Phenols, carbon-oxygen bond formation

Poly(phenylene oxide) PPO, or poly(phenylene ether) PPE, is an engineering polymer developed by General Electric. It concerns the oxidative coupling of phenols discovered in 1956 by Allan S. Hay [21], Oxidative coupling leads to the formation of carbon-oxygen bonds between carbon atoms 2,4, and 6 and the phenolic oxygen atom. To avoid coupling with carbon atoms 2 and 6, alkyl substituents at these two positions were introduced. In addition to the polymer a 4,4 dimer is formed, named diphenoquinone (DPQ). The... 

This reaction allows aryl carbon-heteroatom bond formation via an oxidative coupling of arylboronic acids, stannanes or siloxanes with N-H or O-H containing compounds in air. Substrates include phenols, amines, anilines, amides, imides, ureas, carbamates, and sulfonamides. The reaction is induced by a stoichiometric amount of copper(II) or a catalytic amount of copper catalyst which is reoxidized by atmospheric oxygen. 

A number of methods are available for the preparation of aromatic polymers. The majority of these methods involve the formation of a chemical bond between a carbon atom and a heteroatom. Typical of these are, for example, aromatic polycarbonates the latter are prepared by the reaction of a dihydric phenol with phosgene or derivative thereof.The polymerization proceeds via formation of a carbon-oxygen bond. A similar situation is encountered with the class of polyarylates — the polyesters from dihydric phenols and aromatic diacids. " ... 

For carbon-carbon bond-formation purposes, S 2 nucleophilic substitutions are frequently used. Simple S 2 nucleophilic substitution reactions are generally slower in aqueous conditions than in aprotic organic solvents. This has been attributed to the solvation of nucleophiles in water. As previously mentioned in Section 5.2, Breslow and co-workers have found that cosolvents such as ethanol increase the solubility of hydrophobic molecules in water and provide interesting results for nucleophilic substitutions (Scheme 6.1). In alkylations of phenoxide ions by benzylic chlorides, S/y2 substitutions can occur both at the phenoxide oxygen and at the ortho and para positions of the ring. In fact, carbon alkylation occurs in water but not in nonpolar organic solvents and it is observed only when the phenoxide has at least one methyl substituent ortho, meta, or para). The effects of phenol substituents and of cosolvents on the rates of the competing alkylation processes... 

From the recent advances the heteroatom-carbon bond formation should be mentioned. As for the other reactions in Chapter 13 the amount of literature produced in less than a decade is overwhelming. Widespread attention has been paid to the formation of carbon-to-nitrogen bonds, carbon-to-oxygen bonds, and carbon-to-sulfur bonds [29], The thermodynamic driving force is smaller in this instance, but excellent conversions have been achieved. Classically, the introduction of amines in aromatics involves nitration, reduction, and alkylation. Nitration can be dangerous and is not environmentally friendly. Phenols are produced via sulfonation and reaction of the sulfonates with alkali hydroxide, or via oxidation of cumene, with acetone as the byproduct. 

Phenols can be viewed as stable forms of enol tautomers, and phenolate anions display ambident nucleophilicity at oxygen as weU as C2/C6 and C4 (ortholpara positions). Consequently, phenolate anions are susceptible to C—C bond formation upon reaction with appropriate organic electrophiles (e.g., alkyl halides and sulfonates). When bond formation occurs at a substituted arene carbon, a quatonaty centCT is generated, which may lead to isolation of stable cyclohexadienone products and complete a net alkylative dearomatization (Scheme 15.1) [2]. 

PREPARATION OF PHENOLS, ARYL ETHERS, AND RELATED COMPOUNDS THROUGH THE FORMATION OF OXYGEN-CARBON(sp ) BONDS... 

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