Transcript Alkenes, Reactions

Alkenes, Reactions
R-H
R-X
R-OH
R-O-R
Alkenes
NR
NR



NR

 some
NR
NR
Metals
NR


NR
NR
Oxidation
NR
NR

NR

Reduction
NR

NR
NR

Halogens
NR
NR
NR
NR

Acids
Bases
Alkenes, reactions.
Addition
ionic
free radical
Reduction
Oxidation
Substitution
Reactions, alkenes:
1. Addition of hydrogen (reduction).
2. Addition of halogens.
3. Addition of hydrogen halides.
4. Addition of sulfuric acid.
5. Addition of water (hydration).
6. Addition of aqueous halogens (halohydrin
formation).
7. Dimerization.
8. Alkylation.
9. Oxymercuration-demercuration.
10. Hydroboration-oxidation.
11. Addition of free radicals.
12. Polymerization.
13. Addition of carbenes.
14. Epoxidation.
15. Hydroxylation.
16. Allylic halogenation
17. Ozonolysis.
18. Vigorous oxidation.
1. Addition of hydrogen (reduction).
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— C = C — + H2
+
Ni, Pt, or Pd
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 —C—C—
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H
H
a) Requires catalyst.
b) #1 synthesis of alkanes
CH3CH=CHCH3
2-butene
+
H2, Ni 
CH3CH2CH2CH3
n-butane
Alkanes
Nomenclature
Syntheses
1. addition of hydrogen to an alkene
2. reduction of an alkyl halide
a) hydrolysis of a Grignard reagent
b) with an active metal and acid
3. Corey-House Synthesis
Reactions
1. halogenation
2. combustion (oxidation)
3. pyrolysis (cracking)
heat of hydrogenation:
CH3CH=CH2 + H2, Pt  CH3CH2CH3 + ~ 30 Kcal/mole
ethylene
32.8
propylene
30.1
cis-2-butene
28.6
trans-2-butene
27.6
isobutylene
28.4
fats & oils: triglycerides
O
CH2—O—CCH2CH2CH2CH2CH2CH2CH2CH2CH3
|
O
CH—O—CCH2CH2CH2CH2CH2CH2CH2CH2CH3
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O
CH2—O—CCH2CH2CH2CH2CH2CH2CH3
“saturated” fat
O
CH2—O—CCH2CH2CH2CH2CH=CH2CH2CH2CH3
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O
CH—O—CCH2CH2CH2CH2CH=CH2CH2CH2CH3
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O
CH2—O—CCH2CH2CH=CHCH2CH2CH3
Ω - 3 “unsaturated” oil
Saturated triglycerides are solids at room temperature and
are called “fats”.
butter fat, lard, vegetable shortening, beef tallow, etc.
Unsaturated triglycerides have lower mp’s than saturated
triglycerides. Those that are liquids at room temperature
are called “oils”. (All double bonds are cis-.)
corn oil, peanut oil, Canola oil, cottonseed oil, etc.
polyunsaturated oils + H2, Ni  saturated fats
liquid at RT
solid at RT
oleomargarine
butter substitute
(dyed yellow)
Trans-fatty acids formed in the synthesis of margarine have
been implicated in the formation of “bad” cholesterol,
hardening of the arteries and heart disease. 
2) Addition of halogens.
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—C=C—
+
X2
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 —C—C—
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X
X
a) X2 = Br2 or Cl2
b) test for unsaturation with Br2
CH3CH2CH=CH2
1-butene
+
Br2/CCl4 
CH3CH2CHCH2
Br Br
1,2-dibromobutane
3. Addition of hydrogen halides.
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— C = C — + HX  — C — C —
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H X
a) HX = HI, HBr, HCl
b) Markovnikov orientation
CH3CH=CH2
CH3
CH2C=CH2
+
+
HI
HBr


CH3CHCH3
I
CH3
CH3CCH3
Br
Markovnikov’s Rule:
In der Hinzufügung einer Säure zu einem alkene
wird der Wasserstoff zum Vinylkohlenstoff gehen,
der schon den größeren Anzahl Wasserstoffe hat.
In the addition of an acid to an alkene the
hydrogen will go to the vinyl carbon that already
has the greater number of hydrogens.
Regla de Markovnikov:
En la adición iónica de un ácido al doble enlace de un
alqueno, el hidrógeno de aquél se une al átomo de carbono
que ya tiene el mayor número de hidrógenos.
“Al que tiene, le será dado.”
“El que tiene, recibirá.”
Dans l'addition d'un acide à un alcène l'hydrogène ira au
carbone de vinyle qui a déjà le nombre plus grand de
hydrogène.
알켄에 산의 추가안에 수소는 이미 수소의 더 중대한 수가
있는 비닐 탄소에는에 갈 것이다.
アルケンへの酸の付加で水素はビニールカーボンにへ行く既に
水素の大きい数がある。
В дополнении кислоты к алкен водород будет идти в
углерод винила, который уже имеет больший
номер(число) водорода.
CH3CH2CH=CH2
CH3
CH3CH=CCH3
CH3CH=CHCH3
+
+ HBr
+

HCl
HI


CH3CH2CHCH3
Cl
CH3
CH3CH2CCH3
Br
CH3CH2CHCH3
I
An exception to Markovikov’s Rule:
CH3CH=CH2
CH3
CH3C=CH2
+
+
HBr, peroxides  CH3CH2CH2Br
HBr, peroxides 
“anti-Markovnikov” orientation
note: this is only for HBr.
CH3
CH3CHCH2Br
Markovnikov doesn’t always correctly predict the product!
CH3
CH2=CHCHCH3
+
HI

CH3
CH3CH2CCH3
I
Rearrangement!

Ionic electrophilic addition mechanism
1)
2)
C C
C C
Y
+
YZ
+ Z
RDS
C C
Y
C C
Z Y
+ Z
mechanism for addition of HX
1)
2)
C C
C C
H
+
HX
+ X
RDS
C C
H
C C
X H
+ X
why Markovinkov?
CH3CH=CH2 + HBr
 CH3CHCH2
| 
H
or?
+ Br-

CH3CHCH2
 |
H
CH3CHCH3
|
Br
1o carbocation

2o carbocation
more stable
In ionic electrophilic addition to an
alkene, the electrophile always adds to
the carbon-carbon double bond so as to
form the more stable carbocation.
4. Addition of sulfuric acid.
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—C=C—
+
H2SO4
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 —C—C—
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H
OSO3H
alkyl hydrogen sulfate
Markovnikov orientation.
CH3CH=CH2
+
H2SO4

CH3CHCH3
O
O-S-O
OH
5. Addition of water.
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—C=C— +
H2O, H+
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 —C—C—
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H
OH
a) requires acid
b) Markovnikov orientation
c) low yield 
CH3CH2CH=CH2
+
H2O, H+
 CH3CH2CHCH3
OH
Mechanism for addition of water
RDS
1)
H
+
2)
C C
H
3)
C C
H OH2
C C
C C
H
+ H2O
C C
H OH2
C C
H OH
+ H
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— C = C — + H2O
H+

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—C—C—
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OH H
Mechanism for addition of water to an alkene to form an
alcohol is the exact reverse of the mechanism (E1) for the
dehydration of an alcohol to form an alkene.
Mechanism for dehydration of an alcohol = E1
1)
C C
H OH
+ H
C C
H OH2
RDS
2)
C C
H OH2
C C
H
+ H2O
3)
C C
H
C C
+ H
mechanism for addition of X2
1)
2)
C C
C C
X
+
X--X
+ X
RDS
C C
X
C C
X X
+ X
How do we know that the mechanism isn’t this way?
RDS
C C
X X
One step, concerted, no carbocation
C C
X X
CH3CH=CH2 + Br2 + H2O + NaCl
CH3CH=CH2 + Br--Br
Br
CH3CHCH2
Br Br

CHCHCH2
Br
H2O
+ CH3CHCH2
OH Br
Cl
+ CH3CHCH2
Cl Br
Some evidence suggests that the intermediate is not a
normal carbocation but a “halonium” ion:
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—C—C—
Br 
The addition of X2 to an alkene is an anti-addition.
6. Addition of halogens + water (halohydrin formation):
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— C = C — + X2, H2O  — C — C — + HX
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OH X
a) X2 = Br2, Cl2
b) Br2 = electrophile
CH3CH=CH2
+
Br2(aq.) 
CH3CHCH2 + HBr
OH Br
mechanism for addition of X2 + H2O
1)
C C
2)
H2O +
3)
+
X--X
C C
X
RDS
C C
X
C C
H2O X
-H
C C
H2O X
C C
HO X
+ X
7. Dimerization:
CH3
CH3C=CH2
+
H2SO4, 80oC 
CH3 CH3
CH3C-CH=CCH3
CH3
+
CH3 CH3
CH3C-CH2C=CH2
CH3
CH3
CH3C=CH2 + H
CH3
CH3C
CH3
CH3
CH3CCH3
CH3
CH3 CH3
CH3C CH2CCH3
CH3
+ CH2=CCH3
CH3 CH3
CH3C CH2CCH3
CH3
-H
CH3
CH3
CH3C CH=CCH3
CH3
carbocation as electrophile
CH3 CH3
+ CH3C CH2C=CH2
CH3
8. Alkylation:
CH3
CH3
CH3C=CH2 + CH3CHCH3 + HF, 0oC 
CH3 CH3
CH3C-CH2CHCH3
CH3
2,2,4-trimethylpentane
( “isooctane” )
Used to increase gasoline yield from petroleum and to improve
fuel performance.
CH3
CH3C=CH2 + H
CH2
CH3C
CH3
CH3
CH3CCH3
CH3
+ CH2=CCH3
CH3
CH3 CH3
CH3C CH2CCH3 + CH3CCH3
H
CH3
CH3 CH3
CH3C CH2CCH3
CH3
CH3 CH3
CH3
CH3C CH2CCH3 + CH3CCH3
CH3 H
intermolecular hydride (H:-) transfer
Internal combustion engine (four-stroke).
Also called an Otto engine.
1. Intake stroke: air/fuel mixture is drawn
into the cylinder.
2. Compression stroke: air/fuel mixture is
compressed.
Ignition of air/fuel mixture by spark at
approximately 0o top dead center.
3. Power stroke: expanding gases push
piston down driving crank shaft around.
4. Exhaust stroke: CO2 + H2O are pushed
out of the cylinder.
<http://www.k-wz.de/vmotor/v_omotore.html>
Compression is the key to building a more powerful fourstroke engine. The more the air/fuel mixture is
compressed prior to ignition, the more efficient is the
conversion of heat energy into mechanical motion.
Increasing the compression ratio =>
1. More powerful engine.
2. Lighter engine (greater power to weight ratio).
3. Greater fuel economy.
But, compression of the air/fuel mixture above a certain
point causes “knocking”. 
PV = nRT
TP
If, during compression of an air/fuel mixture, the
temperature goes high enough, the mixture may explode
prematurely.
A knocking sound is produced by an internal combustion
engine when fuel ignites spontaneously and prematurely (preignition) during the compression cycle in an engine’s
combustion chamber. Consequently, the piston will be forced
down when it should be traveling upwards on its compression
stroke.
At best, knocking reduces the performance of the engine; at
worst, it can damage the engine’s moving parts. 
Fuel for four-stroke internal combustion engines:
Gasoline ( historically a waste product from the
production of kerosene ).
Gasoline is a complex mixture of hydrocarbons distilled
from petroleum. It is mixed with air to form an
explosive mixture.
Gasoline + (xs) O2, spark  CO2 + H2O + heat
The fuel limits how high the compression ratio can be
before the engine knocks.
CH3CH2CH2CH2CH2CH2CH3
n-heptane
CH3 CH3
CH3CCH2CHCH3
CH3
2,2,4-trimethylpentane
( “isooctane” )
knocks like crazy at
low compression.
resists knocking
Octane rating: a measure of the resistance of a
fuel to knock in an internal combustion engine at
high compression ratios. Determined by
comparing the fuel to mixtures of:
n-heptane (octane number = 0)
and
2,2,4-trimethylpentane (octane number = 100)
in a test engine.
Tetraethyl lead, (CH3CH2)4Pb, was discovered to
increase the octane rating of gasoline.
Lead is extremely toxic, especially in small children
where exposure leads to nerve damage.
All gasoline in the US is now “lead free”.
Tetraethyl lead has been replaced by “alkylates” and
catalytically reformed hydrocarbons.
Compression vs. Octane Number
5:1
72
6:1
81
7:1
87
8:1
92
9:1
96
10:1 100
11:1 104
12:1 108
Use the octane rating recommended by your car
maker! Using a higher octane gasoline only puts
more of your money into the fuel company’s
pockets.
9. Oxymercuration-demercuration.
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— C = C — + H2O, Hg(OAc)2  — C — C — + acetic
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acid
OH HgOAc
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— C — C — + NaBH4 
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OH HgOAc
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—C—C—
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OH H
alcohol
oxymercuration-demercuration:
a) #1 synthesis of alcohols.
b) Markovnikov orientation.
c) 100% yields. 
d) no rearrangements 
CH3CH2CH=CH2 + H2O, Hg(OAc)2; then NaBH4 
CH3CH2CHCH3
OH
With alcohol instead of water:
alkoxymercuration-demercuration:
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— C =C — + ROH, Hg(TFA)2  — C — C —
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OR HgTFA
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— C — C — + NaBH4 
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OR HgTFA
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—C—C—
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OR H
ether
alkoxymercuration-demercuration:
a) #2 synthesis of ethers.
b) Markovnikov orientation.
c) 100% yields. 
d) no rearrangements 
CH3CH=CH2 + CH3CHCH3, Hg(TFA)2; then NaBH4 
OH
CH3 CH3
CH3CH-O-CHCH3
diisopropyl ether
Avoids the elimination with 2o/3o RX in Williamson Synthesis.
Ethers
nomenclature
syntheses
1. Williamson Synthesis
2. alkoxymercuration-demercuration
reactions
1. acid cleavage
10. Hydroboration-oxidation.
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— C = C — + (BH3)2  — C — C —
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diborane
H
B—
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— C — C — + H2O2, NaOH 
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H
B—
|
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—C—C—
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H
OH
alcohol
hydroboration-oxidation:
a) #2 synthesis of alcohols.
b) Anti-Markovnikov orientation. 
c) 100% yields. 
d) no rearrangements 
CH3CH2CH=CH2 + (BH3)2; then H2O2, NaOH 
CH3CH2CH2CH2-OH
CH3
CH3C=CH2
+ H2O, Hg(OAc)2; then NaBH4 
Markovnikov
CH3
CH3C=CH2
CH3
CH3CCH3
OH
+ (BH3)2; then H2O2, NaOH 
anti-Markovnikov
CH3
CH3CHCH2
OH
Alcohols:
nomenclature
syntheses
1. oxymercuration-demercuration
2. hydroboration-oxidation
3.
4. hydrolysis of a 1o / CH3 alcohol
5.
6.
8.
11. Addition of free radicals.
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|
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— C = C — + HBr, peroxides  — C — C —
|
|
H
X
a) anti-Markovnikov orientation.
b) free radical addition
CH3CH=CH2 + HBr, peroxides  CH3CH2CH2-Br
Mechanism for free radical addition of HBr:
Initiating steps:
1) peroxide  2 radical•
2) radical• + HBr  radical:H + Br• (Br• electrophile)
Propagating steps:
3) Br• + CH3CH=CH2  CH3CHCH2-Br (2o free radical)
•
4) CH3CHCH2-Br + HBr  CH3CH2CH2-Br + Br•
•
3), 4), 3), 4)…
Terminating steps:
5) Br• + Br•  Br2
Etc.
In a free radical addition to an alkene, the electrophilic free
radical adds to the vinyl carbon with the greater number of
hydrogens to form the more stable free radical.
In the case of HBr/peroxides, the electrophile is the
bromine free radical (Br•).
CH3CH=CH2 + HBr, peroxides  CH3CH2CH2-Br
12. Polymerization.
CH2=CH2 + heat, pressure  -(CH2CH2)-n
n = 10,000+
polyethylene
CH3CH=CH2
CH2=CHCl
polymerization  -(CH2CH)-n
CH3
polypropylene
poly… 
-(CH2CH)-n
Cl
polyvinyl chloride (PVC)
Plastics: man-made polymers that at some time in their
manufacture are soft and pliable.
Thermoplastics: plastics that soften when heated.
Free radical polymerization.
R• +
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|
|
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—C=C—  R—C—C• + —C=C— 
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13. Addition of carbenes.
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|
|
— C = C — + CH2CO or CH2N2 , hν  — C — C —

•CH2•
| |
—C=C—
 
•CH2•
CH2
“carbene” adds across the
double bond
| |
— C = C — + CHCl3, t-BuOK 
 -HCl
|
|
— C— C —
CCl2
•CCl2• dichlorocarbene
| |
—C=C—
 
•CCl2•
hv
CH3CH=CH2 + CH2N2
CHCl3, t-BuOK
H
H3C C CH2
C
H2
H
H3C C CH2
C
Cl2
14. Epoxidation.
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C6H5CO3H
— C = C — + (peroxybenzoic acid) 
|
|
— C— C —
O
epoxide
Free radical addition of oxygen diradical.
| |
—C=C—
 
•O•
H3C C C CH3
H H
2-butene
+
C6H5CO3H
peroxybenzoic acid
H H
H3C C C CH3
O
15. Hydroxylation. (mild oxidation)
| |
— C = C — + KMnO4
|
|
 —C—C—
|
|
OH OH
syn
OH
| |
|
|
— C = C — + HCO3H  — C — C — anti
peroxyformic acid
|
|
OH
glycol
CH3CH=CHCH3 + KMnO4  CH3CH-CHCH3
OH OH
2,3-butanediol
test for unsaturation purple KMnO4  brown MnO2
CH2=CH2
+
KMnO4
 CH2CH2
OH OH
ethylene glycol
“anti-freeze”
16. Allylic halogenation.
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|
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|
— C = C — C — + X2, heat  — C = C — C — + HX
|
|
H  allyl
X
CH2=CHCH3 + Br2, 350oC  CH2=CHCH2Br + HBr
a) X2 = Cl2 or Br2
b) or N-bromosuccinimide (NBS)
CH2=CHCH3 + Br2  CH2CHCH3
Br Br
addition
CH2=CHCH3 + Br2, heat  CH2=CHCH2-Br + HBr
allylic substitution
17. Ozonolysis.
| |
|
|
— C = C — + O3; then Zn, H2O  — C = O + O = C —
used for identification of alkenes
CH3
CH3CH2CH=CCH3 + O3; then Zn, H2O 
CH3CH2CH=O
+
CH3
O=CCH3
18. Vigorous oxidation.
=CH2 + KMnO4, heat  CO2
=CHR + KMnO4, heat  RCOOH
=CR2 + KMnO4, heat  O=CR2
carboxylic acid
ketone
CH3CH2CH2CH=CH2 + KMnO4, heat 
CH3CH2CH2COOH + CO2
CH3
CH3
CH3C=CHCH3 + KMnO4, heat  CH3C=O + HOOCCH3
KMnO4  CH3CHCHCH3
OHOH
mild oxidation  glycol
CH3CH=CHCH3
+
CH3CH=CHCH3
+
vigorous oxidation
hot KMnO4  2 CH3COOH
Reactions, alkenes:
1. Addition of hydrogen
2. Addition of halogens
3. Addition of hydrogen halides
4. Addition of sulfuric acid
5. Addition of water/acid
6. Addition of halogens & water (halohydrin formation)
7. Dimerization
8. Alkylation
9. Oxymercuration-demercuration
10. Hydroboration-oxidation
11. Addition of free radicals
12. Polymerization
13. Addition of carbenes
14. Epoxidation
15. Hydroxylation
16. Allylic halogenation
17. Ozonolysis
18. Vigorous oxidation
CH3
CH3C=CH2
isobutylene
“
“
“
+ H2, Pt 
CH3
CH3CHCH3
CH3
+ Br2/CCl4  CH3C-CH2
Br Br
+ HBr
+ H2SO4


CH3
CH3CCH3
Br
CH3
CH3CCH3
O
SO3H
CH3
CH3C=CH2
isobutylene
+ H2O, H+ 
CH3
+ Br2(aq.)  CH3C-CH2Br
OH
“
CH3
CH3C=CH2
CH3
CH3CCH3
OH
+
H2SO4, 80oC 
(dimeriz.)
+
CH3 CH3
CH3C-CH=CCH3
CH3
CH3 CH3
CH3C-CH2C=CH2
CH3
CH3
CH3
CH3C=CH2 + CH3CHCH3 + HF, 0oC 
CH3 CH3
CH3C-CH2CHCH3
CH3
CH3
CH3
CH3C=CH2 + H2O,Hg(OAc)2; then NaBH4  CH3CCH3
OH
“
+ (BH3)2; then H2O2, OH- 
CH3
CH3CHCH2
OH
CH3
CH3C=CH2
isobutylene
“
“
“
CH3
+ HBr, peroxides  CH3CHCH2
Br
CH3
+ polym.

-(CH2C)-n
CH3
+ CH2CO, hv 
CH3
CH3C–CH2
CH2

CH3
CH3C–CH2
O
+ PBA
CH3
CH3C=CH2
isobutylene
“
“
“
+ KMnO4 
CH3
CH3C–CH2
OH OH
CH3
+ Br2, heat  CH2C=CH2 + HBr
Br
CH3
+ O3; then Zn/H2O  CH3C=O + O=CH2
+ KMnO4, heat 
CH3
CH3C=O + CO2