Polyquaternium and Applications

Polyquaternium is an international cosmetic ingredient nomenclature that refers to several polycationic polymers used in the personal care industry.Polyquaternium is a neologism used to emphasize the presence of quaternary ammonium centers in polymers. INCI has approved at least 40 different polymer names as polyquaternium.The different polymers are distinguished by the numerical value following the word "polyquaternium".Polyquaternium-5, polyquaternium-7, and polyquaternium-47 are three examples, each of which is a chemically distinct polymer.These numbers are assigned in the order in which they were registered, not because of their chemical structure.Polyquaterniums are especially useful in conditioners, shampoos, mousses, hair sprays, hair dyes, personal lubricants and contact lens solutions.Because they are positively charged, they can neutralize the negative charge of most shampoos and hair proteins and help smooth hair.Their positive charge also ionically bonds them to hair and skin. some have antimicrobial properties.

Quaternary ammonium cation: 

In chemistry, quaternary ammonium cations, also known as quaternary ammonium salts, are positively charged polyatomic ions with the structure [NR4]+, where R is an alkyl, aryl or organic group.Unlike ammonium ions (NH+4) and primary, secondary or tertiary ammonium cations, quaternary ammonium cations are permanently charged independent of the pH of their solution.Quaternary ammonium salts or quaternary ammonium compounds (quats in oilfield terminology) are salts of quaternary ammonium cations. Polyquats are a variety of engineered polymer forms that provide multiple quaternary ammonium molecules within a larger molecule.Quaternary ammonium compounds are used in consumer applications, including as antimicrobials (such as detergents and disinfectants), fabric softeners and hair conditioners.As an antimicrobial agent, 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 safe for fabrics.

Synthesis

Quaternary ammonium compounds are prepared by alkylation of tertiary amines.The industrial production of commercial quaternary ammonium salts usually involves the hydrogenation of fatty nitriles, which produces primary or secondary amines.These amines were then treated with methyl chloride.The quaternization of alkylamines with alkyl halides is well documented.In the older literature, this was often referred to as the Menshutkin reaction, but modern scientists often refer to it simply as the quaternization reaction.This reaction can be used to generate compounds with alkyl chains of unequal length; for example, when making cationic surfactants, one of the alkyl groups on an amine is often longer than the other.A typical synthesis is the synthesis of benzalkonium chloride from long chain alkyl dimethylamine 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 antistatic agents (eg in shampoos).In liquid fabric softeners, chloride salts are often used.In dryer release strips sulfates are often used.Older aluminum electrolytic capacitors and spermicidal jellies also contain quaternary ammonium salts.Quaternary ammonium compounds are also used in contraceptive preparations, veterinary products, diagnostic tests, vaccine production and nasal preparations.Some scientists have expressed concern about how little is known about the safety of quaternary ammonium disinfectants.As of August 2020, half of the disinfectants recommended by the U.S.Environmental Protection Agency to be effective against COVID-19 contain one of these quaternary ammonium salts, and they often contain the quaternary ammonium salt as the only ingredient.Salmonella and E. coli O157:H7 exposed to quaternary ammonium salts have developed cross-resistance to antibiotics.A concern is the potential impact of the increased use of quaternary ammonium compounds associated with the COVID-19 pandemic on antibiotic resistance in larger microbial communities in natural and engineered settings.

Medicines

Quaternary ammonium compounds have antimicrobial activity.Quaternary ammonium compounds, especially those containing long alkyl chains, are used as antimicrobials and disinfectants.Examples are benzalkonium chloride, benzethonium chloride, methylbenzethonium chloride, cetamate Ammonium Bromide, Didecyldimethylammonium Chloride, and Domiphene Bromide.Also beneficial to fungi, amoebas, and enveloped viruses such as SARS-CoV-2.Most quaternary ammonium compounds are thought to work by disrupting cell membranes or viral envelopes.Some QACs, such as dequalinium and similar double QACs.Quats are lethal to a wide range of organisms except endospores and non-enveloped viruses, none of which have an attackable membrane coating. Endospores can be tackled by adding chemicals that force them to germinate.They are less effective against Gram-negative bacteria, mycobacteria, and bacteria in biofilms because they have additional layers that need to be penetrated or disrupted. Some bacteria such as MRSA have acquired the resistance genes qacA/B and qacC/D, which pump cations out of the cell.