Phenols, from aryl halides

Phenols from aryl halides ArHal ArOH... 

From Aryl Halides.—We have said that phenols are not prepared by the same general reactions as are used in preparing the aliphatic hydroxyl compounds. This is true in general though we shall give an interesting exception. Aliphatic alcohols are most easily synthesized by treating the alkyl halides with silver hydroxide, or with potassium hydroxide. 

Diaryl ethers. This electron-rich and bulky / iV-ligand (1) facilitates the Pd-catalyzed synthesis of diaryl ethers from phenols and aryl halides. 

Table 9.9 Copper/ligand catalyzed diaryl ether formation from aryl halides and phenols.

Pd nanoparticles supported on PANI-NFs are efficient semi-heterogeneous catalysts for Suzuki coupling between aryl chlorides and phenylboronic acid, the homocoupling of deactivated aryl chlorides, and for phenol formation from aryl halides and potassium hydroxide in water and air [493], PANl-NF-supported FeCl3 as an efficient and reusable heterogeneous catalyst for the acylation of alcohols and amines with acetic acid has been presented [494]. Vanadate-doped PANI-NFs and PANI-NTs have proven to be excellent catalysts for selective oxidation of arylalkylsulfides to sulfoxides under nuld conditions [412]. Heterogeneous Mo catalysts for the efficient epoxidation of olefins with ferf-butylhydroperoxide were successfully synthesized using sea urchin-Uke PANI hollow microspheres, constructed with oriented PANI-NF arrays, as support [495]. Pt- and Ru-based electrocatalyst PANI-NFs—PSSA—Ru—Pt, synthesized by the electrodeposition of Pt and Ru particles into the nanofibrous network of PANI-PSSA, exhibited an excellent electrocatalytic performance for methanol oxidation [496]. A Pt electrode modified by PANI-NFs made the electrocatalytic oxidation reaction of methanol more complete [497]. Synthesis of a nanoelectrocatalyst based on PANI-NF-supported... 

The aryl r-butyl ether 15 and silyl ether 18, prepared by the Pd-catalyzed reaction, can be converted easily to phenols 16, and these reactions offer convenient synthetic methods for phenols 16 from aryl halides 14 and 17. Based on this reaction, the first synthesis of 4-chlorobenzofiiran (18c), which is difficult to synthesize by conventional methods, was carried out. Selective mono-r-butoxylation of 2,6-dichloroacetaldehyde dimethylacetal (18a) using P(r-Bu)3 as a ligand gave the r-butyl ether 18b, and subsequent treatment with aq. HCl afforded 4-chlorobenzofuran (18c) in 51 % overall yield. Further conversion of 18c to various 4-substituted benzofurans is possible by Pd-catalyzed substitutions of the 4-chloro group in 18c [6]. 

Apart from aryl halides, other very easily available substrates for nickel-catalysed biaryl (II) synthesis are aryl sulfonates (XII). Method D is very efficient in the homocoupling reactions of substituted aryl sulfonates in good to excellent yields [15], Table 6. Substituted aryl sulfonates are readily obtained from phenols and trifluoromethanesulfonic anhydride, benzenesulfonyl-, tosyl- or methanesulfonyl chloride in pyridine, or in a suitable inert solvent such as dichloromethane in the presence of triethylamine or Hiinig s base. Among other nickel complexes, Ni(dppe)Cl2 and Ni(dppf)Cl2 have been used (10 mo1%) as slightly less versatile catalysts for the homo-couplings of naphthyl sulfonates in refluxing THF, DMF or their mixtures [42]. 

Infrared Spectra Phenols show a characteristic absorption band (usually broad) arising from O — H stretching in the 3400-3600-cm region. Phenols and aryl halides also show the characteristic absorptions that arise from their benzene rings (see Section 14.11C). 

Arenethiols are important intermediates in chemical synthesis. While there are numerous reactions to introduce this functionality starting from aryl halides or phenols, most of these transformations require drastic reaction conditions and tolerate few if any functionalities. Despite the fact that in the last few years the efficiency of palladium-catalyzed cross-coupling reactions for the preparation of aryl ethers and aniline derivatives has improved greatly (see 5.1 and 5.2), analogous methods for the formation of aryl sulfides and especially arenethiols have lagged behind. The first report of a mild palladium-catalyzed synthesis of arenethiols came from Rane et followed by reports from a Zeneca Pharma group and a Merck group (Scheme 5-160). ... 

Many organic compounds are also prepared by hydrolysis of the appropriate halides. Alcohols can be prepared by hydrolysis of alkyl halides (though yields are often poor due to the formation of considerable amounts of olefins and polyolefins) phenols are prepared from aryl halides under pressure, in the presence of concentrated base (Samuel and Scheinmann, private communication), aromatic aldehydes and ketones from gem-dihalides (Doering and Dorfman, 1953), and aromatic acids from trihalides (Ponticorvo and Rittenberg, 1954). 

Triorganostannyl anions are excellent nucleophiles in SrnI processes with aromatic substrates,86 and arylstannanes can be prepared from the photostimulated reactions of Ph3SnNa or Me3SnNa (from R3SnCl + Na) and aryl halides in DMSO, or of aryl amines, via their ammonium salts,88 in liquid ammonia, or of phenols, via their phosphates, in liquid ammonia.89 Examples are given in Equations (11)—(13). 

Aryl halides from phenols and triphen-ylphosphine-halogen adducts, 49, 6... 

Aryldiazonium salts, usually obtained from arylamines, undergo replacement of the diazonium group with a variety of nucleophiles to provide advantageous methods for producing aryl halides, cyanides, phenols and arenes by reductive removal of the diazo group. Coupling reaction of aryldiazonium salts with phenols or arylamines give rise to the formation of azo dyes. 

Sulphuric acid (concentrated). Widely used in desiccators. Suitable for drying bromine, saturated hydrocarbons, alkyl and aryl halides. Also suitable for drying the following gases hydrogen, nitrogen, carbon dioxide, carbon monoxide, chlorine, methane and paraffins. Unsuitable for alcohols, bases, ketones or phenols. Also available with an indicator (a cobalt salt, blue when dry and pink when wet) under the name Sicacide (from Merck) for desiccators. 

A polymer-bound guanidine base 31 has been used for the formation of aryl ethers from suitable phenols and alkyl halides. In addition to serving as a base to affect deprotonation, reagent 31 also acts as a sequestering agent for excess starting phenol (reaction 11).26... 

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