Sodium dodecyl sulfate

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Sodium dodecyl sulfate

Systematic name	Sodium dodecyl sulfate
Chemical formula	C₁₂H₂₅NaO₄S
Molecular mass	288.38 g mol⁻¹
Density	x.xxx g/cm³
Melting point	206 °C
Boiling point	xx.x °C
CAS number	[151-21-3]
SMILES	CCCCCCCCCCCCOS(=O)([O-])=O.[Na+]
Disclaimer and references

Sodium dodecyl sulfate (SDS or NaDS) (C₁₂H₂₅Na O₄S), also known as sodium lauryl sulfate (SLS), is an ionic surfactant that is used in household products such as toothpastes, shampoos, shaving foams and bubble baths for its thickening effect and its ability to create a lather. The molecule has a tail of 12 carbon atoms, attached to a sulfate group, giving the molecule the amphiphilic properties required of a detergent.

It is prepared by sulfonation of dodecanol (lauryl alcohol, C₁₂H₂₅OH) followed by neutralisation with sodium carbonate. It is used in both industrially produced and home-made cosmetics.

Like all detergent surfactants (including soaps), it removes oils from the skin, and can cause skin irritation. It is also irritating to the eyes.

SDS can be converted by ethoxylation to sodium laureth sulfate (also called sodium lauryl ether sulfate; SLES), which is less harsh on the skin, probably because it is not as much of a protein denaturant as is the unethoxylated substance.

It is probably the most researched anionic surfactant compound.

In laboratories, SDS is commonly used in preparing proteins for polyacrylamide gel electrophoresis (SDS-PAGE). SDS works by disrupting non-covalent bonds in the proteins, thereby denaturing them, causing the molecules to lose their native shape (conformation). Also, anions of SDS bind to the main peptide chain at a ratio of one SDS anion for every two amino acid residues. This effectively imparts a negative charge on the protein that is proportional to the mass of that protein (about 1.4 g SDS/g protein). This new negative charge is significantly greater than the original charge of that protein. The electrostatic repulsion that is created by binding of SDS causes proteins to unfold into a rod-like shape thereby eliminating differences in shape as a factor for separation in the gel.

It has recently ^[1] found application as a surfactant in gas hydrate or methane hydrate formation reactions, increasing the rate of formation as much as 700 times.

[edit] Safety concerns relating to SLS

It appears that there are two quite differing views on the safety of using and exposing the body to constant low levels of toxic chemicals such as Sodium Lauryl Sulphate (SLS). Some people are affected by SLS and its derivatives more than others. It is suspected that SLS is linked to a number of skin issues such as dermatitis, and when combined with certain chemicals, SLS may become a carcinogen. SLS is commonly used in research laboratories as the standard skin irritant with which other substances are compared. There are over 150 different names by which SLS and its derivatives are known. Although SLES is slightly less irritating than SLS, the liver is unable to metabolize SLES. The prime reason SLS is used in many soaps, shampoos, washing powders, toothpastes and other bathroom products is its inexpensive cost. SLS is known to cause aphthous ulcers, commonly referred to as "canker sores".

[edit] Data

The critical micelle concentration in pure water at 25°C is 0.0082 M, and the aggregation number at this concentration is usually considered to be about 64. The micelle ionization fraction (α) is around 0.3 (or 30%)^[2].
The Optical refractive index increment of a pure aqueous solution at wavelength 532 nm is about 0.1070 ml/g.

[edit] References

^ Kazuyoshi Watanabe, Shuntaro Imai and Yasuhiko H. Mori. "Surfactant effects on hydrate formation in an unstirred gas/liquid system: An experimental study using HFC-32 and sodium dodecyl sulfate", Chemical Engineering Science Volume 60, Issue 17 , September 2005, Pages 4846-4857.
^ Barney L. Bales, Luis Messina, Arwen Vidal, Miroslav Peric, and Otaciro Rangel Nascimento (1998). "Precision Relative Aggregation Number Determinations of SDS Micelles Using a Spin Probe. A Model of Micelle Surface Hydration". J. Phys. Chem. B 102 (50): 10347-10358..