Alkynes Reactions

Question 1

Alkynes preparation

Answer 1

-Strong base = KOH and NaNH2

Question 2

Addition of HX and X2 ( Markovnikov addition)

Answer 2

Strong acid (HCl)

Question 3

Hydration

Answer 3

-Forms aldehydes and ketones
- 2 steps:
1. Formation of enol (alkene and alcohol)
2. Tautomerism to form carbonyl group
- 2 Types:
= Mercury (II) catalyzed hydration (oxymercuration)
= Hydroboration / Oxidation

Question 4

Mercury (II) - catalyzed hydration (oxymercuration)

Answer 4

• 1 step
• Reagents = HgSO4, H2O, H2SO4
• Terminal alkyne = methyl ketone is formed
• Methyl ketone = C=O in 2nd position
• Internal alkyne = 2 ketones formed

Question 5

Hydroboration / Oxidation

Answer 5

• 2 step process
• Reagents = BH3 / THF
  = H2O2 / OH-
• Anti-markovnikov
• Internal alkynes = 2 ketones
• Terminal alkyne = aldehyde

Question 6

Hydrogenation

Answer 6

-H2
- Catalyst = Pt/C, Pd/C, PtO2
- Produces alkanes via alkenes
- 2 ways
= cis alkenes ( Lindlar catalyst = Pd/ CaCo3/ Pb)
= trans alkenes (Li/NH3 or Na/NH3)

Question 7

Oxidative Cleavage

Answer 7

• KMnO4 in acid/ base or O3
• Products = Carboxylic Acid
• Terminal alkyne = CO2 formed

Question 8

Formation of acetylide anions

Answer 8

• strong base = NaNH2 / NH3

Question 9

Alkylation of acetylide anions

Answer 9

• addition of alkyl group onto anion