Phenoxy intermediate

Where direct amination of chloro compounds has proved unsatisfactory, 4-alkoxy or 4-phenoxy intermediates have sometimes been used for reactions with amines or hydrazine. 

For the isomerization of toluene via methoxy and benzene intermediate, the similar proton activation, which results in the formation of a phenoxy intermediate, is achieved (see Figure 9). As previously, the bond between the zeolitic oxygen atom and the aromatic carbon atom stretches out. A "free" Wheland complex is eventually reached which can reorient to favor the position of the toluene methyl group with the demethylation transition state. 

The formation of the phenoxy intermediate turns to be unlikely to occur as this intermediate remains at similar energy level as observed from the cluster proach (i.e. + 150 kJ/mol), whereas protonation step and Wheland complex energy levels are around +110 kJ/mol with respect to physisorbed toluene. 

Chemical Properties. Lignin is subject to oxidation, reduction, discoloration, hydrolysis, and other chemical and enzymatic reactions. Many ate briefly described elsewhere (51). Key to these reactions is the ability of the phenolic hydroxyl groups of lignin to participate in the formation of reactive intermediates, eg, phenoxy radical (4), quinonemethide (5), and phenoxy anion (6) ... 

When the reaction was carried out on the phenoxy derivative 106, only 107 was obtained (Scheme 44) (88JHC1551). The formation of this product was rationalized assuming a heteroly tic cleavage of the O—N bond followed by isomerization (Scheme 44). If the reaction occurs in the excited triplet state of the molecule, the biradical is the most probable intermediate. 

The authors formulate the mechanism in two steps, first an electron transfer from phenoxide ion to diazonium ion forming a radical pair, followed by attack of the diazenyl radical at the 4-position of the phenoxy radical and a concerted proton release, i. e., without involving the o-complex. Admittedly, there is no experimental evidence against such a concerted process, but also none for it It seems that those authors wanted only to demonstrate the occurrence of radical intermediates, but did not consider the question of the mechanism of the proton release. 

The oxidation generates highly delocalized phenoxy radicals (PhO, Scheme 2.21), which may initiate (i) a radical polymerization process, trapping the reactant (CF) to give a benzyl radical intermediate (QMR), or it may (ii) follow a radical coupling to produce the p-QM p-O-QM, which being a reactive electrophile could undergo cationic polymerization. 

The radicals (14) formed may be trapped with, for example, (10) above. Simple alkyl thiyl radicals such as MeS have been detected as reaction intermediates they are highly reactive. Relatively stable oxygen-containing radicals are also known. Thus the phenoxy radical (15),... 

In a recent study, another method for microwave-assisted heterocycle synthesis leading to a small set of imidazole derivatives has been reported [54], These pharmaceutically important scaffolds were synthesized utilizing polymer-bound 3-N,N-(dimethylamino)isocyanoacrylate. This polymer support was easily prepared by treatment of [4-(bromomethyl)phenoxy]methyl polystyrene with a twofold excess of the appropriate isocyanoacrylate potassium salt in N,N-dimethylformamide (Scheme 7.37). The obtained intermediate was subsequently treated with N,N-di-methylformamide diethyl acetal (DMFDEA) in a mixture of tetrahydrofuran and ethanol to generate the desired polymer-bound substrate. 

The hydroxylation of aromatic compounds using microorganisms is more predictable and a number of processes have been adapted to large scale, for example the preparation of 6-hydroxynicotinic acid1781 and (R)-2-(4-hydroxy-phenoxy)propanoic acid1791, important intermediates to pesticides and herbicides respectively. 

When the decomposition of the zwitterionic intermediate is rate-determining, the effect of the solvent is crucial since it may produce changes in the mechanisms and in the rate-determining step. A recent study of the kinetics of the reactions of 1-chloro-, 1-fluoro- and l-phenoxy-2,4-dinitrobenzene with piperidine, n-butylamine and benzylamine in ethyl acetate and THF indicated that these reactions resemble those in dipolar aprotic solvents when primary amines are the nucleophiles (i.e. that shown in equation 1, with... 

Caldwell, E.S. and Steelink, C. (1969). Phenoxy radical intermediates in the enzymatic degradation of lignin model compounds. Biochimica et Biophysica Acta, 184,420-431. 

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