Butyric acid, putrescine and their mixture as potential fly attractants: Complexation, thermal analysis and volatility characterisation

Mixtures of butyric acid and putrescine form a crystalline amine carboxylate complex in a 2:1 molar ratio irrespective of the initial molar component mixture ratio. This was confirmed through X-ray diffraction, FTIR spectroscopy and elemental analyses. Thermogravimetric analyses proved this complex to be significantly less volatile than the pure constituent components. In thermogravimetric temperature scans, a 90% mass loss of the complex was achieved at 143.4 °C while the same level was achieved at 68.1 °C for both the pure putrescine and butyric acid. A gas permeability parameter Φ_A = M_AD_AP_A/RT (g m^–1s^–1) was developed to quantitatively describe the volatility of the respective components through a stagnant gas layer. This parameter is a function of only material properties and temperature and adequately described the observed mass loss behaviour of pure components as well as the newly formed complex. In a preliminary field trial, mixtures of putrescine and butyric acid were less effective than pure putrescine for attracting flies. This can be attributed to the lower volatility of the putrescine/butyric acid complex and the subsequent suppression of the release rate of the active compounds.