Ethyl 5-iodovalerate
The synthesis of ethyl 5-iodovalerate, the ethyl ester of 5-iodovaleric acid, is an excellent example of a practical application of the Finkelstein reaction in organic synthesis. Alkyl iodide compounds are generally more reactive than the corresponding alkyl bromides in a number of reactions that involve the formation of an organometallic intermediate (e.g. the Grignard Reaction). Alkyl iodides are generally less stable than the corresponding bromides, however. In order to take advantage of the greater long-term stability of the bromides and the greater reactivity of the alkyl iodides, the iodides are frequently generated immediately prior to use.
Ethyl 5-iodovalerate can readily be prepared from the corresponding commercially available bromide via reaction with sodium iodide in acetone. Ethyl 5-bromovalerate (6.25g, 29.8 mmol) is dissolved in 75 mL of dry acetone. Sodium iodide (22.4g, 150 mmol) is then added in small portions over several minutes. The solution is heated to reflux for 48 h followed by cooling to ambient temperature. The resulting mixture is combined with 100 mL of diethyl ether and 100 mL of water. The resulting aqueous phase is extracted with diethyl ether (3X50 mL). The combined organic layers are then washed with 25 mL of a 10% aqueous solution of sodium bisulfite followed by 25 mL of brine. The resulting solution is then dried via magnesium sulfate, filtered, and concentrated in vacuo. The resulting oil is purified via vacuum distillation to afford the iodide. The product can be stored over copper wire to improve shelf life.