Sodium stearate
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| Appearance | white solid |
| Odor | slight, tallow-like odor |
| Density | 1.02 g/cm3 |
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| Solubility | slightly soluble in ethanediol |
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Sodium stearate (IUPAC: Sodium Octadecanoate) is the sodium salt of stearic acid. This white solid is the most common soap. It is found in many types of solid deodorants, rubbers, latex paints, and inks. It is also a component of some food additives and food flavorings.[1]
Use
Having the characteristics of soaps, sodium stearate has both hydrophilic and hydrophobic parts, a carboxylate and a long hydrocarbon chain. These two chemically different components induce the formation of micelles, which present the hydrophilic heads outwards and their hydrophobic (hydrocarbon) tails inwards, providing a lipophilic environment for hydrophobic compounds. The tail part dissolves the grease or dirt and forms the micelle. It is also used in the pharmaceutical industry as a surfactant to aid the solubility of hydrophobic compounds in the production of various mouth foams.
Production
Sodium stearate is produced as a major component of soap upon saponification of oils and fats. The percentage of the sodium stearate depends on the ingredient fats. Tallow is especially high in stearic acid content (as the triglyceride), whereas most fats only contain a few percent. The idealized equation for the formation of sodium stearate from stearin (the triglyceride of stearic acid) follows:
- (C17H35CO2)3C3H5 + 3 NaOH → C3H5(OH)3 + 3 C17H35CO2Na
Sodium stearate can also be made by neutralizing stearic acid with sodium hydroxide.
- C17H35COOH + NaOH → C17H35COONa + H2O
Safety and environmental considerations
Stearate salts, as found in many commercial soaps are of low toxicity, hence their wide use in domestic settings. They do pose some problems for wastewater treatment as they biodegrade relatively slowly and impose a high biological oxygen demand.[1]