carboxylic acids - masarykova univerzita · values of acids acid pk a acid pk a hcooh 3,70 ch 3...
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Carboxylic acids
Preparation of carboxylic acids
oxidation of primary alcohols
oxidation of alkylbenzenes
application of Grignard reagent in reaction with CO2
Preparation of carboxylic acids
hydrolysis of nitriles
Reactivity of carboxyl group
Reactivity:
1) Sensitivity against bases (also majority of
nucleophiles performs itself as bases)
2) Sensitivity against electrophiles – they activate
carbonyl carbon atom for a nucleophilic attack
3) Sensitivity against nucleophilic attack is only limited
- I effect of oxygen - I effect < + M effect
- M effect, - I effect
formation of
dimers
Infrared spektra of carboxylic acids
nC=O = 1700 – 1725 cm-1
nc-O = 1450 – 1390 cm-1
nC=O = 1700 – 1725 cm-1
nc-O = 1450 – 1390 cm-1
nO-H = 2500 – 3300 cm-1
NMR spektrum of carboxylic acids
Solvent CDCl3 (traces of nondeuterated chloroform are visible at d = 7,3 ppm
2 – chloropropionic acid
pKa values of acids
Acid pKa Acid pKa
HCOOH 3,70
CH3COOH 4,74 Cl-CH2-COOH 2,9
CH3CH2COOH 4,87 Cl2CH - COOH 1,3
CH3CH2CH2COOH 4,82 Cl3C - COOH 0,7
F-CH2COOH 2,59
Cl-CH2COOH 2,85
Br-CH2COOH 2,90
N≡C-CH2COOH 2,47
CF3-CH2COOH 3,06
CH3O-CH2COOH 3,57
HO-CH2COOH 3,83
C6H5-CH2COOH 4,31
pKa values of aromatic acids
Hammett equation
Taft equation
Taft equation
s* s*
CH3- 0,0 H- 0,49
C2H5- -0,1 Cl-CH2- 1,05
C3H7- -0,115 Cl2CH- 1,94
(CH3)3C- -0,30 Cl3C- 2,65
HO-CH2- 0,55
NC-CH2- 1,30
Taft constants of substituents with the value higher than zero are showing that the substituents are
more electronwithdrawing than methyl; on the other side constants with value lower than zero are
showing that the substituents are electrondonating species. Value of their electron influence may be
this way quantify.
log k / k0 = * s*
Reactivity of carboxylic acids
By the treatment with bases salts of carboxylic acids are prepared
sodium acetate
ammonium butanoate
potassium benzoate
anilinium trichloracetate
Salts of carboxylic acids
Basicity of carboxylate anion is low
it can reacts with corresponding activated center:
but will be sufficient base for activation some reactions as Perkin
synthesis
formation of
nonsymmetrical
anhydrides
preparations of
esters
Salts of carboxylic acids
application of Ca2+ and Ba2+ salts for preparation of ketones
in combination with calcium formiate aldehyd may be
prepared
Reactivity of carboxyl group
Reactivity:
1) Sensitivity against bases (also majority of
nucleophiles performs itself as bases)
2) Sensitivity against electrophiles – they activate
carbonyl carbon atom for a nucleophilic attack
3) Sensitivity against nucleophilic attack is only limited
- I effect of oxygen - I effect < + M effect
- M effect, - I effect
formation of
dimers
Reactivity of carboxyl group
Acidic catalyst activate the carbonyl group for reactions
proton causes formation of positive
charge at carbonyl carbon atom and at
the same time suppresses acid
dissociation
mechanism of the reaction was proved by
experiments with 18O isotop and is characteristic
for reactions of prim. and sec. alcohols
mechanism typical for esterifications with tert. alcohols
Reactivity of carboxylic function
Estery karboxylových kyselin
R CO
O R1
Nomenclature:
Alkyl (aryl) alkanoate
CH3 CO
O CH3
CH3-CH2-CH2-CH2 CO
O
NO2
H2N
CO
O CH2CH3
COOCH3
H3C
CH3CH2CH2CO
O
H3C
methyl acetate
3-nitrophenyl-pentanoate
ethyl-3-aminobenzoate
methyl-3-methylcyclopentancarboxylate
2-methylcyclohexyl-butanoate
Reactivity of carboxylic acids esters
Hydrolysis of esters acid catalysis
base catalysis
during a base catalysed hydrolysis salts of carboxylic
acids are prepared