Butylated hydroxytoluene

Butylated hydroxytoluene (BHT) is the organic compound with the formula MeC6H2(CMe3)2OH (Me = methyl). This lipophilic (fat-soluble) phenol is primarily used as an antioxidant food additive (E number E321) as well as in cosmetics, pharmaceuticals, jet fuels, rubber, petroleum products, and embalming fluid.

Chemistry
BHT is produced by alkylation reaction of p-cresol with isobutylene. The species behaves as a synthetic analogue of vitamin E, primarily acting as a terminating agent" that suppressed 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. One can see that each BHT consumes two peroxy radicals.

In the chemical industry it is added to tetrahydrofuran and diethyl ether in order to inhibit the formation of dangerous organic peroxides.

Use in foods
BHT was patented in 1947 and received approval of the Food and Drug Administration for use as a food additive and preservative in 1954. BHT reacts with free radicals, slowing the rate of autoxidation in food, preventing changes in the food's color, odor, and taste.

Controversy
Concerns have been raised about the use of BHT in food products. The compound has been banned for use in food in Japan (1958), Romania, Sweden, and Australia. The US has barred it from infant foods. Some food industries have voluntarily eliminated it from their products. However, BHT is also marketed as a health food supplement in capsule form.