Regeneration of phenols

Phenols can be regenerated from the corresponding carboxylates or carbonates by reaction with sodium hydrogen tellnride. 

Cleavage of aryl carboxylates (general procedure) To a solution of NaHTe (prepared from Te (1.30 g, 10 mmol) and NaBH4 (0.90 g, 24 mmol) in EtOH (20 mL)) buffered with AcOH (1.2 ml) in EtOH (5 ml.) is added the aryl carboxylate (5 mmol). The mixture is refluxed for 30 min, poured into ice-H20 (200 mL), extracted with CHCI3 and the 

Cleavage of aryl carbonates (general procedure)To a solution of NaHTe prepared in situ from tellurium powder (1.3 g) and NaBH4 (0.9 g) in EtOH (20 mL) bnffered with deoxygenated HO Ac (1.2 mL in 5 mL EtOH) is added the aryl ethyl carbonate (5 mmol) and the mixture refluxed under N2 for 30 min. The reaction mixture is filtered, the filtrate evaporated and the residue dissolved in H2O. The aqueous layer is slightly acidified with a few drops of HOAc. The respective phenols are obtained in quantitative yields. 

The haloacetate group, also used as a protecting group for the phenolic function, can be removed by treatment with sodium telluride in DME, giving the parent phenol.  

By quenching the reaction with an alkyl halide, alkyl aryl ethers are formed  

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JORGENSEN L V, MADSEN H L, THOMSEN M K, DRAGSTED L o and SKIBSTED L H (1999) Regeneration of phenolic antioxidants from pheroxyl radicals. An ESR and electrochemical study of antioxidant hierarachy, Free Rad Res, 28, 207-20. 

Similarly, the regeneration of phenols 52 from carboxylates 53,115 carbonates 54,116 or allyl ethers 55114 derivatives is performed with nucleophilic tellurium species (Scheme 28). 

Zhang H, Ye L, Zhong H (2002) Regeneration of phenol saturated activated carbon in an electrochemical reactor. J Chem Technol Biotechnol 77 1246-1250... 

Although aminyl radicals are stable towards oxygen, they can oxidi2e other aromatic amines, phenols and thiols (10), and regenerate the diarylamine. Thus, mixtures of phenols and diarylamines frequendy show better antioxidant activity than either one alone. This is called synergism. 

C4 = cost of makeup + cost of regeneration = 0.05 X unit cost of fresh resin /kg -f 0.426 X cost of sodium hydroxide /kg X amount of phenol adsorbed (kg phenol/kg resin)... 

Elimination of phenol gives acetone as co-product and regenerates the acid catalyst. 

The mechanism of the orf/to-dibromination of phenol with NBS in the presence of amines is considered as follows. The hydrogen bonding between phenol and N-bromoamine which are generated from the reaction of NBS and amines (ref. 14), is the driving force, and causes the bromination at one o/t/io-position of phenol and regeneration of the amines. A catalytic amount of the amines is enough because of the regeneration of the amines. The repetition of the above process causes one more substitution at the other orf/io-position of 2-bromophenol. In the cases of 2-substituted phenols the orf/io-bromination can occur only once (Scheme 5). 

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]. 

In some cases it becomes necessary to use a chemical method of regeneration. Thus, phenolic substances, when adsorbed on activated carbons or polymeric adsorbents, are regenerated using aqueous solutions of sodium hydroxide of an appropriate concentration. 

Polymeric adsorbents have also been found to be very useful, and even highly water-loving undesired materials like p-toluene sulphonic acid from waste streams can be recovered via ad.sorption and regeneration with solvents like fv -propanol. In such instances, the regeneration of activated carbons is not satisfactory, even with aqueous sodium hydroxide. Solutes like phenols, substituted phenols, aromatic amines, heterocyclic amines (pyridine, picolines, etc.) can be recovered, in a rewarding way, from aqueous solutions. 

During decomposition of plant remains, many phenolic compounds are released by leaching, microbial degradation or are synthesized by microbial activity. In forestry, problems of natural regeneration and reforestation are connected to the presence of phenolic substances deposited in the soil. Methods for extrachon and identification of toxic substances from different soil types (mineral or organic) are described. The method for extracting of soil phytotoxins is based on the use of ethylacetate and methanol (free phenolics) and alkaline hydrolysis (bound phenolics). 

Consequently, in an inert atmosphere/= 2(1 + k(lls/krcc) > 2. When phenoxyl radicals react only with peroxyl radicals, /= 2 and there is no regeneration. At low dioxygen pressures, phenoxyl radicals react with both peroxyl and alkyl radicals / ranges between 2 and 2(1 +kdis/krec) and increases with decreasing p02- In addition to this, the product of phenol oxidation, quinone, becomes the efficient alkyl radical acceptor at low dioxygen pressure (see earlier). 

Regeneration of superoxide during the oxidation of thiols hints at the possible prooxidant effect of these antioxidants. This suggestion was recently confirmed by Mottley and Mason [212] who have showed that superoxide was formed in the oxidation of DHLA by horseradish peroxidase in the presence of phenol. However, DHLA is dithiolic compound and the other mechanisms such as the concerted mechanism, which has been proposed earlier for flavonoids may be realized (Figure 29.6). 

AUyl ethers are cleaved with sodium hydrogen teUmide with regeneration of the parent phenols. ... 

In flavin-dependent monooxygenases, a flavin-oxygen intermediate reacts with the substrate, also producing water in a second step, and requiring cofactors for regeneration of the flavin moiety. The unusual flavoprotein vanillyl-alcohol oxidase (EC 1.1.3.38), in which the flavin moiety is covalently bound, catalyzes the oxidation of p-substituted phenols as well as deamination, hydroxylation and dehydrogenation reactions [10]. 

A maximum phenol conversion of 65% was reached, due to the fact that the consumption of benzoic acid was higher than that of phenol. Indeed, despite the 1/1 load ratio, the selectivity to those products the formation of which required two moles of benzoic acid per mole of phenol, made the conversion of benzoic acid approach the total one more quickly than phenol. A non-negligible effect of catalyst deactivation was present in fact, when the catalyst was separated from the reaction mixture by filtration, and was then re-loaded without any regeneration treatment, together with fresh reactants, a conversion of 52% was obtained after 2.5 h reaction time, lower than that one obtained with the fresh catalyst, i.e., 59% (Figure 1). The extraction, by means of CH2CI2, of those compounds that remained trapped inside the zeolite pores, evidenced that the latter were mainly constituted of phenol, benzoic acid and of reaction products, with very low amount of heavier compounds, possible precursors of coke formation. 

N.A. Silicic acid, silicates, flavonoids, phenolic acid, nicotine, sterols.100 Regeneration of connective tissue, clotting agent, astringent effect on genitourinary system. 

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