Substituted amides of terpenoic acid were prepared and screened for their effects as repellents of mosquitoes (Culex pipiens pallens and Aedes albopictus). The terpenoic acids were obtained by hydrolysis of nitriles with methanol and sodium hydroxide. The acids were reacted with thionyl chloride to give terpenoic acid chloride, and then transformed with N, N-dialkyl amines (dimethylamine, diethylamine, or n-dipropylamine) to terpenyl amides. Twenty-one derivatives were tested on filter paper and directly on human skin as mosquito repellents. On filter paper, derivatives of citronellal, 1-p-menthene-9-ol, β-campholenic aldehyde, and myrtenal acted like N, N-diethyl-m-toluamide aginst C. pipiens pallens. On human skin, perillyl amides were more repellent than N, N-diethyl-m-toluamide against A. albopictus, and the effect was more long-lasting: for 6 h or more.
