Benzoic acids

1. Dr MY Ansari
Associate Prof. MM College of
Pharmacy
M.M. COLLEGE OF PHARMACY
MAHARISHI MARKANDESHWAR (DEEMED TO BE UNIVERSITY),
MULLANA, AMBALA (INDIA)- 133207
(Established under section 3 of UGC, act 1956)
(Accredited By NAAC with Grade ‘A++’)

2.  Acidity of aromatic acids
 Effect of substituent's on acidity
 Reactions of benzoic acids
Benzoic acid is an organic compound which is described by
the chemical formula C6H5COOH. It consists of a carboxyl group
attached to a benzene ring. Therefore, benzoic acid is said to be
an aromatic carboxylic acid. This compound exists as a
crystalline, colourless solid under normal conditions. The term
‘benzoate’ refers to the esters and salts of C6H5COOH.

3. Electronegative substituent's withdraw
electrons from carboxyl group(X); increase
the K value and for loss of H+
X CH2COH
O
Where X is electron withdraw atom or molecule
Substituent Effects on Acidity

4.  sp2-hybridized carbon is more
electron-withdrawing than sp3, and sp is
more electron-withdrawing than sp2
Ka pKa
6.3 x 10-5 4.2
5.5 x 10-5 4.3
1.4 x 10-2 1.8
COH
O
H2C CH COH
O
COH
O
HC C
Hybridization Effect

5. pKa
Substituent ortho meta para
H 4.2 4.2 4.2
CH3 3.9 4.3 4.4
F 3.3 3.9 4.1
Cl 2.9 3.8 4.0
CH3O 4.1 4.1 4.5
NO2 2.2 3.5 3.4
 Ionization effect is small when
is X less electronegative atom or
groups and vice a versa where as this
effect is larger when substituted on
ortho postions
COH
O
X
Ionization of Substituted Benzoic Acids

6.  one carboxyl group acts as an electron-
withdrawing group toward the other;
effect decreases with increasing separation
Oxalic acid
Malonic acid
Heptanedioic acid
1.2
2.8
4.3
COH
O
HOC
O pKa
HOCCH2COH
O
O
HOC(CH2)5COH
O O
Dicarboxylic Acids

7. (82%)
1. Mg,
diethyl
ether
2. CO2
3. H3O+ CH3
CO2H
Br
CH3
Example for synthesis of aromatic acids from Aryl Halide

8.  converts an alkyl halide to a carboxylic acid
having one more carbon atom than the starting
halide
 limitation is that the halide must be reactive
toward substitution by SN2 mechanism
RX RCOH
O
–
•
•
•
•C N
RC •
•
N
SN2
H3O+
heat
+ NH4
+
Preparation of aromatics acids from
Nitriles as a methods of Hydrolysis

9. NaCN
DMSO
(dimethyl sulfoxide)
(77%)
H2O
H2SO4
heat
(92%)
CH2Cl CH2CN
CH2COH
O
Example

10. BrCH2CH2CH2Br
NaCN H2O
H2O, HCl heat
(77-86%)
NCCH2CH2CH2CN
(83-85%)
HOCCH2CH2CH2COH
O
O
Example: Dicarboxylic Acid

11. 1. NaCN
2. H+
(60% from 2-pentanone)
H2O
HCl, heat
CH3CCH2CH2CH3
O
CH3CCH2CH2CH3
OH
CN
CH3CCH2CH2CH3
OH
CO2H
Synthesis via Cyanohydrin from ketone compounds

12. Thank you
M.M. COLLEGE OF PHARMACY
MAHARISHI MARKANDESHWAR (DEEMED TO BE UNIVERSITY),
MULLANA, AMBALA (INDIA)- 133207
(Established under section 3 of UGC, act 1956)
(Accredited By NAAC with Grade ‘A++’)