Ch. 9 - Alkyne Reactions

Front 1

Preparation of alkynes

Back 1

ELIMINATION OF DIHALIDES

1.loss of 2 HX to form an alkyne

2. Goes from alkene to alkyl dihalide(halogenation) to alkyne compound (USE OF KOH)

3. takes place through vinylic halide intermdeiate

Front 2

Addition of HX

Back 2

* Alkyne compound

*HX

*1st step give halogenated alkene, 2nd gives dihalogenated alkane

*Markovnikov

*

Front 3

Addition of X2

Back 3

*Alkyne with X2

*1st step gives dihalogenated alkene, 2nd gives tetrehalogenated alkane

*Trans stereochem

*vinylic carbocation

Front 4

Hydration of ALkynes via water catalyzed Hg(II) ion

Back 4

*Alkyne + H2SO4 in water catalyzed by HgSO4

*Gives ketone on an alkane

*Markovnikov

*enol intermediate (vinylic alcohol)

*mixture of both possible ketones occurs on hydration of unsemtrical alkyne

Front 5

Hydroboration-Oxidation of alkynes

Back 5

* alkyne + BH3 in THF

*if internal alkyne, Ketone
if terminal alkyne, Aldehyde

*Anti-markovnikov

Front 6

reduction of alkynes

Back 6

* Alkyne + H2 w/ Pd/C catalyst or Lindlar catalyst
----->gives cis alkene product

*Alkane(complete reduction) or alkene(lindlar catalyst)

*can also use Alkali metals (Li) to reduce alkynes via an intermediate anion radical
----->gives trans product

Front 7

Oxidative cleavage of alkynes

Back 7

* alkyne + KMnO4 or )3

*internal alkyne gives carboxylic acids
terminal alkynes give CO2 + carboxylic acid

Front 8

Acetylene

Back 8

H-C-triple bond-C-H

*can be deprotonated by the conjugate base of any acid with pKa above 25

Front 9

Alkylation of Acetylide anions

Back 9

*acetylide anion with alkyl halide

*forms new alkyne

*1.acetylene alkylation gives terminal alkyne, 2. terminal alkyne alkylation gives internal alkyne.

*Can only alkylate PRIMARY alkyl halides