Sodium Lauryl Sulfate: Structure, Uses, Properties

The sodium lauryl sulfate is an organic salt formed by the union of the sodium ion Na + and lauryl sulfate ion n -C 11 H 23 CH 2 OSO 3 . Its chemical formula is CH 3 – (CH 2 ) 10 -CH 2 -O-SO 3 Na + . It is also known as sodium dodecyl sulfate because the hydrocarbon chain has 12 carbon atoms. It is a component of bubble bath products.

Sodium lauryl sulfate is a compound that acts on the surface that is between two phases, for example, between liquid and gas, or between water and oil. This makes it able to act as a detergent as it binds to oil or grease droplets, or small portions of dirt, and separates them from the water in the form of a floating particle, which is then easily rinsed off.

It also serves as a dispersant for ingredients in food products, improving their texture and is used in pet shampoo because it repels fleas and ticks. It also acts as a humectant in animal medicine and is used in agriculture, in paints, in plastics, and in chemical and biology research.

There are studies that indicate that it breaks the membranes that surround some viruses and bacteria, working in some cases as an antimicrobial agent.

Structure

Sodium lauryl sulfate or sodium dodecyl sulfate is an ionic organic compound consisting of a sodium Na + cation and a n -C 11 H 23 CH 2 OSO 3 dodecyl sulfate anion . The n is placed in your compact formula to indicate that it is a straight chain (unbranched).

The dodecyl sulfate anion has a linear hydrocarbon chain of 12 carbon atoms attached to a sulfate -OSO 3 by oxygen, so it has a single negative charge.

Nomenclature

– Sodium lauryl sulfate

– Sodium dodecyl sulfate

– SLS ( Sodium Lauryl Sulphate )

Properties

Physical state

White or cream colored solid in the form of crystals, flakes, or powder.

Molecular weight

288.38 g / mol

Melting point

205.5 ºC

Specific weight

Greater than 1.1 at 20 ºC

Solubility

It is moderately soluble in water: 15 g / 100 mL at 20 ºC.

Other properties

Sodium lauryl sulfate is an ionic surfactant or surfactant. This means that it has an effect on the surface that separates two immiscible phases.

It is an anionic surfactant because the part that performs the surfactant action is the lauryl sulfate anion C 11 H 23 CH 2 OSO 3 and not sodium Na + .

It is an amphiphilic compound, this means that a part of the molecule has an affinity for water (it is hydrophilic) and another section has similarity or attraction to oils and fats and repels water (it is hydrophobic).

The hydrophilic portion is where the negative charge of the anion, that is, the oxygens of the OSO 3 group of the molecule, is found. The hydrophobic fraction is the hydrocarbon chain or C 11 H 23 CH 2 -.

It is easily biodegradable and only weakly toxic.

Mechanism of action as a surfactant

The action it performs as a surfactant is to modify or change the surface tension, especially in aqueous solutions. This allows it to emulsify fats and oils.

The mechanism of action is that it is located on the contact surface between both liquids, where the surface tension decreases.

To do this, the head or hydrophilic part OSO 3  is placed in contact with the water and the tail or hydrophobic portion C 11 H 23 CH 2 – is placed inside the oil or fat.

Obtaining

It is derived from coconut or palm oil, among other oils. Lauryl acid is obtained from these, which is a fatty acid. This undergoes a reduction process (the opposite of oxidation) to obtain lauryl alcohol.

To obtain sodium lauryl sulfate, lauryl alcohol is reacted with sulfuric acid H 2 SO 4 and acid lauryl sulfate is obtained. Then the latter, being an acid, is neutralized with sodium hydroxide NaOH.

n -C 11 H 23 CH 2 OH (lauryl alcohol) + H 2 SO 4  → n -C 11 H 23 CH 2 OSO 3 H (acid lauryl sulfate)

n -C 11 H 23 CH 2 OSO 3 H + NaOH → n -C 11 H 23 CH 2 OSO 3 Na + (sodium lauryl sulfate)

Applications

Due to its ability as a surfactant or surfactant, sodium lauryl sulfate serves as a detergent, emulsifier, dispersant, humectant, etc.

In cleaning

It is one of the main components of dishwashing liquids. It is also essential in toothpastes or toothpaste, as it acts in the formation of foam, it is moisturizing and dispersing in these and many other cleaning products.

In cosmetics

It is used in lotions, shampoos, gels, bubble baths, ointment bases, creams and hair bleaches, among other items.

Here are some of its other uses:

In the food industry

Sodium dodecyl sulfate is used very frequently in the food industry, for example, in pastes and creams to allow a good dispersion of the ingredients, and in fruit juices, among other foods.

It generally acts as a dispersant, emulsifier and thickener. Improves the texture of certain baked goods. Increases stability and lengthens food shelf life.

In veterinary applications

Sodium lauryl sulfate acts as a flea and tick repellent, which is why it is used in shampoo for dogs and cats.

It also serves as a wetting agent in some antibiotics and antimicrobials for oral or topical administration (external use) for animals. It has application in anthelmintic drugs.

In pharmaceuticals

Sodium lauryl sulfate has wide application in the pharmaceutical industry for its surfactant properties. It works as an emulsifier, dispersant, humectant, among many other actions.

It also has the characteristic of acting as a transport vehicle in various medications, for example, in those drugs that it is desired to penetrate through the buccal mucosa.

In medicine

Some sources of information report that sodium lauryl sulfate has antiviral action against some viruses and bacteria.

For example, it works against the HIV virus or human immunodeficiency virus, against herpes simplex type 2 and against the human papilloma virus. In addition, it has a microbicidal action against chlamydia.

Its powerful protein denaturing activity inhibits the infectious activity of viruses by solubilizing the viral envelope by disrupting it. Its microbicidal activity works against some types of enveloped and non-enveloped viruses.

Sodium lauryl sulfate has been used in the preparation of blood samples for red blood cell count.

In various applications

– In the metallurgical industry: in the electrodeposition of metals, especially zinc and nickel.

– In agriculture: as a microbicide, fungicide, bactericide and as an emulsifier in insecticides.

– In paints and removal agents: as an emulsifier and penetrant in lacquers, varnishes and paint removers.

– In the plastics and rubber industry: as an additive for plastics and latex. Improves the tensile strength of certain polymers. In emulsion polymerization.

In rocket fuels: as an antifoam agent.

In chemical and biological research laboratories

Sodium lauryl sulfate serves as a research tool in biochemistry. It is widely used for its ability to disrupt or disorder membranes of microorganisms.

Its abilities to disrupt tissue structure and to inhibit the activity of certain enzymes lead biochemists to use it as a key component of many of the reagents used to purify acids from the nucleus of cells, such as RNA and DNA, or nucleic acids. .

The membranes of microorganisms are mainly made up of proteins and lipids (fats). Being a detergent with a negative charge, sodium lauryl sulfate adsorbs or adheres strongly to the structure of proteins, neutralizing all positive charges. It thus forms internal hydrophobic associations, giving each protein the same overall net negative charge.

This is the reason why it is used in the electrophoretic separation of proteins and lipids, since proteins have a negative charge and mobilize differently against an electric field.

It is also used to determine the relative strength of gluten in samples of flour or ground wheat. Gluten is a type of protein found in wheat.

Gluten particles are hydrated by sodium lauryl sulfate and sediment. The greater the sediment volume, the greater the strength of the gluten proteins in the sample.

Sodium lauryl sulfate is also used in the characterization of NH 4 + quaternary ammonium compounds . It is also used as a reference surfactant compound in toxicity tests for aquatic and mammalian species.

In the oil industry

Sodium dodecyl sulfate is used as an antiemulsifier in the oil extraction technique by hydraulic fracking (from English hydraulic fracking ) of rock formations rich in this. It serves to avoid the formation of emulsions in the fracture fluid.

References

  1. US National Library of Medicine. (2019). Sodium dodecyl sulfate. Recovered from: pubchem.ncbi.nlm.nih.gov.
  2. Farrell Jr., RE (2010). Resilient Ribonucleases. Sodium dodecyl sulfate. In RNA Methodologies (Fourth Edition). Recovered from sciencedirect.com.
  3. Righetti, G. and Boschetti, E. (2013). Detailed Methodologies and Protocols. In Low-Abundance Proteome Discovery. Recovered from sciencedirect.com.
  4. Kirk-Othmer (1994). Encyclopedia of Chemical Technology. Fourth Edition. John Wiley & Sons.
  5. (2016). Wheat and Flour Testing. In Wheat Flour. Recovered from sciencedirect.com.
  6. Franz-Montan, M. et al. (2017). Nanostructured systems for transbuccal drug delivery. In Nanostructures for Oral Medicine. Recovered from sciencedirect.

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