quaternary ammonium compound

Quaternary ammonium cation. The R groups may be the same or different alkyl or aryl groups. Also, the R groups may be connected.

Quaternary ammonium cations, also known as quats, are positively charged polyatomic ions of the structure NR₄⁺, R being an alkyl group or an aryl group.^[1] Unlike the ammonium ion (NH₄⁺) and the primary, secondary, or tertiary ammonium cations, the quaternary ammonium cations are permanently charged, independent of the pH of their solution. Quaternary ammonium salts or quaternary ammonium compounds (called quaternary amines in oilfield parlance) are salts of quaternary ammonium cations with an anion.

Synthesis

Quaternary ammonium compounds are prepared by alkylation of tertiary amines, in a process called quaternization.^[2] Typically one of the alkyl groups on the amine is larger than the others.^[3] A typical synthesis is for benzalkonium chloride from a long-chain alkyldimethylamine and benzyl chloride:

CH₃(CH₂)_nN(CH₃)₂ + ClCH₂C₆H₅ → CH₃(CH₂)_nN(CH₃)₂CH₂C₆H₅]⁺Cl^-

Applications

Quaternary ammonium salts are used as disinfectants, surfactants, fabric softeners, and as antistatic agents (e.g. in shampoos). In liquid fabric softeners, the chloride salts are often used. In dryer anticling strips, the sulfate salts are often used. Spermicidal jellies also contain quaternary ammonium salts.

As antimicrobials

Quaternary ammonium compounds have also been shown to have antimicrobial activity. ^[4] Certain quaternary ammonium compounds, especially those containing long alkyl chains, are used as antimicrobials and disinfectants. Examples are benzalkonium chloride, benzethonium chloride, methylbenzethonium chloride, cetalkonium chloride, cetylpyridinium chloride, cetrimonium, cetrimide, dofanium chloride, tetraethylammonium bromide, didecyldimethylammonium chloride and domiphen bromide. Also good against fungi, amoeba, and enveloped viruses,^[5] quats act by disrupting the cell membrane. Quaternary ammonium compounds are lethal to a wide variety of organisms except endospores, Mycobacterium tuberculosis, non-enveloped viruses, and Pseudomonas spp.

In contrast to phenolics, quaternary ammonium compounds are not very effective in the presence of organic compounds. Yet, they are very effective in combination with phenols. Quaternary ammonium compounds are deactivated by soaps, other anionic detergents, and cotton fibers.^[5] Also, they are not recommended for use in hard water. Effective levels are at 200 ppm.^[6] They are effective at temperatures up to 212 °F (100 °C).

Along with sodium hypochlorite, quaternary ammonium salts are the primary chemicals used in foodservice industry as sanitizing agents.

As phase transfer catalysts

In organic synthesis, quaternary ammonium salts are employed as phase transfer catalysts (PTC). Such catalysts accelerate reactions between reagents dissolved in immiscible solvents. The highly reactive reagent dichlorocarbene is generated via PTC by reaction of chloroform and sodium hydroxide.

Osmolytes

Quaternary ammonium compounds are present in osmolytes, specifically glycine betaine, which stabilize osmotic pressure in cells.^[7]

Health effects

Quaternary ammonium compounds can display a range of health effects, amongst which are mild skin and respiratory irritation ^[8] up to severe caustic burns on skin and gastro-intestinal lining (depending on concentration), gastro-intestinal symptoms (e.g., nausea and vomiting), coma, convulsions, hypotension and death.^[9]

They are thought to be the chemical group responsible for anaphylactic reactions that occur with use of neuromuscular blocking drugs during general anaesthesia in surgery.^[10] Quaternium-15 is the single most often found cause of allergic contact dermatitis of the hands (16.5% in 959 cases)^[11]

See also

• Benzalkonium chloride, benzethonium chloride, methylbenzethonium chloride, cetalkonium chloride, cetylpyridinium chloride, cetrimonium, cetrimide, dofanium chloride, tetraethylammonium bromide, and domiphen bromide – antimicrobial ingredients found in various over-the-counter products
• Carnitine
• Cetyl trimethylammonium bromide (CTAB), stearalkonium chloride – cationic surfactants commonly used in toiletries
• Choline
• Cocamidopropyl betaine (CAPB), a common Zwitterionic surfactant used ubiquitously in toiletries
• Denatonium, the most bitter compound known
• Dimethyldioctadecylammonium chloride
• Paraquat, an herbicide
• Polyquaternium, designations for quaternary ammonium-containing polymers used for personal care products
• Quaternary ammonium muscle relaxants
• Tetra-n-butylammonium bromide and Aliquat 336, common phase transfer catalysts
• Tetramethylammonium chloride
• Tetramethylammonium hydroxide

References

External links

• Toxicities of quaternary ammonium