727 A SIMPLE METHOD FOR ESTIMATING VAPORIZATION PROPERTIES OF PHEROMONE-LIKE ACETATES FROM THEIR MOLECULAR STRUCTURES Bohumir KOUTEK, Michal HOSKOVEC and Jan VRKO institute of Organic Chemistry and Biochemistry, Czechoslovak Academy of Sciences, 166 10 Prague 6 Received September 6, 1990 Accepted November 6, 1990 A simple computational method has been developed to determine vapor pressures of pheromone- -like acetates. The input parameters required, i.e. critical temperatures and critical pressures are obtained from the known molecular structures by using group contribution methods. Sub- sequently, the vapor pressures are estimated by the three parameter corresponding states equa- tion of Lee and Kesler. The validity of this approach was tested on a homogeneous experimental material (eleven C10 to C16 acetates) by standard methods of statistical analysis, as well as by comparison of the results with corresponding experimental data. When compared with GC based experimental values, the estimated vapor pressures show mean relative error <±10%, achieving thus a better accuracy than other experimental methods when compared among them- selves. A close correlation, viz. In t,12 —0294 In P + 182 (r = 09986) has been found between first order half-lives for evaporative loss of acetates from rubber septa and calculated vapor pressures. Over the past two decades there has been a massive increase in the amount of research aimed at studying the chemistry of pheromones as well as possible applications these pheromones might have in the control of insect populations' . Chemical studies of sex pheromones have shown that, with few exceptions, females release a blend of several chemical components in a specific ratio and release rate4'5. Hence, to mimic a pheromone-releasing insect in practical applications, it became necessary to develop controlled release systems for use in monitoring, mass trapping, and aerial dissemination control programs. It is generally supposed6'7 that the release charac- teristics of pheromones depend primarily on two factors: (i) on material used for formulating pheromones, and (ii) on evaporative properties (e.g. vapor pressures, heats of vaporization and diffusion coefficients) of pheromones themselves. One convenient material that has been widely used is the rubber septum and its release characteristics have been studied in detail5'8. This material is supposed to exhibit first order emissive properties, which means that a linear dependence exists between the logarithm of pheromone concentration and time. On the other hand, only little is known at present about the fundamental physico-chemical characteristics of Collect. Czech. Chem. Commun. (Vol. 56) (1991)