Question

The most suitable reagent for the following conversion, is:

• A. \(Na/liquid NH_3 \)
• B. \(H_2, Pd/C, quinoline \)
• C. \(Zn/HCI \)
• D. \( Hg^{2+}/H^{+}, H_2O \)

Answer 1

The Correct Option is B

  To determine the most suitable reagent for the conversion: transforming an alkyne to cis-alkene. The reaction under consideration is:

The reaction is focused on converting an alkyne (1-butyne) to a cis-alkene (cis-2-butene).

1. Wilkinson's Catalyst/ Lindlar's Catalyst Reaction: This method involves using hydrogen gas in the presence of Pd/C and quinoline to selectively stop the reduction of the alkyne at the alkene stage. It's commonly known as a semi-hydrogenation reaction.
2. Understanding the Options:
   • \(Na/liquid NH_3\): This reagent is used for the trans selective reduction of alkynes to alkenes.
   • \(H_2, Pd/C, quinoline\): Known for the semi-hydrogenation leading to cis-alkene formation. This is the correct option.
   • \(Zn/HCl\): Generally used in Clemmensen reduction, not suitable for selective alkene formation.
   • \(Hg^{2+}/H^{+}, H_2O\): Typically used in hydration reactions, not involved in direct hydrogenation.

Thus, the most suitable reagent for converting an alkyne to cis-alkene is \(H_2, Pd/C, quinoline\). This reagent helps to stop the reaction at the alkene stage, providing the desired cis configuration.