topic 8. additions to alkenes and alkynes (chapter 8...
TRANSCRIPT
D.M. Collard 2007
TOPIC 8. ADDITIONS TO ALKENES AND ALKYNES (Chapter 8 and parts of chapters 7, 10 and 11)
L
OBJECTIVES
1. Describe mechanisms for addition reactions of alkenes and alkynes2. Predict the structure of the product(s) of addition reactions3. Understand the mechanisms which explain the regiochemical and
stereochemical outcome of addition reactions4. Use combination of substitution, elimination and addition chemistry to
propose synthetic routes to useful value-added compounds
D.M. Collard 2007
ADDITION REACTIONSAddition of H2- H2/Pd (alkene, alkyne)- H2/Lindlar catalyst (alkyne → cis alkene)- dissolving metal reduction (alkyne → trans alkene)
Addition of H-Hal- Markovnikov- anti-Markovnikov
Addition of H2O- H3O+ (regiochemistry)- Oxymercuration-demercuration (regiochemistry, stereochemistry)- Hydroboration-oxidation (regiochemistry, stereochemistry)- hydration of alkynes (regiochemistry)
Addition of Hal2- Hal2 (regiochemistry, stereochemistry)- Hal2/H2O (regiochemistry)
Generation and reaction of carbenesEpoxidationNucleopihilic ring opening reactions of epoxides (H2O, ROH, HCN, RMgHal)syn-HydroxylationOxidative cleavage of alkenes and alkynes- KMnO4- Ozonolysis
Radical Polymerization
~MAKE FLASHCARDS AFTER EACH LECTURE~
Lecture 1
Lecture 2
Lecture 3
Lecture 4
Lecture 5
HYDROGENATION OF ALKENESAND ALKYNES
Hydrogenation of Alkenes
CH3
CH3 H2Pd or Pt
Prob:7.40-42;
8.30e,g,i,37,45
S:7.12-7.14
D.M. Collard 2007
Hydrogenation of AlkynesComplete Hydrogenation
cis-Semihydrogenation
C CH2
Pt or Pd
C C
H2Pd/CaCO3
N
C C2Li, 2CH3OH
NH3 (solvent)
C C
Li
Li
Li
Dissolving Metal Reduction
D.M. Collard 2007
PREVIEW OF REACTIVITYAlkenes and Alkynes are Weakly _____ and Weakly
_____________
C C
E
C C E
H Br
S:8.1
ADDITION OF HYDROGEN HALIDESTO ALKENES AND ALKYNES
Overview
C CHC C
BrBrH
CH3CH3
I
C C C C ClH
H
Prob:8.27,28a,b,f,j,29b-g,35
S:8.2-8.3;18.19;
10.9
D.M. Collard 2007
Addition of H-Hal to AlkenesMechanism
C C H Br
Regiochemistry
Markovnikov’s Rule
In the addition of HX to an unsymmetrical alkene, the hydrogen adds to the
_____________ substituted carbon and the X groups adds to the
_____________ substituted carbon.
C CH2
H3C
H3CH Br
D.M. Collard 2007
The Basis of Markovnikov’s Rule: Stability of Carbocations
C C
HH
H
C CH2
H3C
H3CHBr
Mechanistic Restatement of Markovnikov’s RuleIn the ionic addition of HX to an unsymmetrical alkene, protonation gives the more stable carbocation as an intermediate.
The more substituted carbocation is formed. Remember hyperconjugation!
Stereochemistry of H–Hal Addition to Alkenes
Br
H Br
BrCH
D.M. Collard 2007
Anti-Markovnikov Addition of H-Hal to Alkenes
Mechanistic Rationale for Anti-Markovnikov Addition
C CH2
H
H3CH Br
Addition of H-Hal to Alkynes
R C C H
R C C R'
HClCCl4
D.M. Collard 2007
~ MAKE FLASHCARDS ~
HydrogenationDissolving metal reductionHydrogenation over Lindlar catalystMarkovnikov addition of H-HalAnti-Markovnikov addition of H-Hal
…..more next lecture
ADDITION REACTIONSAddition of H2- H2/Pd (alkene, alkyne)- H2/Lindlar catalyst (alkyne → cis alkene)- dissolving metal reduction (alkyne → trans alkene)
Addition of H-Hal- Markovnikov- anti-Markovnikov
Addition of H2O- H3O+ (regiochemistry)- Oxymercuration-demercuration (regiochemistry, stereochemistry)- Hydroboration-oxidation (regiochemistry, stereochemistry)- hydration of alkynes (regiochemistry)
Addition of Hal2- Hal2 (regiochemistry, stereochemistry)- Hal2/H2O (regiochemistry)
Generation and reaction of carbenesEpoxidationNucleopihilic ring opening reactions of epoxides (H2O, ROH, HCN, RMgHal)syn-HydroxylationOxidative cleavage of alkenes and alkynes- KMnO4- Ozonolysis
Radical Polymerization
~MAKE FLASHCARDS AFTER EACH LECTURE~
Lecture 1
Lecture 2
Lecture 3
Lecture 4
Lecture 5
D.M. Collard 2007
Addition of Water to Alkenes
C C
H OH2
H2O
H2SO4
SYNTHESIS OF ALCOHOLSBY HYDRATION OF ALKENES
L
Prob:8.27c,32,5811.33,35(a-g),38(a,d),
39,46,48
S:8.4-8.11
Proceeds via Markovnikov addition
D.M. Collard 2007
Rearrangements During Acid Catalyzed Hydration of Alkenes
Intermediate carbocations can rearrange.
H2SO4
H2OCH3 OH
CH3
H
CH3
OHHnot:
Oxymercuration-Demercuration of Alkenes
e.g.,
Step 1: Oxymercuration
Step 2: Demercuration
C C
(CH3CO2)2HgH2O
HO Hg OCH3
O
NaBH4NaOH
HO Hg OCH3
O
HO H
1. (CH3CO2)2Hg H2O
2. NaBH4, NaOH
OH
D.M. Collard 2007
Mechanism
O Hg O
OO
O Hg
O
H2O
Hydroboration-Oxidation: Anti-MarkovnikovHydration of Alkenes
e.g.,
Step 1: Hydroboration
Step 2: Oxidation
C CB2H6
H BH2
H2O2NaOH
H BH2 H OH
CH3 CH3H
OH
1. B2H6
2. H2O2 NaOH
D.M. Collard 2007
Mechanism: Regiochemistry
BH
HB
H2O2NaOH, H2O
B2H6 BH3
Stereochemistry
CH3CH3
H
B
CH3H
OH
D.M. Collard 2007
R C C HR
C CH
H2O
Hg++, H2SO4
H
HO
Hydration of Alkynes (covered in 16.5B)
SYNTHETIC STRATEGIES Prob:7.24
CN
Problem: Synthesize cis-1-cyano-2-methylcyclohexane (shown below) using any hydrocarbon.
D.M. Collard 2007
Problem: Female houseflies attract males with a pheromone which has been shown to be Z-9-tricosene (C23H46). Synthesize this compound starting with organic compounds containing 13 or less carbon atoms.
H Hn-C8H17 n-C13H27
ADDITION REACTIONSAddition of H2- H2/Pd (alkene, alkyne)- H2/Lindlar catalyst (alkyne → cis alkene)- dissolving metal reduction (alkyne → trans alkene)
Addition of H-Hal- Markovnikov- anti-Markovnikov
Addition of H2O- H3O+ (regiochemistry)- Oxymercuration-demercuration (regiochemistry, stereochemistry)- Hydroboration-oxidation (regiochemistry, stereochemistry)- hydration of alkynes (regiochemistry)
Addition of Hal2- Hal2 (regiochemistry, stereochemistry)- Hal2/H2O (regiochemistry)
Generation and reaction of carbenesEpoxidationNucleopihilic ring opening reactions of epoxides (H2O, ROH, HCN, RMgHal)syn-HydroxylationOxidative cleavage of alkenes and alkynes- KMnO4- Ozonolysis
Radical Polymerization
~MAKE FLASHCARDS AFTER EACH LECTURE~
Lecture 1
Lecture 2
Lecture 3
Lecture 4
Lecture 5
D.M. Collard 2007
ADDITION OF BROMINE AND CHLORINETO ALKENES AND ALKYNES
Overview C C Cl Cl
Br
Br
Br
Br50% S,S trans 50% R,R trans
+HCCl3
CCl4
C C Cl ClClCl
CCl4
Cl2
Br2
2 Cl2
L
Prob:8.30(c,d),
31,54
S:8.12-8.14;8.18
Addition of Hal2 to AlkenesStereochemistry
CH3H3CHH
HH3CCH3H
H3CH
Br
Br
CH3H
Br
Br
CH3
H3C
H
H
Br
Br
H
H3C
CH3
H
Br2
Br2 H3CH
Br
Br
HCH3
D.M. Collard 2007
Mechanism
CH3H3CHH
Br Br
Formation of Halohydrins
C C Cl OHCl2
H2O
CH3 CH3OH
Br
Br2H2O
D.M. Collard 2007
Mechanism
H
CH3
H
H
Cl2H2O
Cl Cl
Addition of Hal2 to Alkynes
R C C H
R C C R'
Br2
HCCl3
D.M. Collard 2007
ADDITION REACTIONSAddition of H2- H2/Pd (alkene, alkyne)- H2/Lindlar catalyst (alkyne → cis alkene)- dissolving metal reduction (alkyne → trans alkene)
Addition of H-Hal- Markovnikov- anti-Markovnikov
Addition of H2O- H3O+ (regiochemistry)- Oxymercuration-demercuration (regiochemistry, stereochemistry)- Hydroboration-oxidation (regiochemistry, stereochemistry)- hydration of alkynes (regiochemistry)
Addition of Hal2- Hal2 (regiochemistry, stereochemistry)- Hal2/H2O (regiochemistry)
Generation and reaction of carbenesEpoxidationNucleopihilic ring opening reactions of epoxides (H2O, ROH, HCN, RMgHal)syn-HydroxylationOxidative cleavage of alkenes and alkynes- KMnO4- Ozonolysis
Radical Polymerization
~MAKE FLASHCARDS AFTER EACH LECTURE~
Lecture 1
Lecture 2
Lecture 3
Lecture 4
Lecture 5
ADDITION OF CARBENES TO ALKENES
What is a Carbene?
What is a Carbenoid?
H2C N N
ClCCl
Cl HK OtBu
CH2
I CH2 I I CH2 Zn I
L29 S:8.15
D.M. Collard 2007
Additions to Alkenes
Mechanism
CH3H3CHH
CH2
C CCH2N2
orCH2I2, Zn
CH2
CCl2
HCH3HCHCl3
KOtBu
Synthesis
EPOXIDES
O
O
O
R O O HRCO3H
(peroxyacid)
RCO3H(peroxyacid)
OO
O
O OOHOOH
Cl
Mg2
2
mCPBAMMPP
Prob:11.43,44
S:11.13-11.15
D.M. Collard 2007
Nucleophilic Ring-opening
O OHHO
H3O+
orHO-, H2O
OOH
OH
Stereochemistry
O OHRO
RO
ORHO
ROH, H+O
Regiochemistry
D.M. Collard 2007
O OH
O OHC C R
NC
CC
R
O OHRHN
NH2R
C N
H2O
liquid NH3
CH3OH
excess
Addition of Other Nucleophiles
OXIDATION OF ALKENESAND ALKYNES
Syn-Hydroxylation of Alkenes
C C HO OH
OH
OH
1. OsO42. NaHSO3
orKMnO4,
NaOH, H2Ocold
KMnO4, NaOH, H2O
cold
Prob:8.27(k,n),30
(j,k),46,47
S:8.16-8.17,8.20
D.M. Collard 2007
Oxidative Cleavage of AlkenesPermanganate Oxidation
1. KMnO4NaOH, H2O, Δ
2. H3O+
1. KMnO4NaOH, H2O, Δ
2. H3O+
O
OHO
O
OH
CO2
+
+
1. O3, –78 °C2. Zn, CH3CO2H O
HO
H
OO
O OO
O
Ozonolysis
D.M. Collard 2007
Oxidative Cleavage of Alkynes
Problem: Compound X (C10H18) gave pentanoic acid upon reaction with basic potassium permanganate followed by acidification. What is the structure of compound X?
R C C R'
1. O32. CH3CO2H
or1. KMnO4, NaOH2. H3O+
R R'HOOH
O O
ADDITION REACTIONSAddition of H2- H2/Pd (alkene, alkyne)- H2/Lindlar catalyst (alkyne → cis alkene)- dissolving metal reduction (alkyne → trans alkene)
Addition of H-Hal- Markovnikov- anti-Markovnikov
Addition of H2O- H3O+ (regiochemistry)- Oxymercuration-demercuration (regiochemistry, stereochemistry)- Hydroboration-oxidation (regiochemistry, stereochemistry)- hydration of alkynes (regiochemistry)
Addition of Hal2- Hal2 (regiochemistry, stereochemistry)- Hal2/H2O (regiochemistry)
Generation and reaction of carbenesEpoxidationNucleopihilic ring opening reactions of epoxides (H2O, ROH, HCN, RMgHal)syn-HydroxylationOxidative cleavage of alkenes and alkynes- KMnO4- Ozonolysis
Radical Polymerization
~MAKE FLASHCARDS AFTER EACH LECTURE~
Lecture 1
Lecture 2
Lecture 3
Lecture 4
Lecture 5
D.M. Collard 2007
R OO
O RO
RADICAL POLYMERIZATION OFALKENES (CHAIN-GROWTH POLYMERS)
About 60 x 109 pounds of ethylene are manufactured and used each year, primarily to make polyethylene
Roll of Radical Initiator (Chain Initiation)
H2C CH2radical
initiatorE (CH2CH2)n E
n~40,000E = end group
L S:10.10
Chain-Growth (Chain Propagation)
End of Growth (Chain Termination)
H2C CH2+ R CH2CH2 (CH2CH2)n CH2CH2(n+1)
H2C CH2R
R CH2CH2
2 Polymer CH2CH2
combination
disproportionationPolymer CH
Polymer CH2CH3
CH2
Polymer CH2CH2 CH2CH2 Polymer
D.M. Collard 2007
Common Chain-Growth Polymers
H2C CH2
Monomer Polymer Name(s)
polyethylene
polypropylene
(CH2 CH2)n
(CH2 CH)n
CH3
poly(vinyl chloride), PVC(CH2 CH)n
Cl
polyacrylonitrile, "Orlon"(CH2 CH)n
CN
poly(methyl methacrylate)Lucite, Plexiglass
(CH2 C)n
CH3
CO2CH3
Cl
CN
CO2CH3
SYNTHETIC STRATEGIES
Add to your chart of organic reactions
No more reactions! For now!!!
C CH
Br
C CH
OHC C
C CH
H
SubstnSubstn
Br, hν
Zn, HBr
substitutions
subs
titutio
nsElimn
Elimn
C C
BrBr
Elimn
Elimn
Addn
Additions
Addn
Additions
Addn
H2/Pt
Add n
Addn
H2/Pt
Prob:8.21-
8.26,44
S:8.21
D.M. Collard 2007
DESIGNING SYNTHESESOne Step SynthesesThis is just the opposite of learning reactions - just think backwards. Although one step syntheses are relatively easy, they are harder than learning reactions.
Two Step SynthesesThis is involves considerable imagination and is quite different than “just the opposite of learning reactions”. You must be able to conceive of the intermediate. However, there is a direct link between the intermediate and both the product and the starting material. Think “retro” (retrosynthesis) -how do you synthesize the product from anything? Can you then synthesize your proposed synthetic intermediate from the starting material?
Starting material(s) Productstep 1 step 2reaction
intermediate
? ?
Three Step SynthesesThree design of three-step organic syntheses requires a little more imagination and can be a little more difficult than two-step syntheses. You must be able to conceive of two intermediates. In this case there may not be a clear link between intermediate one and the product or intermediate two and the starting material. Again “think retro”. Can you think of ANY compounds that could be converted to the product by chemistry you know? Can you then think of one or more compounds that could be converted to these proposed intermediates by chemistry you know? Can any of these second proposed intermediates be synthesized from the starting material?
Starting material(s) Productstep 1 step 3step 2reaction
intermediate 1reactionintermediate 2
Productinterm. A
interm. B
interm. C
interm. Dinterm. E
interm. F
interm. G
Potential
starting
material(s)
D.M. Collard 2007
Problem: Solomons 8.31(b). Show how 1-butyne could be synthesized from each of the following: (b) 1-chlorobutane
Cl
Problem:Br From any alkane
D.M. Collard 2007
Problem:
From
Br
Problem:From
BrHO
Br
D.M. Collard 2007
Problem: Propose a synthesis of 1-methyl-1,2-cyclopentanediol (with the two hydroxy groups trans to one another) from methylcyclopentane.
CH3 OH
OH
CH3
Prob:11.30,35,37,38,46
Problem: An insect physiologist required 4Z-hexen-2-ol for the study of insect pheromones. Propose a synthesis of 4Z-hexen-2-ol from propene.
OH
D.M. Collard 2007
TOPIC 8 ON EXAM 4
Types of Questions- Describe addition reaction mechanisms- Predict the products of addition reactionsThe problems in the book are good examples of the types of problems on the exam.
Preparing for Exam 4:- Work as many problems as possible. - Work in groups.- Do the “Learning Group Problem” at the end of the chapter.- Work through the practice exam