Phenols decarboxylative

Synthetic phenol capacity in the United States was reported to be ca 1.6 x 10 t/yr in 1989 (206), almost completely based on the cumene process (see Cumene Phenol). Some synthetic phenol [108-95-2] is made from toluene by a process developed by The Dow Chemical Company (2,299—301). Toluene [108-88-3] is oxidized to benzoic acid in a conventional LPO process. Liquid-phase oxidative decarboxylation with a copper-containing catalyst gives phenol in high yield (2,299—304). The phenoHc hydroxyl group is located ortho to the position previously occupied by the carboxyl group of benzoic acid (2,299,301,305). This provides a means to produce meta-substituted phenols otherwise difficult to make (2,306). VPOs for the oxidative decarboxylation of benzoic acid have also been reported (2,307—309). Although the mechanism appears to be similar to the LPO scheme (309), the VPO reaction is reported not to work for toluic acids (310). 

A Methylamino)phenol. This derivative, also named 4-hydroxy-/V-methy1ani1ine (19), forms needles from benzene which are slightly soluble in ethanol andinsoluble in diethyl ether. Industrial synthesis involves decarboxylation of A/-(4-hydroxyphenyl)glycine [122-87-2] at elevated temperature in such solvents as chlorobenzene—cyclohexanone (184,185). It also can be prepared by the methylation of 4-aminophenol, or from methylamiae [74-89-5] by heating with 4-chlorophenol [106-48-9] and copper sulfate at 135°C in aqueous solution, or with hydroquinone [123-31 -9] 2l. 200—250°C in alcohoHc solution (186). 

Other routes for the preparation of phenol are under development and include the Dow process based on toluene. In this process a mixture of toluene, air and catalyst are reacted at moderate temperature and pressure to give benzoic acid. This is then purified and decarboxylated, in the presence of air, to phenol (Figure 23.5). 

The shikimate pathway is the major route in the biosynthesis of ubiquinone, menaquinone, phyloquinone, plastoquinone, and various colored naphthoquinones. The early steps of this process are common with the steps involved in the biosynthesis of phenols, flavonoids, and aromatic amino acids. Shikimic acid is formed in several steps from precursors of carbohydrate metabolism. The key intermediate in quinone biosynthesis via the shikimate pathway is the chorismate. In the case of ubiquinones, the chorismate is converted to para-hydoxybenzoate and then, depending on the organism, the process continues with prenylation, decarboxylation, three hydroxy-lations, and three methylation steps. - ... 

It has become clear that benzoate occupies a central position in the anaerobic degradation of both phenols and alkylated arenes such as toluene and xylenes, and that carboxylation, hydroxylation, and reductive dehydroxylation are important reactions for phenols that are discussed in Part 4 of this chapter. The simplest examples include alkylated benzenes, products from the carboxylation of napthalene and phenanthrene (Zhang and Young 1997), the decarboxylation of o-, m-, and p-phthalate under denitrifying conditions (Nozawa and Maruyama 1988), and the metabolism of phenols and anilines by carboxylation. Further illustrative examples include the following ... 

The disassembly mechanism of dendron 27 is illustrated in Fig. 5.22. Cleavage of the trigger initiates the cyclization of a dimethylurea derivative to release phenol 28. The latter can undergo 1,8-elimination followed by decarboxylation to release one reporter unit and to generate quinone methide 29. In the next step, a nucleophile (most likely a solvent molecule) presumably reacts with the highly electrophilic quinone methide to generate the phenol 30. Similarly, we hypothesize that one more 1,8-elimination and four 1,6-eliminations take place to lead to the release of all six reporters. 

Following the enzymatic cleavage, azaquinone methide was rapidly eliminated and decarboxylation occurred, leading to internal cyclization that released a urea derivative and phenol 35. The latter was disassembled as previously described to generate two equivalents of phenol 36, which was further fragmented to release the four reporter groups. 

The disassembly pathway of molecular probe 39 is initiated by catalytic cleavage of phenylacetic acid by PGA, elimination of azaquinone methide, decarboxylation, and cyclization to release dimethylurea derivative and phenol 40 (Fig. 5.38). The latter rapidly undergoes double quinone methide elimination to release the two reporter units and by-product 41. The output of these cascade... 

It seems most likely that the presence of the styrene compound was at least partially responsible for the inhibition of prickly sida germination and root length, since ferulic acid alone (prickly sida seed without carpels plus ferulic acid) had no effect on prickly sida germination or root length (Table XI). The decarboxylation of phenolic acids to corresponding styrenes is known from studies on fungi and bacteria (60, 61). However, in a number of studies directly concerned with the microbial decomposition of ferulic acid, as well as other phenolic acids, no mention is made of any styrene compounds produced as a result of phenolic acid decarboxylation (62, 63, 64, 65). 

The low specificity of electron-donating substrates is remarkable for laccases. These enzymes have high redox potential, making them able to oxidize a broad range of aromatic compounds (e.g. phenols, polyphenols, methoxy-substituted phenols, aromatic amines, benzenethiols) through the use of oxygen as electron acceptor. Other enzymatic reactions they catalyze include decarboxylations and demethylations [66]. 

Decarboxylase Decarboxylation of amino adds and simple phenolic adds, primarily p-hydroxylated L-dopa, tyrosine... 

Decarboxylation of 4 to phenol 7 occurs but only few expected compounds derived from oxidation of phenol were detected in traces such as fumaric acid. 

At alkaline conditions (pH=l 1) no phenol, hydroquinone were detected. This is possibly due to the fact that the rate of phenol oxidation increases under alkaline conditions with optimum pH between 9.5 and 13 [17] and so once it is formed, it is readily oxidised. The absence of phenol and increased concentration of p-hydroxybenzoic acid could be also explained by reduced decarboxylation rates under conditions of high pH, which would result in the oxidation of p-hydroxybenzaldehyde to form p-hydroxybenzoic acid. 

Landete and others (2009) reported that Lactobacillus plantarum have the ability to metabolize phenolic compounds found in olive products (such as oleuropein, hydroxytyrosol, and tyrosol, as well as vanillic, p-hydroxybenzoic, sinapic, syringic, protocatechuic, and cinnamic acids). For example, oleuropein was metabolized mainly to hydroxytyrosol, whereas protocatechuic acid was decarboxylated to catechol by the enzymatic actions. 

Related to a class of a,y-diketoacids that has previously been shown to bind to NS5B [64], is the mono-ethyl ester of meconic acid 25. This compound was identified as a selective inhibitor of NS5B HCV polymerase (IC50 = 2.3 pM) and is competitive with the diketoacids. SAR studies have demonstrated the requirement for the carboxylic acid. A variety of different permutations of esters, acids, amides, and decarboxylated compounds were prepared without any improvement in binding affinity or in the cell-based replicon assay [65]. The 4,5-dihydroxypyrimidine-6-carboxylic acids, a hybrid of the a,y-diketoacids and meconic acid, envisioned as chelators of the essential Mg2+ ions in the active site of NS5B, are also active in the polymerase assay (26, IC5o = 5.8pM). While alkylation of the phenol of the hybrid is tolerated, methylation of the heterocyclic hydroxyl groups or the carboxylic acid, as well as decarboxylation, leads to... 

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