Download Alcohols

Organic Chemistry, 6th Edition
L. G. Wade, Jr.
Chapter 10
Structure and Synthesis
of Alcohols
Structure of Alcohols
• Hydroxyl (-OH) functional group
• Oxygen is sp3 hybridized.
Chapter 10
2
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.
Chapter 10
3
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.
Chapter 10
4
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
Chapter 10
5
Naming Priority
•
•
•
•
•
•
Acids
Esters
Aldehydes
Ketones
Alcohols
Amines
•
•
•
•
•
Chapter 10
Alkenes
Alkynes
Alkanes
Ethers
Halides
6
Hydroxy Substituent
• When -OH is part of a higher priority class of
compound, it is named as hydroxy.
• Example:
4-hydroxybutanoic acid
Chapter 10
7
Common Names
• Alcohol can be named as alkyl alcohol.
• Useful only for small alkyl groups.
• Examples:
isobutyl alcohol
sec-butyl alcohol
=>
Chapter 10
8
Naming Diols
• Two numbers are needed to locate the two
-OH groups.
• Use -diol as suffix instead of -ol.
hexane-1,6- diol
Chapter 10
9
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
Chapter 10
10
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
para-cresol
3-chlorophenol
meta-chlorophenol
Chapter 10
11
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.
Chapter 10
12
Boiling Points
=>
Chapter 10
13
Solubility in Water
Solubility decreases as the size
of the alkyl group increases.
Chapter 10
14
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
Chapter 10
15
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
Chapter 10
16
2-Propanol
• “Rubbing alcohol”
• Catalytic hydration of propene
Chapter 10
17
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!
Chapter 10
18
Table of Ka Values
=>
Chapter 10
19
Formation of Alkoxide
Ions
React methanol and ethanol with sodium
metal (redox reaction).
React less acidic alcohols with more
reactive potassium.
Chapter 10
20
Formation of
Phenoxide Ion
Phenol reacts with hydroxide ions to form
phenoxide ions - no redox is necessary.
O
O H
+
OH
+
HOH
pKa = 15.7
pKa = 10.0
Chapter 10
21
Synthesis (Review)
• Nucleophilic substitution of OH- on alkyl
halide
• Hydration of alkenes
water in acid solution (not very effective)
oxymercuration - demercuration
hydroboration - oxidation
Chapter 10
22
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.
Chapter 10
23
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
Chapter 10
24
Some Grignard
Reagents
Chapter 10
25
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.
Chapter 10
26
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.
Chapter 10
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Synthesis of 1° Alcohols
Grignard + formaldehyde yields a primary
alcohol with one additional carbon.
Chapter 10
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Synthesis of 2º Alcohols
Grignard + aldehyde yields a secondary
alcohol.
Chapter 10
29
Synthesis of 3º Alcohols
Grignard + ketone yields a tertiary alcohol.
Chapter 10
30
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.
=>
Chapter 10
31
Grignard + Acid
Chloride (1)
• Grignard attacks the carbonyl.
• Chloride ion leaves.
Chapter 10
32
Grignard and Ester
• Grignard attacks the carbonyl.
• Alkoxide ion leaves! ? !
Chapter 10
33
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.
Chapter 10
34
Limitations of Grignard
• No water or other acidic protons like
O-H, N-H, S-H, or -C—C-H. Grignard
reagent is destroyed, becomes an
alkane.
• No other electrophilic multiple bonds,
like C=N, CN, S=O, or N=O.
Chapter 10
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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
Chapter 10
36
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.
Chapter 10
37
Lithium Aluminum Hydride
• Stronger reducing agent than sodium
borohydride, but dangerous to work with.
• Converts esters and acids to 1º alcohols.
Chapter 10
38
Comparison of
Reducing Agents
• LiAlH4 is stronger.
• LiAlH4 reduces more
stable compounds
which are resistant
to reduction.
=>
Chapter 10
39
Catalytic Hydrogenation
• Add H2 with Raney nickel catalyst.
• Also reduces any C=C bonds.
Chapter 10
40
End of Chapter 10
Chapter 10
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