Complex Formation by Grinding in a Mortar

Complex formation only by grinding a mixture in a mortar was examined for a variety of combinations of the surfactant and aromatic compounds. The CTAB, MTAB, LTAB and DTAB surfactants were selected along with hydrophilic aromatic compounds containing hydroxyl, carboxyl and imino groups, and hydrophobic aromatic compounds such as acridine, anthracene, biphenyl and phenanthrene. Table 4.2 shows the results of the complex formation, in which the letters A, B and C mean that the complex was formed completely, partly and hardly, respectively. (The asterisk indicates that the single crystals have been analysed by X-rays). It is clear that  

In order to clarify the above different characteristics, the structures of the crystals obtained from an aqueous solution were compared. The crystal structures of the complexes composed of aromatic compounds with a hydroxyl group have already been shown in the previous section CTAB- -cyanophenol (II), CTAB-p-cresol (III), CTAB-o-iodophenol (V), MTAB-o-iodophenol (VI), LTAB-o-iodophenol (VII) and DTAB-o-iodophenol (VIII). For the o-iodophenol complexes there are two structural groups  

For the complex crystals with the carboxyl group, I and IX, the carboxyl groups make a dimer structure directly or through solvent water molecules. When the aromatic crystals with the dimer structure were ground in a mortar, the dimer structure is probably conserved. Since the dimer structure is too large, it may be difficult to be inserted between the anti-parallel alkyl chains. When the aromatic compounds with a carboxyl group are dissolved in aqueous solution, the dimer structure may be loosened allowing easy insertion between the alkyl chains. 

In the previous section, it has been made clear that the hydrogen bond formation of the aromatic compound with the bromide anion reinforces the complex formation. However, 

Aromatic compound CTAB MTAB LTAB DTAB 

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