2,4,6-Tri-''tert''-butylphenol (2,4,6-TTBP) is a

phenol Phenol (also known as carbolic acid, phenolic acid, or benzenol) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile and can catch fire. The molecule consists of a phenyl group () ...

symmetrically substituted with three ''tert''-butyl groups and thus strongly sterically hindered. 2,4,6-TTBP is a readily oxidizable

aromatic compound Aromatic compounds or arenes are organic compounds "with a chemistry typified by benzene" and "cyclically conjugated." The word "aromatic" originates from the past grouping of molecules based on odor, before their general chemical properties were ...

and a

weak acid Acid strength is the tendency of an acid, symbolised by the chemical formula , to dissociate into a proton, , and an anion, . The dissociation or ionization of a strong acid in solution is effectively complete, except in its most concentrated s ...

. It oxidizes to give the deep-blue 2,4,6-tri-''tert''-butylphenoxy radical. 2,4,6-TTBP is related to 2,6-di-''tert''-butylphenol, which is widely used as an

antioxidant Antioxidants are Chemical compound, compounds that inhibit Redox, oxidation, a chemical reaction that can produce Radical (chemistry), free radicals. Autoxidation leads to degradation of organic compounds, including living matter. Antioxidants ...

in industrial applications. These compounds are colorless solids.

Preparation

The preparation of 2,4,6-tri-tert-butylphenol has been studied extensively. As early as 1890, Wilhelm Koenigs described the acid-catalyzed reaction of

with

isobutylene Isobutylene (or 2-methylpropene) is a hydrocarbon with the chemical formula . It is a four-carbon branched alkene (olefin), one of the four isomers of butylene. It is a colorless flammable gas, and is of considerable industrial value. Product ...

. Many other reports have appeared. Yields up to 90% have been reported. Typical side products are the result of incomplete alkylation: 4-''tert''-butylphenol (4-TBP), 2,4-di-''tert''-butylphenol (2,4-DTBP), 2,6-di-''tert''-butylphenol (2,6-DTBP). 2,5-Di-''tert''-butylphenol (2,5-DTB) has been observed. 2,4,6-tri-''tert''-butylphenol is also found as a

by-product A by-product or byproduct is a secondary product derived from a production process, manufacturing process or chemical reaction; it is not the primary product or service being produced. A by-product can be useful and marketable or it can be cons ...

in the synthesis of the disubstitution products 2,4-DTBP and 2,6-DTBP, which are more widely used antioxidants. : A synthesis of 2,4,6-tri-''tert''-butylphenol has been described that is also suitable as a teaching experiment.

Methyl tert-butyl ether Methyl ''tert''-butyl ether (MTBE), also known as ''tert''-butyl methyl ether, is an organic compound with a structural formula (CH3)3COCH3. MTBE is a volatile, flammable, and colorless liquid that is sparingly soluble in water. Primarily used a ...

is used as the

alkylating agent Alkylation is a chemical reaction that entails transfer of an alkyl group. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion, or a carbene (or their equivalents). Alkylating agents are reagents for effecting ...

and

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...

as catalyst. 2,4,6-TTBP is being obtained in 69% yield. :

Properties

2,4,6-Tri-''tert''-butylphenol is a white solid which dissolves in many organic solvents, but not in aqueous or alcoholic alkaline solutions. The green-blue coloring with iron(III)chloride, which is characteristic for phenols, does not occur in 2,4,6-TTBP. The compound is oxidizable in air but practically non-biodegradable. As an electron-rich aromatic, 2,4,6-tri-''tert''-butylphenol can also be easily oxidized electrochemically. In the alkaline, the phenolate anion formed is first oxidized in a

reversible reaction A reversible reaction is a reaction in which the conversion of reactants to products and the conversion of products to reactants occur simultaneously. : \mathit aA + \mathit bB \mathit cC + \mathit dD A and B can react to form C and D or, in the ...

to the phenoxy radical. The stable radical is oxidized by further electron withdrawal to the phenoxonium cation, which reacts in water to give 2,4,6-tri-''tert''-butyl-4-hydroxy-2,5-cyclohexadienone. : In acidic media, the hydroxydienone is dealkylated with the cleavage of the tert-butyl group in the 4-position to the 2,6-di-''tert''-butylhydroquinone, which is oxidized to the end product 2,6-di-''tert''-butyl-1,4-benzoquinone. : The oxidation of 2,4,6-tri-''tert''-butylphenol in the alkaline to the intensely blue-colored phenoxy radical can also occur with

potassium ferricyanide Potassium ferricyanide is the chemical compound with the formula K3 e(CN)6 This bright red salt contains the octahedral molecular geometry, octahedrally coordination compound, coordinated ferricyanide, e(CN)6− ion. It is soluble in wat ...

. The 2,4,6-tri-''tert''-butylphenoxy radical forms blue crystals on cooling to -70 °C which are stable at room temperature for several weeks and only gradually turn yellow. The phenoxy radical reacts with oxygen as a diradical to form a 4,4'-linked peroxide forming yellow crystals. :

Applications

The electron-rich 2,4,6-tri-''tert''-butylphenol can easily be oxidized to the phenoxy radical, which in the 4-position adds phenols, as well as alcohols and thiols to the corresponding cyclohexadienones. The cyclohexadienones, also referred to in the literature as , cleave the 4-position tert-butyl group upon heating under acidic conditions and aromatizes back to the substituted phenol. The reaction can be used for the synthesis of 2,6-di-''tert''-butyl-4-methoxyphenol, which is frequently used as an antioxidant. : 2,4,6-TTBP is used as

stabilizer Stabilizer, stabiliser, stabilisation or stabilization may refer to: Chemistry and food processing * Stabilizer (chemistry), a substance added to prevent unwanted change in state of another substance ** Polymer stabilizers are stabilizers used ...

s, free-radical scavengers and antioxidants in technical applications, such as in

fuel A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy or to be used for work (physics), work. The concept was originally applied solely to those materials capable of releasing chem ...

hydraulic fluid A hydraulic fluid or hydraulic liquid is the medium by which power is transferred in hydraulic machinery. Common hydraulic fluids are based on mineral oil or water. Examples of equipment that might use hydraulic fluids are excavators and backho ...

s and

lubricating oil A lubricant (sometimes shortened to lube) is a substance that helps to reduce friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move. It may also have the function of transmitting forces ...

s, as well as in elastomeric and thermoplastic polymers. Because of its pronounced

persistence Persistence or Persist may refer to: Math and computers * Image persistence, in LCD monitors * Persistence (computer science), the characteristic of data that outlives the execution of the program that created it * Persistence of a number, a ma ...

, its high tendency for

bioaccumulation Bioaccumulation is the gradual accumulation of substances, such as pesticides or other chemicals, in an organism. Bioaccumulation occurs when an organism absorbs a substance faster than it can be lost or eliminated by catabolism and excretion. T ...

and

aquatic toxicity Aquatic toxicology is the study of the effects of manufactured chemicals and other anthropogenic and natural materials and activities on aquatic organisms at various levels of organization, from subcellular through individual organisms to commun ...

, 2,4,6-TTBP is only of low industrial use and is even forbidden, for example, in

Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

. The phenoxy radical of 2,4,6-TTBP is also described as a sterically demanding

protecting group A protecting group or protective group is introduced into a molecule by chemical modification of a functional group to obtain chemoselectivity in a subsequent chemical reaction. It plays an important role in multistep organic synthesis. In man ...

in a

reagent In chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a ...

for the transfer of a nucleophilic dimethylaminomethyl group CH₃)₂-N-CH₂-to form

tertiary amines In chemistry, amines (, ) are organic compounds that contain carbon-nitrogen bonds. Amines are formed when one or more hydrogen atoms in ammonia are replaced by alkyl or aryl groups. The nitrogen atom in an amine possesses a lone pair of elec ...

Regulation

On January 23, 2024, on the basis of its being toxic for reproduction and being persistent, bioaccumulative, and toxic (PBT), 2,4,6-TTBP was added to EU REACH's Candidate List of Substances of Very High Concern ( SVHC) for Authorization.

References

{{DEFAULTSORT:Tri-tert-butylphenol, 2, 4, 6- Alkylphenols Tert-butyl compounds