Phenol 2-halophenols

Finally, it may be pointed out that substances such as phenols, halophenols, polynuclear aromatic and heterocyclic compounds are well suited for micro and... 

When reactant mineralization is the treatment goal (no residual dissolved organic material), a useful measure of reaction lifetime might be achievement of a satisfactory mineralization, e.g., 95% generation of maximum possible CO2. For simple reactants such as PCE, this corresponds essentially to the same reaction time as 95% PCE disappearance (see Fig.5). For more complex reactants, such as benzene and all other aromatics in particular (phenols, halophenols, PCBs, etc), the time required for 95% appearance of final CO2 may be several multiples of the reactant 95% disappearance time. This same point was emphasized recently by Matthews [45]. 

Other halophenols are miticides, bactericides, and leather preservatives. Halophenols account for about 5% of phenol uses. 

Other salts, especially fluoride salts, (e.g., KF) can be used to perform nucleophilic substitution. As is well known, halides, and particularly the fluoride anions, are rather powerful Lewis bases and can exert a catalytic effect on aromatic nucleophilic substitutions in dipolar aprotic solvents. Phenols can be alkylated in the presence of KF (or CsF) absorbed on Celite64,65 or Et4NF.66 Taking advantage of this reaction, halophenols and dihalides with bisphenols have been successfully polymerized in sulfolane at 220-280°C by using KF as the base. 

In contrast to the high reactivity of meta- and para-substituted halophenols, ortho-halo-phenols give low yields, even after prolonged reaction times with the [Rh(COD)Cl]2/... 

Halogenated Aromatic Compounds Halogenated Cresols Halogenated Ethers and Epoxides Halogenated Phenolic Compounds Halophenols Chlorophenol Dichlorophenol Halophenols Pentachlorophenol PCP Tetrachlorophenol Trichlorophenol... 

The formation of 3-halophenols in the metabolism of chlorobenzene, bromobenzene, and fluorobenzene215 cannot be explained on the basis of arene oxides as intermediates. These metabolites may represent examples of a direct hydroxylation of the ring. Besides, the magnitude of the isotopic effects observed during the metabolic formation of such meta-substituted phenols... 

Oxidative phenolic coupling.1 The vancomycin antibiotics are polypeptides with bridging diphenyl ether groups. Evans et al. have shown in model systems such as 1 that cyclization to o-halophenolic peptides (2) can be accomplished by oxidation with thallium(III) nitrate in THF-methanol or CH2Cl2-methanol followed by CrCl2 reduction of a para-quinol intermediate (a). In three cases the yield of cyclic products was 40-48%. 

Halophenols are readily hydrogenated to give cyclohexanols by use of Raney Ni-A1 alloy in a saturated barium hydroxide solution under mild conditions.78 For example, when Raney Ni-Al alloy (12 g) was added slowly to a mixture of pentachlorophenol (1.73 g, 6.5 mmol) and a saturated aqueous solution of Ba(OH)2 at 60°C, cyclohexanol was obtained in 91 % yield. It has been suggested that halophenols are first hydrogenated to halocyclohexanols and then dehalogenated to give cyclohexanols, since phenol itself gave only a trace amount of cyclohexanol with an almost quantitative recovery of phenol under these conditions. 

The photochemistry of the halogenated anilines had received little attention until about 10 years ago, when the elucidation of the mechanisms of the photolysis of the halophenols, as described above, raised the question of the more general applicability of the obtained results. As will be detailed below, there are indeed close similarities between the halogenated phenols and anilines, but characteristic differences also exist. 

Singular examples to form aromatic ethers are a base-catalyzed, multistep, one-pot reaction of aryl methyl ketones with the appropriate fluorinated arylidenemalonitriles, the mercury acetate assisted synthesis of pentahalophenylvinyl ethers from vinyl acetate and the corresponding phenol, and the radical displacements in aryloxycyclohexadienones (e.g., 27) by halophenols. 2,3-Dichloro-5,6-dicyanohydroquinone (28) and products such as 29 are readily formed when cyclohexadienone 27 is treated with different phenols. 

Quinones from phenols Under acidic conditions (70% perchloric acid in HOAc) phenols are converted to p-benzoquinones at room temperature. The oxidation proceeds even with p-halophenols such as 2,4,6-trihalophenols, giving 2,6-dihalo-p-benzoquinones in high yields. 

During the 160 years since the discovery of phenol, thousands of studies were conducted on halophenols, partly due to their significance in the theory of hydrogen bonding indeed their hydrogen bonding abilities can be varied nearly continuously over a wide pATj range from 10.2 to 0.4 - ". 

In the case of 3-X-phenols, the X-protonated structures are local minima, but they are consistently above the high-energy ipio-protonated phenols, except for 3-iodophenol in which an ipio-protonation is less favourable by 13 kImol than an I-protonation. The calculated PAs for the X-protonated 3-halophenols are the following 613 kImoC for 3-fluorophenol, 676 kJmol for 3-chlorophenol, 680 kImoC for 3-Br-phenol and 704 kImoC for 3-iodophenol, using the same level of theory. 

The reversible conversion of phenols to dienone intermediates is an important transformation in the synthesis of natural products. This rearrangement occurs efficiently in superacid solutions The corresponding version for the halophenols to give halodienones has been reviewed in an earlier volume of this series. 4-Bromo-2,4,6-trialkylcyclohexa-2,5-dienones have recently been synthesized by electrophilic bromination of the corresponding phenols. 

Chlorophenol is also reactive and irradiation in water leads to its conversion into resorcinoP" or in methanol to yield 3-methoxyphenol in 94% yield. Photoamidation with N-methylacetamide of 3-chlorophenol is also efficient and resnlts in the formation of the phenol 241 in a yield of 77%. Intramolecnlar amidation arises on irradiation of 242 in basic methanol. This resnlts in the formation of the indole derivative 243 as well as the methoxylated prodnct 244. More complex halophenols such as 245 are also photochemically reactive, but this yields a complex mixture of products including a benzofuran. The formation of this must be similar to the cychzations described earlier and involves the attack of a radical, produced by the C—I bond fission, on the other ring . 3-Nitrophenol is converted on irradiation in aqueous solution into a variety of products such as nitrocatechols, nitroresorcinol and resorcinol itself... 

This idea is based on the assumption that hydration of the radical cation occurs predominantly at the ipso position. This is reasonable on the basis of estimates" of the charge distribution in fluorobenzene radical cation. The mechanism in equation 15 is, however, not likely for oxidative dehalogenation of halophenols" at pH 4.5 since the halophenol radical cations would deprotonate before they had a chance to react with water. With substituted phenols, therefore, the observed semiquinones are probably produced via equation 14. 

From ortho-Halophenols From oitho-Alkynyl-phenols... 

Palladium(0)-catalysed coupling of an orf/to-halophenolic ether (thioether) with a terminal alkyne (or with an alkynylboronic ester ) and ring closure promoted with an electrophile - iodine has been most often used - is an excellent method to make both benzothiophenes °° ° and benzofurans. ortfto-AIkynyl-phenols can be comparably closed with palladium catalysis in the presence of copper(II) halides to give the corresponding 3-halo-benzofurans, ° and ortfto-alkynyl pyridin-2- and -3-yl acetates likewise ring close with iodine, generating furopyridines. ... 

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