Formation Alkoxides

from Alcohols
React methanol and ethanol with sodium
metal (redox reaction).

CH3CH2OH + Na CH3CH2O Na + 1/2 H2

React less acidic alcohols with more

reactive potassium.
(CH3)3C OH + K (CH3)3CO K + 1/2 H2

=>
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 Generating Alkoxides
from Alcohols
• Alcohols are weak acids – requires a strong
base to form an alkoxide such as NaH, sodium
amide NaNH2, and Grignard reagents (RMgX)

• Alkoxides are bases used as reagents in

organic chemistry

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Formation of Phenoxide Ion

Phenol reacts with hydroxide ions to form

phenoxide ions - no redox is necessary.

O H O
+ OH
+ HOH
pKa = 15.7
pKa = 10.0

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3
 Grignard Reagents
• Formula R-Mg-X (reacts like R:- +MgX)
• Stabilized by anhydrous ether
• Iodides most reactive
• May be formed from any halide
– primary
– secondary
– tertiary
– vinyl
– aryl =>
4
 Some Grignard Reagents

Br
ether MgBr
+ Mg

Cl MgCl
ether
CH3CHCH2CH3 + Mg CH3CHCH2CH3

CH3C CH2
ether
Br + Mg CH3C CH2 =>
MgBr

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 Organolithium Reagents
-
• Formula R-Li (reacts like R: +Li)

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CH3OH + NaH
Methanol

CH3CH2OH + NaNH 2
Ethanol
OH
CH3CHCH3 + CH3Li
Isopropyl alcohol

OH + CH3MgBr

Cyclohexanol
CH3
CH3 C OH + 2K
CH3
tert-Butyl alcohol 7
 Reaction with Carbonyl

• R:- attacks the partially positive carbon in the

carbonyl.
• The intermediate is an alkoxide ion.
• Addition of water or dilute acid protonates the
alkoxide to produce an alcohol.

R
C O R C O R C OH
HOH
OH
=>
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 Synthesis of 1° Alcohols
Grignard + formaldehyde yields a primary
alcohol with one additional carbon.

CH3 H H CH3 H
H3C C CH2 C MgBr C O CH3 CH CH2 CH2 C O MgBr
H
H H H

CH3 H
HOH
CH3 CH CH2 CH2 C O H
H

=>
9
 Synthesis of 2º Alcohols

Grignard + aldehyde yields a secondary

alcohol.
CH3 H H3C CH3 CH3
H3C C CH2 C MgBr C O CH3 CH CH2 CH2 C O MgBr
H
H H H

CH3 CH3
HOH
CH3 CH CH2 CH2 C O H
H

=>
10
 Synthesis of 3º Alcohols

Grignard + ketone yields a tertiary alcohol.

CH3 H H3C CH3 CH3
H3C C CH2 C MgBr C O CH3 CH CH2 CH2 C O MgBr
H3C
H H CH3

CH3 CH3
HOH
CH3 CH CH2 CH2 C O H
CH3

=>
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 How would you
synthesize…
OH CH2OH
CH3CH2CHCH2CH2CH3

OH
C CH3
CH2CH3
=>

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 Grignard Reactions with
Acid Chlorides and Esters
• Use two moles of Grignard reagent.
• The product is a tertiary alcohol with
two identical alkyl groups.
• Reaction with one mole of Grignard
reagent produces a ketone intermediate,
which reacts with the second mole of
Grignard reagent.
=>

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 Grignard + Acid
Chloride (1)
• Grignard attacks the carbonyl.
• Chloride ion leaves.
H3C CH3
R MgBr C O R C O MgBr
Cl
Cl
CH3 CH3
R C O MgBr R C + MgBrCl
O
Cl
Ketone intermediate =>

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 Grignard and Ester (1)

• Grignard attacks the carbonyl.

• Alkoxide ion leaves! ? !
H3C CH3
R MgBr C O R C O MgBr
CH3O
OCH3

CH3 CH3
R C O MgBr R C + MgBrOCH3
O
OCH3
Ketone intermediate =>
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 Second step of reaction
• Second mole of Grignard reacts with the
ketone intermediate to form an alkoxide ion.
• Alkoxide ion is protonated with dilute acid.
CH3 CH3
R MgBr + R C R C O MgBr
O
R

HOH
CH3
R C OH
R =>
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How would you synthesize...

Using an acid chloride or ester.

OH
CH3
CH3CH2CCH3 C
CH3 OH

OH
CH3CH2CHCH2CH3 =>

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