Insect sex pheromones : Effect of temperature on evaporation rates of acetates from rubber septa.

The half-lives (t 1/2) for evaporative loss ofn-alkyl andn-alkenyl acetates from rubber septa were determined at temperatures varying from 15 to 35 °C. The changes int 1/2 with temperature gave high correlations with the equation, Int 1/2 = ΔH/RT+y o where ΔΔH is the heat of vaporization,R is the gas constant,T is the absolute temperature, andy o is a constant. Half-lives changed dramatically with temperature and the degree of change with temperature increased with increasing molecular weight. For mixtures, component ratios changed with temperature, but the degree was modest. At 20 °C there was a 7.5-fold ratio oft 1/2 between members of the homologousn-alkyl orn-alkenyl acetates differing by two carbon atoms. The large change int 1/2 with temperature and with number of carbon atoms is a consequence of the thermodynamic relationships and the temperature range of pheromone usage. Therefore, a similar degree of change inf 1/2 with temperature and number of carbon atoms will apply to other formulations of the same type (those in which the rate of evaporation is first order). The values oft 1/2 at 20 °C mainly agreed very well with those reported previously at room temperature. However, our previously reported values for pentadecyl and hexadecyl acetate were revised. Half-lives were shown to depend on the vapor pressure of a compound in the formulation substrate, but not on the vapor pressure of the pure compound.