Preparation Of Alkynes

Question 1

How can alkynes be made from 1,2 dibromoalkane?

Answer 1

React with 2 equivalents of strong base (2NaNH3)
2 molecules of NaBr are eliminated
Two SN2 reactions

Question 2

How can alkynes be prepared from terminal alkynes?

Answer 2

2 x NaNH2 + RX

Changes both Hs to Rs
Can use other electrophilic species instead of RX such as aldehydes, ketones, epoxides and CO2
NaNH2 deprotonates and makes a reactive anion

Question 3

How can you form a primary homoproparagylic alcohol from a terminal anion?

Answer 3

React with epoxide and then H+ to protonate

Question 4

How can you form a secondary homoproparagylic alcohol from a terminal anion?

Answer 4

React with RCHO aldehyde and then protonate

Question 5

How can you form a tertiary homoproparagylic alcohol from a terminal anion?

Answer 5

React with a ketone and then protonate

Question 6

How do you form a carboxylic acid functional group to the end of a terminal anion?

Answer 6

React with CO2 and then H+

Question 7

How do you add another R group to the end of a terminal anion?

Answer 7

Add RX

Question 8

How can alkynes be formed from aldehydes?

Answer 8

React the aldehyde with 6BuOK, THF and (MeO)2 POCHNH2 to get a terminal alkyne

React aldehyde with Ph3P, CBr4 and then BuLi to to get a terminal alkyne