Download Phenols

Phenols
Phenol




OH
The antiseptic property
of phenol was discovered
in 1865 by Joseph Lister,
a physician in Scotland.
Listerine, named after him, contains phenol
as the active ingredient.
Today, over two million tons of phenol are
made each year in the US alone.
Phenol is used for resins, glue to make
plywood, plastics, and pharmaceuticals.
Examples of Phenols
OH
OH
OH
CH(CH3)2
OCH3
OCH3
CH3
C
O
H
vanillin
eugenol (cloves; dental
analgesic/antiseptic)
O
CH3O
HO
N
C
CH3
CH3
OH
HO
thymol
in thyme)
bisphenol-A
OH
O
C
OCH3
H
capsaicin (hot peppers;
analgesic, anti-inflammatory)
methyl salicylate
(oil of wintergreen)
More phenols…
OH
OH
(CH3)3C
OH
OH
C(CH3)3
(CH3)3C
C(CH3)3
C15H29
CH3
urushiol(s)
(poison ivy, oak)
OCH3
BHT
(food preservative)
BHA
(food preservative)
OH
OH
Cl
Cl
Cl
Cl
Cl
pentachlorophenol
(wood preservative)
OH
HO
OH
OH
resveratrol
(antioxidant in red grapes)
CH2CH2CH2CH2CH2CH3
n-hexyl resorcinol (antiseptic)
Slight Acidity of Phenol


Phenol has a Ka = 10-10 (pKa =10)
Alcohols have a Ka = 10-16 (pKa =16)
OH
ROH

O
RO
+
H
+
H
The reason phenol is more acidic than an
alcohol is resonance stabilization of the
phenolate anion (next slide)
Resonance of Phenolate ion
O
O
O
O
O
Substituents that stabilize an anion enhance the acidity of phenol.
Phenol has a pKa = 10; p-nitrophenol has a pKa = 7.1
Picric acid (2,4,6-trinitrophenol)

2,4,6-trinitrophenol is so acidic that it is
called picric acid; it has a Ka = 10-1 (pKa =1)

The enhanced acidity compared to phenol
itself (Ka = 10-10) is due to the increased
resonance stabilization of the conjugate
base (phenolate anion) by the nitro groups:
O
O
N
O
O
O
N
O
O
O
N
O
IR spectrum of phenol
O-H
C=C
C-O
IR spectrum of cyclohexanol
O-H
C-O
IR spectrum of 1-butanol
O-H
O-H
C-O
C-O
CH3CH2CH2CH2OH
OH
OH
H
H
H
H
H
H
H
H
CH2
CH2
CH3
CH3CH2CH2CH2OH
CH2
CDCl3 (solvent)
OH
CH3
CH2
CH3CH2CH2CH2OH
CH2
O
CH2
OH
CH3
CH2
O
CH2
OH
CH2
Summary of Spectral Features
IR:
O-H stretch, 3600-3000 cm-1, broad
(alcohols and phenols)
C-O stretch, 1250 to 1050 cm-1, (higher
for phenols than for alcohols)
13C-NMR:
C-O, 60-65 d (alcohols);
~160 d (phenols)
1H-NMR:
-CH2-O, 3.5 d