Question

Write a short note on Frankland’s reaction.

Answer 1

Hint: Frankland’s reaction is similar to Wurtz’s reaction. The only difference there is that in Frankland’s reaction, zinc is used in place of sodium used in the Wurtz reaction.

Complete step by step answer:
- Frankland’s reaction is the preparation of di-alkyl zinc from zinc and alkyl iodide. The first synthesis organometallic compound to be formed was diethyl zinc.
- This reaction is somewhat similar to the Wurtz reaction. The only difference is that in place of sodium metal, zinc metal is used instead.
- The general reaction is supposed to occur as shown below
\begin{align*}R-X+2Zn+X-R\rightarrow R-R+2ZnX\end{align*}
- The reaction was discovered by Edward Frankland in July 1849. This reaction is regarded as a key event in organic and organometallic chemistry.
- Symmetry of alkanes can be prepared by using this reaction. Dry ether is used as a solvent in this reaction which helps to form free radicals and to prevent zinc from moisture.
- The alkanes obtained by this method contain an even number of carbons and alkanes with an odd number of carbon atoms cannot be obtained by this method.

Additional Information”. Haloalkanes and zinc are taken in the ratio of 2:1. If they are taken in a ratio of 1:1, RZnI is formed instead of R-R.

Note: Alkyl zinc has found many applications in organic synthesis because the addition of alkyl zinc to aldehydes in the presence of a chiral catalyst affords secondary alcohols with a high level of enantioselectivity.