quaternary ammonium compound

Quaternary ammonium cation. Any or all of the R groups may be the same or different alkyl groups. Also, any of the R groups may be connected.

Quaternary ammonium cations, also known as quats, are positively charged polyatomic ions of the structure NR₄⁺ with R being alkyl groups. 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 cations are synthesized by complete alkylation of ammonia or other amines. For possible synthesis route, see amines.

Quaternary ammonium salts or quaternary ammonium compounds (called quaternary amines in oilfield parlance) are salts of quaternary ammonium cations with an anion. They are used as disinfectants, surfactants, fabric softeners, and as antistatic agents (e.g. in shampoo). In liquid fabric softeners, the chloride salts are often used. In dryer anticling strips, the sulfate salts are often used. This is also a common ingredient in many spermicidal jellies.

In organic chemistry, quaternary ammonium salts are used as phase transfer catalysts for reactions involving immiscible solvent systems, such as the synthesis of dichlorocarbene with chloroform and sodium hydroxide.

Synthesis

The synthesis of this cation from ammonia is referred to as quaternization.

Through exhaustive methylation, or the Hofmann Elimination process, a quaternary ammonium iodide salt is formed. The alpha-carbon (relative to the nitrogen) is deprotonated once by a hydroxide anion from H₂O and the electrons form an alkene. Subsequently, the electrons from the carbon-nitrogen bond are pushed onto the nitrogen. This sets up a tertiary amine as the leaving group.^[1]

Large quaternary ammonium salts are typically obtained by alkylating tertiary amines. This process begins with a tertiary amine, to which is added a cationic alkyl group from an alkyl chloride. Typically one of the alkyl groups on the amine is larger than the rest.^[2] The equation for this is:

RN(CH₃)₂ + ClR → N(CH₃)₂R₂⁺ + Cl⁻

where R is the large alkyl group.

Antimicrobial use

Certain long alkyl chain quaternary ammonium compounds 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,^[3] quats act by disrupting the cell membrane and proteins. Quats kill just about everything except endospores, Mycobacterium tuberculosis, lipid-containing viruses, and Pseudomonas spp. (some Pseudomonas spp. can even grow in solutions of quats, subsisting on them).

In contrast to phenolics, quats are not very effective in the presence of organic compounds. Yet quats are very effective in combination with phenols. Quats are deactivated by soaps, other anionic detergents, and cotton fibers.^[4] Also, they are not recommended to be used in hard water. Effective levels are at 200 ppm.^[5] They are effective at temperatures up to 212ºF.^[6]

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

Health effects

If inhaled or in contact with the skin, quats may cause skin and respiratory irritation.^[7] They are proposed to be the responsible group for causing anaphylactic reactions to occur to neuromuscular blocking drugs during general anaesthesia in surgery.^[8]

References

See also

• Choline
• Carnitine
• 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
• Denatonium; the most bitter compound known
• Cetyl trimethylammonium bromide (CTAB), stearalkonium chloride; cationic surfactants commonly used in toiletries
• Cocamidopropyl betaine (CAPB), a very common Zwitterionic surfactant used ubiquitously in toiletries
• Tetra-n-butylammonium bromide and Aliquat 336; common phase transfer catalysts
• Polyquaternium; designations for quaternary ammonium-containing polymers used for personal care products
• Paraquat; an herbicide
• Quaternary ammonium muscle relaxants

External links

• Toxicities of quaternary ammonium