Quaternary Ammonium Compounds
Quaternary ammonium cations, also known as quaternary ammonium salts, quaternary ammonium
compounds or "Quats", are salts of quaternary ammonium cations with an anion.
The quats are ammonium compounds in which four organic groups are linked to a nitrogen atom that
produces a positively charged ion (cation). In these quaternary ammonium compounds, the organic
radical is the cation, and chlorine is usually the anion.
Quats are positively charged ions of the structure NR4+ with R being alkyl groups. Unlike ammonium
NH3 itself and primary, secondary, or tertiary ammonium cations, the quaternary ammonium cations
are permanently charged, independent of the pH of their solution and they are stable with a long shelf
life. Quaternary ammonium cations are synthesized by complete alkylation of ammonia or other
Any or all of the R groups may be the same or different alkyl groups. Also, any of the R groups may be
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. The equation for this is:
The general formula of a quaternary ammonium compound (quat) is:
RN(CH3)2 + ClR N(CH3)2R2+ + Cl−
where R is the large alkyl group.
They are good penetrants and, thus, have value for porous surfaces. They are natural wetting agents
with built-in detergent properties and are referred to as synthetic surface-active agents. Thus, they can
be applied through foaming.
The majority of applications for quaternary ammonium compounds (Quats) are related to their very
strong affinity for surfaces, which makes them powerful surfactants. The quaternary ammonium
compounds adsorb on almost any surface resulting in the formation of a monolayer. As most surfaces,
including skin, mucosa and hair, are charged negatively, they attract the positively charged quaternary
General structure and examples of quaternary ammonium compounds (QACs)
The quaternary ammonium compounds contain a hydrophobic has an oily character and thus it repels
water. When absorbed on surfaces this oily group extends outwards from the surface as illustrated
The formation of this monolayer of oil and the neutralization of surfaces, as well as their good wetting
and adhesive properties, form the basis for the utilization of quaternary ammonium compounds
(Quats) in many different fields of application.
Certain long alkyl chain quaternary ammonium compounds are used as antimicrobials and
disinfectants. For a QAC to have a high antimicrobial activity, at least one of the R groups must have a
chain length in the range C8 to C18
The bactericidal action of quaternary compounds has been attributed to inactivation of energy-
producing enzymes, denaturation of proteins, and disruption of the cell membrane. These agents are
bacteriostatic, fungistatic, and sporistatic and also inhibit algae. They are bactericidal for gram-positive
bacteria and moderately active against gram-negative bacteria (such as E. coli, P. aeruginosa and S.
Typhimurium). Lipophilic viruses (such as herpes simplex, vaccinia, influenza and adenoviruses) are
inactivated. They are not tuberculocidal or sporicidal, and they do not inactivate hydrophilic viruses.
The quats act against microorganisms differently than do chlorine and iodine compounds. They form a
residual antimicrobial film after being applied to surfaces. Although the film is bacteriostatic, these
compounds are selective in the destruction of various microorganisms. The quats do not kill bacterial
spores but can inhibit their growth. Quaternary ammonium compounds are more stable in the
presence of organic matter than are chlorine and iodine sanitizers, although their bactericidal
effectiveness is impaired by the presence of organic matter. Stainless steel and polycarbonate are
more readily sanitized by the quats than are either the abraded polycarbonate or mineral resin
Quats are nonconcorrosive and nonirritating to the skin, and have no taste or odor in use dilutions.
The concentration of quat solutions is easy to measure. The quats are low in toxicity and can be
neutralized or made ineffective by using any anionic detergent. Quat sanitizers are generally more
effective in the alkaline pH range. However the effect of pH may vary with bacterial species, with
gram-negative bacteria being more susceptible to quats in the acid pH range and gram-positive
microbes in the alkaline range.
They are inactivated by anionic detergents (soaps), by many nonionic detergents, and by calcium,
magnesium, ferric, and aluminum ions. Also, they are not recommended to be used in hard water.
Effective levels are at 200 ppm.
The quaternary ammonium compounds should not be combined with cleaning compounds for
subsequent cleaning and sanitizing because they are inactivated through detergent ingredients such
as anionic wetting agents. However, an increase in alkalinity through formulation with compatible
detergents may enhance the bactericidal activity of the quats.
The quats have the following major advantages:
• Colorless and odorless
• Stable against reaction with organic matter
• Resistant to corrosion of metals and not affected by hard water
• Stable against temperature fluctuation with a long shelf life
• Nonirritating to the skin
• Effective at a high pH with detergency and soil penetration ability
• Effective against mold growth
• Good surfactants that provide a residual antimicrobial film