2.6- Di-t-butylphenol

Phenols Substituted phenols 4-Methyl-2, 6-di-t-butylphenol (VI) No Often used in non-toxic formulations. Very low level of staining. Widely used to protect polymers during synthesis and fabrication. Volatility restricts high-temperature and long-term use. 

The peroxide decomposer will drastically reduce the number of radicals, which can then be more effectively mopped up by the chain-breaking materials. A widely used combination is 4-methyl-2,6,di-t-butylphenol and dilauryl thiodipropionate. It is possible to envisage most powerful combinations where a chain-breaking antioxidant, a regenerating agent, a peroxide decomposer, a metal deactivator and an ultraviolet absorber are all employed together. 

Furthermore, the reaction of several hindered phenols, such as 2,6-di-t-butyl-4-methylphenol, 3,5-di-t-butyl-4-hydroxybenzyl alcohol, and 2,6-di-t-butylphenol, with BTMA Br3 were carried out in dichloromethane in the presence of water, t-butyl alcohol, or aq. sodium hydroxide at room temperature. Sequential reaction processes were provided by the obtained products. As an example, we show the reaction of 2,6-di-t-butyl-4-methylphenol with BTMA Br3 in Fig. 26 (ref. 34). 

The arylation of electron-rich arenes, such as azulene (55)206 and heteroarenes, has been sporadically described. Under similar conditions phenols undergo arylation, which is preferably directed at the ort/zo-positions, probably due to the involvement of palladium phenolate intermediates.188,207 Polysubstitution occurs readily.208 The para-position can be attacked only with the sterically hindered 2,6-di-t-butylphenol.209 Similar ortho-diarylation of arenes bearing carbonyl groups (acetophenone, anthrone, benzanilide, etc.) shows that the or//zo-di reeling effect of the substituent is more important than its other electronic effects.189... 

An important antioxidant for many products is butylated hydroxytoluene (BHT), more properly named 4-methyl-2,6-di-t-butylphenol. Acid-catalyzed electrophilic aromatic substitution of a t-butyl cation at the activated positions ortho to the hydroxy group of /)-cresol yields this product, p-Cresol is obtained from coal tar or petroleum. 

For the oxidation of 2,6-di-t-butylphenol (42) to diphenoquinone (45) nickel peroxide has proved to be the most suitable reagent At the nickel hydroxide electrode 42 can be oxidized in 92 % yield to 45 (Eq. (8)). For this conversion a temperature of 50-70 °C is necessary, at 25 C the oxidation is very slow. 

The reagents which have been used here to illustrate these interesting reactions are periodic acid for the oxidation of 2,6-di-t-butylphenol,56 and a Celite-supported silver carbonate reagent for the oxidation of 2,6-dimethyl phenol, and 2,4,6-trimethylphenol57 (Expt 6.129). 

Di-t-butylphenol (2.06 g, 10 mmol) is dissolved in dimethylformamide (10 ml), an aqueous solution of 4 m periodic add (3.5 g, 4 ml) added, and the solution stirred at 85-95 °C (hot water bath) for 4-5 minutes. The coloured product partially crystallises out by this time. After 5-10 minutes at room temperature, the reaction mixture is diluted with 50 per cent aqueous methanol (8-10 ml), and the product isolated by filtration and washed with cold methanol. The resultant is recrystallised from aqueous acetone to give the product (94%) as brown-red needles, m.p. 245-247 °C. 

All benchmark chemicals, anthracene (AN), chlorpyrifos (CP), 2,6-di-t-butylphenol (DBP), y-hexachlorocyclohexane (HCH), and trichloroethylene (TCE) absorb UV light between 200-300 nm, but only anthracene and chlorpyrifos absorb solar photons (> 295 nm) rapidly enough to undergo direct photoreactions at significant rates. Table 15.2 summarizes the UV spectral properties of AN, CP, DBP, and two other compounds, p-nitroanisole (I) (PNA) and dinitramide ion (II) (DN ion), both of which directly photolyze in sunlight. 

In general, the introduction of spatially hindered phenols into coordination compounds may produce stable free-radical forms [138b—140]. A series of metal complexes with redox ligands, containing derivatives of 2,6-di-t-butylphenols n- or a-connected, or vicinal fragments in the coordination environment of the central metal atom, were synthesized in this way 7i-aryl [141], Tt-cr-allyl [142] compounds, nitrile complexes [143], metal glioximates [144], salicylaldiminates [145,146], por-phyrines [147-149], and phthalocyanines [150,151],... 

If both or o-positions of phenol are substituted by t-butyl groups, the reactivity of the compound is reduced regardless of the individual features of the system considered. This decrease in the reactivity of 2,6-di-t-butylphenols as compared to other phenols having similar Zo+ values may be attributed mainly to steric effects. These compounds,... 

Bellamy and Williams (1960) assumed that increasing volume of ortho alkyl substituents in phenols could enhance the lifetime of free 0—H groups. The 0—H group of 2,6-di-t-butylphenols was claimed to be free even in polar solvents. By contrast, Denisov et al. (1964) published... 

Let us now turn to paradox 2 (see p. 149) a lack of apparent sterio effect for 2,6-dimethylphenols in a polar medium (Fig. 2) while different Hammett equations were found for 2,6-dimethylphenols in non-polar media (e.g., Howard and Ingold, 1963b). The data of Table 6 suggest a gradation in the diminution of K when ortho substituents are introduced to phenol. Accordingly, the ratio (simple phenols while it is about 2 for 2,6-dimethylphenols. Thus equation (37) indicates a possible compensation for 2,6-disubsti-tuted phenols as K is decreased by ortho substituents, the rate constant k2 has to be multiplied by an increased factor expressing enhanced contribution of free phenol molecules to the overall rate. In case of 2,6-di-t-butylphenols, however, even the partial rate constant of free molecules ( j) is so markedly reduced that the compensation by the factor (ac + K)l(K + 1) is no longer effective. 

Other Derivatives of Isobutylene. The production of many smaller-volume chemicals is based on high-purity isobutylene. The major chemicals are para-t-butylphenol, di-t-butyl-p-cresol (butylated hydroxytoluene, BHT), 2,6-di-t-butylphenol, t-butylamine, t-butyl mercaptan, and isobutyl aluminum compounds. Isobutylene usage by each of these six ranged from 8 to 18 million lb. The total volume of isobutylene that went for small-volume chemical production was about 140 million lb in 1997. 

The substituted phenols and cresols constitute about half the total volume of this group. Para-t-butylphenol is produced by the alkylation of phenol with isobutylene. The principal applications for this derivative are in the manufacture of modified phenolic resins for the rubber industry and in surface coatings. BHT is obtained from isobutylene and p-cresol. Technical-grade BHT is an antioxidant for plastics and elastomers, and is a gum inhibitor in gasoline. Food-grade BHT is an antioxidant in edible oils, preserves, and many other foods. 2,6-Di-t-butylphenol is used to produce a wide range of plastics additives, antioxidants, and gasoline additives. 

Aryl substituents in either the 2- or 2,6-position cause a downfield shift of the OH stretching frequency in CCI due to the formation of an intramolecular hydrogen bond to the aromatic ring 170) (phenol 3605 cm-1, 2-phenylphenol and 2,6-diphenyl-phenol 3555 cm "1 2,4,6-triphenylphenol 3553 cm-1). Under the same conditions t-butyl-phenols give rise to higher frequencies (2,6-di-t-butylphenol and 2,4,6-tri-t-butylphenol 3645 cm-1, compared with phenol 3612 cm-1)171). 

Hindered phenols including 2,6-di-t-butylphenol are protected using BoCjO-DMAP, while deprotection is accomplished with TFA at room temperature in 3 M HCl/dioxane at reflux. ... 

Both the catalysed and uncatalysed decompositions can be stopped by a radical inhibitor such as 2,6-di-t-butylphenol, but after a period the inhibitor is consumed and the decomposition recommences. If an alkyl halide or alkyne is added to the system, the evolution of hydrogen is quenched, and the substrates show the reactions which are characteristic of stannyl radicals. 

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