Question

1) Sodium amide is used in the synthesis of alkyne from dihalides. Explain when two molar equivalents of NaNH₂ are required and when three molar equivalents are required followed by protonation with NH₄Cl. Provide the complete condition(s) required for each instances. 2) Provide two methods to synthesize 2-methyl-1-pentene. Consider using different alkyl halides and the appropriate base for the two methods.

Answer 1

Vicinal or geminal dihalide alkanes show elimination reaction with bases like sodium amide in liquid ammonia.

1. When non terminal alkynes are formed two equivalent of sodium amide is used.

2. When terminal alkynes are formed 3 equivalent of sodium amide is used. The proton attached to the terminal alkynes is acidic therefore it requires 1 sodium amide molecule per alkyne extra.

(Strong base and high temperatures used in the reaction therefore we use liquid ammonia to lower the temperature. Also in higher temperature there is chances of isomerisation of alkynes instead of terminal alkynes, 2-alkaline is formed)