Phenol s

Phenols

Ar-OH

Phenols

Ar-OH

Phenols are compounds with an

Phenols are compounds with an –  – OH groupOH group attached

attached to an to an aromatic aromatic carbon. carbon. Although theyAlthough they share the same functional group with alcohols, share the same functional group with alcohols, where the

where the –  – OH group is attached to an aliphaticOH group is attached to an aliphatic carbon, the chemistry of phenols is

carbon, the chemistry of phenols is very differentvery different from that of alcohols.

Nomenclature.

Nomenclature.

Phenols are

Phenols are usually namusually named as ed as substituted phenols. substituted phenols. TheThe methylphenols are

methylphenols are given the given the special namspecial name, cresols. e, cresols. Some otherSome other  phenols are named as hydroxy compounds.

 phenols are named as hydroxy compounds.

OH OH phenol phenol OH OH Br  Br  m m-bromophenol-bromophenol CH CH₃₃ OH OH o o-cresol-cresol OH OH COOH COOH salicylic acid salicylic acid OH OH OH OH OH OH OH OH OH OH OH OH catechol

catechol resorcinolresorcinol _{hydroquinonehydroquinone}

COOH COOH

OH OH

 p

physical properties

 phenols are polar and can hydrogen bond  phenols are water insoluble

 phenols are stronger acids than water and will dissolve in 5% NaOH

 phenols are weaker acids than carbonic acid and do not dissolve in 5% NaHCO₃

Intramolecular hydrogen bonding is possible in some ortho-substituted phenols. This intramolecular

hydrogen bonding reduces water solubility and increases volatility. Thus, o -nitrophenol is steam

distillable while the isomeric p-nitrophenol is not.

N O H O O o-nitrophenol bp 100oC at 100 mm 0.2 g / 100 mL water  volatile with steam

OH

NO₂

 p-nitrophenol bp decomposes

1.69 g / 100 mL water  non-volatile with steam

phenols, syntheses:

1. From diazonium salts

2. Alkali fusion of sulfonates N₂ H₂O,H+ OH SO₃ Na _NaOH,H2O 300o ONa H+ OH

Reactions:

alcohols phenols

1. HX NR

2. PX₃ NR

3. dehydration NR

4. as acids phenols are more acidic

5. ester formation similar

Phenols, reactions: 1. as acids

2. ester formation 3. ether formation

4. Electrophillic Aromatic Substitution

a) nitration f) nitrosation

b) sulfonation g) coupling with diaz. salts

c) halogenation h) Kolbe

d) Friedel-Crafts alkylation i) Reimer-Tiemann e) Friedel-Crafts acylation

as acids:

with active metals:

with bases:

CH₄ < NH₃ < HCCH < ROH < H₂O < phenols < H₂CO₃ < RCOOH < HF

Acidity increasing OH Na ONa sodium phenoxide + H₂(g) OH + NaOH ONa + H₂O SA SB WB WA

CH₄ < NH₃ < HCCH < ROH < H₂O < phenols < H₂CO₃ < RCOOH < HF OH + NaOH ONa + H₂O SA SB WB WA

water insoluble _{water soluble} OH

+ NaHCO₃ NR _{phenol < H}

insoluble

soluble

insoluble

insoluble

soluble

soluble

water 5% NaOH 5% NaHCO₃

 phenols

carboxylic acids

We use the ionization of acids in water to measure acid strength (Ka): HBase + H₂O H₃O+  _{+ Base} -Ka = [H₃O+ _{][ Base ] / [ HBase]} ROH Ka ~ 10-16 _{- 10}-18 ArOH Ka ~ 10-10

ROH + H₂O H₃O+ _{+ RO}

-ArOH + H₂O H₃O+  _{+ ArO}

-OH OH O O O O O

Resonance stabilization of the phenoxide ion, lowers the PE of the products of the

ionization, decreases the ΔH, shifts the equil farther to the right, makes phenol more

effect of substituent groups on acid strength?

OH

G + H2O

O

G + H3O

Electron withdrawing groups will decrease the negative

charge in the phenoxide, lowering the PE, decreasing the ΔH, shifting the equil farther to the right, stronger acid.

Electron donating groups will increase the negative charge in the phenoxide, increasing the PE, increasing the ΔH,

 Number the following acids in decreasing order of acid strength (let # 1 = most acidic, etc.)

OH OH OH OH OH

NO₂ CH3 Br 

SO₃H COOH OH CH₂OH

2. ester formation (similar to alcohols) OH CH₃ + CH₃CH₂C O OH H+ CH₃CH₂C O O H₃C + H₂O OH COOH salicyclic acid + (CH₃CO)₂O O COOH C H₃C O aspirin

O COOH C H₃C O aspirin analgesic anti-inflamatory antipyrretic anticoagulant Reye's syndrome

not to be used by children with high fevers!

OH NH C H₃C O acetaminophen aspirin substitute Tylenol Kidney damage!

3. ether formation (Williamson Synthesis)

Ar-O _Na- +  _{+ R-X   Ar-O-R + NaX}

note: R-X must be 1o _{or CH} 3

Because phenols are more acidic than water, it is possible to generate the phenoxide in situ using NaOH.

OH

CH₃

+ CH₃CH₂Br, NaOH

OCH₂CH₃

4. Electrophilic Aromatic Substitution

The – OH group is a powerful activating group in EAS and an ortho/para director. a) nitration OH OH NO₂ NO₂ O₂N

polynitration!

OH Br ₂ (aq.) OH Br  Br  Br  _{no catalyst required} use polar solvent

polyhalogenation!

c) sulfonation OH H₂SO₄, 15-20oC OH SO₃H H₂SO₄, 100oC OH SO₃H

At low temperature the reaction is non-reversible and the lower Eact ortho- product is formed (rate control).

At high temperature the reaction is reversible and the more stable para- product is formed (kinetic control).

d) Friedel-Crafts alkylation. OH + H₃C C CH₃ CH₃ Cl  AlCl₃ OH C CH₃ CH₃ H₃C

e) Friedel-Crafts acylation OH CH₃CH₂CH₂C O Cl +  AlCl3 OH O

Do not confuse FC acylation with esterification: OH CH₃CH₂CH₂C O Cl + _O O

OH O OH CH₃CH₂CH₂C O Cl + _O O  AlCl₃

f) nitrosation

OH

HONO

OH

NO

EAS with very weak electrophile NO+

OH CH₃ NaNO₂, HCl OH CH₃ NO  p-nitrosophenol

g) coupling with diazonium salts

(EAS with the weak electrophile diazonium)

OH CH₃ + N₂ Cl benzenediazonium chloride CH₃ OH N N an azo dye

h) Kolbe reaction (carbonation) ONa + CO₂ 125 o_{C, 4-7 atm.} OH COONa sodium salicylate H+ OH COOH salicylic acid EAS by the weakly

electrophilic CO₂

O C O

i) Reimer-Tiemann reaction OH CHCl₃, aq. NaOH 70oC H+ OH CHO salicylaldehyde