Complex Formation of Perfumes with Cationic Surfactants and the Enhanced Thermal Stability

Abstract

Abstract Seven crystalline molecular complexes were formed between perfumes such as guaiacol, 2-methylindole, and skatole and cationic surfactants such as hexadecyl-, tetradecyl-, dodecyl-, and decyltrimethylammonium bromide from an aqueous or methanol solution at low temperatures (< 10 °C). The crystal structures were determined by X-rays. The structures are very similar to each other, that is, the perfume molecules are packed in the layers of the alkyl chains of the surfactant molecules. Those packings are substantially the same as the common packing pattern observed in complexes between the surfactants and the aromatic compounds. The thermal analysis showed that the volatilization temperatures of the perfumes increased significantly when the perfumes are packed in the complex crystals. Moreover, the molar loss ratio of the perfume with increasing the temperature decreased with increasing the length of the alkyl chain of the surfactant. This suggests that thermal stability of the perfumes can be controlled by forming the complexes with the surfactants containing different alkyl chains.