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Synthesis and Characterization of Ethyl Formate Precursor for Activated Release Application.

Ethyl formate (EF) is a generally-recognized-as-safe flavoring agent commonly used in the food industry. It is a naturally-occurring volatile with insecticidal and antimicrobial properties, promising as an alternate fumigant to methyl bromide which is undesirable due to its ozone depletion in the stratosphere and toxic properties. However, EF is highly volatile, flammable, and susceptible to hydrolytic degradation. These properties present considerable end-use challenges. In this study, a precursor of EF was synthesized via the condensation reaction of adipic acid dihydrazide and triethyl orthoformate to form diethyl N,N'-adipoyldiformohydrazonate, as confirmed by Fourier transformed infrared and solid-state nuclear magnetic resonance spectroscopies. Differential scanning calorimetry analysis showed that the precursor had a melting point of 174°C. The physical properties of the precursor were studied using scanning electron microscopy and dynamic light scattering analysis, which showed that the precursor made up of agglomerated particulates with irregular shapes and sizes. The resulting precursor was non-volatile and remained stable under dry condition but could be hydrolyzed readily to trigger the release of EF. The release behaviors of EF from the precursor was evaluated by citric acid-catalyzed hydrolysis, showing that 0.38 ± 0.008 mg EF/mg precursor was released after 2 h at 25°C, representing about 98% of the theoretical loading. Both EF release rate and its total release amount decreased significantly (p<0.05) with decreasing temperature and relative humidity. The conversion of the highly volatile EF into a solid-state precursor, in conjunction with the activated release strategy, can be useful for controlled release of EF for fumigation and other applications in destroying insect pests and inhibiting the proliferation of spoilage microorganisms.