BHT or Hydroxy toluene butylate or Butylated hydroxytoluene or Toluene hydroxylated butylate or 2,6-di-tert-butyl-p-cresol, is an organic chemical compound, lipophilic phenol, obtained synthetically by the reaction of 4-methylphenol with isobutylene and catalysed by sulphuric acid.

The synthesis process takes place in different steps:

• Preparation. The raw materials are p-cresol (a phenol) and isobutene (a hydrocarbon).
• Alkylation. p-cresol is reacted with isobutene in the presence of a catalyst, such as sulphuric acid, at a controlled temperature and pressure. This process is known as alkylation and attaches the tert-butyl groups to the p-cresol molecule.
• Separation. The reaction mixture is then separated to isolate the 2,6-di-tert-butyl-p-cresol by various methods, including distillation, in which the mixture is heated and the components that vaporise at different temperatures are separated.
• Purification.  The separated product is purified to remove any unreacted materials and by-products by processes such as washing, filtration and drying.
• Quality control. The final product is tested to ensure that it meets the necessary quality standards.

It appears as a white, stable but photosensitive powder. Flammable. Incompatible with oxidising agents, acid chlorides, bases, brass, acid anhydrides, copper, copper alloys, steel.

What it is used for and where

Food

A synthetic antioxidant generally considered safe in food. It has the ability to control free radicals by eliminating peroxyl radicals and to control free radical generation by inhibiting or retarding oxidation (1). The FDA-authorised maximum use dose is 0.02% in meat and meat products from the meat processing industry.

Ingredient included in the list of European food additives as E321, antioxidant.

Cosmetics

BHT is a restricted ingredient as   a Relevant Item in the Annexes of the European Cosmetics Regulation 1223/2009. Ingredient at risk: 2,6-Di-Tert-Butyl-4-Methylphenol

Product Type, body parts: a) Mouthwash b) Toothpaste c) Other leave-on and rinse-off products. Maximum concentration in ready for use preparation    a) 0,001 % b) 0,1 % c) 0,8 %

From 1 July 2023 cosmetic products containing that substance and not complying with the restrictions shall not be placed on the Union market. From 1 January 2024 cosmetic products containing that substance and not complying with the restrictions shall not be made available on the Union market.

It is included in formulations of shower gels, shampoos, lipsticks as an antioxidant to improve the stability of fat-soluble cosmetics and prevent their deterioration. 

Antioxidant agent. Ingredient that counteracts oxidative stress and prevents cell damage. Free radicals, pathological inflammatory processes, reactive nitrogen species and reactive oxygen species are responsible for the ageing process and many diseases caused by oxidation.

Fragrance. It plays a decisive and important role in the formulation of cosmetic products as it provides the possibility of enhancing, masking or adding fragrance to the final product, increasing its marketability. It is able to create a perceptible pleasant odour, masking a bad smell. The consumer always expects to find a pleasant or distinctive scent in a cosmetic product. 

Other uses

Also used in petroleum products, rubber, plastic foam as an antioxidant stabiliser, polyester resin, ABS resin, polyethylene, polystyrene, cellulose, transformer oil, white and clear latex.

In natural rubber processing it acts as an antioxidant and stabiliser 

Safety

BHT is a skin and eye irritant but no conclusions can be drawn on the additive's potential for skin sensitisation. It is considered safe by EFSA in animal feed (2) but this study recommends monitoring and limiting its use (3) and suggests that BHT consumption should not exceed 0.5 mg/kg body weight (4).

For more information:

BHT studies

Typical commercial product characteristicsBHT Butylated Hydroxy Toluene

Appearance	White powder
Boiling Point	265ºC
Melting Point	69-71ºC
Flash Point	127ºC
Density	1.048
PSA	20.23000
Vapor Pressure	0.0±0.6 mmHg at 25°C
Vapor density	7.6
LogP	5.32
Refraction Index	1.499
Sulphate SO4	≤ 0.002 w/%
Arsenic	≤ 1 mg/kg
Cauterized residue	≤ 0.004 w/%
Free phenol (p-cresol)	≤ 0.01 w/%
Water	≤0.1%
Safety

• Molecular Formula   C₁₅H₂₄O
• Linear Formula [(CH₃)₃C]₂C₆H₂(CH₃)OH
• Molecular Weight 220.356 g/mol
• Exact Mass    220.182709
• UNII: 1P9D0Z171K
• CAS: 128-37-0  
• DSSTox Substance ID  
• IUPAC  2,6-ditert-butyl-4-methylphenol
• InChl=  1S/C15H24O/c1-10-8-11(14(2,3)4)13(16)12(9-10)15(5,6)7/h8-9,16H,1-7H3
• InChl Key      NLZUEZXRPGMBCV-UHFFFAOYSA-N
• SMILES  CC1=CC(=C(C(=C1)C(C)(C)C)O)C(C)(C)C
• EC Number: 204-881-4  
• FEMA Number: 2184
• PubChem Substance ID 329749182
• MDL number MFCD00011644
• Beilstein Registry Number 1911640

Synonyms

• 2,6-Di-tert-butyl-4-methylphenol
• Butylated hydroxytoluene
• Butylhydroxytoluene
• 2,6-Di-tert-butyl-p-cresol
• 2,6-Di-t-butyl-4-methylphenol
• Ionol
• Parabar 441
• Paranox 441
• 2,6-Di-tert-butyl-4-cresol
• DBPC
• Dibunol
• Stavox
• Phenol, 2,6-bis(1,1-dimethylethyl)-4-methyl-
• BHT
• Ionol CP
• Antrancine 8
• Butylated hydroxytoluol
• Vulkanox KB
• Impruvol
• Topanol
• Dalpac
• 2,6-ditert-butyl-4-methylphenol
• Di-tert-butyl-p-cresol
• Dibutylated hydroxytoluene
• Deenax
• Ionole
• Vianol
• Antioxidant KB
• 3,5-Di-tert-butyl-4-hydroxytoluene
• Antioxidant 4K
• Sumilizer BHT
• Topanol O
• Topanol OC
• Vanlube PC
• Antioxidant DBPC
• Sustane BHT
• Tenamene 3
• Vanlube PCX
• Antioxidant 29
• Antioxidant 30
• Nonox TBC
• Tenox BHT
• Chemanox 11
• Ionol 1
• Agidol
• Catalin CAO-3
• Advastab 401
• Ionol (antioxidant)
• BUKS

References______________________________________________________________________

(1) Zahid MA, Eom JU, Parvin R, Seo JK, Yang HS. Changes in Quality Traits and Oxidation Stability of Syzygium aromaticum Extract-Added Cooked Ground Beef during Frozen Storage. Antioxidants (Basel). 2022 Mar 11;11(3):534. doi: 10.3390/antiox11030534.

(2) EFSA Panel on Additives and Products or Substances used in Animal Feed (FEEDAP), Bampidis V, Azimonti G, Bastos ML, Christensen H, Dusemund B, Fašmon Durjava M, Kouba M, López-Alonso M, López Puente S, Marcon F, Mayo B, Pechová A, Petkova M, Ramos F, Sanz Y, Villa RE, Woutersen R, Finizio A, Teodorovic I, Aquilina G, Bories G, Gropp J, Nebbia C, Innocenti M. Safety and efficacy of a feed additive consisting of butylated hydroxytoluene (BHT) for all animal species (Katyon Technologies Limited). EFSA J. 2022 May 10;20(5):e07287. doi: 10.2903/j.efsa.2022.7287. 

(3) Abou-Hadeed AH, Mohamed AT, Hegab DY, Ghoneim MH. Ethoxyquin and Butylated Hydroxy Toluene Distrub the Hematological Parameters and Induce Structural and Functional Alterations in Liver of Rats. Arch Razi Inst. 2021 Dec 30;76(6):1765-1776. doi: 10.22092/ari.2021.356439.1844. 

(4) Lobo V, Patil A, Phatak A, Chandra N. Free radicals, antioxidants and functional foods: Impact on human health. Pharmacogn Rev. 2010 Jul;4(8):118-26. doi: 10.4103/0973-7847.70902.