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Quaternary ammonium cation. The R groups may be the same or different alkyl 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. 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.

Contents

Synthesis

Quaternary ammonium compounds are prepared by alkylation of tertiary amines, in a process called quaternization.[1] Typically one of the alkyl groups on the amine is larger than the others.[2] 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.

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As antimicrobials

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,[3] 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. (some Pseudomonas spp. can even grow in solutions of quats, subsisting on them).

In contrast to phenolics, quaternary ammonium compounds are not very effective in the presence of organic compounds. Yet quats are very effective in combination with phenols. Quaternary ammonium compoundss are deactivated by soaps, other anionic detergents, and cotton fibers.[3] Also, they are not recommended for use in hard water. Effective levels are at 200 ppm.[4] They are effective at temperatures up to 212 ºF.

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. 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.

Health effects

Quaternary ammonium ions can cause skin and respiratory irritation.[5] They are thought to be the chemical group responsible anaphylactic reactions that occur with use of neuromuscular blocking drugs during general anaesthesia in surgery.[6]

References

  1. ^ Smith, Michael B.; March, Jerry (2001), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (5th ed.), New York: Wiley-Interscience, ISBN 0-471-58589-0 
  2. ^ Kosswig, K. “Surfactants” in Ullmann’s Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a25_747.
  3. ^ a b Specific Antimicrobials, outline of lecture by Stephen T. Abedon, Ohio State U., URL accessed Dec 2008.
  4. ^ The Use of Disinfectants In the Swine Industry, Mark G. Ladd, North Carolina State Univ., URL accessed Dec 2008.
  5. ^ http://www.ehjournal.net/content/pdf/1476-069x-8-11.pdf
  6. ^ Harper, N. J. et al (2009): "Suspected anaphylactic reactions associated with anaesthesia", Anaesthesia, 64(2):199-211

See also

External links


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