Lecture# Phenol

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    Phenols Ar-OH

    Phenols are compounds with an OH group

    attached to an aromatic carbon. Although they

    share the same functional group with alcohols,

    where the OH group is attached to an

    aliphatic carbon, the chemistry of phenols is

    very different from that of alcohols.

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    Nomenclature.

    Phenols are usually named as substituted phenols. The

    methylphenols are given the special name, cresols. Some otherphenols are named as hydroxy compounds.

    OH

    phenol

    OH

    Br

    m-bromophenol

    CH3

    OH

    o-cresol

    OH

    COOH

    salicylic acid

    OH

    OH

    OH

    OH

    OH

    OH

    catechol resorcinol hydroquinone

    COOH

    OH

    p-hydroxybenzoic acid

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    phenols, syntheses:

    1. From diazonium salts

    2. Alkali fusion of sulfonates

    N2H2O,H

    +

    OH

    SO3 Na NaOH,H2O

    300o

    ONaH+ OH

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    as acids:

    with active metals:

    with bases:

    CH4 < NH3 < HCCH < ROH < H2O < phenols < H2CO3 < RCOOH < HF

    OH

    Na

    ONa

    sodium phenoxide

    + H2(g)

    OH

    + NaOH

    ONa

    + H2O

    SA SB WB WA

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    2. ester formation (similar to alcohols)

    OH

    CH3+ CH3CH2C

    O

    OH

    H+

    CH3CH2CO

    O

    H3C

    + H2O

    OH

    COOH

    salicyclic acid

    + (CH3CO)2O

    O

    COOH

    CH3C

    O

    aspirin

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    3. ether formation (Williamson Synthesis)

    Ar-O-Na+ + R-X Ar-O-R + NaX

    note: R-X must be 1o or CH3

    Because phenols are more acidic than water, it is possible

    to generate the phenoxide in situ using NaOH.

    OH

    CH3

    + CH3CH2Br, NaOH

    OCH2CH3

    CH3

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    4. Electrophilic Aromatic Substitution

    TheOH group is a powerful activating group in EAS

    and an ortho/para director.

    a) nitration

    OH OH

    NO2

    NO2

    O2Npolynitration!

    OHdilute HNO3

    OHOH

    NO2

    NO2

    +

    HNO3

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    OH

    Br2 (aq.)

    OH

    Br

    Br

    Br no catalyst required

    use polar solvent

    polyhalogenation!OH

    Br2, CCl4

    OH OH

    Br

    Br

    +

    non-polar solvent

    b) halogenation

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    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 stablepara-

    product is formed (kinetic control).

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    d) Friedel-Crafts alkylation.

    OH

    + H3C C CH3

    CH3

    Cl

    AlCl3

    OH

    C CH3

    CH3

    H3C

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    e) Friedel-Crafts acylation

    OH

    CH3CH2CH2CO

    Cl+

    AlCl3

    OH

    O

    Do not confuse FC acylation with esterification:

    OH

    CH3CH2CH2CO

    Cl+ O

    O

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    OH

    O

    OH

    CH3CH2CH2CO

    Cl+ O

    O

    AlCl3

    Fries rearrangement of phenolic esters.

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    f) nitrosation

    OHHONO

    OH

    NO

    EAS with very weak electrophile NO+

    OH

    CH3 NaNO2, HCl

    OH

    CH3

    NO

    p-nitrosophenol

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    g) coupling with diazonium salts

    (EAS with the weak electrophile diazonium)

    OH

    CH3+

    N2 Cl

    benzenediazoniumchloride

    CH3

    OH

    N

    N

    an azo dye

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    h) Kolbe reaction (carbonation)

    ONa

    + CO2125oC, 4-7 atm.

    OH

    COONa

    sodium salicylate

    H+

    OH

    COOH

    salicylic acid

    EAS by the weaklyelectrophilic CO2

    O C O