carboxylic acids - masarykova univerzita · values of acids acid pk a acid pk a hcooh 3,70 ch 3...

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