Synthesis 1:g-Nonanoic Lactone, The Fragrance of Coconut

[Bunce, R.A.; Reeves, H.D. J. Chem. Ed. 1990, 67, 69-70]

Introduction. The product of this reaction has the fragrance of coconut. In order to understand the mechanism of the first step, you need to read section 23.12 and see problems 23.50 and 23.51 in McMurry (6th ed.). Amberlyst-15 is a resin that serves as a source of strong acid in non-aqueous media.

Experimental

Note: There are several extractions in the first reaction and you need to be sure you know where your product is at all times. Use the 1 h reflux period to consider what the purpose is for all of the extractions/washings.

3-Nonenoic Acid: Mix 1.04 g of malonic acid and 1.14 g of heptanal in a 25-mL round bottom flask and then add 2 mL triethylamine. Add a boiling chip and reflux the mixture for 1 h. Cool the reaction to room temperature and then transfer it to a separatory funnel using 10-20 mL ether. Wash the ether layer in the funnel with 10 mL ice cold 10% HCl and discard the aqueous layer. Wash the ether layer with 10 mL of 5% NaOH and discard the ether layer. Return the aqueous layer to the funnel and wash it with 10 mL of ether and discard the ether. Reacidify the aqueous layer with 10 mL of 10% HCl and extract it with 10 mL of ether. Discard the aqueous layer. Wash the ether layer with saturated NaCl, dry it over MgSO4, filter off the drying agent, and evaporate off the ether on the rotovap. Characterize this product.

g-Nonanoic Lactone: Place the 3-nonenoic product from above in a 25-mL round bottom flask with an equal weight of Amberlyst-15 and 2-mL of heptane. Reflux the mixture vigorously for 1 h then cool it to room temperature. Filter away the Amberlyst-15 by passing the mixture through a pipet with a cotton plug and then wash the catalyst in the pipet with 5 mL ether. Evaporate off the ether and heptane on the rotovap. Vacuum distill the resulting oil using a short-path distillation apparatus and the house vacuum. Characterize the final product.