Butylated hydroxytoluene

Butylated hydroxytoluene (BHT), also known as dibutylhydroxytoluene, is a lipophilic organic compound, chemically a derivative of phenol, that is useful for its antioxidant properties. BHT is widely used to prevent free radical-mediated oxidation in fluids (e.g. fuels, oils) and other materials, and the regulations overseen by the U.S. F.D.A.—which considers BHT to be "generally recognized as safe"—allow small amounts to be added to foods. Despite this, and the earlier determination by the National Cancer Institute that BHT was noncarcinogenic in an animal model, societal concerns over its broad use have been expressed. BHT has also been postulated as an antiviral drug, but as of December 2022, use of BHT as a drug is not supported by the scientific literature and it has not been approved by any drug regulatory agency for use as an antiviral. 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 as a natural product. The fruit lychee also produces BHT in its pericarp. Several fungi (for example Aspergillus conicus) living in olives produce BHT. The chemical synthesis of BHT in industry has involved 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 has been prepared from 2,6-di-tert-butylphenol by hydroxymethylation or aminomethylation followed by hydrogenolysis. 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: RO2• + ArOH → ROOH + ArO• RO2• + ArO• → nonradical products where R is alkyl or aryl, and where ArOH is BHT or related phenolic antioxidants.