2-Heptanone is an effective mite-repellant to protect honey bees and helps to reduce bee collapse. An efficient way to prolong and stabilize the release of 2-heptanone is by deketalization of its ketals with either glycerol (Gly-Ket) or polyvinyl alcohol (PVAl-Ket). The synthesized ketals were characterized by 1H and 13C NMR spectroscopy, and for PVAl-Ket also DSC. Two set ups were used for monitoring the concentration of the 2-heptanone: a 1.5 L environmental chamber and a miniaturized set up for up to 10 vials, each having a 20 mL volume. Deketalizations were catalyzed by phosphoric acid with the temperature and relative humidity of 30 oC and about 80 %, resp., resembling bee hive conditions. The deketalizations were optimal between pH values of 2.0 and 2.5 for Glyc-Ket and 2.0 and 3.5 for PVAl-Ket. Headspace gas chromatography was applied to monitor 2-heptanone vapor released by the ketals. For Gly-Ket, the 2-heptanone concentration could also be directly monitored from the liquid emulsion containing the ketal using 1H NMR spectroscopy. The measurements indicated that the 2-heptanone release lasted at reasonably high levels for at least 23 days with PVAl-Ket and 42 days with Gly-Ket (i.e. 2 brood cycles with the latter). In contrast to the pure ketone, which evaporates rapidly, the concentration of 2-heptanone released from the ketals remained relatively stable. An alternative physicochemical approach to release the 2-heptanone will also be briefly discussed.

Prolonging and stabilizing the release of 2-heptanone as mite repellant for the protection of honey bees

ACS Spring Meeting 2021

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