phenols. phenol the antiseptic property of phenol was discovered in 1865 by joseph lister, a...
TRANSCRIPT
Phenols
Phenol
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.
OH
Examples of Phenols
OH
CH3
CH(CH3)2
HO
CH3ON
C
O
H
OH
OCH3
eugenol (cloves; dental analgesic/antiseptic)
OH
OCH3
COH
vanillin
capsaicin (hot peppers; analgesic, anti-inflammatory)
OH
COCH3
O
methyl salicylate(oil of wintergreen)
thymol in thyme)
CH3 CH3
OHHO
bisphenol-A
More phenols…
OH
OH
C15H29
urushiol(s)(poison ivy, oak)
OH
C(CH3)3(CH3)3C
CH3
OH
C(CH3)3(CH3)3C
OCH3BHT (food preservative)
BHA (food preservative)
OH
Cl
Cl
Cl
Cl
Cl
pentachlorophenol(wood preservative)
OH
OH
CH2CH2CH2CH2CH2CH3
n-hexyl resorcinol (antiseptic)
HO
OH
OH
resveratrol(antioxidant in red grapes)
Slight Acidity of Phenol
Phenol has a Ka = 10-10 (pKa =10) Alcohols have a Ka = 10-16 (pKa =16)
The reason phenol is more acidic than an alcohol is resonance stabilization of the phenolate anion (next slide)
OH O
+ H
ROH + HRO
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
N
O
O
O
N
O
O
O
N
O
O
IR spectrum of phenol
O-H
C=CC-O
IR spectrum of cyclohexanol
O-H C-O
O-H C-OO-HC-O
CH3CH2CH2CH2OH
IR spectrum of 1-butanol
OH
OH
H
H
H
H
H
H
H
H
CDCl3 (solvent)
CH2 OH
CH3
CH3CH2CH2CH2OH
CH2
CH2
CH3CH2CH2CH2OH
CH3
CH3
CH2
CH2
CH2
CH2
CH2 O
CH2 O
OH
OH
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 alcohols phenols
1H-NMR:-CH2-O, 3.5