Denatonium
Extremely bitter chemical compound
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Denatonium was discovered in 1958 during research on local anesthetics by T. & H. Smith of Edinburgh, Scotland, and registered under the trademark Bitrex.
Dilutions of as little as 10 ppm are unbearably bitter to most people. Denatonium salts are usually colorless and odorless solids, but are often traded as solutions. They are used as aversive agents (bitterants) to prevent accidental ingestion. Denatonium is used in denatured alcohol, antifreeze, preventive nail biting preparations, respirator mask fit-testing, animal repellents, liquid soaps, shampoos, and Nintendo Switch game cards to prevent accidental swallowing or choking by children. It is not known to pose any long-term health risks.
The name denatonium reflects the substance's primary use as a denaturant and its chemical nature as a cation, hence -onium as a Neo-Latin suffix.
Structure, synthesis, and physical properties
Denatonium is a quaternary ammonium cation. It is composed as a salt with any of several anions, such as benzoate or saccharinate. It can be obtained by the quaternization of lidocaine, a popular anesthetic, with benzyl chloride or a similar reagent. To obtain other salts, like the benzoate, the formed denatonium chloride is subjected to an anion exchange reaction with sodium benzoate, or first sodium hydroxide to make denatonium hydroxide followed by neutralization with benzoic acid. Other similar compounds are procaine and benzocaine.
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Biochemistry
Denatonium in humans is recognized by eight distinct bitter taste receptors: TAS2R4, TAS2R8, TAS2R10, TAS2R39, TAS2R43, TAS2R16, TAS2R46, and TAS2R47, being by far the most sensitive to the compound.
Denatonium can act as a bronchodilator by activating bitter taste receptors in the airway smooth muscle.
In chickens, over-activation of the bitter taste receptors by denatonium (added to food) causes apoptosis of the jejunal epithelial cells.
Detection by animals
Animals are known to have different sensitivities to the effects of denatonium.
Humans are able to detect denatonium at much lower concentrations than rodents.
Dog taste receptors have much lower sensitivity to denatonium in vitro compared to human ones.
Denatonium is recognized not only by human bitter taste receptors, but also by taste receptors from cartilaginous fishes (sharks and rays) in vitro, which diverged from humans about 462 million years ago and belongs to a different branch of the jawed vertebrates.
Applications
The bitterness of the compound guides most applications of denatonium. Denatonium benzoate is used to denature ethanol so that it cannot be consumed recreationally, exempting it from alcoholic beverage taxes and sales restrictions. One designation in particular, SD-40B, indicates that ethanol has been denatured using denatonium benzoate.
Denatonium is commonly included in placebos used in clinical trials to mimic the bitter taste of certain medications.
Denatonium benzoate is an ingredient in certain nail polishes and varnishes designed to discourage nail biting, as the bitter denatonium serves as an aversive.
Denatonium also discourages consumption of poisonous alcohols such as methanol and additives such as ethylene glycol. It is also added to many kinds of harmful liquids, including solvents (such as nail polish remover), paints, varnishes, toiletries and other personal care items, and various other household products. It is also added to less hazardous aerosol products (such as gas dusters) to discourage inhalant abuse of the volatile vapors.
In 1995, the U.S. state of Oregon required that denatonium benzoate be added to products containing sweet-tasting ethylene glycol and methanol such as antifreeze and windshield washer fluid to prevent poisonings of children and animals. In December 2012, U.S. manufacturers voluntarily agreed to add denatonium benzoate to antifreeze sold nationwide.
It is used in some animal repellents (especially for such large mammals as deer). It has been used to safeguard rat poisons from human consumption, as human taste is more sensitive to the compound.
Nintendo Switch and Nintendo Switch 2 game cartridges are coated in denatonium benzoate to prevent young children from consuming them, intentionally or not.
Lithium button cells, which can cause severe internal injuries if swallowed, are sometimes coated with denatonium benzoate to discourage small children from swallowing them.