1. Sovia Aprina Basuki
KIMIA ORGANIK II
FARMASI UMM
2013

2. Mahasiswa dapat:
 Menggambarkan struktur asam karboksilat,
 memberi nama asam karboksilat,
 menjelaskan sifat keasaman
 Menjelaskan konsep penarik dan pendorong elektron
 Menjelaskan efek orto pada asam karboksilat
aromatik, menjelaskan sifat-sifat fisika asam
karboksilat.
 Menuliskan reaksi-reaksi pembuatan asam
karboksilat
 Menuliskan reaksi-reaksi asam karboksilat
 Menuliskan rumus umum asam dikarboksilat
 Menyebutkan sifat-sifat asam dikarboksilat

3. Organic Chemistry, 7th edition, John
McMurry
Organic Chemistry, T. W. Graham
Solomons
 Organic Chemistry, Fessenden and
Fessenden

5. A general acyl group (blue) as an acylium ion (top centre), as an
acyl radical (top right), in a ketone (top left), an aldehyde (bottom
left), ester (bottom centre) or amide (bottom right). (R1, R2, R3 =
organyl substituents or hydrogen).

6. Structure and Bonding
• Carboxylic acids are compounds containing a carboxy
group (COOH).
• The structure of carboxylic acids is often abbreviated
as RCOOH or RCO2H, but keep in mind that the central
carbon atom of the functional group is doubly bonded
to one oxygen atom and singly bonded to another.

7. The two most important features of the carbonyl group are:
·Because oxygen is more electronegative than either carbon or hydrogen,
the C—O and O—H bonds are polar.

8.  Carboxylic Acids, R-COOH
 If derived from open-chain alkanes, replace the
terminal -e of the alkane name with -oic acid
 The carboxyl carbon atom is C1
Common names: IUPAC Common
HCO2H methanoic acid formic acid
CH3CO2H ethanoic acid acetic acid
CH3CH2CO2H propanoic acid propionic acid
CH3CH2CH2CO2H butanoic acid butyric acid
CH3CH2CH2CH2CO2H pentanoic valeric acid
8

9. 5 4 3 2 1
C — C — C — C — C = O
δ γ β α used in common names

10. Carboxylic acids, common names:
…
CH3(CH2)4CO2H caproic acid
CH3(CH2)5CO2H ---
CH3(CH2)6CO2H caprylic acid
CH3(CH2)7CO2H ---
CH3(CH2)8CO2H capric acid
CH3(CH2)9CO2H ---
CH3(CH2)10CO2H lauric acid

11.  Compounds with CO2H bonded to a ring are named
using the suffix -carboxylic acid
 The CO2H carbon is not itself numbered in this
system
 Use common names for formic acid (HCOOH) and
acetic acid (CH3COOH)
11

12. COOH
special names
COOH COOH COOH
CH3
CH3
CH3
benzoic acid
o-toluic acid m-toluic acid p-toluic acid

13. salts of carboxylic acids:
name of cation + name of acid: drop –ic acid, add –ate
CH3CO2Na sodium acetate or sodium ethanoate
CH3CH2CH2CO2NH4 ammonium butyrate
ammonium butanoate
(CH3CH2COO)2Mg magnesium propionate
magnesium propanoate

15.  Carboxylic acids transfer a proton to water to give
H3O+ and carboxylate anions, RCO2
15
, but H3O+ is a
much stronger acid
 The acidity constant, Ka,, is about 10-5 for a typical
carboxylic acid (pKa ~ 5)

16.  Fluoroacetic, chloroacetic, bromoacetic, and
iodoacetic acids are stronger acids than acetic acid
 Multiple electronegative substituents have
synergistic effects on acidity
17

17.  If pKa of given acid and the pH of the medium
are known, % of dissociated and undissociated
forms can be calculated using the Henderson-
Hasselbalch eqn
18

18. 19
The Inductive Effect in Aliphatic Carboxylic Acids

19. 20

20. Substituted Benzoic Acids
Recall that substituents on a benzene ring either donate or
withdraw electron density, depending on the balance of their
inductive and resonance effects. These same effects also
determine the acidity of substituted benzoic acids.
[1] Electron-donor groups destabilize a conjugate base, making
an acid less acidic—The conjugate base is destabilized
because electron density is being donated to a negatively
charged carboxylate anion.
21

21. [2] Electron-withdrawing groups stabilize a conjugate base, making an
acid more acidic. The conjugate base is stabilized because
electron density is removed from the negatively charged
carboxylate anion.
22

22. 23
Figure 19.8
How common substituents
affect the reactivity of a
benzene ring towards
electrophiles and the acidity of
substituted benzoic acids

23.  Subtituen posisi orto dari turunan asam benzoat selalu
meningkatkan sifat keasaman senyawa tersebut karena
subtituen ini mengurangi resonansi luar cincin.
 Efek orto pada asam benzoat tidak tergantung pada jenis
substituen apakah cenderung menarik atau melepaskan
elektron.
 Efek resonansi sangat berpengaruh terhadap kekuatan
asam. Subtituen yang berada pada posisi orto akan
mengurangi resonansi luar cincin sehingga akan
meningkatkan kekuatan asam.
 Senyawa turunan asam benzoat yang mempunyai
kekuatan asam tertinggi adalah senyawa turunan asam
benzoate yang subtituennya terletak pada posisi orto.

24. 1. Wujud
Pada temperatur kamar, asam karboksilat yang bersuku rendah
adalah zat cair yang encer, suku tengah berupa zat cair yang
kental, dan suku tinggi berupa zat padat yang tidak larut dalam
air.
Rumus Struktur T d
H-COOH 101
CH3-COOH 118
CH3-CH2-COOH 141
CH3-CH2-CH2-COOH 163
CH3-CH2-CH2-CH2-COOH 187
2. Titik didih dan titik leleh
Asam karboksilat membentuk ikatan
hidrogen berupa siklik dimer
antarmolekul. Ikatan hidrogen yang kuat
ini menyebabkan TD dan TL lebih tinggi
dari alkohol yang bersesuaian.

25. 3. Kelarutan
 Carboxylic acids are proton donors toward weak and strong
bases, producing metal carboxylate salts, RCO + M
2
 Carboxylic acids with more than six carbons are only slightly
soluble in water, but their conjugate base salts are water-soluble
4. Daya hantar listrik
Asam karboksilat dapat terionisasi sebagian dalam air,
sehingga termasuk senyawa elektrolit lemah.
R-COOH ⇋ R-COO- + H+

26. 27
[1] Oxidation of 1° alcohols
[2] Oxidation of alkyl benzenes

27. 28
[3] Oxidative cleavage of alkynes

28. 1. Reaksi dengan Basa (penyabunan)
R-COOH + NaOH → R-COONa + H2O
2. Reaksi esterifikasi
sabun
H2SO4
R-COOH + R’-OH → R-COOR’ + H2O
Asam karboksilat Alkohol Ester
3. Reaksi dengan PCl5
R-COOH + PCl5 → R-CO-Cl + POCl3 + HCl
Alkanoilklorida
4. Reaksi dengan NH3
R-COOH + NH3 → R-CONH2 + H2O
Amida
5. Reaksi dengan Cl2
CH3-CH2-COOH + Cl2 → R-CHCl-COOH + HCl
Asam 2-monokloropropanoat

29. Reactions of Carboxylic Acids
The most important reactive feature of a carboxylic acid is its polar O—H
bond, which is readily cleaved with base.

30. • The nonbonded electron pairs on oxygen create electron-rich
sites that can be protonated by strong acids (H—A).
• Protonation occurs at the carbonyl oxygen because the resulting
conjugate acid is resonance stabilized (Possibility [1]).
• The product of protonation at the OH group (Possibility [2])
cannot be resonance stabilized.

31. • The polar C—O bonds make the carboxy carbon electrophilic. Thus,
carboxylic acids react with nucleophiles.
• Nucleophilic attack occurs at an sp2 hybridized carbon atom, so it
results in the cleavage of the  bond as well.

32. Carboxylic Acids—Strong Organic BrØnsted-Lowry Acids
• Carboxylic acids are strong organic acids, and as such, readily react
with BrØnsted-Lowry bases to form carboxylate anions.

33. • An acid can be deprotonated by a base that has a conjugate
34
acid with a higher pKa.
• Because the pKa values of many carboxylic acids are ~5, bases
that have conjugate acids with pKa values higher than 5 are
strong enough to deprotonate them.

35. • Carboxylic acids are relatively strong acids because
deprotonation forms a resonance-stabilized conjugate base—a
carboxylate anion.
• The acetate anion has two C—O bonds of equal length (1.27 Å)
and intermediate between the length of a C—O single bond
(1.36 Å) and C=O (1.21 Å).

36. • Ethoxide, the conjugate base of ethanol, bears a negative charge
on the O atom, but there are no additional factors to further
stabilize the anion. Because ethoxide is less stable than acetate,
ethanol is a weaker acid than acetic acid.
• Phenoxide, the conjugate base of phenol, is more stable than
ethoxide, but less stable than acetate because acetate has two
electronegative O atoms upon which to delocalize the negative
charge, whereas phenoxide has only one.

37. Figure 19.7
Summary: The relationship
between acidity and conjugate
base stability for acetic acid,
phenol, and ethanol
• Note that although resonance stabilization of the conjugate base is
important in determining acidity, the absolute number of resonance
structures alone is not what is important!

38. • Resonance stabilization accounts for why carboxylic
acids are more acidic than other compounds with O—H
bonds—namely alcohols and phenols.
• To understand the relative acidity of ethanol, phenol
and acetic acid, we must compare the stability of their
conjugate bases and use the following rule:
- Anything that stabilizes a conjugate base A:¯ makes the
39
starting acid H—A more acidic.

39. HOOC-COOH oxalic acid
HO2C-CH2-CO2H malonic acid
HO2C-CH2CH2-CO2H succinic acid
HO2C-CH2CH2CH2-CO2H glutaric acid
HOOC-(CH2)4-COOH adipic acid
HOOC-(CH2)5-COOH pimelic acid

40. CO2H
CO2H
CO2H
CO2H
CO2H
CO2H
phthalic acid isophthalic acid
terephthalic acid
H COOH
C
C
H COOH
H COOH
C
C
HOOC H
maleic acid fumaric acid