –
Physical properties

   Methanal is a gas, other lower members of
    aldehydes and ketones are liquids.
   Benzenecarbaldehyde is a colourless liquid
    with almond smell.
   Ethanal and propanone are miscible with water
    due to the formation of H-bond with water
    molecules while benzenecarbaldehyde is
    insoluble in water.
Carbonyl compounds –
Chemical properties

1. Reduction ( to alcohol)            OH
                        R.A.
     O    C                           C

                                          H
R.A.: 1. Can be H2 / Pt, Ni or Pd
         (also reduce C=C and CC)
      2. Na/ Hg in ethanol
         (also reduce RX)
      3. LiAlH4, NaBH4
         (for LiAlH4, also reduce acid & acid derivative)
Carbonyl compounds –
Chemical properties

1. Reduction (To alkane)
   Clemmensen Reduction / Wolff-Kishner
   Reduction
                                 H

     O   C                       C

                                     H
 a. Clemmensen reduction: Zn / Hg in conc.HCl
 b. Wolff-Kishner reduction: NH2NH2 in NaOH
   Carbonyl compounds –
   Chemical properties

   2. Oxidation
      Special oxidation of aldehyde
      Serve as a test to distinguish aldehyde from
      ketone. (These are very important tests)
      a. With Fehling’s solution

RCHO + Cu(OH)2 + NaOH     RCOONa   +   Cu2O   +   OH2
Carbonyl compounds –
Chemical properties

2. Oxidation (cont’d)
   b. With Tollen’s reagent / Silver mirror test
   RCHO + Ag2O + NH3            RCOONH4 + Ag + H2O

           Ag(NH3)2OH
         (Tollen's reagent)


  Tollen’s reagent is formed from silver nitrate solution
  and aq. ammonia
  This is called silver mirror test.
Carbonyl compounds –
Chemical properties

2. Oxidation (cont’d)
   Oxidize aldehyde to acid
 R              MnO4 - / H + ,        R
     C   O                                 C   O
 H           (or Cr2O72-/ H + ,   )   HO
Carbonyl compounds –
Chemical properties

2. Oxidation (cont’d)
   Oxidize ketone to acid
       O                                     R
                      excess O.A.
CH3    C   CH2CH3                                C   O
                    reflux for long time
                                            HO
                                           (bond breaking)


This reaction is not good method because you
cannot control where the bond break.
Carbonyl compounds –
Chemical properties

3. Iodoform reaction
       O                    O                                O
           I2, NaOH             I2, NaOH                            -
 H3C   C              I3C   C                  CHI3 +        C     O Na+
                                           yellow ppt.


                                           O                         OH

This is served as a test for H3C           C             ,   H3C     C

                                                                     H
     Carbonyl compounds –
     Chemical properties

     4. Nucleophilic Addition reaction
                                        +
                                       H    OH2
Nu        C   O          Nu   C   O               Nu   C    OH

Energy Profile




                                      Reaction Coordinate
Carbonyl compounds –
Chemical properties

4. Nucleophilic Addition reaction (cont’d)
   Reactivity:
H             R             R            Ar            Ar
    C   O          C   O        C   O          C   O        C    O
H              H            R              H           Ar

    Factors affecting reactivity:
    Electronic Factor
    Positive inductive effect of alkyl group make the carbonyl
    carbon to be less positive.
Carbonyl compounds –
Chemical properties

4.   Nucleophilic Addition reaction (cont’d)
     Factors affecting reactivity:
     Electronic Factor
     Benzenecarbaldehyde has low reactivity due to
     the loss of resonance energy when attacked by
     nucleophile.
Carbonyl compounds –
Chemical properties

4. Nucleophilic Addition reaction (cont’d)
   Electronic Factor

                           Nu
                       O                  O
                   C                  C
                                 Nu
                   H                      H




                       O
               +   C

                   H
Carbonyl compounds –
Chemical properties

4. Nucleophilic Addition reaction (cont’d)
   Steric Factor
   Carbonyl carbon change from sp2 to sp3
   hybridization which leads to increase in crowding.
   If the R group is more bulky, the intermediate will
   be more unstable.
 Carbonyl compounds –
 Chemical properties

 4. Nucleophilic Addition reaction (cont’d)
    With HCN (or KCN / H+)

                                          +
                                   H2O / H
HCN +   C   O       NC    C   OH              HOOC   C   OH

                     cyanohydrin
Carbonyl compounds –
Chemical properties

4. Nucleophilic Addition reaction (cont’d)
   With HCN (or KCN / H+)
   Mechanism                     +
                                      H   OH2
CN        C   O     NC   C   O                  NC   C   OH



             +                +
     C   O +H     CN     C   O                  NC   C   OH
                                  H

 The carbonyl compound is regenerated when alkali
 is added to cyanohydrin.
    Carbonyl compounds –
    Chemical properties

    4. Nucleophilic Addition reaction (cont’d)
       With NaHSO3                         OH
            O
                  + NaHSO3                   C
            C
                                              SO3Na

On cooling, the bisulphite addition compound is crystallized.
This reaction is a method for purification and separation
of carbonyl compound (also identification). The carbonyl
compound is regenerated by addition of alkali.
Carbonyl compounds –
Chemical properties

4. Nucleophilic Addition reaction (cont’d)
   With NaHSO3

                             OH              O
O
                             C       NaOH
C     + NaHSO3                               C
                             SO3Na
Carbonyl compounds –
Chemical properties

4. Nucleophilic Addition reaction (cont’d)
   With ROH (Ketal / Acetal formation) OR
                                  OH
      O
                ROH                          ROH              C
                                  C                    R'            H
      C                   R'           H
                dry HCl                      dry HCl
 R'       H                    OR                             OR
                           hemiacetal                       acetal

                                  OH                         OR
      O
                ROH                          ROH              C
                                  C                    R'            R''
      C                   R'           R''
                dry HCl                      dry HCl
 R'       R''                     OR                          OR
                               hemiketal                    ketal
Carbonyl compounds –
Chemical properties

4. Nucleophilic Addition reaction (cont’d)
   With ROH (Ketal / Acetal formation)
   Carbonyl compound is regenerated if H+ is
   added with water.
   Acetal and ketal are used as a protecting
   group.
Carbonyl compounds –
Chemical properties

4. Nucleophilic Addition reaction (cont’d)
   With ROH (Ketal / Acetal formation)
O           COOC2H5                    O         COO
                           OH
                                                       + C2H5OH
                      (not possible)
            OH   OH

dry HCl     C    C
                                               OH2

        O                                  O
                 COOC2H5    OH                   COO
    O                                  O               + C2H5OH
Carbonyl compounds –
Chemical properties

5. Condensation reaction
                               G
     O                     N

     C + :NH2    G         C       + H2O
 Carbonyl compounds –
 Chemical properties

 5. Condensation reaction (cont’d)               -
                                                O
    Mechanism:     O
                                  :NH2    G     C
                     C
                                                  +
                                              H  N H
                                                G
Nucleophilic addition
                                                    proton shift
followed by elimination
                              G                OH
                          N

                                  + H2O         C
                          C

                                              H N G
 Carbonyl compounds –
 Chemical properties

 5. Condensation reaction (cont’d)
    With hydroxylamine             OH
       O                           N
       C       :NH2   OH           C     + H2O

                                 oxime
From aldehyde, product is aldoxime
From ketone, product is ketoxime
They are white solids.
The reaction can thus serve as a test for carbonyl
compounds.
Carbonyl compounds –
Chemical properties

5. Condensation reaction (cont’d)
   With hydrazine
                                        NH2
      O                             N
      C        :NH2   NH2           C      + H2O
                hydrazine
                               hydrazone
Carbonyl compounds –
Chemical properties

5. Condensation reaction (cont’d)
   With phenylhydrazine
                                H
     O                 H            N
     C      :NH2   N           N
                                               + H2O
                               C

                             phenylhydrazone
           phenylhydrazine
Carbonyl compounds –
Chemical properties

5. Condensation reaction (cont’d)
   With 2,4-dinitrophenylhydrazine
                                   O2N
                               H
   O                 H             N                 NO2
   C      :NH2   N             N
                         NO2                               + H2O
                               C


                                       orange ppt.
                 NO2
Carbonyl compounds –
Chemical properties

5. Condensation reaction (cont’d)
   With 2,4-dinitrophenylhydrazine

  This method is used for identification of
  original carbonyl compound by checking the
  melting point of the derivatives.
Carbonyl compounds –
Chemical properties

5. Condensation reaction (cont’d)
   With 2,4-dinitrophenylhydrazine
   Criteria on choosing a suitable derivative for
   identification:
   1. Little side product
   2. Reaction should be easily carried out
   3. Derivatives should be easily purified.
   4. The difference in melting point between the derivatives
      of consecutive members is large.
Carbonyl compounds –
Chemical properties

6. With PCl5
   H   O                H   Cl

   C   C       + PCl5   C   C     + POCl3

   H                    H   Cl

                            alcoholic KOH
                            reflux

                        C   C
Carbonyl compounds –
Chemical properties

7. Aldol Condensation
     H   O           H   O                         H    H    O
                                 conc. KOH
 H   C   C       H   C   C                   H3C   C    C    C
             H               H                                    H
     H               H                             OH   H
         -hydrogen
                                                        warming

                                                   H     H   O
Carbonyl compounds
should contain -hydrogen            H2O +   H3C   C    C    C
                                                                  H
    Carbonyl compounds –
    Chemical properties

    7. Aldol Condensation (cont’d)
       Mechanism:
                  O                        O                             O

             C    C                    C   C                     C       C
                      H                          H                           H
             H                                                       O

-hydrogen   HO
                                                             C       C
                                                                         H



                          H        O                     H           O
                                           OH2
                      C   C    C   C                 C   C   C       C
                                       H                                     H
                          OH                             O
Carbonyl compounds –
Chemical properties

7. Aldol Condensation (cont’d)
   The carbonyl compounds should contain -
   hydrogen.
   The -hydrogen in carbonyl compound is quite
   acidic since the anion (carbanion) is resonance
   stabilized.
              O                        O

         C    C                   C    C
                  H                        H
Carbonyl compounds –
Chemical properties

7. Aldol Condensation (cont’d)
Example:                     H              H   H    O

                                    H   C   C   C    C
    H   H   H   O
                        conc. KOH                        H
                                        H   H
H   C   C   C   C                                    H       H   H

                    H                       H   C    C       C   C   H
    H   H   H
                                                OH   H       H   H


            H   H       H               O       warming
        H   C   C       C   C   C       C
                                            H
            H   H       H   H   CH2CH3
Carbonyl compounds –
Chemical properties

Crossed aldol condensation reaction
           O                           OH
                          conc. NaOH
       C       + CH3CHO                C    CH2CHO
           H
                                       H
Carbonyl compounds –
Chemical properties

8. Cannizaro Reaction
       O                                      O

       C       conc. NaOH       CH2OH         C
           H                                      ONa
                                    +



Dismutation reaction (disproportionation)
Benzaldehyde (with no -H) is oxidised, and at the
same time, reduced.
Carbonyl compounds –
Chemical properties

9. With Schiff’s Reagent
   Only aldehyde will turn it purple.
Carbonyl compounds –
Uses of carbonyl compounds

Uses:
1. Methanal in the manufacture of urea-
   methanal resin.
2. Propanone as a solvent and a raw material in
   the manufacture of perspex.

								
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