Dehydroxylation, of phenols

DEHYDROXYLATION OF PHENOLS HYDROGENOLYSIS OF PHENOLIC ETHERS BIPHENYL... 

Pyrolysis of 4-ethylguaiacol yielded 4-ethylphenoI by cleavage of the O-C (alkyl) and O-C (aryl) bonds . Similarly, methyl-, dimethyl- and vinylphenols originated from guaiacol intermediates. It has also been reported that phenol is a secondary pyrolysis product of guaiacol and derivatives. Phenol, cresol, ethylphenol, dimethylphenol, propytphenol and methylcatechol were the main components of the oil fraction in the fourth step. Traces of hydrocarbons such as toluene and styrene were produced by the dehydroxylation of phenols in this fraction. 

Novel aromatic carboxylation reactions have been observed in the anaerobic transformation of phenols to ben2oates (82). A mixed anaerobic microbial consortium apparentiy transforms phenol (33) through an intermediate to ben2oic acid (34) via dehydroxylation. This reaction has not yet been widely exploited for its obvious synthetic value. 

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 ... 

Brackmann R, G Fuchs (1993) Enzymes of anaerobic metabolism of phenolic compounds. 4-hydroxybenzoyl-CoA reductase (dehydroxylating) from a denitrifying Pseudomonas sp. Eur J Biochem 213 563-571. 

It can be concluded from these observations that whereas benzoate produced by the carboxylation of phenols can be degraded, dehydroxylation with the formation of substituted benzoates may produce stable terminal metabolites. 

The anaerobic degradation of phenol proceeds by carboxylation of phenyl phosphate, followed by dehydroxylation, and fission of the ring after partial reduction (Brackmann and Fuchs 1993). 

The degradation pathway of p-cresol in groundwater appears to proceed by oxidation of the methyl group to first give the corresponding benzaldehyde, then benzoic acid (Kuhn et al. 1988 Smolenski and Suflita 1987 Suflita et al. 1988, 1989). The hydroxybenzoic acid then can be either decarboxylated or dehydroxylated to phenol or benzoic acid, respectively. 

Reduction of Phenols and Phenolic Esters and Ethers175 Hydro-de-hydroxylation or Dehydroxylation, etc. 

A corollary of this statement is the following If these polyaromatic or polycyclic saturated structures are present in the carbon skeleton of coal, they should be identified in the short-contact-time liquefaction products. The possibility of some isomerization reactions in the carbon skeleton cannot be excluded totally, but the most important fact is that no dramatic aromatization of hydroaromatic rings or saturation of aromatic rings takes place under these conditions. Many of the chemical functions also are stable under these conditions, especially the O, S, and N heterocyclic aromatic structures. Water formation by phenol dehydroxylation is minimal. In coal liquefaction under our conditions, even at long reaction times (up to 90 min) in the absence of an added catalyst, the -OH bonded to a monoaromatic ring is stable. Under the same conditions, dehydroxylation of polyaromatic phenols does occur (10). 

Our interest in the enzymatic functionalization of phenol derived from our discovery of a Mn- and K-dependent Carboxylase enzyme isolated from some anaerobic bacteria growing on phenol. This enzyme converts, under mesophilic conditions, very specifically phenol into 4-OH-benzoate that is thereafter dehydroxylated to benzoic acid and metabolized (Scheme 1) [5]. 

With H-MFI, the p-/o-HAP ratio was much higher this is indicative of shape-selectivity effects. With all the catalysts, HAP selectivity was poor, phenol being the main product because of the rapid dissociation of PA [9,10]. Very fast deactivation as a result of coke deposition and zeolite dehydroxylation was also observed. Catalyst stability can, however, be considerably improved by use of equimolar mixtures of PA and water or of phenol and acetic acid (AA) instead of PA [11]. 

Dehydroxylation of 4-tert-butyl-2,6-dimethoxyphenol was achieved in the following way. The phenol as its diethyl phosphate in tetrahydrofuran/t-butanol was added to 100% ammonia into which small pieces of lithium were introduced over 1 hour. Further lithium was added to maintain a blue cobur whereby... 

Phenolic acid derivatives (cinnamic acids) and degradation products of flavonoids (phenylpropionic and phenylacetic acids) suffer transformations by caecal bacteria. The following transformations have been observed dehydroxylation of 3,4-dihydroxy derivatives to give 3-hydroxy compounds, demethylation of o-hydroxy-methoxyphenolic acids, reduction of the double bonds of cinnamic acids to yield the corresponding phenylpropionic acids, decarboxylation of cinnamic and phenylacetic acids (only when 4-hydroxyl is present), hydroxylation of... 

Water, CO, and methane were the major light products and reached yields of 0.0058, 0.0038 and 0.0048 respectively, after 30 min. Both methane and carbon monoxide were primary products whereas water, evolved by ring dehydroxylation, was largely a secondary product from the reactions of phenolic units. 

Musliner-Gates dehydroxylation of (+ )-bulbocapnine (31) generated ( + )-laureline (32). Also, reduction of the diethyl phosphate ester of ( + )-bulbo-capnine with lithium in liquid ammonia afforded the phenol (33). ... 

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