Denatonium Benzoate
Denatonium benzoate (de-an-TOE-nee-um BEN-zoh-ate) is generally regarded as having the most bitter taste of any compound known to science. It is sold under the trade name of Bitrex. Although denatonium benzoate has a powerful taste, it is colorless and odorless. The taste is so strong, however, that most people cannot tolerate a concentration of more than 30 parts per million of denatonium benzoate. Solutions of denatonium benzoate in alcohol or water are very stable and retain their bitter taste for many years. Exposure to light does not lessen the compound’s bitter taste.
Denatonium benzoate compound was discovered in 1958 by a scientist named W. Barnes, who was working for the chemical firm of T. & H. Smith, in Edinburgh, Scotland. Barnes was interested in developing a new anesthetic, more powerful than those already available to physicians. He
decided to focus his research on lidocaine, a very popular anesthetic, and compounds chemically related to it. In one line of his experiments, Barnes added a single benzoyl group (benzoic acid with a hydrogen removed: C6H5COO) to a nitrogen atom in lidocaine. The resulting compound was
denatonium benzoate. Although the compound had little effectiveness as an anesthetic, Barnes noted that it had a peculiar odor and taste. The Smith company decided to exploit this unusual property of denatonium benzoate, and obtained a patent for it under the name of Bitrex. Today, the primary manufacturer of Britex in the world is the Macfarlan Smith corporation of Edinburgh.
The process by which denatonium benzoate is made is a proprietary secret of the Macfarlan Smith corporation. A proprietary secret is a method of making a product for which a company holds a patent and the details of which it does not disclose to the general public.
One of the first and most important uses of denatonium benzoate was as an additive to methanol (methyl alcohol; wood alcohol). Although ethanol (ethyl alcohol; grain alcohol) has some harmful effects on humans, especially if taken in excess, it is relatively safe to drink in beer, wine, and other alcoholic drinks. By contrast, methanol is highly toxic. Anyone who accidentally or intentionally consumes methanol is likely to experience serious health effects, including death. By adding a small amount of denatonium benzoate to methanol, consumers are discouraged—and usually prevented—from drinking the substance.
Denatonium benzoate has many other applications. For example, it can be used in a dilute solution to brush on the fingernails of people who are compulsive fingernail-biters. Some parents use a similar solution on the thumbs of children who suck their thumbs more than they should. Denatonium benzoate is also used as an animal repellent. Products containing denatonium benzoate can be sprayed on trees, brushes, crops, and other material to prevent deer from grazing on those products. One of the product’s first applications was as a treatment on pig’s tails to prevent pigs from biting each other. The coatings on electric cables are sometimes
impregnated with a denatonium benzoate solution to discourage rats from chewing on them.
Some of the other applications in which denatonium benzoate has been used include the following:
• In liquid laundry detergents;
• In fabric conditioners;
• In toilet cleaners;
• In disinfectants;
• In household antiseptics;
• In kitchen, bathroom, and floor cleaners;
• In paint products and paint brush cleaners;
• In personal care products, including bath foam, soaps, perfume and after shave lotions, nail polish remover,
shampoo, and shower gel;
• In pesticides, such as insecticides, rodenticides, slug
bait, and ant bait;
• In herbicides; and
• In a wide variety of automotive care products, such as
antifreezes, coolants, and car cleaning materials.
In all of these cases, the purpose of adding denatonium benzoate is to change the taste of the product just enough to prevent someone, especially children, from eating a substance that could cause them harm.
Despite its bitter taste, denatonium benzoate appears to pose little or no hazard to human health. Exposure to the pure compound may cause respiratory discomfort, but only people working with the substance directly are likely to encounter this problem.
