Denatonium benzoate is the most-bitter tasting chemical compound known to man. Used as an aversive agent to prevent accidental ingestion, the bittering agent is added to many cleaning and health and beauty products, and can be found in everything from anti-freeze to anti-nail biting solutions. Denatonium benzoate typically comes as salts, but is also available as a solution.
Denatonium benzoate was reportedly discovered by accident in 1958. According to Chemistry World, Scottish researchers at Edinburgh pharmaceutical company MacFarlan Smith discovered the incredible bitterness of denatonium benzoate while researching dental aesthetic, lignocaine.
The compound is now traded under the name Bitrex® – a blend of the words ‘bitter’ and ‘rex’ (Latin for king). Originally, it was used to prevent pigs from eating their own tails, and those of other pigs.
Denatonium has the chemical identification number (CID) 19518 in PubChem’s chemical database. The compound weighs 446.58116 g/mol and has a molecular formula of C28 H3 4N 2O3.
The compound is made up of a salt with an inert anion, such as benzoate or saccharide. Similar to lidocaine in structure, it is closely related to benzocaine. As well as being colourless and odourless, Denatonium is non-reactive, so can be added to a base compound without affecting its primary use.
How it functions
Human taste-buds can detect five main types of flavour: sweetness, sourness, saltiness, savouriness and bitterness. Of these, bitter-tasting foods are experienced most intensely (humans have evolved to associate bitter-tasting things with poison).
How intensely people respond to bitter flavours depends on their genetic makeup. The TAS2R38 gene holds the key to how much an individual is able to detect bitter flavours, such as quinine found in tonic water.
Human taste-buds can identify the existence of quinine at a concentration of 0.008 moles per cubic meter. In contrast, humans can detect the extreme bitterness of denatonium benzoate even when highly diluted, at a concentration of just 0.000008 moles per cubic meter.
In Europe and some states of America, the addition of denatonium benzoate is required in automotive products, such as anti-freeze and windshield washer fluids. Many everyday household items, such as window cleaners, disinfectants and washing powder, contain an amount of denatonium benzoate to discourage accidental swallowing.
The compound is added to many poisonous substances that children may come into contact with. For example, it can be used as a coating agent on children’s toys and is added to various pesticides, plant food sticks and rat poisons to discourage consumption.
Today, denatonium benzoate is most widely used to denature ethanol. The bittering agent makes ethanol taste highly unpleasant – to discourage recreational consumption, and thus make it exempt from taxes and sales restrictions that usually apply to alcohol.
Denatonium benzoate has several applications in the agricultural industry, helping to discourage cannibalism in pigs and prevent bovine mastitis. The compound is also used to cover outdoor cables and wires to stop rats nibbling on them and makes an excellent repellent when applied to tender shoots and branches, helping to prevent animals from chewing and damaging property.