lecture 23 amines - university of texas at...
TRANSCRIPT
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Chemistry 328N
Lecture 23
Amines
April 12, 2016
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Chemistry 328N
Michael Reaction Michael reaction: conjugate addition of an enolate
anion to an ,-unsaturated carbonyl compound!!
Following are two examples
– in the first, the nucleophile is the anion of malonic ester
– in the second, it is the enolate anion of acetoacetic ester
An excellent route to 1,5 dicarbonyl compounds
Arthur Michael
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Chemistry 328N
Michael Reaction
+
3-Buten-2-one (Methyl vinyl ketone)
Diethyl propanedioate (Diethyl malonate)
O
EtOC
CH2
EtOC
O
O
EtOC
CHCH2 CH2 CCH 3
EtOC
O
O
OEt O
- Na
+
EtOHCH2 =CHCCH 3
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Chemistry 328N
Michael Reaction
+
2-Cyclohex- enone
Ethyl 3-oxobutanoate (Ethyl acetoacetate)
O
O
OO
CH3 C
CH2
EtOC
O
EtOC
CH
CH3 C
O
EtO-
Na+
EtOH
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Chemistry 328N
Retro-synthesis of 2,6-Heptadione
+
lost by decarboxylation
formed in a Michael reaction
Ethyl acetoacetate
Methyl vinyl ketone
O O OO
CO2 H
CO2 Et
O O
CH3 CCH 2 CH2 CH2 CCH 3 CH3 CCH-CH 2 CH2 CCH 3
CH3 CCH 2 CH2 =CHCCH 3
from acetoacetic
ester
Always gives a 1,5-dicarbonyl product
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Chemistry 328N
The Michael reaction is a useful method forforming carbon-carbon bonds….1,5 dicarbonyls
Michael Addition
O O
12
34
5
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Chemistry 328N
Michael Addition
It is also useful in that the product of the reaction can undergo an intramolecularaldol condensation to form a six-membered ring. One such application is called the Robinson annulation.
This reaction enabled the first synthesis of steroids
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Chemistry 328N
The Robinson Annelation: 1. Michael addition
O
H2C CHCCH3
CH3
O
O
OCH3
O
O
CH2CH2CCH3
KOH, methanol
+
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Chemistry 328N
Robinson annelation: 2. aldol condensation
OCH3
O
O
CH2CH2CCH3
NaOH
heat
OH
O CH3
O
not isolated;
dehydrates under
reaction conditions
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Chemistry 328N
OCH3
O
O
CH2CH2CCH3
NaOH
heat
O
O
CH3
OH
O CH3
O
Robinson annelation: 3. elimination
Robert Robinson
Nobel 1947
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Chemistry 328N
Testosterone Cortisone
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Chemistry 328N
The Signature Page
Claisen Condensation: -ketoesters
Dieckmann: Cyclic -ketoesters
Aldol: , -unsaturated aldehydes and ketones
Acetoacetic ester synthesis: decorated acetones
Malonic ester synthesis: decorated acetic acids
Michael Reaction: 1-5 dicarbonyl compounds
Grignard Reaction: Alcohols
Wittig Reaction: Alkenes. …, etc
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Chemistry 328N
Otto Paul Hermann Diels
1876-1954
Kurt Alder
1902-1958
The Diels-Alder Reaction
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Chemistry 328N
• The Diels-Alder reaction is an addition reaction between
a 1,3-diene and an alkene (called a dienophile), that
forms a new six-membered ring.
Diels-Alder Reaction:
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Chemistry 328N
Predict the products
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Chemistry 328N
All Diels-Alder reactions:
1. are initiated by heat; that is, the Diels-Alder
reaction is a thermal reaction.
2. form new six-membered rings.
3. involve breaking three bonds and making
two new bonds and one new bond.
4. are concerted; that is, all bonds are broken and
new bonds formed in a single step.
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Chemistry 328N
4 Rules that govern the Diels-Alder reaction
1. The diene can react only from the s-cis conformation.
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Chemistry 328N18
2. Electron-withdrawing substituents in the
dienophile increase the reaction rate.
• The conjugated diene acts as a nucleophile and the
dienophile acts as an electrophile.
• Electron-withdrawing groups make the dienophile more
reactive
• If Z is an electron-withdrawing group, then the reactivity of
the dienophile increases as follows:
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Chemistry 328N
The carbonyl group is electron-withdrawing
and activates dienophiles
Common dienophiles
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Chemistry 328N
+
benzene 100°C
(100%)
H2C CHCH CH2 H2C CH CH
O
CH
O
Example
CH
Ovia:
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Chemistry 328N
3. The stereochemistry of the dienophile
is retained.
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Chemistry 328N
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Chemistry 328N
only product
+H2C CHCH CH2
Example
C C
C6H5 COH
H H
O
H
C6H5
H
COH
O
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Chemistry 328N
only product
+H2C CHCH CH2
Example
C C
C6H5
COHH
H
O
H
C6H5
H
COH
O
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Chemistry 328N
+
C C
COCH3H
H
O
CH3OC
O H
H
COCH3
O
COCH3
O
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Chemistry 328N
is thesame as
H
H
COCH3
O
COCH3
O
H
H
COCH3
O
COCH3
O
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Chemistry 328N
4. When endo and exo products are
possible, the endo product is preferred.
endo and exo indicate the orientation of Z.
endo = on the side of the big bridge
exo = on the side of the small bridge
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Chemistry 328N
The endo product is preferred!
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Chemistry 328N
Some nomenclature
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Chemistry 328N
Nomenclature of Bicyclic Systems
Bicyclo [#.#.#]alkane
Where # is the number of carbons on the bridges (in
decreasing order) and the alkane name includes all the
carbons in the compound.
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Chemistry 328N
Numbering begins at a bridgehead, goes around the
largest ring first, to give the lowest number to any
functionality on the ring.
O
7-Methyl-bicyclo[4.2.0]octan-3-one
1
23
4
5
6
7
8
Nomenclature of Bicyclic Systems
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Chemistry 328N
If substituents are present, number the bridge ring
system beginning at on bridge-head, proceeding first
along the longest bridge to the other bridge-head.
The shortest bridge is named last
Some nomenclature
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Chemistry 328N
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Chemistry 328N
Amines
Organic derivatives of ammonia.
Many are biologically active.
=>
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Chemistry 328N
Biologically active amines
Morphine
Strychnine
Quinine
Methamphetamine
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Chemistry 328N
AMINES Tend to have foul odors (two of the amines
produced in decaying flesh have suggestive names - cadaverine and putresine)
Essential to life as constituents of amino acids
Occur in many drugs and vitamins
Essential starting materials for many synthetic processes
Skatol
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Chemistry 328N
Nomenclature of Amines
IUPAC name – Remove final “e” of longest alkane group and replace by “amine”. The name is one word.
1-butanamine
CH3CH2CH2CH2NH2 CH3CHCH2NH2
CH32-methylpropanamine
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Chemistry 328N
IUPAC Nomenclature of secondary
and tertiary Amines• Find the longest chain bonded to the nitrogen
• Final “e” is replaced with “amine”
• Number the carbon to which nitrogen is bonded
• Number any substituents on the alkyl chain
• Use italicized N- for each additional substituent(s) on the nitrogen
N,N-dimethylethanamine
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Chemistry 328N
IUPAC Names
Name is based on longest carbon chain.
-e of alkane is replaced with -amine.
Substituents on nitrogen have N- prefix.
CH3CH2CHCH2CH2CH3
N(CH3)2
N,N-dimethyl-3-hexanamine
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Chemistry 328N
Amine as Substituent
On a molecule with a higher priority
functional group, the amine is named as a
substituent. The substituent name is amino.
NH2CH2CH2CH2COOH
NHCH3
OH
-aminobutyric acid or
4-aminobutanoic acid
2-methylaminophenol
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Chemistry 328N
Basicity of Amines
1. Alkylamines are slightly stronger bases than ammonia.
2. Alkylamines differ very little in basicity.
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Chemistry 328N
Amine Conj. Acid pKa
NH3 NH4+ 9.3
CH3CH2NH2 CH3CH2NH3+ 10.8
(CH3CH2)2NH (CH3CH2)2NH2+ 11.1
(CH3CH2)3N (CH3CH2)3NH+ 10.8
Basicity of Amines in Aqueous Solution
Notice that the difference separating a primary,
secondary, and tertiary amine is only 0.3 pK units.
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Chemistry 328N
Effect of Structure on Basicity
1. Alkylamines are slightly stronger bases than ammonia.
2. Alkylamines differ very little in basicity.
3. Arylamines are much weaker bases thanammonia.
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Chemistry 328N
H2N••
Decreased basicity of arylamines
+HN
H
H
+
NH2+
•• +H3N
pKa = 4.6
pKa =10.6
Stronger
acid
Weaker
acid
Stronger
base
Weaker
base
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Chemistry 328N
Decreased basicity of arylamines
C6H5NH2 (C6H5)2NH (C6H5)3N
4.6 0.8 ~-5
Increasing delocalization makes diphenylamine
a weaker base than aniline, and triphenylamine
a weaker base than diphenylamine.
pKa of conjugate acid
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Chemistry 328N
p-Nitroaniline
NH2
O
N
O
– ••
••
••
••
+
••
••
O
N
O
– ••
••
••
••••
••
–
NH2
++
Lone pair on amine nitrogen is conjugated with
p-nitro group—more delocalized than in aniline
itself. Delocalization lost on protonation.
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Chemistry 328N
Effect is Cumulative
Aniline is 3800 times more basic than
p-nitroaniline.
Aniline is ~1,000,000,000 times more
basic than 2,4-dinitroaniline.
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Chemistry 328N
Synthesis of Amines
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Chemistry 328N
Alkylation of Ammonia
This method doesn't work well in practice.
Usually gives a mixture of primary, secondary,
and tertiary amines, plus the quaternary salt.
NH3
RXRNH2
RXR2NH
RX
R3NRX
R4N+
X–
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Chemistry 328N
Example
CH3(CH2)6CH2BrNH3
CH3(CH2)6CH2NH2
(45%)
+
CH3(CH2)6CH2NHCH2(CH2)6CH3
(43%)
As octylamine is formed, it competes with
ammonia for the remaining 1-bromooctane.
Reaction of octylamine with 1-bromooctane gives
N,N-dioctylamine.