Chemistry and Manufacture
Distearyldimethylammonium chloride or DSDMAC (INCI: Distearyldimonium Chloride) is a twin-tailed fatty quaternary ammonium organic compound or fatty quat (see Figure 1).1 The nitrogen atom is covalently bonded to two stearyl, i.e., n-octadecyl, groups and two methyl groups, and bears a positive charge that is balanced by a chloride anion. The molecular weight of DSDMAC (C38H80N•Cl) is 586.5 g/mol.
There are many possible synthetic pathways for the commercial preparation of DSDMAC,2–4 one of which begins with stearic acid (see Figure 2). Although fatty amines including those used to synthesize DSDMAC can be derived from a variety of commodity chemicals—i.e., fatty acids, fatty alcohols or alpha olefins, the typical precursor for DSDMAC is stearic acid, which is obtained from the hydrogenation and hydrolysis of triglycerides (fats and oils) from animal or plant sources and separation of the resulting fatty acids by distillation. Given the personal care industry’s preference for plant-derived ingredients, the stearic acid that is used to prepare cosmetic grade DSDMAC is typically obtained from nut or vegetable oils, e.g. palm, coconut, soy, etc.
In Figure 2, stearic acid is first condensed with ammonia (NH3) to liberate water and form the primary amide, stearamide, which is then catalytically dehydrated to yield stearonitrile. Following purification, this fatty nitrile is hydrogenated in the presence of excess NH3 to form the primary fatty amine stearamine. In the subsequent reaction, a different set of hydrogenation conditions is employed to reduce two equivalents of stearamine to the secondary amine, distearylamine, which simultaneously liberates an equivalent of NH3.