Isolating Isoamyl acetate

Esters are known to produce a catalog of uniquely smelling compounds. One such compound is isoamyl acetate (3-methylbutyl acetate), which is a naturally occurring compound produced from ripening fruit.¹ It produces an amazing banana odour and is used as a flavourant in a variety of applications.¹ To synthesize this banana-smelling acetate, we can perform a Fischer Esterification (Scheme 1 ) with isoamyl alcohol (10 mL), glacial acetic acid (15 mL), and some drops of sulfuric acid as the catalyst.

Scheme 1. Reaction scheme of the Fischer esterification of isoamyl alcohol with acetic acid.²

After refluxing the reaction mixture for an hour, the mixture was poured into a separatory funnel, and a sodium bicarbonate solution was added to neutralize the excess acetic acid. The funnel was capped, inverted, shaken, and frequently vented to relieve the pressure.³ The funnel was inverted again and placed in a flask ring clamp to allow the layers to separate. After isolating each layer, benchtop NMR spectroscopy was used to determine which layer was which (organic or aqueous) and the success of the extraction was also validated (Figure 1).

Figure 1. ¹H (60 MHz) NMR spectra of the organic (top) and aqueous (bottom) layers from the liquid-liquid extraction. The carbon satellites of sodium acetate are denoted by black stars, the purple star corresponds to the residual chloroform signal, and the signals corresponding to residual isoamyl alcohol in the aqueous phase are denoted by red stars. Note that 20 µL of the isolated organic layer was added to 0.6 mL of deuterated chloroform and the aqueous layer was ran neat for these analyses.

Benchtop NMR spectroscopy is a great tool to confirm the success of a liquid-liquid extraction, as an aliquot of the layers formed during an extraction can be taken for a proper assessment of their composition. Based on the ¹H NMR spectrum we can deem the synthesis of isoamyl acetate as successful. To note, conducting carbon and 2D NMR experiments can further substantiate this assessment.

With our instruments, one can determine whether a subsequent extraction should be performed, a different solvent should be used, or a different technique should be employed to isolate the desired compound.

If you have any questions about how benchtop NMR instruments could be incorporated into your synthetic chemistry workflows extractions, please don’t hesitate to contact us.

References

[1] Am. Chem. Soc. Publications Home page (post) 2007 (accessed January 30, 2025)  

[2] Westfield State University, Esterification: the synthesis of isoamyl acetate (accessed January 30, 2025) 

[3] Raydo, M. L.; Church, M. S.; Taylor, Z. W.; Taylor, C. E.; and Danowitz A. M.

J. Chem. Ed. 2015 92, 139-142.