SolutionsAlkynes
1. From acetylene to 2-hexyne
Propose a synthesis of 2-hexyne from acetylene and the alkyl halides you need.
1) NaNH2, NH3 and CH3CH2CH2Br: 1-pentyne. 2) NaNH2, NH3 and CH3I: 2-hexyne.
Primary halides should be used: with secondary and tertiary ones the alkynide, a strong base, gives mainly elimination.
2. Cis, trans or alkane
What is obtained from 3-hexyne with: a) H2, Pd/C; b) H2, Lindlar catalyst; c) Na/liquid NH3?
- Hexane.
- cis-3-Hexene.
- trans-3-Hexene.
3. Hydration
What product does hydration of 1-hexyne with H2SO4/HgSO4 give? And its hydroboration-oxidation?
Hydration (Markovnikov) gives 2-hexanone; hydroboration-oxidation (anti-Markovnikov) gives hexanal. In both cases an enol is formed first, which tautomerizes to the carbonyl compound.