Synthesis and formulation of diethyltoluamide as an insect repellent

During World War II more than 10,000 chemical substances were tested as insect repellents. Perhaps the best and all-purpose repellent developed since then is diethyltoluamide, which in various tests has been shown to be the most effective agent against a wide variety of insects. In this study diethyltoluamide was synthesized and formulated as a gel. Reaction of primary acid with thionylchloride produced acyl halide, which in reaction with diethylamine produced diethyltoluamide, with 96% yield. Reaction of diethylamine with ethyl ester of primary acid did not yield diethyltoluamide even in different experimental conditions. For production of diethyltoluamid gel, various gelling agents such as carbapol and hydroxy propyl methylcellulose (HPMC) were tested. The results showed that a suitable gel could be formulated by HPMC. Physical stability, spread and viscosity of gels were evaluated. The gels that contained 14 and 18% of diethyltoluamide were stable. Rheograms of the gels that were plotted by brockfild viscometer showed that the gels have a psudoplastic characteristic.