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2,6-Bis(tert-butyl)-4-methylphenol  (1994)

CAS no 128-37-0

Synonyms
Butylhydroxytoluene
BHT
E 321 (as a food additive)
2,6-Bis(1,1-dimethylethyl)-4-
methylphenol

Physical data
Melting point: 70░C
Boiling point: 265░C
Vapour pressure
ca 0.3 Pa (25░C)
Water solubility:
1.1 mg/l (20░C)

BHT is produced from isobutene and 4-methylphenol (p-cresol). By using an aluminium catalyst, which bonds with the hydroxylic acid during the reaction, the alkylation can be made to take place on the carbon next to  the hydroxyl group. Acid-catalysed alkylation can also be used. As in most chemical reactions, a mixture of reaction products is obtained, in the present case, apart from BHT itself, mostly including 2-tert-4-methylphenol. This product can be used as a technical grade for addition to rubber, plastic and lubricant. If BHT is required as a food product, the reaction product has to be purified. European output of BHT in 1989 was estimated at 18,000 tonnes. 

This substance is used in low concentrations as a stabiliser/antioxidant in many types of products. The greater part of all BHT, 70-80% is used for stabilising rubber and plastic. It works by cleaving a hydrogen radical which can capture the free radicals and peroxide radicals formed, which above all attack double bonds. Thus it is the double bonds in products like ordinary fats, lubricants, rubber, oil, cosmetics and foodstuffs which require longer durability with BHT. The fat does not turn rancid. The reason why BHT is sufficiently non-toxic to be used in foodstuffs is that the tert-butyl groups surround the hydroxyl group. Due to the alkyl groups being so bulky, the hydroxyl group is screened off from possibilities of chemical activity, and above all from the possibility of hydrogen bonding.

Because BHT is not so dangerous for health and is added in small amounts, which means that it does not have to be declared to the Products Register, the quantity of BHT entered in the Register is clearly an underestimate of the amount of the substance used in Sweden. Moreover, not all large BHT-containing groups of products like cosmetics and foodstuffs are entered in the Register. Consumption of BHT in Germany is estimated at 1,500 – 1,600 tonnes annually, of which about 70% is used as an additive in plastic and rubber. 

Mixtures of BHT and other butylphenols are also used as antioxidants in faint binders and various oils. About 70 tonnes of these other butylphenols were consumed in Sweden during 1994.

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