Carboxylic Acid (PowerPoint)

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					Carboxylic Acid
      A. Preparation
1.    Oxidation of primanry alcohol
      H                          O                     O
               MnO4 / H+                 MnO4 / H+
CH3   C   OH                     C                     C
                           CH3       H           CH3       OH
      H
     A. Preparation
2.       From acid nitrile

                             H+
     R      C    N   + H2O        RCOOH
     A. Preparation
3.   For aromatic acid
             CH3
                   MnO4 / H+        COOH




             CH2CH3                  COOH
                      MnO4   / H+
    B. Physical properties
1. The boiling point and melting point are higher
   than corresponding ester due to the existence
   of H-bond between the molecules of acid.
   Lower members of aliphatic acids are liquid with
   pungent smell.
2. Lower members of aliphatic acids are soluble in
   water due to the formation of extensive H-bond
   with water molecules.
    B. Physical properties
3. Molecular mass of acids is found to be
   doubled when dissolved in benzene due to
   the formation of dimer via H-bond
   formation.
                O H      O
        R   C                C   R
                O     H O
     C. Chemical Properties
1.   Acid character

     RCOOH + H2O                RCOO   + H3O+


          [RCOO  ][ H 3O  ]
     Ka =
             [RCOOH ]
       C. Chemical Properties
 1. Acid character (cont’d)
Acid                               Ka at 25oC / mol dm-3

Methanoic acid (HCOOH)                  1.7 x 10-4
Ethanoic acid (CH3COOH)                 1.7 x 10-5
Propanoic acid (CH3CH2COOH)             1.3 x 10-5
Benzenecarboxylic acid (Ph-COOH)        6.5 x 10-5
Phenol (Ph-OH)                         1.3 x 10-10
Methanol (CH3OH)                       1.0 x 10-16
    C. Chemical Properties
1. Acid character (cont’d)
   Carboxylic acid is more acidic than
   alcohol and phenol due to the
   comparatively more stable carboxylate
   anion than alkoxide and phenoxide ion.
   The equilibrium position thus lie
   closer to the right hand side.
                 O                O
         R   C            R   C
                 O                O
    C. Chemical Properties
1. Acid character (cont’d)
   The resulting resonance hybrid of the
   carboxylate anion is more stable than that of
   phenoxide ion due to the equal contribution of
   the two canonical forms.
   On passing up the homologous series, the
   members become less acidic since alkyl group is
   electron donating which makes the negative
   charge on the resulting carboxylate anion to be
   more intensified and thus less stable.
C. Chemical Properties
          Acid    Ka / 25oC
     H
                  1.4 x 10-3
Cl   C    COOH

     H
     H
                  5.1 x 10-2
Cl   C    COOH

     Cl
     Cl
                  2.2 x 10-1
Cl   C    COOH

     Cl
    C. Chemical Properties
1. Acid character (cont’d)
   Chlorine replacing hydrogen in alkyl
   group of the acid causes the acid to be
   more acidic since the chlorine has an
   negative inductive effect.
   This causes the negative charge in the
   carboxylate anion to be spread through
   the ion more effectively, i.e. more stable.
          C. Chemical Properties
 2.       Esterification
                O             conc. H2SO4                   O
      R    C      + HOR'                        R       C         + H2O
                OH              reflux                      OR'
Forward reaction is an acid-catalyzed esterification
while the backward reaction is acid-catalyzed
hydrolysis of ester.
                O                 +                     O
                                 H
      R     C         + H2O                 R       C     + HOR'
                OR'                                     OH
    C. Chemical Properties
2. Esterification (cont’d)
   Saponification:
   In alkaline medium (hydrolysis of ester).
   (Not a equilibrium reaction)
            O                          O
                          OH
    R   C         + H2O        R   C       + HOR'
            OR'                        O
         C. Chemical Properties
3.       Reduction
                                               H
              O
                   1. LiAlH4 / dry ether
     R    C                                R   C   OH
                      2. water
              OH
                                               H

LiAlH4 is a very strong reduction agent
(especially in organic compound).
N.B. NaBH4 cannot reduce carboxylic acid.
     C. Chemical Properties
4.       Replacement of –OH by -X
           O                    O
                    PCl5
     R     C   OH           R   C   Cl + POCl3 + HCl
           O                    O
                    PCl3
     R     C   OH           R   C   Cl   + H3PO3
           O                    O
                    SOCl2
     R     C   OH           R   C   Cl + SO2 + HCl
         C. Chemical Properties
5.       Formation of amide
          O                       O
                   NH3
     R    C   OH             R    C   O NH4+    (RCOONRH3)
                   (RNH2)



                                  O
                                            + H2O
                             R    C   NH2
                                  O
                            ( R   C   NRH )
     C. Chemical Properties
6.   Decarboxylation

                1. NaOH
      RCOOH               RH + CO2
              2. NaOH /
      C. Chemical Properties
7.    Chlorination
                     red P
     CH3COOH + Cl2           CH2COOH + HCl
                         o
                     100 C
                             Cl
     C. Chemical Properties –
     Special reaction for methanoic acid
1.   Oxidation
     O
              + [O]              H2O + CO2
 H   C   OH
     O
              + Ag2O + NH3              Ag + (NH4)2CO3 + H2O
H    C   OH
              Tollen's reagent
     C. Chemical Properties –
     Special reaction for methanoic acid
2.   Dehydration
          O
                   conc. H2SO4
                                 H2O + CO
     H    C   OH

     How can you test CO?
     1. turn citrated blood cherry red.
     2. burn with blue flame the gas turn lime
     water milky.
     C. Chemical Properties –
     Special reaction for methanoic acid
3.   Decomposition by heating
         O
                          H2 + CO2
     H   C   OH
                         (absent of air)
      C. Chemical Properties –
      Special reaction for methanoic acid
4.    With neutral FeCl3
      O

 H    C   OH   + FeCl3     Fe(HCOO)3     red solution
      O

CH3   C   OH   + FeCl3     (CH3COO)3Fe     reddish brown ppt.
    Ethanedioic acid (Oxalic acid)
A. Preparation
1. Oxidation of ethene
                                                  O   O
          MnO4 / OH             excess [O]
CH2=CH2               CH2-CH2                HO   C   C   OH

                      OH OH
    Ethanedioic acid (Oxalic acid)
A. Preparation
2. Ozonolysis of ethyne

            O3 / CCl4           O   O
   HC CH                   HO   C   C   OH
            Zn dust / H+
    Ethanedioic acid (Oxalic acid)
B. Physical Properties
   1. It is a colourless solid.
   2. It is quite soluble in water.
    Ethanedioic acid (Oxalic acid)
C. Chemistry Properties
   1. As an acid
   2. Formation of acid chloride
   3. Formation of ester
    Ethanedioic acid (Oxalic acid)
c. Chemistry Properties
   4. With oxidising agent
                 MnO4 / H+
      (COOH)2                    2 CO2 + H2O
                 60 oC - 70 oC

      It is used as a primary standard in
      volumetric analysis.
    Ethanedioic acid (Oxalic acid)
c. Chemistry Properties
   5. With conc. sulphuric acid
              conc. H2SO4
    (COOH)2                 CO + CO2 + H2O
 Butenedioic acid

   H             H         H           COOH
        C    C                 C   C
HOOC             COOH   HOOC           H
       maleic acid         fumaric acid
    Butenedioic acid
     A. Difference in physical porperties

                Maleic acid (cis-) Fumaric acid (trans-)

Melting point        132oC                302oC
  Density         1.50 g / dm3        1.64 g / dm3

  Solubility        Soluble         Sparingly soluble
  Acidity:
    Ka1             1 x 10-3            1 x 10-12
    Ka2             6 x 10-7            4 x 10-5
    Butenedioic acid
A. Difference in physical porperties (cont’d)
                OH2
     C4H4O4             C3H3O2COO + H3O+
               [C3H3O2COO ][H3O ]
        K a1 
                    [C4 H 4O4 ]
                  OH2
 C3H3O2COO                  OOCC2H2COO + H3O+
               [  OOCC2 H 2COO ][H3O ]
       Ka2   
                     [C3H3O2COO ]
    Butenedioic acid
B. Reasons for the differences
1. Melting point
   Melting involves the breaking of
   intermolecular bond. The cis-isomer
   has intramolecular H-bond since the
   acid group are close together and this
   reduce the extent of formation of
   intermolecular H-bond.
    Butenedioic acid
B. Reasons for the differences
1. Melting point (cont’d) H             H
                              C    C
                    HO    C             C   O
                              O    HO
 Trans-isomer can form intermolecular H-bond
 only since the 2 acid groups are too far apart.
 Also, packing of the molecules in trans-isomer
 is better as it has a more symmetrical structure.
    Butenedioic acid
B. Reasons for the differences
2. Density
   The intermolecular force in cis-isomer is
   weaker and so molecules are packed
   less closely together, leading to lower
   density than the trans-isomer.
    Butenedioic acid
B. Reasons for the differences
3. Solubility
   Since intermolecular force in cis-isomer is
   weaker, it is more easily broken on
   adding to water and thus more soluble. In
   cis-isomer, there is a net dipole moment,
   it is thus more soluble in a polar
   solvent.
     Butenedioic acid
B. Reasons for the differences
4. Acidity
   Ka1 for trans-isomer is smaller than that of
   cis-isomer. In cis-isomer, after the first proton is
   released, the anion exists in resonance which
   causes it to be more stable than that of trans-
   isomer. And thus the equilibrium position
   shift to the right hand side.
       Butenedioic acid
B. Reasons for the differences
4. Acidity (cont’d)
        H               H           H           H
                C   C                   C   C
   O    C               C   O   O   C               C   O

            O       H O             O H         O

   But on releasing the second proton, such extra
   stability may be lost and therefore Ka2 is smaller
   for cis-isomer.
    Butenedioic acid
C. Difference in chemical properties
        H            H                o H               H
                         heated to 100 C
             C   C                          C       C
    O   C            C   O              C               C   O
                                    O
            OH   H O                            O

 The ease of formation of acid anhydride indicates
 that maleic acid is the cis-isomer.
 Since the C=C bond cannot be rotated, the two
 acid groups in trans-isomer are not close enough
 to lose a molecule of water in the same way.

				
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