Butylated hydroxytoluene (BHT), also known as dibutylhydroxytoluene, is a lipophilic organic compound, chemically a derivative of phenol, that is useful for its antioxidant properties. European and U.S. regulations allow small amounts to be used as a food additive. In addition to this use, BHT is widely used to prevent oxidation in fluids (e.g. fuel, oil) and other materials where free radicals must be controlled.
Video Butylated hydroxytoluene
Occurrence
Phytoplankton, including the green algae Botryococcus braunii, as well as three different cyanobacteria (Cylindrospermopsis raciborskii, Microcystis aeruginosa and Oscillatoria sp.) are capable of producing BHT. Confirmation was made via gas chromatography-mass spectrometry analysis.
Maps Butylated hydroxytoluene
Production
Industrially, BHT is prepared by the reaction of p-cresol (4-methylphenol) with isobutylene (2-methylpropene) catalyzed by sulfuric acid:
- CH3(C6H4)OH + 2 CH2=C(CH3)2 -> ((CH3)3C)2CH3C6H2OH
Alternatively, BHT is prepared from 2,6-di-tert-butylphenol by hydroxymethylation or aminomethylation followed by hydrogenolysis.
Reactions
The species behaves as a synthetic analog of vitamin E, primarily acting as a terminating agent that suppresses autoxidation, 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:
- RO2o + ArOH -> ROOH + ArOo
- RO2o + ArOo -> nonradical products
where R is alkyl or aryl, and where ArOH is BHT or related phenolic antioxidants. Each BHT consumes two peroxy radicals.
Applications
BHT is listed under several categories in catalogues and databases, such as food additive, household product ingredient, industrial additive, personal care product/cosmetic ingredient, pesticide ingredient, plastic/rubber ingredient and medical/veterinary/research.
Food additive
BHT is primarily used as an antioxidant food additive. In the United States, it is classified as generally recognized as safe (GRAS) based on a National Cancer Institute study from 1979 in rats and mice. It is approved for use in the U.S. by the Food and Drug Administration: For example, 21 CFR § 137.350(a)(4) allows BHT up to 0.0033% by weight in "enriched rice", while 9 CFR § 381.147(f)(1) allows up to 0.01% in poultry "by fat content". It is permitted in the European Union under E321.
Since the 1970s, BHT has been steadily replaced with butylated hydroxyanisole (BHA). Some food companies have voluntarily eliminated BHT from their products or have announced that they were going to phase it out.
Antioxidant
BHT is also used as an antioxidant in products such as cosmetics, pharmaceuticals, rubber, electrical transformer oil (at 0.35%), and embalming fluid. In the petroleum industry, where BHT is known as the fuel additive AO-29, it is used in hydraulic fluids, turbine and gear oils, and jet fuels. BHT is also used to prevent peroxide formation in diethyl ether and other laboratory chemicals.
Some additive products contain BHT as their primary ingredient, while others contain the chemical merely as a component of their formulation, sometimes alongside butylated hydroxyanisole (BHA).
Derivatives
Health effects
The US Food and Drug Administration classifies BHT as generally recognized as safe (GRAS) as a food preservative when used according to approved uses. There is, however, some debate surrounding a possible link between BHT and cancer risk, asthma, and behavioral issues in children; some studies show a potential to increase risk and some to decrease risk. Because of this uncertainty, the consumer group Center for Science in the Public Interest recommend to avoid BHT and puts BHT in its "caution" column. The National Cancer Institute determined in 1979 that it was noncarcinogenic in a mouse model. BHT has low acute toxicity, as do other closely related phenol antioxidants. For example, the LD50 of 2,6-di-tert-butylphenol is greater than 9 g/kg.
In early stage research, BHT has shown anti-viral activity.
References
External links
- Why are BHA and BHT in foods? Are they safe?
- CDC - NIOSH Pocket Guide to Chemical Hazards
Source of article : Wikipedia
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