Anodic oxidation of phenolic compounds. Part III. Anodic hydroxylation of phenols. A simple general synthesis of 4-alkyl-4-hydroxycyclo-hexa-2,5-dienones from 4-alkylphenols

Abstract

The oxidation of simple, monohydric phenols at a lead dioxide anode in aqueous sulphuric acid has been studied.The effects of current density, electrolysis time, pH, concentration of phenol, and method of anode preparation on conversion and product distribution have been investigated, and optimal conditions for anodic hydroxylation of simple phenols have been deduced. In all cases studied the hydroxy-group entered the 4-position : thus 4-substituted phenols gave 4-substituted 4-hydroxycyclohexa-2.5-dienones, and phenols without substituents at C-4 gave p-benzoquinones. The former reaction provides a simple and efficient synthesis of these cyclohexa-2.5dienone derivatives. A mechanism involving hydrolysis of an anodically generated phenoxonium ion is suggested. Evidence is presented which indicates that the phenoxonium ion is formed by ' chemical ' oxidation with anodically generated lead dioxide. The lead dioxide anode is superior to carbon, nickel, and platinum anodes for hydroxylation.

Facile and Highly Diastereoselective Formation of a Novel Pentacyclic Scaffold by Direct Anodic Oxidation of 2,4‐Dimethylphenol

“…Depending on the reaction conditions these particular compounds arose in notable quantities. Since the electrolysis of 1 in acidic media promotes the formation of quinols and quinolethers, [10] a variety of neutral and basic electrolytes were studied. The nature of the electrolyte had a severe impact on the reaction outcome.…”

Electrode passivation caused by polymerization of different phenolic compounds

“…These radicals can be further oxidized to quinones (14, 14 , Scheme 1) or can react irreversible (dimerization) to form dimeric products (15)(16)(17), Scheme 3 [7,8]). Such dimers can be oxidized again to produce radical (18,Scheme 4 [7,9,10]), which can couple with the phenoxy radical (3, Scheme 1) or with other dimeric radical (18,Scheme 3) to produce the polymer (19), as shown in Scheme 4. These schemes illustrate a possible route for the polymer film formation, through the coupling C O C, though any coupling through dimers shown in Scheme 3 may occur.…”

Water treatment and reuse in breweries

“…Furthermore, electrochemical methods of treatment are favoured because they are neither subject to failure due to variation in wastewater strength nor due to the presence of toxic substances, and require less hydraulic retention time (Simate et al, 2011). This method of treating wastewater came into existence when it was first used to treat sewage generated onboard by ships (Bockris, 1977), but extensive investigation of this technology commenced in the 1970s, when Nilsson and others investigated the anodic oxidation of phenolic compounds (Nilsson, Ronlan, & Parker, 1973). Figure 20.4 shows a conceptual diagram of an electrochemical reactor for wastewater electro-oxidation (Anglada et al, 2009).…”