Transcript Alcohols

CHE 242
Unit V
Structure and Reactions of
Alcohols, Ethers and
Epoxides; Basic Principles of
NMR Spectroscopy
CHAPTER TEN
Terrence P. Sherlock
Burlington County College
2004
Classify these:
C H3
C H3
CH
C H3
C H 2O H
C H3
C
OH
C H3
OH
OH
C H3
Chapter 10
CH
C H2C H3
=>
2
Name these:
C H3
C H3
CH
C H 2O H
2-methyl-1-propanol
OH
C H3
CH
C H2C H3
2-butanol
C H3
C H3
C
OH
OH
C H3
2-methyl-2-propanol
Br
C H3
3-bromo-3-methylcyclohexanol
=>
Chapter 10
3
Naming Priority
•
•
•
•
•
•
Acids
Esters
Aldehydes
Ketones
Alcohols
Amines
•
•
•
•
•
Alkenes
Alkynes
Alkanes
Ethers
Halides
=>
Chapter 10
4
Hydroxy Substituent
• When -OH is part of a higher priority class of
compound, it is named as hydroxy.
• Example:
OH
C H 2C H 2C H 2C O O H
also known as GHB
4-hydroxybutanoic acid
=>
Chapter 10
5
Glycols
• 1, 2 diols (vicinal diols) are called glycols.
• Common names for glycols use the name of
the alkene from which they were made.
C H 2C H 2
C H2C H2C H3
OH OH
OH OH
1,2-ethanediol
1,2-propanediol
ethylene glycol
propylene glycol
Chapter 10
=>
6
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.
OH
• Methyl phenols are cresols.
OH
H 3C
4-methylphenol
para-cresol
Cl
3-chlorophenol
meta-chlorophenol
=>
Chapter 10
7
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
8
Boiling Points
=>
Chapter 10
9
Solubility in Water
Solubility decreases as the size
of the alkyl group increases.
Chapter 10
=>
10
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
11
Table of Ka Values
C H3
OH
=>
Chapter 10
12
Formation of Alkoxide
Ions
React methanol and ethanol with sodium
metal (redox reaction).
C H 3 C H 2 OH
+
Na
C H3 C H2 O
Na
+
1
/2 H 2
React less acidic alcohols with more
reactive potassium.
(C H 3)3 C
OH
+
(C H 3 )3 C O
K
K
+
1
/2 H 2
=>
Chapter 10
13
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
=>
Chapter 10
14
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
15
Glycols (Review)
• Syn hydroxylation of alkenes
osmium tetroxide, hydrogen peroxide
cold, dilute, basic potassium
permanganate
• Anti hydroxylation of alkenes
peroxyacids, hydrolysis
=>
Chapter 10
16
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
17
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
18
Some Grignard
Reagents
Br
+
e th e r
Mg
Cl
M gC l
C H 3 C HC H 2 C H 3
C H3C
Br
MgB r
+
Mg
C H2
+
Mg
ether
e th e r
C H 3 C HC H 2 C H 3
C H3C
C H2
=>
MgB r
Chapter 10
19
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
20
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
HO H
Chapter 10
=>
21
OH
Synthesis of 1° Alcohols
Grignard + formaldehyde yields a primary
alcohol with one additional carbon.
H3C
C H3
H
C
C
H
C H2
C H3
H
C
MgB r
O
C H3
CH
H
C H2
C H2
H
O
MgB r
H
H
C H3
C H3
C
CH
H
C H2
C H2
C
HO H
O
H
H
=>
Chapter 10
22
Synthesis of 2º Alcohols
Grignard + aldehyde yields a secondary
alcohol.
H3C
C H3
H
C
C
H
C H2
C H3
H3C
C
MgB r
O
C H3
CH
C H3
C H2
C H2
H
O
MgB r
H
H
C H3
C H3
C
CH
C H3
C H2
C H2
C
O
HOH
H
H
=>
Chapter 10
23
Synthesis of 3º Alcohols
Grignard + ketone yields a tertiary alcohol.
H3C
C H3
H
C
C
H
C H2
H
C H3
H3C
C
MgB r
O
C H3
CH
C H3
C H2
C H2
H3C
O
MgB r
C H3
C H3
C H3
C
CH
C H3
C H2
C H2
C
O
HOH
H
C H3
=>
Chapter 10
24
How would you
synthesize…
OH
C H2OH
C H 3 C H 2 C HC H 2 C H 2 C H 3
OH
OH
C
C H3
C H3
C H2C H3
Chapter 10
=>
25
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
26
Grignard + Acid
Chloride (1)
• Grignard attacks the carbonyl.
• Chloride ion leaves.
C H3
H3C
R
C
MgB r
O
R
Cl
C
O
O
MgB r
Cl
C H3
R
C
C H3
MgB r
R
+
C
M g B rC l
O
Cl
Ketone intermediate
Chapter 10
=>
27
Grignard and Ester (1)
• Grignard attacks the carbonyl.
• Alkoxide ion leaves! ? !
C H3
H3C
R
C
MgB r
O
R
C
C H3O
C
O
OC H3
MgB r
OC H3
C H3
R
O
C H3
MgB r
R
+
C
M g B rO C H 3
O
Ketone intermediate
Chapter 10
=>
28
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.
C H3
C H3
R
MgB r
+
R
R
C
O
C
O
MgB r
R
HOH
C H3
R
C
R
Chapter 10
OH
=>
29
How would you
synthesize...
Using an acid chloride or ester.
OH
C H3
C H3C H2C C H3
C
C H3
OH
OH
C H 3 C H 2 C HC H 2 C H 3
Chapter 10
=>
30
Grignard Reagent +
Ethylene Oxide
• Epoxides are unusually reactive ethers.
• Product is a 1º alcohol with 2 additional
carbons.
O
O
MgB r
+
C H2
MgB r
C H2C H2
C H2
HO H
O
H
C H2C H2
Chapter 10
=>
31
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
32
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
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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.
O
H
C
H
C
H
H
O
H
H3O
+
O
C
H
=>
Chapter 10
34
H
Lithium Aluminum Hydride
• Stronger reducing agent than sodium
borohydride, but dangerous to work with.
• Converts esters and acids to 1º alcohols.
O
H
C
OC H3
LAH
H3O
Chapter 10
+
O
H
C
H
=>
35
Comparison of
Reducing Agents
• LiAlH4 is stronger.
• LiAlH4 reduces more
stable compounds
which are resistant
to reduction.
=>
Chapter 10
36
Catalytic Hydrogenation
• Add H2 with Raney nickel catalyst.
• Also reduces any C=C bonds.
OH
O
OH
H 2 , R a ne y N i
NaB H4
=>
Chapter 10
37
POWER POINT IMAGES FROM
“ORGANIC CHEMISTRY, 5TH EDITION”
L.G. WADE
ALL MATERIALS USED WITH PERMISSION OF AUTHOR
PRESENTATION ADAPTED FOR BURLINGTON COUNTY COLLEGE
ORGANIC CHEMISTRY COURSE
BY:
ANNALICIA POEHLER STEFANIE LAYMAN
CALY MARTIN
Chapter 10
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