Quaternary ammonium cation

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

In organic chemistry, quaternary ammonium cations, also known as quats, are positively-charged polyatomic ions of the structure [NR4]+, where R is an alkyl group, an aryl group [1] or organyl group. Unlike the ammonium ion (NH+4) 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. Polyquats are a variety of engineered polymer forms which provide multiple quat molecules within a larger molecule.

Contents

Quats are used in consumer applications including as antimicrobials (such as detergents and disinfectants), fabric softeners, and hair conditioners. As an antimicrobial, they are able to inactivate enveloped viruses (such as SARS-CoV-2). Quats tend to be gentler on surfaces than bleach-based disinfectants, and are generally fabric-safe. [2]

"Top" view of Bu4N as determined by X-ray crystallography. OBINIXBu4N1.png
"Top" view of Bu4N as determined by X-ray crystallography.
"Side" view of Bu4N as determined by X-ray crystallography. OBINIXBu4N2.png
"Side" view of Bu4N as determined by X-ray crystallography.

Synthesis

Quaternary ammonium compounds are prepared by the alkylation of tertiary amine. Industrial production of commodity quat salts usually involves hydrogenation of fatty nitriles, which can generate primary or secondary amines. These amines are then treated with methyl chloride. [4]

The quaternization of alkyl amines by alkyl halides is widely documented. [5] In older literature this is often called a Menshutkin reaction, however modern chemists usually refer to it simply as quaternization. [6] The reaction can be used to produce a compound with unequal alkyl chain lengths; for example when making cationic surfactants one of the alkyl groups on the amine is typically longer than the others. [7] A typical synthesis is for benzalkonium chloride from a long-chain alkyldimethylamine and benzyl chloride:

Reactions

Quaternary ammonium cations are unreactive toward even strong electrophiles, oxidants, and acids. They also are stable toward most nucleophiles. The latter is indicated by the stability of the hydroxide salts such as tetramethylammonium hydroxide and tetrabutylammonium hydroxide even at elevated temperatures. The halflife of Me4NOH in 6M NaOH at 160 °C is >61 h. [8]

Because of their resilience, many unusual anions have been isolated as the quaternary ammonium salts. Examples include tetramethylammonium pentafluoroxenate, containing the highly reactive pentafluoroxenate (XeF−
5) ion. Permanganate can be solubilized in organic solvents, when deployed as its NBu +
4 salt. [9] [10]

With exceptionally strong bases, quat cations degrade. They undergo Sommelet–Hauser rearrangement [11] and Stevens rearrangement, [12] as well as dealkylation under harsh conditions or in presence of strong nucleophiles, like thiolates. Quaternary ammonium cations containing N−C−C−H units can also undergo the Hofmann elimination and Emde degradation.

Benzalkonium chloride is a common type of quat salt used as a biocide, a cationic surfactant, and as a phase transfer agent. ADBACs are a mixture of alkylbenzyldimethylammonium chlorides, in which the alkyl group has various even-numbered alkyl chain lengths. Benzalkonium chloride Structure V.1.svg
Benzalkonium chloride is a common type of quat salt used as a biocide, a cationic surfactant, and as a phase transfer agent. ADBACs are a mixture of alkylbenzyldimethylammonium chlorides, in which the alkyl group has various even-numbered alkyl chain lengths.

Examples

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. Older aluminium electrolytic capacitors and spermicidal jellies also contain quaternary ammonium salts. Quats are also used in contraception formulations, veterinary products, diagnostic testing, vaccine production, and nasal formulations. [14]

Concerns have been raised about the level of understanding of safety profile of quat disinfectants on people. As of August 2020, half of disinfectants the United States Environmental Protection Agency suggested as effective against COVID-19 contained one of the quats, and often a quat as the sole ingredient. [15] Salmonella and E. coli O157:H7 exposed to quats have developed cross resistance to antibiotics. A subject of concern is the potential effect of increased use of quats related to COVID-19 pandemic on antibiotic resistance in a larger microbial community in nature and engineered environment. [16]

Medicines

Buscopan is one of many spasmolytics (anti-spasm drugs) that feature the quaternary ammonium functional group. Butylscopolamine skeletal.svg
Buscopan is one of many spasmo­lytics (anti-spasm drugs) that feature the quaternary ammonium functional group.

Quaternary ammonium compounds have antimicrobial activity. [18] 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, amoebas, and enveloped viruses (such as SARS-CoV-2), [19] [20] most quaternary ammonium compounds are believed to act by disrupting the cell membrane or viral envelope. [21] (Some QACs, such as dequalinium and similar bis-QACs, show evidence of a different mode of action.) [22]

Quaternary ammonium compounds are lethal to a wide variety of organisms except endospores and non-enveloped viruses, both having no accessible membrane coat to attack. It is possible to solve the endospore problem by adding chemicals which force them to germinate. [23] [24] They have reduced efficacy against gram-negative bacteria, mycobacteria, and bacteria in biofilms due to them having additional layers that need to be penetrated or disrupted. Some bacteria such as MRSA have acquired resistance genes, qacA/B and qacC/D, that pump the cation out of the cell. [22]

Phase transfer catalysts

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

Anion exchange resins, in the form of beads, contain quaternary ammonium ions bound to a polymer. Ion exchange resin beads.jpg
Anion exchange resins, in the form of beads, contain quaternary ammonium ions bound to a polymer.

Fabric softeners and hair conditioners

In the 1950s, distearyldimethylammonium chloride (DHTDMAC), was introduced as a fabric softener. This compound was discontinued because the cation biodegrades too slowly. Contemporary fabric softeners are based on salts of quaternary ammonium cations where the fatty acid is linked to the quaternary center via ester linkages; these are commonly referred to as betaine-esters or ester-quats and are susceptible to degradation, e.g., by hydrolysis. [26] Characteristically, the cations contain one or two long alkyl chains derived from fatty acids linked to an ethoxylated ammonium salt. [27] Other cationic compounds can be derived from imidazolium, guanidinium, substituted amine salts, or quaternary alkoxy ammonium salts. [28]

The antistatic qualities that make quaternary ammonium salts useful as fabric softeners also make them useful in hair conditioners and shampoos. [29] The idea was pioneered by Henkel with a 1984 patent. [30] Examples include cetrimonium chloride and behentrimonium chloride. [31]

Plant growth retardants

Cycocel (chlormequat chloride) reduces plant height by inhibiting the production of gibberellins, the primary plant hormones responsible for cell elongation. Therefore, their effects are primarily on stem, petiole, and flower stalk tissues. Lesser effects are seen in reductions of leaf expansion, resulting in thicker leaves with darker green color. [32]

Natural occurrence

Several quaternary ammonium derivatives exist in nature. [33] Prominent examples include glycine betaine, choline, carnitine. butyrobetaine, homarine, and trigonelline. Glycine betaine, an osmolyte, stabilizes osmotic pressure in cells. [34]

Glycine betaine is a naturally occurring quaternary ammonium cation. Its degradation product, trimethylamine, is responsible for the odor of spoiled fish. Betain2.svg
Glycine betaine is a naturally occurring quaternary ammonium cation. Its degradation product, trimethylamine, is responsible for the odor of spoiled fish.
Choline is a quat compound. Choline-skeletal.svg
Choline is a quat compound.

Choline is a precursor for the neurotransmitter acetylcholine. Choline is also a constituent of lecithin, which is present in many plants and animal organs. [35] It is found in phospholipids. For example, phosphatidylcholines, a major component of biological membranes, are a member of the lecithin group of fatty substances in animal and plant tissues. [36]

Carnitine participates in the beta-oxidation of fatty acids.[ citation needed ]

1-Oleoyl-2-palmitoyl-phosphatidylcholine 1-Oleoyl-2-almitoyl-phosphatidylcholine Structural Formulae V.1.png
1-Oleoyl-2-palmitoyl-phosphatidylcholine

Health effects

Quaternary ammonium compounds can display a range of health effects, amongst which are mild skin and respiratory irritation [37] up to severe caustic burns on skin and the gastrointestinal wall (depending on concentration), gastrointestinal symptoms (e.g., nausea and vomiting), coma, convulsions, hypotension and death. [38]

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. [39] Quaternium-15 is the single most often found cause of allergic contact dermatitis of the hands (16.5% in 959 cases). [40]

Possible reproductive effects in laboratory animals

Quaternary ammonium-based disinfectants (Virex and Quatricide) were tentatively identified as the most probable cause of jumps in birth defects and fertility problems in caged lab mice. The quat ingredients in the disinfectants include alkyl dimethyl benzyl ammonium chloride (ADBAC) and didecyl dimethyl ammonium chloride (DDAC). [41] [42] A similar link was tentatively identified in nurses. [43] The studies contradict earlier toxicology data reviewed by the U.S. Environmental Protection Agency (U.S. EPA) and the EU Commission. [44]

Quantification

The quantification of quaternary ammonium compounds can be challenging. Some methods include precipitation of solid salts with tetraphenylborate. Another method, an Epton titration, involves partitioning between water-chloroform in the presence of an anionic dye. Individual cations are detectable by ESI-MS and NMR spectroscopy. [4]

See also

Related Research Articles

<span class="mw-page-title-main">Amine</span> Chemical compounds and groups containing nitrogen with a lone pair (:N)

In chemistry, amines are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines, trimethylamine, and aniline. Inorganic derivatives of ammonia are also called amines, such as monochloramine.

<span class="mw-page-title-main">Ammonium</span> Chemical compound

The ammonium cation is a positively charged polyatomic ion with the chemical formula NH+4 or [NH4]+. It is formed by the protonation of ammonia. Ammonium is also a general name for positively charged (protonated) substituted amines and quaternary ammonium cations, where one or more hydrogen atoms are replaced by organic or other groups.

<span class="mw-page-title-main">Surfactant</span> Substance that lowers the surface tension between a liquid and another material

Surfactants are chemical compounds that decrease the surface tension or interfacial tension between two liquids, a liquid and a gas, or a liquid and a solid. The word "surfactant" is a blend of surface-active agent, coined c. 1950. As they consist of a water-repellent and a water-attracting part, they enable water and oil to mix; they can form foam and facilitate the detachment of dirt.

<span class="mw-page-title-main">Benzalkonium chloride</span> Surfactant and antiseptic agent

Benzalkonium chloride, also known as alkyldimethylbenzylammonium chloride (ADBAC) and by the trade name Zephiran, is a type of cationic surfactant. It is an organic salt classified as a quaternary ammonium compound. ADBACs have three main categories of use: as a biocide, a cationic surfactant, and a phase transfer agent. ADBACs are a mixture of alkylbenzyldimethylammonium chlorides, in which the alkyl group has various even-numbered alkyl chain lengths.

<span class="mw-page-title-main">Zinc chloride</span> Chemical compound

Zinc chloride is the name of inorganic chemical compounds with the formula ZnCl2·nH2O, with x ranging from 0 to 4.5, forming hydrates. Zinc chloride, anhydrous and its hydrates are colorless or white crystalline solids, and are highly soluble in water. Five hydrates of zinc chloride are known, as well as four forms of anhydrous zinc chloride. This salt is hygroscopic and even deliquescent. Zinc chloride finds wide application in textile processing, metallurgical fluxes, and chemical synthesis. No mineral with this chemical composition is known aside from the very rare mineral simonkolleite, Zn5(OH)8Cl2·H2O.

<span class="mw-page-title-main">Phosphonium</span> Family of polyatomic cations containing phosphorus

In chemistry, the term phosphonium describes polyatomic cations with the chemical formula PR+
4. These cations have tetrahedral structures. The salts are generally colorless or take the color of the anions.

A fabric softener or fabric conditioner is a conditioner that is applied to laundry after it has been washed in a washing machine. A similar, more dilute preparation meant to be applied to dry fabric is known as a wrinkle releaser.

Triethylamine is the chemical compound with the formula N(CH2CH3)3, commonly abbreviated Et3N. It is also abbreviated TEA, yet this abbreviation must be used carefully to avoid confusion with triethanolamine or tetraethylammonium, for which TEA is also a common abbreviation. It is a colourless volatile liquid with a strong fishy odor reminiscent of ammonia. Like diisopropylethylamine (Hünig's base), triethylamine is commonly employed in organic synthesis, usually as a base.

<span class="mw-page-title-main">Counterion</span> Ion which negates another oppositely-charged ion in an ionic molecule

In chemistry, a counterion is the ion that accompanies an ionic species in order to maintain electric neutrality. In table salt the sodium ion is the counterion for the chloride ion and vice versa.

<span class="mw-page-title-main">Dimethyl sulfate</span> Chemical compound

Dimethyl sulfate (DMS) is a chemical compound with formula (CH3O)2SO2. As the diester of methanol and sulfuric acid, its formula is often written as (CH3)2SO4 or Me2SO4, where CH3 or Me is methyl. Me2SO4 is mainly used as a methylating agent in organic synthesis.

<span class="mw-page-title-main">Diazonium compound</span> Group of organonitrogen compounds

Diazonium compounds or diazonium salts are a group of organic compounds sharing a common functional group [R−N+≡N]X− where R can be any organic group, such as an alkyl or an aryl, and X is an inorganic or organic anion, such as a halide.

<span class="mw-page-title-main">Iminium</span> Polyatomic ion of the form >C=N< and charge +1

In organic chemistry, an iminium cation is a polyatomic ion with the general structure [R1R2C=NR3R4]+. They are common in synthetic chemistry and biology.

In chemistry, a phase-transfer catalyst or PTC is a catalyst that facilitates the transition of a reactant from one phase into another phase where reaction occurs. Phase-transfer catalysis is a special form of catalysis and can act through homogeneous catalysis or heterogeneous catalysis methods depending on the catalyst used. Ionic reactants are often soluble in an aqueous phase but insoluble in an organic phase in the absence of the phase-transfer catalyst. The catalyst functions like a detergent for solubilizing the salts into the organic phase. Phase-transfer catalysis refers to the acceleration of the reaction upon the addition of the phase-transfer catalyst.

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<span class="mw-page-title-main">Dequalinium</span> Chemical compound

Dequalinium is a quaternary ammonium cation and bolaamphiphile commonly available as the dichloride salt. It is useful as an antiseptic and disinfectant. The bromide, iodide, acetate, and undecenoate salts are known as well. Dequalinium chloride is the active ingredient of several medications.

<span class="mw-page-title-main">Tetramethylammonium chloride</span> Chemical compound

Tetramethylammonium chloride is one of the simplest quaternary ammonium salts, with four methyl groups tetrahedrally attached to the central N. The chemical formula (CH3)4N+Cl− is often abbreviated further as Me4N+Cl−. It is a hygroscopic colourless solid that is soluble in water and polar organic solvents. Tetramethylammonium chloride is a major industrial chemical, being used widely as a chemical reagent and also as a low-residue bactericide in such processes as hydrofracking. In the laboratory, it has fewer synthetic chemical applications than quaternary ammonium salts containing longer N-alkyl substituents, which are used extensively as phase-transfer catalysts.

Polymers with the ability to kill or inhibit the growth of microorganisms such as bacteria, fungi, or viruses are classified as antimicrobial agents. This class of polymers consists of natural polymers with inherent antimicrobial activity and polymers modified to exhibit antimicrobial activity. Polymers are generally nonvolatile, chemically stable, and can be chemically and physically modified to display desired characteristics and antimicrobial activity. Antimicrobial polymers are a prime candidate for use in the food industry to prevent bacterial contamination and in water sanitation to inhibit the growth of microorganisms in drinking water.

<span class="mw-page-title-main">Quaternary compound</span> Chemical compound made of four elements

In chemistry, a quaternary compound is a compound consisting of exactly four chemical elements.

<span class="mw-page-title-main">Tetramethylammonium</span> Polyatomic ion (N(CH₃)₄, charge +1)

Tetramethylammonium (TMA) is the simplest quaternary ammonium cation. It has the chemical formula [Me4N]+ and consists of four methyl groups attached to a central nitrogen atom. The cation is isoelectronic with neopentane. It is positively-charged and can only be isolated in association with a counter-ion. Common salts include tetramethylammonium chloride and tetramethylammonium hydroxide. Tetramethylammonium salts are used in chemical synthesis and in pharmacological research. It confers no color to its salts.

In chemistry, a fatty amine is loosely defined as any amine possessing a mostly linear hydrocarbon chain of eight or more carbon atoms. They are typically prepared from the more abundant fatty acids, with vegetable or seed-oils being the ultimate starting material. As such they are often mixtures of chain lengths, ranging up to about C22. They can be classified as oleochemicals. Commercially important members include coco amine, oleylamine, tallow amine, and soya amine. These compounds and their derivatives are used as fabric softeners, froth flotation agents, corrosion inhibitors, lubricants and friction modifiers. They are also the basis for a variety of cosmetic formulations.

References

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