Ketalization of 2‐heptanone to prolong its activity as mite repellant for the protection of honey bees

BACKGROUND 2‐Heptanone is a volatile liquid known to be effective in protecting honey bees from parasitic mite infestations in hives. The present study aimed to show that chemical derivatives of 2‐heptanone would release the ketone for a significantly longer time than it takes for the pure ketone to evaporate and preferably for as long as two brood cycles of a honey bee (42 days). RESULTS A liquid ketal of 2‐heptanone with glycerol (Glyc‐Ket) and solid ketals of the ketone with polyvinyl alcohol (PVAl‐Ket), containing different amounts of the ketone, were synthesized. The fully resolved 1H and 13C nuclear magenetic resonance (NMR) spectra of the ketals are discussed. In the case of the polymer, differential scanning calorimetry (DSC) of a ketal was also compared with the unketalized polyvinyl alcohol. The length of time for which 2‐heptanone was released by the ketals was determined by gas chromatography‐mass spectrometry of the headspace. In the case of Glyc‐Ket, the concentration of the 2‐heptanone in the liquid phase was also monitored by 1H NMR spectroscopy. The deketalization was pH dependent, ranging between 2.0 and 2.5 for Glyc‐Ket and between 2.0 and 3.5 for PVAl‐Ket. CONCLUSION Under bee hive conditions, the release of 55 mmol 2‐heptanone from Glyc‐Ket lasted for 42 days, whereas the release of the ketone from the PVAl‐Ket with a similar amount of the ketone lasted for 23 days, versus a maximum of 17 days for an equivalent amount of the pure ketone. These ketals therefore have the potential to be effective mite repellants for the protection of honey bees. © 2019 Society of Chemical Industry