A Study on Synthesis of para-menthane-3,8-diol (PMD) - A Safe Mosquito Repellent Active Ingredient

Abstract

Active ingredient para-menthane-3,8-diol (PMD) is evaluated as effective in repelling insects in general and is recommended by the Centers for Disease Control and Prevention as an insect repellent, especially against mosquitoes worldwide. The present study attempted to evaluate the suitable conditions for the synthesis of PMD from two sources of materials that are pure (±)-citronellal (∼ 96%) and lemon eucalyptus (Eucalyptus citriodora) essential oil (∼ 60% citronellal) by treatment of sulfuric acid in a biphasic medium (H2O/essential oil). The one-factor-at-a-time method was used to determine the optimal conditions for the synthesis of PMD from pure (±)-citronellal. The effect of various factors such as oil-to-water ratio (citronellal to sulfuric acid aqueous solution), acid concentration (sulfuric acid), reaction temperature, and reaction time on the PMD yield and conversion of citronellal was investigated. The highest PMD yield (95.6%) with excellent conversion of citronellal (98.5%) was obtained at optimal conditions such as, oil to water ratio of 1:2, acid concentration of 0.75% (w/w), reaction temperature of 60°C, and reaction time of 6 h. These optimal conditions were applied to synthesize PMD from Eucalyptus citriodora essential oil. From 200 grams of essential oil and applied optimal conditions, PMD was obtained with a yield of 91.5%.