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Butylated hydroxytoluene

Butylated hydroxytoluene

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Encyclopedia
Butylated hydroxytoluene (BHT), also known as butylhydroxytoluene, is a lipophilic
Lipophilic
Lipophilicity, , refers to the ability of a chemical compound to dissolve in fats, oils, lipids, and non-polar solvents such as hexane or toluene. These non-polar solvents are themselves lipophilic — the axiom that like dissolves like generally holds true...

 (fat-soluble) organic compound
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...

 that is primarily used as an antioxidant
Antioxidant
An antioxidant is a molecule capable of inhibiting the oxidation of other molecules. Oxidation is a chemical reaction that transfers electrons or hydrogen from a substance to an oxidizing agent. Oxidation reactions can produce free radicals. In turn, these radicals can start chain reactions. When...

 food additive
Food additive
Food additives are substances added to food to preserve flavor or enhance its taste and appearance.Some additives have been used for centuries; for example, preserving food by pickling , salting, as with bacon, preserving sweets or using sulfur dioxide as in some wines...

 (E number
E number
E numbers are number codes for food additives that have been assessed for use within the European Union . They are commonly found on food labels throughout the European Union. Safety assessment and approval are the responsibility of the European Food Safety Authority...

 E321) as well as an antioxidant additive in cosmetics
Cosmetics
Cosmetics are substances used to enhance the appearance or odor of the human body. Cosmetics include skin-care creams, lotions, powders, perfumes, lipsticks, fingernail and toe nail polish, eye and facial makeup, towelettes, permanent waves, colored contact lenses, hair colors, hair sprays and...

, pharmaceuticals, jet fuel
Jet fuel
Jet fuel is a type of aviation fuel designed for use in aircraft powered by gas-turbine engines. It is clear to straw-colored in appearance. The most commonly used fuels for commercial aviation are Jet A and Jet A-1 which are produced to a standardized international specification...

s, rubber
Rubber
Natural rubber, also called India rubber or caoutchouc, is an elastomer that was originally derived from latex, a milky colloid produced by some plants. The plants would be ‘tapped’, that is, an incision made into the bark of the tree and the sticky, milk colored latex sap collected and refined...

, petroleum
Petroleum
Petroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface. Petroleum is recovered mostly through oil drilling...

 products, electrical transformer oil
Transformer oil
Transformer oil or insulating oil is usually a highly-refined mineral oil that is stable at high temperatures and has excellent electrical insulating properties. It is used in oil-filled transformers, some types of high voltage capacitors, fluorescent lamp ballasts, and some types of high voltage...

, and embalming
Embalming
Embalming, in most modern cultures, is the art and science of temporarily preserving human remains to forestall decomposition and to make them suitable for public display at a funeral. The three goals of embalming are thus sanitization, presentation and preservation of a corpse to achieve this...

 fluid.

Production


BHT is prepared by the reaction of p-cresol
P-Cresol
p-Cresol, also 4-methylphenol, is a phenol, with formula C6H4.It is a positional isomer; the other two are m-cresol and o-cresol. P-cresol is a major component in pig odor. . For more information see cresol. 4-methylphenol is a component in human sweat. It is a component of human odour attractive...

 (4-methylphenol) with isobutylene
Isobutylene
Isobutylene is a hydrocarbon of significant industrial importance. It is a four-carbon branched alkene , one of the four isomers of butylene. At standard temperature and pressure it is a colorless flammable gas.-Uses:...

 (2-methylpropene) catalysed by sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...

:
CH3(C6H4)OH + 2 CH2=C(CH3)2 → ((CH3)3C)2CH3C6H2OH

Alternatively, BHT is prepared from 2,6-di-tert-butylphenol
2,6-Di-tert-butylphenol
2,6-Di-tert-butylphenol is an organic compound with the structural formula 2,6-2C6H3OH. This colourless solid alkylated phenol and its derivatives are used industrially as UV stabilizer and an antioxidant for hydrocarbon-based products ranging from petrochemicals to plastics...

 by hydroxymethylation or aminomethylation followed by hydrogenolysis
Hydrogenolysis
Hydrogenolysis is a chemical reaction whereby a carbon–carbon or carbon–heteroatom single bond is cleaved or undergoes "lysis" by hydrogen. The heteroatom may vary, but it usually is oxygen, nitrogen, or sulfur. A related reaction is hydrogenation, where hydrogen is added to the molecule, without...

. Approximately 4M kg/y are produced.

Reactions


The species behaves as a synthetic analogue of vitamin E
Vitamin E
Vitamin E is used to refer to a group of fat-soluble compounds that include both tocopherols and tocotrienols. There are many different forms of vitamin E, of which γ-tocopherol is the most common in the North American diet. γ-Tocopherol can be found in corn oil, soybean oil, margarine and dressings...

, primarily acting as a terminating agent that suppresses autoxidation
Autoxidation
Autoxidation is any oxidation that occurs in open air or in presence of oxygen and/or UV radiation and forms peroxides and hydroperoxides. A classic example of autoxidation is that of simple ethers like diethyl ether, whose peroxides can be dangerously explosive. It can be considered to be a slow,...

, a process whereby unsaturated (usually) organic compounds are attacked by atmospheric oxygen. BHT stops this autocatalytic reaction by converting peroxy radicals to hydroperoxides. It effects this function by donating a hydrogen atom:
RO2. + ArOH → ROOH + ArO.
RO2. + ArO. → nonradical products

where R is alkyl or aryl, and where ArOH is BHT or related phenolic antioxidants. One can see that each BHT consumes two peroxy radicals.

Controversy


In the 1970s, Benjamin Feingold
Benjamin Feingold
Benjamin F. Feingold, M.D., was a pediatric allergist from California, who proposed in 1973 that salicylates, artificial colors, and artificial flavors cause hyperactivity in children...

, a San Francisco MD who established the Feingold diet
Feingold diet
The Feingold diet is a food elimination program developed by Ben F. Feingold, MD to treat hyperactivity. It eliminates a number of artificial colors and artificial flavors, aspartame, three petroleum-based preservatives, and certain salicylates. There has been much debate about the efficacy of...

, claimed that BHT could produce hyperactivity in some children. In addition, some controversy surrounds the link of BHT to cancer risk, some studies showing the potential to increase and some showing a decrease in risk. Some food industries have voluntarily eliminated this additive from their products, and since the 1970s it has been steadily replaced with the less studied BHA
Butylated hydroxyanisole
Butylated hydroxyanisole is an antioxidant consisting of a mixture of two isomeric organic compounds, 2-tert-butyl-4-hydroxyanisole and 3-tert-butyl-4-hydroxyanisole. It is prepared from 4-methoxyphenol and isobutylene. It is a waxy solid used as a food additive with the E number E320...

.

BHT is marketed as a health food supplement in capsule form. It has been reported to have anti-viral effects, particularly in use against herpes family viruses and in combination with L-lysine
Lysine
Lysine is an α-amino acid with the chemical formula HO2CCH4NH2. It is an essential amino acid, which means that the human body cannot synthesize it. Its codons are AAA and AAG....

 and vitamin C
Vitamin C
Vitamin C or L-ascorbic acid or L-ascorbate is an essential nutrient for humans and certain other animal species. In living organisms ascorbate acts as an antioxidant by protecting the body against oxidative stress...

. This latter use has made it into some of the more popular literature.

Closely related phenol antioxidants exhibit low toxicity. For 2,6-di-tert-butylphenol
2,6-Di-tert-butylphenol
2,6-Di-tert-butylphenol is an organic compound with the structural formula 2,6-2C6H3OH. This colourless solid alkylated phenol and its derivatives are used industrially as UV stabilizer and an antioxidant for hydrocarbon-based products ranging from petrochemicals to plastics...

, the is greater than 9 g/kg.

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