Many detergents, cleaning products and shampoos contain a chemical called sodium lauryl sulfate. Despite its long chemical name, sodium lauryl sulfate can be colloquially explained in simple terms---it's a soap. As such, it aids in the removal of dirt and grease from hair, clothing and skin and has distinct chemical properties.
Features
The chemical makeup of sodium lauryl sulfate is relatively simple, and the molecule is small. According to the "CRC Handbook of Chemistry and Physics," its chemical formula is NaC12H25SO4, meaning that it consists of a twelve-carbon tail, with hydrogen atoms attached to the carbons, plus an SO4, or sulfate group, head. The sodium atom, Na, is present only to counter the charge on the sulfate---sulfate is negatively charged, and sodium is positively charged.
Function
As a soap, sodium lauryl sulfate is an emulsifying agent, which means that it has two distinct molecular regions. The tail, made up of carbon and hydrogen, sinks into fat, grease and oil. The head, composed of the sulfate group, doesn't sink into fat, because it's fat insoluble. Instead, the sulfate group is water soluble and stays outside the fat. Fat droplets become surrounded by soap molecules with tails in the fat and heads outside the fat, producing a unit called a micelle.
Effects
Micelles, unlike fat droplets, can dissolve in water. Although fat is water insoluble, in a micelle, the fat is surrounded by water-soluble sulfate heads of soap-like sodium lauryl sulfate. As such, water and soap work together to surround fat, lift it from hair and clothing and wash it away. Micelle formation, explain Reginald Garrett, Ph.D., and Charles Grisham, Ph.D., in their book "Biochemistry," is favorable and happens easily.
Considerations
Sodium lauryl sulfate works well as a soap in soft water, but doesn't work well in hard water. Hard water contains calcium and magnesium salts, explain Garrett and Grisham, but soft water does not. The calcium and magnesium bond to lauryl sulfate, displacing sodium, and cause the soap to precipitate, or fall out of solution in solid form. When it precipitates, it can't form micelles, can't cause fat to dissolve in water and no longer acts as a detergent.
Production
Production of sodium lauryl sulfate requires the reaction of a chemical called lauryl alcohol with sulfuric acid, which is a source of sulfate. Lauryl alcohol comes from plants, including coconut, and is a derivative of chemical components of plant oils called fatty acids. Chemists can reduce fatty acids to produce alcohols like lauryl alcohol, explain Mary Campbell, Ph.D., and Shawn Farrell, Ph.D., in their book "Biochemistry," and lauryl alcohol can then be treated with sulfuric acid to produce soap.
References
- "CRC Handbook of Chemistry and Physics"; David Lide; 1974
- "Biochemistry"; Reginald Garrett, Ph.D. and Charles Grisham, Ph.D.; 2007
- "Biochemistry"; Mary Campbell, Ph.D. and Shawn Farrell, Ph.D.; 2005
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