2,6-di-tert-butyl-p-cresol (BHT, Butilidrossitoluene) is an organic compound primarily used as an antioxidant. Its main function in cosmetics, food, and industrial products is to prevent oxidation and spoilage, extending the shelf life of products. It is widely used in cosmetics, foods, pharmaceuticals, and industrial products to protect oxygen-sensitive ingredients.

Chemical Composition and Structure

BHT is a phenolic derivative with the chemical formula C₁₅H₂₄O. Its structure consists of an aromatic ring with two tert-butyl groups positioned ortho to the hydroxyl (-OH) group, giving BHT excellent antioxidant properties. This structure allows BHT to donate an electron to free radicals, effectively interrupting the chain reactions that lead to oxidation.

Physical Properties

2,6-di-tert-butyl-p-cresol typically appears as a white or pale yellow crystalline powder. It is lipophilic, meaning it dissolves well in fats and oils, making it suitable for use in oil-based formulations. It has high thermal and chemical stability, making it effective even in small concentrations to prevent oxidative deterioration.

The name describes the structure of the molecule:

• 2,6-di Indicates the presence of two substituents attached to the benzene ring at positions 2 and 6.
• tert-butyl refers to tertiary butyl groups, which are the substituents attached to the benzene ring. A tert-butyl group is a functional group with the formula -C(CH₃)₃.
• p-cresol is the base molecule to which the tert-butyl groups are attached. Cresols are organic compounds that are methylphenols. The prefix 'p-' indicates that the hydroxyl group (-OH) is attached to the benzene ring in the para position, opposite the tert-butyl groups.

Production Process

BHT is synthesized through the reaction of p-cresol (an aromatic compound) with isobutylene in the presence of an acid catalyst. This process yields the final compound, 2,6-di-tert-butyl-p-cresol, which is then purified for use in various products. 

• 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.

What it is for and where

2,6-di-tert-butyl-p-cresol is used in the food, cosmetic and pharmaceutical fields for its antioxidant properties. It is in fact a preservative.

Cosmetics

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. 

Food

Used to prevent the rancidity of oils and fats in foods.

Packaging 

Used in food packaging to prevent the oxidation of the contained food.

Fuels and Lubricants

Added to fuels and lubricants to prevent deposit formation.

Veterinary Medicine

Used in some veterinary products as preservative.

Safety

The use of BHT in food has been a matter of some debate due to potential health concerns. However, regulatory agencies like the US Food and Drug Administration (FDA) have deemed it generally recognized as safe (GRAS) in low amounts. Some studies have shown potential risks with high doses, but the concentrations typically used in food are much lower.

Alternative: Its sister compound, butylated hydroxyanisole (BHA), has similar properties and is also used in food preservation.

Environmental Concerns: BHT is not easily biodegradable, and there have been some concerns about its persistence in the environment.

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).

The most relevant studies on this chemical compound have been selected with a summary of their contents:

2,6-di-tert-butyl-p-cresol studies

• Molecular Formula: C₁₅H₂₄O
• Linear Formula [(CH₃)₃C]₂C₆H₂(CH₃)OH
• Molecular Weight: 220.356 g/mol
• UNII: 1P9D0Z171K
• CAS: 128-37-0  950-56-1  25377-21-3  102962-45-8  42615-30-5  50356-19-9  50641-99-1  52683-46-2  53571-70-3  58500-82-6  83047-16-9  97123-41-6  36631-28-4  290348-23-1  259752-53-9  1394965-02-6  1456709-94-6  2055662-96-7  338986-13-3
• EC Number: 204-881-4  246-911-9
• FEMA Number: 2184

Synonyms:

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

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.

Abstract. This study was accomplished by comparing the oxidative stability of (0.1%) Syzygium aromaticum extract (SAE) and (0.02%) butylated hydroxytoluene (BHT)-added cooked ground beef with an antioxidant free-control sample during frozen storage. All samples showed a non-significant (p > 0.05) effect on pH, thawing loss, redness, and yellowness values during storage. Incorporation of BHT and SAE led to a significant (p < 0.05) reduction in thiobarbituric acid-reactive substances (TBARS) and volatile levels as an active antioxidant. The generation of less volatiles found in SAE-treated samples up to 6 months (p < 0.05) of storage. Therefore, SAE-protected ground beef can lead to lower lightness, lipid oxidation, and volatile compounds levels after cooking compared with control and BHT samples.

(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. 

Abstract. The current experiment aimed to assess the effect of the synthetic antioxidants ethoxyquin (EQ) and/or butylated hydroxytoluene (BHT) on the liver function tests, hematological parameters, and liver histoarchitecture in rats. A total of 50 male Sprague-Dawley rats were divided into five groups of 10 animals per group. The first group served as the control and did not receive any treatments, and the second group served as the vehicle control and was orally administrated 1 ml of corn oil day after day for consecutive 45 and 90 days. The third group (EQ) was orally administered 1 ml of EQ dissolved in corn oil day after day for consecutive 45 and 90 days in a dose of 1/5 LD50, and the fourth group (BHT) was orally received 1 ml of BHT dissolved in corn oil day after day for consecutive 45 and 90 days in a dose of 1/5 LD50. The fifth group (combination group) was orally administered both EQ and BHT at the same doses and durations described above. The present results showed that the final body weight was significantly decreased in the EQ- or BHT-treated group particularly at 90 days of exposure to both compounds. Furthermore, the liver weight was significantly elevated in EQ, BHT, and co-exposed groups at 45 and 90 days of exposure, compared to the control group. Moreover, EQ, BHT, and their co-exposure caused a significant elevation in the levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) enzymes, as well as total bilirubin at 45 and 90 days of exposure. On the other hand, there was no significant change in the total albumin. Hemoglobin value, red blood cells, white blood cells, platelets, and differential leucocyte count at 45 and 90 days of exposure were significantly decreased. Histopathological significant findings in the liver were observed as vascular congestions, vacuolations, hydropic degenerations, lipidosis, and swelling, particularly in the co-exposed group for 90 days. These findings confirmed the hepatotoxic potential of EQ and BHT; therefore, it is recommended to control and limit the utilization of such chemicals.

(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.

Abstract. In recent years, there has been a great deal of attention toward the field of free radical chemistry. Free radicals reactive oxygen species and reactive nitrogen species are generated by our body by various endogenous systems, exposure to different physiochemical conditions or pathological states. A balance between free radicals and antioxidants is necessary for proper physiological function. If free radicals overwhelm the body's ability to regulate them, a condition known as oxidative stress ensues. Free radicals thus adversely alter lipids, proteins, and DNA and trigger a number of human diseases. Hence application of external source of antioxidants can assist in coping this oxidative stress. Synthetic antioxidants such as butylated hydroxytoluene and butylated hydroxyanisole have recently been reported to be dangerous for human health. Thus, the search for effective, nontoxic natural compounds with antioxidative activity has been intensified in recent years. The present review provides a brief overview on oxidative stress mediated cellular damages and role of dietary antioxidants as functional foods in the management of human diseases.