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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

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Acetylene

� welding torches.

� In pure oxygen reaches 2800°C.

� Explodes to decompose to its elements

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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

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Bond Lengths

� More s character, so shorter length.

� Three bonding overlaps, so shorter.

Bond angle is 180°, so linear geometry. =>

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acetylide

� Acetylene → acetylide� NH2

-,

� not by OH- or RO-.

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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

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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

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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.

=>

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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