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Chapter 10 Structure and Synthesis of Alcohols

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Title: Chapter 10 Structure and Synthesis of Alcohols


1
Chapter 10 Structure and Synthesis of Alcohols
Organic Chemistry, 6th Edition L. G. Wade, Jr.
2
Structure of Alcohols
  • Hydroxyl (-OH) functional group
  • Oxygen is sp3 hybridized.

3
Classification
  • Primary carbon with OH is bonded to one other
    carbon.
  • Secondary carbon with OH is bonded to two other
    carbons.
  • Tertiary carbon with OH is bonded to three
    other carbons.
  • Aromatic (phenol) OH is bonded to a benzene
    ring.

4
IUPAC Nomenclature
  • Find the longest carbon chain containing the
    carbon with the -OH group.
  • Drop the -e from the alkane name, add -ol.
  • Number the chain, starting from the end closest
    to the -OH group.
  • Number and name all substituents.

5
Unsaturated Alcohols
  • Hydroxyl group takes precedence. Assign that
    carbon the lowest number.
  • Use alkene or alkyne name.

4-penten-2-ol pent-4-ene-2-ol

6
Naming Priority
  • Acids
  • Esters
  • Aldehydes
  • Ketones
  • Alcohols
  • Amines
  • Alkenes
  • Alkynes
  • Alkanes
  • Ethers
  • Halides

7
Hydroxy Substituent
  • When -OH is part of a higher priority class of
    compound, it is named as hydroxy.
  • Example


4-hydroxybutanoic acid
8
Common Names
  • Alcohol can be named as alkyl alcohol.
  • Useful only for small alkyl groups.
  • Examples

sec-butyl alcohol
gt
isobutyl alcohol
9
Naming Diols
  • Two numbers are needed to locate the two -OH
    groups.
  • Use -diol as suffix instead of -ol.

hexane-1,6- diol
10
Glycols
  • 1, 2 diols (vicinal diols) are called glycols.
  • Common names for glycols use the name of the
    alkene from which they were made.

ethane-1,2- diol
propane-1,2- diol
ethylene glycol
propylene glycol

11
Naming Phenols
  • -OH group is assumed to be on carbon 1.
  • For common names of disubstituted phenols, use
    ortho- for 1,2 meta- for 1,3 and para- for 1,4.
  • Methyl phenols are cresols.

4-methylphenol
3-chlorophenol
para-cresol
meta-chlorophenol
12
Physical Properties
  • Unusually high boiling points due to hydrogen
    bonding between molecules.
  • Small alcohols are miscible in water, but
    solubility decreases as the size of the alkyl
    group increases.

13
Boiling Points
14
Solubility in Water
15
Methanol
  • Wood alcohol
  • Industrial production from synthesis gas
  • Common industrial solvent
  • Fuel at Indianapolis 500
  • Fire can be extinguished with water
  • High octane rating
  • Low emissions
  • But, lower energy content
  • Invisible flame

16
Ethanol
  • Fermentation of sugar and starches in grains
  • 12-15 alcohol, then yeast cells die
  • Distillation produces hard liquors
  • Azeotrope 95 ethanol, constant boiling
  • Denatured alcohol used as solvent
  • Gasahol 10 ethanol in gasoline
  • Toxic dose 200 mL ethanol, 100 mL methanol

17
2-Propanol
  • Rubbing alcohol
  • Catalytic hydration of propene

18
Acidity of Alcohols
  • pKa range 15.5-18.0 (water 15.7)
  • Acidity decreases as alkyl group increases.
  • Halogens increase the acidity.
  • Phenol is 100 million times more acidic than
    cyclohexanol!

19
Table of Ka Values
gt
20
Formation of Alkoxide Ions
  • React methanol and ethanol with sodium metal
    (redox reaction).

React less acidic alcohols with more reactive
potassium.
21
Formation of Phenoxide Ion
  • Phenol reacts with hydroxide ions to form
    phenoxide ions - no redox is necessary.

O
O
H
O
H







H
O
H
p
K



1
5
.
7
a
p
K



1
0.0
a
22
Synthesis (Review)
  • Nucleophilic substitution of OH- on alkyl halide
  • Hydration of alkenes
  • water in acid solution (not very effective)
  • oxymercuration - demercuration
  • hydroboration - oxidation

23
Organometallic Reagents
  • Carbon is bonded to a metal (Mg or Li).
  • Carbon is nucleophilic (partially negative).
  • It will attack a partially positive carbon.
  • C - X
  • C O
  • A new carbon-carbon bond forms.

24
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

25
Some Grignard Reagents
26
Organolithium Reagents
  • Formula R-Li (reacts like R- Li)
  • Can be produced from alkyl, vinyl, or aryl
    halides, just like Grignard reagents.
  • Ether not necessary, wide variety of solvents can
    be used.

27
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.

28
Synthesis of 1 Alcohols
  • Grignard formaldehyde yields a primary alcohol
    with one additional carbon.

29
Synthesis of 2º Alcohols
  • Grignard aldehyde yields a secondary alcohol.

30
Synthesis of 3º Alcohols
  • Grignard ketone yields a tertiary alcohol.

31
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.
    gt

32
Grignard Acid Chloride (1)
  • Grignard attacks the carbonyl.
  • Chloride ion leaves.

33
Grignard and Ester
  • Grignard attacks the carbonyl.
  • Alkoxide ion leaves! ? !

34
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.

35
Limitations of Grignard
  • No water or other acidic protons like O-H, N-H,
    S-H, or -CC-H. Grignard reagent is destroyed,
    becomes an alkane.
  • No other electrophilic multiple bonds, like CN,
    C?N, SO, or NO.

36
Reduction of Carbonyl
  • Reduction of aldehyde yields 1º alcohol.
  • Reduction of ketone yields 2º alcohol.
  • Reagents
  • Sodium borohydride, NaBH4
  • Lithium aluminum hydride, LiAlH4
  • Raney nickel

37
Sodium Borohydride
  • Hydride ion, H-, attacks the carbonyl carbon,
    forming an alkoxide ion.
  • Then the alkoxide ion is protonated by dilute
    acid.
  • Only reacts with carbonyl of aldehyde or ketone,
    not with carbonyls of esters or carboxylic acids.

38
Lithium Aluminum Hydride
  • Stronger reducing agent than sodium borohydride,
    but dangerous to work with.
  • Converts esters and acids to 1º alcohols.

39
Comparison of Reducing Agents
  • LiAlH4 is stronger.
  • LiAlH4 reduces more stable compounds which are
    resistant to reduction.
    gt

40
Catalytic Hydrogenation
  • Add H2 with Raney nickel catalyst.
  • Also reduces any CC bonds.

41
End of Chapter 10
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