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AFB QO I 2007/08 1
Química Orgânica I
Ciências Farmacêuticas
Bioquímica
Química
AFB QO I 2007/08 2
alkynes
AFB QO I 2007/08 3
Adaptado de:
� Organic Chemistry, 6th Edition; L. G. Wade, Jr.
� Organic Chemistry, 6th edition; McMurry’s
AFB QO I 2007/08 4
Name these:
CH3 CH
CH3
CH2 C C CH
CH3
CH3
CH3 C C CH2 CH2 Br
CH3 C CH
propyne
5-bromo-2-pentyne
5-bromopent-2-yne
=>
2,6-dimethyl-3-heptyne
2,6-dimethylpept-3-yne
2
AFB QO I 2007/08 5
Examples
CH2 CH CH2 CH
CH3
C CH
4-methyl-1-hexen-5-yne
4-methylhex-1-en-5-yne
CH3 C C CH2 CH
OH
CH3
4-hexyn-2-ol
hex-4-yn-2-ol=>
AFB QO I 2007/08 6
Common Names
Named as substituted acetylene.
CH3 C CH
methylacetylene
(terminal alkyne)
CH3 CH
CH3
CH2 C C CH
CH3
CH3
isobutylisopropylacetylene
(internal alkyne) =>
AFB QO I 2007/08 7
Physical Properties
� Nonpolar, insoluble in water.
� Soluble in most organic solvents.
� Boiling points similar to alkane of same size.
� Less dense than water.
� Up to 4 carbons, gas at room temperature.
=> AFB QO I 2007/08 8
Acetylene
1836 - Edmund Davy"a new carburet of hydrogen."
An application of the discovery of acetylene gas by British chemist Edmund Davy in 1836 through the chemical reaction of calcium carbide with water. Acetylene produces light...
http://www.latalaia.net/eng/aparador.asp?art=585&mail=1
3
AFB QO I 2007/08 9
Acetylene
Gustaf Dalén Marcellin Berthelot1860 - acetylene
AFB QO I 2007/08 10
Acetylene
� welding torches.
� In pure oxygen reaches 2800°C.
� Explodes to decompose to its elements
AFB QO I 2007/08 11
Synthesis of Acetylene
� Heat coke with lime in an electric furnace to form calcium carbide.
� Then drip water on the calcium carbide.
H C C H Ca(OH)2CaC2 + 2 H2O +
C CaO3 + +CaC2 CO
coke lime
*This reaction was used to produce light
for miners’ lamps and for the stage. =>
*
AFB QO I 2007/08 12
Electronic Structure
The sigma bond is sp-sp overlap.
•The two pi bonds are unhybridized p overlaps at 90°
=>
4
AFB QO I 2007/08 13
Bond Lengths
� More s character, so shorter length.
� Three bonding overlaps, so shorter.
Bond angle is 180°, so linear geometry. =>
AFB QO I 2007/08 14
acetylide
� Acetylene → acetylide� NH2
-,
� not by OH- or RO-.
AFB QO I 2007/08 15
Acidity Table
=>AFB QO I 2007/08 16
Forming Acetylide Ions
� H+ can be removed from a terminal alkyne by sodium amide, NaNH2.
• NaNH2 is produced by the reaction of ammonia with sodium metal.
=>
5
AFB QO I 2007/08 17 AFB QO I 2007/08 18
Alkynes from Acetylides
� Acetylide ions are good nucleophiles.
� SN2 reaction with 1° alkyl halides lengthens the alkyne chain.
=>
AFB QO I 2007/08 19
Acetylide as base
� Acetylide ions can also remove H+
� If back-side approach is hindered, elimination reaction happens via E2.
=>AFB QO I 2007/08 20
Addition to Carbonyl
Acetylide ion + carbonyl group yields an alkynol (alcohol on carbon adjacent to triple bond).
+H2OO
H
HHR C C C O H
=>
C O+R C C R C C C O
6
AFB QO I 2007/08 21
Add to Formaldehyde
Product is a primary alcohol with one more carbon than the acetylide.
+ C O
H
H
CH3 C C CH3 C C C
H
H
O
=>
+H2O OH
HH
CH3 C C C O H
H
H
AFB QO I 2007/08 22
Add to Aldehyde
Product is a secondary alcohol, one R group from the acetylide ion, the other R group from the aldehyde.
+ C OCH3
H
CH3 C C CH3 C C C
CH3
H
O
=>
+H2O OH
HH
CH3 C C C O H
CH3
H
AFB QO I 2007/08 23
Add to Ketone
Product is a tertiary alcohol.
+ C OCH3
CH3
CH3 C C CH3 C C C
CH3
CH3
O
=>
+H2O OH
HH
CH3 C C C O H
CH3
CH3
AFB QO I 2007/08 24
Synthesis of alkynes
� Molten KOH or alcoholic KOH at 200°C favors an internal alkyne.
� Sodium amide, NaNH2, at 150°C, followed by water, favors a terminal alkyne.
CH3 C C CH2 CH3200°C
KOH (fused)CH3 CH CH CH2 CH3
Br Br
=>
, 150°CCH3 CH2 C CH
H2O2)
NaNH21)CH3 CH2 CH2 CHCl2
7
AFB QO I 2007/08 25
double dehydrohalogenation
KOH
ethanol
NaNH2
NaNH2
R C C R
Br
H
Br
H
C C
R
H R
Br
C CR R
R C C R
Br
H
Br
H
C CR R
AFB QO I 2007/08 26
alkynes
reactions
AFB QO I 2007/08 27
Migration of Triple Bond
=>AFB QO I 2007/08 28
Addition Reactions
� Similar to addition to alkenes.
� Pi bond becomes two sigma bonds.
� Usually exothermic.
� One or two molecules may add.
=>
8
AFB QO I 2007/08 29
Addition of Hydrogen
� reduce alkyne to alkane
� Lindlar’s catalyst,
alkyne to a cis-alkene.
� sodium in liquid ammonia
alkyne to a trans-alkene.
=>AFB QO I 2007/08 30
Lindlar’s Catalyst
� Powdered BaSO4 coated with Pd, poisoned with quinoline.
� H2 adds syn, so cis-alkene is formed.
=>
AFB QO I 2007/08 31
Na in Liquid Ammonia
� Use dry ice to keep ammonia liquid.
� As sodium metal dissolves in the ammonia, it loses an electron.
� The electron is solvated by the ammonia, creating a deep blue solution.
NH3 + Na + Na+
NH3 e-
=>
http://www.cci.ethz.ch/experiments/Na-NH3fl/en/stat.html
AFB QO I 2007/08 32
MechanismStep 1: An electron adds to the alkyne, forming a radical anion
Step 2: The radical anion is protonated to give a radical
Step 3: An electron adds to the alkyne, forming an anion
=>
Step 4: Protonation of the anion gives an alkene
9
AFB QO I 2007/08 33
Addition of Halogens� Cl2 and Br2 add to alkynes to form
vinyl dihalides.
� May add syn or anti, so product is mixture of cis and trans isomers.
� Difficult to stop the reaction at dihalide.
CH3 C C CH3
Br2 CH3C
Br
C
Br
CH3
+CH3
C
Br
C
CH3
Br
Br2
CH3 C
Br
Br
C
Br
Br
CH3
=> AFB QO I 2007/08 34
Addition of HX
� HCl, HBr, and HI add to alkynes to form vinyl halides.
� For terminal alkynes, Markovnikovproduct is formed.
� If two moles of HX is added, product is a geminal dihalide.
CH3 C C H CH3 C CH2
BrHBr HBr
CH3 C CH3
Br
Br
=>
AFB QO I 2007/08 35
HBr with Peroxides
Anti-Markovnikov product is formed with a terminal alkyne.
HBrCH3 C C
H
H
H
Br
BrROOR
=>
CH3 C C H CH3 C C
HH
Br
HBr
ROOR
mixture of E and Z isomers
AFB QO I 2007/08 36
Hydration of Alkynes
� Mercuric sulfate in aqueous sulfuric acid adds H-OH to one pi bond with a Markovnikov orientation, forming a vinyl alcohol (enol) that rearranges to a ketone.
� Hydroboration-oxidation adds H-OH with an anti-Markovnikovorientation, and rearranges to an aldehyde.
=>
10
AFB QO I 2007/08 37
Mechanism for Mercuration
� Mercuric ion (Hg2+) is electrophile.
� Vinyl carbocation forms on most-sub. C.
� Water is the nucleophile.
CH3 C C H CH3 C+
C
Hg+
H
Hg+2
H2O
CH3 CH
Hg+
C
O+
H H
H2OCH3 CH
Hg+
C
OH
H3O+
CH3 CH
H
C
OH
an enol=>
AFB QO I 2007/08 38
Enol to Keto (in Acid)� Add H+ to the C=C double bond.
� Remove H+ from OH of the enol.
CH3 C C
OH
H
H
H
H2O
CH3 C C
O
H
H
H
CH3 CH
H
C
OH
H3O+
CH3 C C
OH
H
H
H
A methyl ketone
=>
AFB QO I 2007/08 39
Hydroboration Reagent
� Di(secondaryisoamyl)borane, called disiamylborane.
� Bulky, branched reagent adds to the least hindered carbon.
� Only one mole can add.
=>
BCH
CH
H
CH3
CHCH3H3C
H3C
HC CH3
H3C
AFB QO I 2007/08 40
Hydroboration -Oxidation� B and H add across the triple bond.
� Oxidation with basic H2O2 gives the enol.
CH3 C C H CH3 C
H
C
HBSia2
Sia2 BH CH3 COH
H
C
H
H2O2
NaOH
=>
11
AFB QO I 2007/08 41
Enol to Keto (in Base)
� H+ is removed from OH of the enol.
� Then water gives H+ to the adjacent carbon.
CH3 CO
H
C
H
HOH
CH3 CO
H
C
H
H
OHCH3 C
OH
H
C
H
CH3 CO
H
C
H
An aldehyde
=>AFB QO I 2007/08 42
Oxidation of Alkynes
� Similar to oxidation of alkenes.
� Dilute, neutral solution of KMnO4
oxidizes alkynes to a diketone.
� Warm, basic KMnO4 cleaves the triple bond.
� Ozonolysis, followed by hydrolysis, cleaves the triple bond.
=>
AFB QO I 2007/08 43
Reaction with KMnO4
� Mild conditions, dilute, neutral
� Harsher conditions, warm, basic
CH3 C
O
C
O
CH2 CH3
H2O, neutral
KMnO4CH3 C C CH2 CH3
O C
O
CH2 CH3CH3 C
O
O +H2O, warm
, KOHKMnO4CH3 C C CH2 CH3
=>AFB QO I 2007/08 44
Ozonolysis
� Ozonolysis of alkynes produces carboxylic acids (alkenes gave aldehydes and ketones).
� Used to find location of triple bond in an unknown compound.
=>
HO C
O
CH2 CH3CH3 C
O
OHH2O(2)
O3(1)CH3 C C CH2 CH3 +
12
AFB QO I 2007/08 45 AFB QO I 2007/08 46
An organomagnesium compound (a Grignard reagent)
An organolithium compound
RMgX
RLi
R2 CuLi
A lithium
diorganocopper compound
(a Gilman reagent)
Organometalic Compounds
� C-M
AFB QO I 2007/08 47
Nomenclature
� CH3Limethyl lithium
� CH3MgBr
methyl magnesium bromide
AFB QO I 2007/08 48
2.5 - 1.2 = 1.3
2.5 - 1.0 = 1.5
2.5 - 1.6 = 0.9
2.5 - 1.9 = 0.6
Difference in Electronegativity
C-M Bond
Percent Ionic character*
60
52
36
24
C-Li
C-Mg
C-Zn
C-Hg
*Percent ionic character = EC - EM
EC
x 100
2.5 - 1.9 = 0.6 24C-Cu
Organometalic Cmpds
� Carbon-metal bonds are polar covalent
13
CH3CH
2O CH
2CH
3
O
CH3CH
2CH
2CH
2CH
3
O
O
........
........
........
........
........
........
........
........
Ethers work especiallyEthers work especiallyEthers work especiallyEthers work especially
well since they can well since they can well since they can well since they can
make complexes withmake complexes withmake complexes withmake complexes with
GrignardGrignardGrignardGrignard reagents reagents reagents reagents
and solvate them. and solvate them. and solvate them. and solvate them.
O
Mg BrCH3
O
........
........
........
........
solvents
50
MgX
C
Grignard Reagents
� basic and nucleophilic
� highly polar C-Mg bond
http://www.nndb.com/people/260/000099960/
AFB QO I 2007/08 51
+
1-Chlorobutane
Butylmagnesium chloride
etherCH3 CH2 CH2 CH2 Cl Mg
CH3 CH2 CH2 CH2 MgCl
Grignard reagents
� Grignard reagents are formed by reaction of an alkyl halide with magnesium metal in diethyl ether or tetrahydrofuran (THF)
AFB QO I 2007/08 52
Grignard Reagents
14
AFB QO I 2007/08 53
+
+1-Chlorobutane
Butyllithium
pentaneCH3 CH2 CH2 CH2 Cl 2 Li
LiClCH3 CH2 CH2 CH2 Li
Organolithium reagents
� Organolithium reagents are formed by reaction of an alkyl halide with lithium metal in a hydrocarbon solvent such as pentane
AFB QO I 2007/08 54
2 CH3 CH2 CH2 CH2 Li + CuIor THF
diethyl ether
(CH 3 CH2 CH2 CH2 ) 2 Cu - Li + + LiI
Butyllithium Copper(I)
iodide
Lithium dibutylcopper
(a Gilman reagent)
Gilman Reagents
� Prepared from an organolithiumreagent and copper(I) iodide
AFB QO I 2007/08 55
Gilman Reagents
� Gilman reagents can be used to form new carbon-carbon bonds by cross-coupling with alkyl or vinylic halides
(CH3)2CuLi + CH3(CH2)8CH2I CH3(CH2)8CH2CH3 + LiI + CH3Cuor THF
ether
AFB QO I 2007/08 56
Organozinc Reagents
much less reactive than either RLi or RMgX to aldehydes and ketones.
Simmons-Smith reaction
15
AFB QO I 2007/08 57
Acetylenic Reagents
AFB QO I 2007/08 58
Weaker
acid
Stronger
acid
pKa 51pKa 15.7
++ H-OHCH3 CH2 -MgBr Mg(OH)BrCH3 CH2 -Hδδδδ+δδδδ-
Organometallics as bases
� Organometallics are strong bases and react with any proton donor stronger than the alkane from which they are derived
Any Any Any Any ----OOOO----HHHH, , , , ----SSSS----HHHH, or , or , or , or ----NNNN----HHHH bondsbondsbondsbonds
are sufficiently acidic to react.are sufficiently acidic to react.are sufficiently acidic to react.are sufficiently acidic to react.
CH3: COH
O
RCH
4RCOO++++ ++++
---- ----
----........
........
----++++++++CH
3: CH
4H OH :O H
........ --------CH3: CH
4H O R :O R
........++++++++
The reaction with HThe reaction with HThe reaction with HThe reaction with H2222O also means that you must rigorously O also means that you must rigorously O also means that you must rigorously O also means that you must rigorously
exclude water ( and water vapor = air ) from your reactions.exclude water ( and water vapor = air ) from your reactions.exclude water ( and water vapor = air ) from your reactions.exclude water ( and water vapor = air ) from your reactions.This reaction of an This reaction of an This reaction of an This reaction of an alkyllithiumalkyllithiumalkyllithiumalkyllithium compound with water is generally compound with water is generally compound with water is generally compound with water is generally
not useful unless you use Dnot useful unless you use Dnot useful unless you use Dnot useful unless you use D2222O, which is a way of placing a O, which is a way of placing a O, which is a way of placing a O, which is a way of placing a
deuterium atom in your compound.deuterium atom in your compound.deuterium atom in your compound.deuterium atom in your compound.
CH3: D OD :O DDCH
3---- ----........
........++++ ++++
CH3
Br Li CH3
Li++++
LiLiLiLi++++ LiLiLiLi++++
Br Li D
etheretheretherether
LiLiLiLi DDDD2222OOOO
etheretheretherether
phenyllithiumphenyllithiumphenyllithiumphenyllithium
Deuterated compounds
16
61
Organometalic Coupling
+ LiBrCH3CH2CH2CH2LiCH3CH2CH2CH2Brpentane
2Li
CH3CH2Ch2Ch2CH2Cu-Li
+CuI+CH3CH2CH2CH2Li
++ LiI + CH3Cu
CH3
(CH3)2CuLi
I
AFB QO I 2007/08 62
� http://dmdl.uvm.edu/chem/6_ch141.html
� http://www.cem.msu.edu/~reusch/VirtualText/addyne1.htm
� http://www.chem.uic.edu/web1/OCOL-II/WIN/ALKENE/F4.HTM
� http://www.mhhe.com/physsci/chemistry/carey/student/olc/graphics/carey04oc/ref/ch14organometalliccompounds.html#Nomenclature
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