DENATONIUM BENZOATE

CAS NO: 3734-33-6
EC NO: 223-095-2

SYNONYMS:
DENATONIUM BENZOATE; 3734-33-6; Bitrex; Lidocaine benzyl benzoate; Anispray; Aversion; Gori; Denatonium (benzoate);Caswell No. 083BB; THS-839; UNII-M5BA6GAF1O; Denatonium benzoate anhydrous; WIN 16568; BENZYLDIETHYL; Denatonii benzoas [INN-Latin]; EINECS 223-095-2;Benzoate de denatonium [INN-French]; Benzoato de denatonio [INN-Spanish]; M5BA6GAF1O;Denatonium benzoate [USAN:INN:BAN];EPA Pesticide Chemical Code 009106; NSC 157658; Denatonium benzoate granules; N-Benzyl-2-((2,6-dimethylphenyl)amino)-N,N-diethyl-2-oxoethanaminium benzoate; MFCD00031578; Benzyldiethyl((2,6-xylylcarbamoyl)methyl)ammonium benzoate; Benzyldiethyl[(2,6-xylylcarbamoyl)methyl]ammonium benzoate; Benzoato de denatonio; Benzoate de denatonium; 2-[diethylbenzylamino]-N-(2,6-dimethylphenyl)acetamide, benzoic acid; Denatoniumbenzoate
Benzenemethanaminium, N-(2-((2,6-dimethylphenyl)amino)-2-oxoethyl)-N,N-diethyl-, benzoate (1:1); Benzenemethanaminium, N-[2-[(2,6-dimethylphenyl)amino]-2-oxoethyl]-N,N-diethyl-, benzoate (1:1) ; DENATONIUM BENZOATE; 3734-33-6; Bitrex; Denatonium (benzoate); Lidocaine benzyl benzoate; DENATONIUM BENZOATE; 3734-33-6; Bitrex; Denatonium (benzoate); Lidocaine benzyl benzoate; Anispray; Aversion; Gori; THS-839; Caswell No. 083BB; UNII-M5BA6GAF1O; Denatonium benzoate anhydrous; WIN 16568; Denatonii benzoas [INN-Latin]; EINECS 223-095-2; Benzoate de denatonium [INN-French]; Benzoato de denatonio [INN-Spanish]; M5BA6GAF1O; Denatonium benzoate [USAN:INN:BAN]; EPA Pesticide Chemical Code 009106; Anispray; Aversion; Gori; THS-839; Caswell No. 083BB; UNII-M5BA6GAF1O; Denatonium benzoate anhydrous; WIN 16568; Denatonii benzoas [INN-Latin]; EINECS 223-095-2; Benzoate de denatonium [INN-French]; Benzoato de denatonio [INN-Spanish]; M5BA6GAF1O; Denatonium benzoate [USAN:INN:BAN]; EPA Pesticide Chemical Code 009106; BENZOATE DE DÉNATONİUM;DENATONIUM BENZOATE; 3734-33-6; BİTREX; DENATONİUM (BENZOATE); LİDOCAİNE BENZYL BENZOATE; DENATONIUM BENZOATE; 3734-33-6; BİTREX; DENATONİUM (BENZOATE); LİDOCAİNE BENZYL BENZOATE; ANİSPRAY; AVERSİON; GORİ; THS-839; CASWELL NO. 083BB; UNII-M5BA6GAF1O; DENATONİUM BENZOATE ANHYDROUS; WIN 16568; DENATONİİ BENZOAS [INN-LATİN]; EINECS 223-095-2; BENZOATE DE DENATONİUM [INN-FRENCH]; BENZOATO DE DENATONİO [INN-SPANİSH]; M5BA6GAF1O; DENATONİUM BENZOATE [USAN:INN:BAN]; EPA PESTİCİDE CHEMİCAL CODE 009106; ANİSPRAY; AVERSİON; GORİ; THS-839; CASWELL NO. 083BB; UNII-M5BA6GAF1O; DENATONİUM BENZOATE ANHYDROUS; WIN 16568; DENATONİİ BENZOAS [INN-LATİN]; EINECS 223-095-2; BENZOATE DE DENATONİUM [INN-FRENCH]; BENZOATO DE DENATONİO [INN-SPANİSH]; M5BA6GAF1O; DENATONİUM BENZOATE [USAN:INN:BAN]; EPA PESTİCİDE CHEMİCAL CODE 009106; BENZOATE DE DÉNATONİUM; DENATONIUM BENZOATE; 3734-33-6; Bitrex; Denatonium (Benzoate); Lidocaine Benzyl Benzoate; DENATONIUM BENZOATE; 3734-33-6; Bitrex; Denatonium (Benzoate); Lidocaine Benzyl Benzoate; Anispray; Aversion; Gori; THS-839; Caswell No. 083BB; UNII-M5BA6GAF1O; Denatonium Benzoate Anhydrous; WIN 16568; Denatonii Benzoas [INN-Latin]; EINECS 223-095-2; Benzoate De Denatonium [INN-French]; Benzoato De Denatonio [INN-Spanish]; M5BA6GAF1O; Denatonium Benzoate [USAN:INN:BAN]; EPA Pesticide Chemical Code 009106; Anispray; Aversion; Gori; THS-839; Caswell No. 083BB; UNII-M5BA6GAF1O; Denatonium Benzoate Anhydrous; WIN 16568; Denatonii Benzoas [INN-Latin]; EINECS 223-095-2; Benzoate De Denatonium [INN-French]; Benzoato De Denatonio [INN-Spanish]; M5BA6GAF1O; Denatonium Benzoate [USAN:INN:BAN]; EPA Pesticide Chemical Code 009106; BENZOATE DE DÉNATONİUM; Benzoate de dénatonium; bıtrex; bitrex; BİTREX

DENATONIUM BENZOATE

Denatonium, usually available as denatonium benzoate (under trade names such as Denatrol, BITTERANT-b, BITTER+PLUS, Bitrex or Aversion) and as denatonium saccharide (BITTERANT-s), is the most bitter chemical compound known, with bitterness thresholds of 0.05 ppm for the benzoate and 0.01 ppm for the saccharide.[2] It was discovered in 1958 during research on local anesthetics by MacFarlan Smith of Edinburgh, Scotland, and registered under the trademark Bitrex.[3]
Dilutions of as little as 10 ppm are unbearably bitter to most humans. Denatonium salts are usually colorless and odorless solids but are often traded as solutions. They are used as aversive agents (bitterants) to prevent inappropriate ingestion. Denatonium is used in denatured alcohol,[4] antifreeze, nail biting preventions, respirator mask fit-testing, animal repellents, liquid soaps, and shampoos. It is not known to pose any long-term health risks.[2]
The name denatonium is a portmanteau word reflecting the substance's primary use as a denaturant and its chemical nature as a cation, whence the New Latin suffix -onium.
Structure and physical properties
Denatonium is a quaternary ammonium cation. It is a compound of a salt with an inert anion like benzoate or saccharide. The structure of denatonium is related to the local anesthetic lidocaine, differing only by the addition of a benzyl group to the amino nitrogen. Other similar compounds are procaine and benzocaine.[5]
One of the chemical names for the compound is lidocaine benzylbenzoate, although denatonium only denotes the quaternary ammonium cation species itself, and does not necessitate the benzoate counterion.
Biochemistry
Denatonium in humans is recognized by eight distinct bitter taste receptors: TAS2R4, TAS2R8, TAS2R10, TAS2R39, TAS2R43, TAS2R16, TAS2R46, TAS2R47, with TAS2R47 being by far the most sensitive to the compound.[6][7]
Denatonium can act as a bronchodilator by activating bitter taste receptors in the airway smooth muscle.[8]
Applications
The bitterness of the compound guides most applications of denatonium. Denatonium benzoate is used to denature ethanol so that it is not treated as an alcoholic beverage with respect to taxation and sales restrictions. One designation in particular, SD-40B, indicates that ethanol has been denatured using denatonium benzoate.
Denatonium is commonly included in placebo medications used in clinical trials to match the bitter taste of certain medications.[2]
Denatonium also discourages consumption of harmful alcohols like methanol, and additives like ethylene glycol. Denatonium is used in rubbing alcohol as an inactive ingredient. 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, special nail polish for preventing nail biting, 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.[9] In December 2012, U.S. manufacturers voluntarily agreed to add denatonium benzoate to antifreeze sold nationwide.[10]
Animals are known to have different sensitivities to the effects of denatonium. 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,[11] as humans are able to detect denatonium at much lower concentrations than rodents.[12]
The video game company Nintendo applies a coating containing denatonium benzoate to the game cards for their Nintendo Switch gaming console to deter children from ingesting them due to their small size.[13]

History of Denatonium Benzoate:
Discovery of denatonium benzoate:
Denatonium benzoate was accidentally discovered in 1958 by a Scottish pharmaceutical company by the name of MacFarlan Smith in Edinburgh5. This discovery came about during research to improve the anesthetic properties of lidocaine.

The laboratory was already extracting brucine (bitter compound) in order to denature alcohols, but denatonium benzoate being more bitter and devoid of toxicity, the latter quickly became the ideal denaturant. It is also from the name of its use of denaturant that this compound derives its name, the trade name being linked to the English word bitter meaning bitter 5. Another of the first applications of Bitrex as an aversion agent was a cream designed to prevent pigs from eating their neighbor's tail5.

Legislation of denatonium benzoate:
As early as 1960, denatonium benzoate, under the brand name Bitrex, was authorized in the United States and the United Kingdom in perfumes, perfumery, cosmetics and other industrial uses. Since then, it has been recognized as a denaturing agent and aversion agent in more than 40 countries5.

In 1993, it was authorized in the European Union as a denaturant of alcohol with a view to exemption from excise duty6.

In 1995, French law, by decree, made it compulsory for manufacturers to add denatonium benzoate or another repellant to antifreeze and heat transfer fluids containing monoethyleneglycol7.

Since 1999, it has been compulsory to use it in certain pesticides5.

Structure and properties of denatonium benzoate:
Structure of Denatonium Benzoate:
Denatonium benzoate is a synthetic salt comprising an anion (the benzoate) associated with a cation (a quaternary ammonium). The cation has a structure similar to the local anesthetic, lidocaine, from which it differs only by the addition of a benzyl group on the tertiary amine.

Denatonium can be combined with other anions in salt form such as saccharinate ion to form denatonium8 saccharinate or chloride ion to form denatonium9 chloride.

Physicochemical properties
Denatonium benzoate is soluble in water1, ethanol, methanol, butanol, isopropanol and chloroform4.

The melting point of denatonium benzoate is 168 ° C3.

Sensory property
Denatonium benzoate has a detection limit of 10 ppb and a recognition threshold of bitterness of 0.05 ppm, which makes it as bitter as quassine, the most bitter known natural compound with a recognition threshold of bitterness of 0.06 ppm10.

The nature of the anion with which the denatonium salt is associated modifies the concentration of the bitterness recognition threshold. Thus, for denatonium saccharinate and denatonium chloride, the latter is 0.01 ppm and 0.1 ppm respectively9.

Denatonium benzoate is really very bitter around 10 ppm11.

Dermatology of denatonium benzoate:
Denatonium benzoate is considered harmless to the skin in cosmetic products at the doses used (0.0006%) 11.

Use of Denatonium Benzoate:
Denatonium benzoate is mainly used for its bitter taste as a denaturant, repellant, aversion agent, or bitter.

In the European Union, denatonium benzoate is used as a denaturant in alcohols, mainly for exemption from excise duty6.

It is also used to discourage the consumption of toxic alcohols such as methanol and ethylene glycol. In France, manufacturers add a minimum of 20 ppm of denatonium benzoate in products containing ethylene glycol, this concerns antifreeze, heat transfer fluids and windshield washer products7.

Denatonium benzoate is recommended in the fight for the protection of children and the reduction of household accidents due to the absorption of household products (detergents, laundry products, softeners), cosmetics, perfumes and bath products (shampoo). The intense bitterness of denatonium benzoate forces a child to spit out the product immediately after putting it in the mouth12.

Denatonium benzoate is used as an additive in products for the control of rodents (vole, nutria, rat, mouse) and deer13.

Denatonium benzoate is also used in bitter nail polish to combat nail biting mania (onychophagia).

OVERVIEW
DENATONYUM 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.
Names
DENATONYUM BENZOATE Preferred IUPAC name
N-Benzyl-2-(2,6-dimethylanilino)-N,N-diethyl-2-oxoethan-1-aminium benzoate
Other names
N-Benzyl-2-[(2,6-dimethylphenyl)amino]-N,N-diethyl-2-oxoethan-1-aminium benzoate
Identifiers
CAS Number
3734-33-6 ☑
ChEMBL 
ChEMBL1371493 ☒
ChemSpider 
18392 ☑
ECHA InfoCard    100.020.996
PubChem CID
19518
UNII 
M5BA6GAF1O ☑
CompTox Dashboard (EPA)
DTXSID8034376 Edit this at Wikidata
InChI[show]
SMILES[show]
Properties
Chemical formula
C28H34N2O3
Molar mass    446.581
Appearance    white crystalline
Melting point    163 to 170 °C (325 to 338 °F; 436 to 443 K)
Hazards
R-phrases (outdated)    R22 R36 R37 R38
S-phrases (outdated)    S26 S36[1
STE AVERSIVE AGENTS
Denatonium benzoate (Bitrex®) has been used in the United States for over 20 years as an alcohol denaturant. In recent years, it has been heavily promoted for inclusion in household products, gardening products, and cosmetics to prevent accidental ingestions by children. A concentrated solution of denatonium benzoate which would be sold directly to the public for addition to household products is available in USA. The efficacy and safety studies on denatonium benzoate are limited and may be subject to varying interpretations when viewed in the context of a potential poisoning situation. Safety data indicate a low toxicity profile. However, there are significant gaps in knowledge, especially relating to chronic toxicity in humans, teratogenicity, and human hypersensitivity potential [59]. A 33-year-old man developed asthma and urticaria from exposure to denatonium benzoate in an insecticidal spray. He had previously developed the same symptoms following exposure to an alcohol-based skin disinfectant and other products denatured with denatonium benzoate. The cause of his symptoms was thus likely to be an immunologic mechanism of the immediate hypersensitivity-type. Currently available, admittedly limited data indicate that denatonium benzoate may actually have a low toxicity profile. Considering its wide availability as a denaturant for alcohol, it is surprising that human toxicity has been reported only once. However, denatonium toxicity may have been unrecognized because it is usually not included on product-ingredient lists since it represents a small percentage of the total chemical make-up of the product. No data exist on acute ocular or inhalation exposure in humans, chronic skin exposure in humans or animals, or chronic inhalation exposure in humans or animals. Its safety on broken or abraded skin has not been investigated. There are no teratogenicity studies.
In July 1991, The American Academy of Veterinary and Comparative Toxicology passed a resolution to encourage the use of a bittering agent to limit the ingestion of hazardous materials by companion animals [60]. Rodgers [61] expressed the view that some of the products, such as caustics and hydrocarbons, to which aversive agents might be added may produce toxicity with a single swallowing and it is unlikely that the addition of an adversive agent would have a beneficial effect on the outcome of such ingestions. He suggested that addition of denatonium benzoate might actually increase the potential for toxicity of such ingestions because vomiting might increase the risk of aspiration. He therefore recommended the use of denatonium benzoate in a limited number of products including those containing ethylene glycol, methanol and toxic pesticides.
In summary, denatonium benzoate appears to be safe when used at low concentrations as an aversive agent. However, there are limited data about whether aversive agents have an impact on either the number or the severity of pediatric ingestions, and its use should not be a substitute for other preventive measures such as child-resistant closures.
Denatonium is a rather more convenient name than phenylmethyl-[2- [(2,6-dimethylphenyl)amino]-2-oxoethyl]-diethylammonium. It is a quaternary ammonium cation, with two ethyl arms, one benzyl and one larger amide one, and usually comes as a benzoate - a salt of benzoic acid. Its claim to fame is simple, unpleasant but valuable - denatonium benzoate is the most bitter substance yet discovered.
This unreactive, colourless, odourless compound was first produced accidentally in 1958 by Scottish pharmaceutical manufacturer T & H Smith, later Macfarlan Smith, where researchers were experimenting with variants of an anaesthetic for dentists called lignocaine. It was soon discovered that just a few parts per million of denatonium benzoate were enough for this aggressively unpleasant compound to render a substance distasteful to humans.Quinine, the archetypal bitter substance associated with this gene, is used as the benchmark for bitterness, and is helpful in demonstrating just how strong denatonium benzoate is. The human tongue can pick up the bitter kick of quinine at a concentration of around 0.008 moles per cubic metre. By contrast, denatonium benzoate requires a thousandth of that concentration to be detected.
Our outstanding reaction to denatonium benzoate is likely to be an accidental function of the way the TAS2R taste receptors on the tongue react to this particular compound. But this is an accident that has found plenty of use, as denatonium benzoate is marketed under names like Bitrex, BITTER+PLUS and Aversion, which are all varieties of bitterants or aversive agents.
The idea is simple - if you have something that may be consumed but shouldn't be, you add some denatonium benzoate and even small quantities of it will put people off. Children, who inevitably are the most likely to try to consume substances they shouldn't, with as many as 30,000 a year taken to hospital in the UK alone with suspected poisoning, seem particularly sensitive to the bitter attack of denatonium, making it ideal for the job.
Some of the applications are straightforward - in the otherwise sweet-tasting but poisonous antifreeze ethylene glycol, for instance, and in rat poison (luckily rat tongues are a lot less sensitive to the compound). Rather more sneakily, ethanol can be ‘denatured' by adding denatonium, making it undrinkable. This means it can be sold without the large tax burden that usually accompanies an alcoholic drink, when the alcohol is to be used for cleaning or as fuel - a particularly common application with the increasing use of bioethanol.
If denatonium benzoate were a member of a team it would be the prickly one that no one else gets on with, but that everyone remembers. Our sense of taste may be one of the weaker senses, but it still remains a fundamental helper in ensuring we don't eat things we shouldn't. Celebrity chefs may spend their lives pursuing gastronomic pleasures, tracking down the latest taste sensation, but denatonium benzoate is always there to remind us that bad taste can be just as useful as tasty treats. And that's so much more useful than a dose of kryptonite.
Meera Senthilingam
So remember that sour taste in your mouth. Science writer Brian Clegg there bringing some bitterness to your day, with the chemistry of denatonium benzoate. Next week, the medical ailments of a famous Frenchman.
enatonium 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;
Denatonium Benzoate
by Jean-Patrick Holvoet, Master in Electro Mechanical Engineering. ©2014
Denatonium Benzoate is a bittering agent. It is considered the bitterest chemical compound with a range of uses in the manufacture of cleaners, automotive supplies as well as health and beauty items. Commercially, this compound is available as a white crystalline powder, but denatonium benzoate granules or solutions are also available.
HistoryBitrex (r)According to Chemistry World, denatonium benzoate was an accidental formulation by researchers at T & H Smith, a Scottish pharmaceutical firm that was the precursor for Macfarlan Smith Ltd. In 1958, staff at the laboratory was working with lignocaine, a dental anesthetic, when they discovered the extreme bitterness of denatonium benzoate in powder form. Due to the extreme taste, denatonium benzoate was used as an aversive agent. It is available under the trade name Bitrex®, which is a portmanteau of the words bitter and rex for king. The first known application for Bitrex® was as an aversant for pigs that were cannibalizing their own tails or those of other pigs.
Biochemical Structure
Chemical formula: C21H29N2O . C7H5O2The chemical database PubChem assigned a chemical identification number or CID of 19518 to denatonium. It has a chemical weight of 446.58116 g/mol and a molecular formula of C28 H3 4N 2O3. Denatonium benzoate is a compound of salt with an inert anion such as benzoate or saccharide. Its structure is similar to lidocaine and is closely related to Novocain and benzocaine. It is odorless, colorless and non-reactive, making it a suitable additive that does not interfere with the primary purpose of the base compound.
How it WorksHumans can typically sense sweet, sour, salty, savory and bitter-tasting stuff. Of these flavors, bitter-tasting chemicals elicit the most reaction. Sensitivity to bitter flavors depends on genetics: The TAS2R38 gene determines a person's ability to detect the bitterness associated with substances such as quinine, which is an ingredient in tonic water. It is also the standard for this type of bitter flavor. At a concentration of 0.008 moles per cubic meter, the human tongue can detect the presence of quinine. For denatonium benzoate, a concentration of 0.000008 moles per cubic meter is discernible to humans.
Applications
Bitterants such as denatonium benzoate are useful as aversive additives to prevent accidental ingestion of hazardous automotive compounds. In Europe and in some U.S. states, addition of denatonium benzoate is required in ethylene glycol or anti-freeze and windshield washer fluids. Common household products such as window cleaners, disinfectants, laundry detergent and insecticide include a certain amount of denatonium benzoate to discourage consumption by mouth.
It is applied on surfaces of toys as a bittering agent to prevent substantial consumption of hazardous materials. It is also applied on outdoor cables and wires to discourage rodents from chewing on parts and equipment. Denatonium benzoate is an aversive agent added to various pesticides, plant food sticks and rodenticides to suppress swallowing especially when young children come in contact with these poisonous substances.
By far, the most common use of denatonium benzoate is to denature alcohol, making it unfit for human consumption and exempt from tariffs that normally apply to alcohol.
In livestock farming, denatonium benzoate is used to prevent cannibalism in pigs and aspiration mastitis in cattle. It acts as a repellant when applied to young shoots, branches and other surfaces to discourage nibbling by animals, thereby preventing damage to property.
We thought you might ask that. So here are lots of perfectly correct answers to that question.
Bitrex is...
Denatonium Benzoate - to give it its full, technical name. Ironically, that's a bit of a mouthful. So we call it Bitrex®.
The bitterest substance known to man, woman or child. That's according to The Guinness World Records.
A substance that's put into household, garden and automotive products to ensure that if a child or animal ever tried to swallow it, they would spit it straight out before they could be poisoned.
Completely harmless if consumed. It just tastes really, really horrible.
A lifesaver. Literally.
The product of a happy accident. Bitrex was discovered in 1958 by a team of Macfarlan Smith scientists who were working on a new local anaesthetic. Our chemists realised immediately that they had found a remarkable substance - the world's most bitter material - and quickly put it to good use...Helping to make accidental poisoning a thing of the past.Bitrex is not...
A substitute for other common sense precautions for preventing poisoning, such as keeping chemicals out of a child's reach, using safety closures properly and reading labels carefully.
But we pioneered this child safety additive precisely because we know what it's like to be a parent. We understand that parents get harassed, tired, and up to their eyes. And that is why Bitrex is there. For the moments of inattention when most accidents happen.
natonium benzoate
Chemical structure of DenatoniumChemical structure of benzoate
Systematic name    N-benzyl-2-(2,6-dimethylphenylamino)-
N,N-diethyl-2-oxoethanaminium benzoate
Chemical formula    C21H29N2O·C7H5O2
Molecular mass    446.58 g/mol
Density    x.xxx g/cm³
Melting point    166-170 °C
Boiling point    xx.x °C
CAS number    [3734-33-6]
SMILES    S=CC1=CC=CC(C)=C1NC(C[N+](CC)(CC)
CC2=CC=CC=C2)=O.O=C([O-])C3=CC=CC=C3
Disclaimer and references
Denatonium, usually available as denatonium benzoate (or under trade names such as Bitrex or Aversion) and as denatonium saccharide, is the most bitter compound known. It was discovered in 1958 during research on local anesthetics by Macfarlan Smith of Edinburgh, Scotland. Dilutions of as little as 10 ppm are unbearably bitter to most humans. Denatonium salts are usually colorless and odorless solids but are often traded as solutions. They are used as aversive agents to prevent accidental ingestion. Denatonium is used in denatured alcohol, antifreeze, nail biting preventions, animal repellents, liquid soaps, and shampoos. It is not known to pose any long-term health risks although exposure may be irritating and unpleasant.
Structure and physical properties
Denatonium is a quaternary ammonium cation. It is a compound of a salt with an inert anion like benzoate or saccharide. The structure of denatonium is related to the local anesthetic lidocaine, differing only by the addition of a benzyl group to the amino nitrogen.
ApplicationsThe bitterness of the compound guides most applications of denatonium. Denatonium is used to denature ethanol so that it is not taxed as an alcoholic beverage. One designation in particular, SD-40, indicates that ethanol has been denatured using denatonium. In fact, the common name for this chemical, denatonium alludes to this application. 
Denatonium also discourages consumption of harmful alcohols like methyl alcohol and ethylene glycol. Denatonium is therefore often used in rubbing alcohol as an inactive ingredient. It is also added to all kinds of harmful liquids including solvents, paints, varnishes, toiletries, and other household products. 
Since 1995, when the State of Oregon required that it be added to antifreeze and windshield wiper fluid, the compound has been increasingly found in these substances throughout the world. The addition of denatonium is credited with saving children and animals who might otherwise drink sweet antifreeze or wiper fluid and get ethylene glycol or methanol poisoning respectively. Other uses include nail polish for preventing nail biting, and as animal repellent (especially for big game like deer). 
It should be noted that animals are known to have different sensitivities to the effects of denatonium. It has been used to safeguard rat poisons from human consumption, so presumably rats are not deterred by it, although there is evidence that a small percentage of rodents do avoid such baits. Some cats have been known to be tempted by them it may not be as effective a deterrent for cats as it is for humans, or perhaps some cats are not deterred due to a genetic factor similar to that affecting human perceptions of the taste of phenylthiocarbamide.