Surfactants hydroquinone complexes

The produced quinone makes black complexes within the original hydroquinone very easily. As shown in Figure 4.48, when the crystals of hydroquinone and quinone are placed separately, the dark-violet crystals of the complex, which are called quinhydron, appear between the two crystalline samples. We tried to stabilize hydroquinone by making complexes with various surfactant molecules containing quaternary ammonium salts, such as alkyltrimethylammonium halides, benzyl(alkyl)dimethyl-ammonium chloride, and ethyl(hexadecyl)dimethylammonium bromide (ECDAB). After many trials, complex crystals suitable for X-ray analysis were formed with benzyl(hexadecyl)dimethylammonium chloride (BCDAC) and ECDAB, as shown in Figure 4.49. 

The crystal structure of the complex of hydroquinone and BCDAC (XXXV) viewed along the fe-axis is shown in Figure 4.50. The complex is composed of one BCDAC and one and a half hydroquinone molecules (A- and B-HQ, respectively) in the asymmetric unit. The B-HQ is situated on the twofold axis between the cationic and anionic moieties of the surfactant molecules. The A- and B-HQ molecules have two QH groups with a cis conformation. The conformation of the hexadecyl group of BCDA cation is all trans. 

Consequently, complex formation of hydroquinone with surfactant molecules was investigated. In this section, four surfactant molecules with different alkyl chains are described, because they are considered to be safe for human health. As shown in Figure 4.55, they are benzyl(octadecyl)dimethylammonium chloride (BSDAC), benzyl(hexadecyl)dimethylammonium chloride (BCDAC), benzyl(tetradecyl)dimethyl-ammonium chloride (BMDAC) and benzyl(dodecyl)dimethylammonium chloride... 

After this, the complex of BCDAC and hydroquinone was selected, because the surfactant BCDAC has been used previously in ophthalmic solutions. First, the stability of the complex was checked when it was mixed with several ointments. The complex was mixed with hydrophilic ointment (HO), hydrophilic petrolatum (HP), white petrolatum (WP), plastibase (PB) and zinc oxide ointment (ZO). The colour value. 

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