2,4,6-Trisubstituted phenol

Secondary aromatic amines, such as phenyl beta-naphthylamine. have been used as antioxidants in elastomers, but the preferred antioxidants for plastics have been 2,6-disubstituted and 2,4,6-trisubstituted phenols. These hindered phenols serve as chain transfer agents with the macroradicals which are produced by the degradation of polymers. 

Since 2,4,6-trisubstituted phenols are readily oxidized to fairly stable phenoxy radicals, this system has been used to construct various biradical species. The bisphenol 6 below loses three hydrogens to form the very stable crystalline radical galvinoxyl.86... 

SCHEME 61. Oxidation of 2,4,6-trisubstituted phenols with t-BuOOH-heteropolyacid... 

However with 2,4,6-trisubstituted phenols electron-transfer occurs followed by nucleophilic attack by nitrile solvent. Alkyl group rearrangement or loss ultimately leads to benzoxazole products. 

Eleven years later Haubein (1964) applied for a patent for the N-methylcar-bamate group of 2,4-6-trisubstituted phenols as selective herbicides. 2,6-Di-/-butyl-... 

Scheme 6.20. This ruthenium catalyst (10 mol%) was active for the cydization of ds-1 -ethynyl-2-vinyloxiranes to afford various 2,6-disubstituted phenols in reasonable yields. Under similar conditions, 1,1,2,2,-tetrasubstituted oxiranes gave the 2,3,6-trisubstituted phenols with a skeleton reorganization [22]. The 1,2-deuterium shift of the alkynyl deuterium of d-Sle was indicative of mthenium vinylidene intermediates (Scheme 6.20).

Naphthol can successfully be dimerized oxidatively, selectively through the o-site to give (22) using copper(II)-amine complexes (70%) or manganese(III) acetylacetonate (69%), and o-o coupling is the major paAway (90%) on ferricyanide oxidation of the trisubstituted phenol (23) to the orthodiphenoqui-none (24). In this context it is of interest that a compound obtained (74%) on ferricyanide oxidation of... 

The 1,3-disubstituted phosphinite (171) (AP) 149 ppm) can be prepared by reaction of the precursor diol with two equivalents of Pr 2PCl in THF with DMAP (Equation (42)).398 The unsymmetrical tertiary phosphite (172) was synthesized by reaction of two equivalents of phenol with the dichloroprecursor (173) (Equation (43)).399 Similar to (173) is (174) (Scheme 12), prepared by stoichiometric reaction of the trisubstituted phenol and PC13. 0 This general approach was also employed in the preparation of the Q-symmetric phosphite (175). 1 The cyclic phosphite (175) is remarkably stable with respect to oxidation. Even after reflux in toluene or acetone/water in the presence of air for 24 h, no decomposition was observed, strongly contrasting with the behavior of P(OPh)3. Phosphite (175) displays very good stability to hydrolysis. 

The analysis of the co- condensation products of the commercial melamine formaldehyde resin Kauramin 700 (BASF AG) with the same trisubstituted phenols gives the stmctures given in Scheme 8. These structures confirm that the phenolic resin covalently bonds into the melamine network [120]. 

Oxidative coupling polymerizations represent a general reaction for the preparation of high molecular weight linear polymers from many 2,6-di- and 2,3,6-trisubstituted phenols. When the ortho substituents on the phenols are relatively unhindered alkyl or aryl groups, the poly(phenylene oxide) is the chief product (40,41). Bulky ortho substituents, eg, fe/t-butyl, lead to the formation of... 

HR modification with MA is accompanied by secondary reactions. Branches and crosslinks can appear by intermolecular grafting or by direct radicalic processes between species. Another possible reaction allowed by the presence of some impurities (Si, HjO, Na", K", Ca, Mg ) is MA decomposition, which can evolve toward explosion. To avoid secondary reactions, additives are introduced into the system (phenols, di- and trisubstituted phenols, Cu-naphthenate and acetylace-tone, halogenated triazine, triazols, phenylenediamine, phenylenecatechol). 

Catalytic hydrogenation in acetic anhydride-benzene removes the aromatic benzyl ether and forms a monoacetate hydrogenation in ethyl acetate removes the aliphatic benzyl ether to give, after acetylation, the diacetate. Trisubstituted aDcenes can be retained during the hydrogenolysis of a phenolic benzyl ether. ... 

The final structure of resins produced depends on the reaction condition. Formaldehyde to phenol (F/P) and hydroxyl to phenol (OH/P) molar ratios as well as ruction temperahne were the most important parameters in synthesis of resols. In this study, the effect of F/P and OH/P wt%, and reaction temperature on the chemical structure (mono-, di- and trisubstitution of methyrol group, methylene bridge, phenolic hemiformals, etc.) was studied utilizing a two-level full factorial experimental design. The result obtained may be applied to control the physical and chemical properties of pre-polymer. 

F/P molar ratio showed an increasing effect, while ruction temperature demonstrated a decreasing effect on mono-substitution of methylol group. Three independent variables demonstrated no statistically significant effect on di-substitution of methylol groups. Trisubstitution of methylol groups, para methylol phenols, o-p methylme brid, dirnCT formation, the amount of firee phenols, and the fraction of o-p Vp-p were dependent on all of the three indqrendent variables. 

Intermolecular hydroalkoxylation of 1,1- and 1,3-di-substituted, tri-substituted and tetra-substituted allenes with a range of primary and secondary alcohols, methanol, phenol and propionic acid was catalysed by the system [AuCl(IPr)]/ AgOTf (1 1, 5 mol% each component) at room temperature in toluene, giving excellent conversions to the allylic ethers. Hydroalkoxylation of monosubstituted or trisubstituted allenes led to the selective addition of the alcohol to the less hindered allene terminus and the formation of allylic ethers. A plausible mechanism involves the reaction of the in situ formed cationic (IPr)Au" with the substituted allene to form the tt-allenyl complex 105, which after nucleophilic attack of the alcohol gives the o-alkenyl complex 106, which, in turn, is converted to the product by protonolysis and concomitant regeneration of the cationic active species (IPr)-Au" (Scheme 2.18) [86]. 

To summarize the conclusions from the foregoing data, which of course are not sufficient for broad generalizations, we found that the additivity principle predicts reactivities of a correct order of magnitude for 1,2-disubstituted and 1,3,5-trisubstituted compounds. In general, the observed reactivities were somewhat lower than the predicted ones, with the exception of sites located para or ortho to a phenolic hydroxyl adjacent... 

Application of the alcohol interchange reaction (method 6) is limited by certain phenols and also di and trisubstituted glyoxides (while the reaction of metals with glycols gives only monosubstituted derivatives) [745, 621, 575, 1584,1369]. As redox processes (method 7) can be considered the Grignard-type reactions — the interaction of metal alkyls with carbonyl compounds,... 

Crosslinking has no specific direct effect on thermal degradation crosslinks can be either weak points (e.g., tertiary carbons in polyester or anhydride-cured epoxies) or thermostable structural units (e.g., trisubstituted aromatic rings in phenolics, certain epoxies, or certain thermostable polymers). Indirect effects can be observed essentially above Tg crosslinking reduces free volume and thus decreases 02 diffusivity. It also prevents melting, which can be favorable in burning contexts. 

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