Electrooxidation phenol

Silphinene (56) is a member of the angularly fused triquinane class of natural products, and has been the focus of many synthetic endeavours [66]. Yamamura and coworkers made excellent use of their intramolecular electrooxidative phenol cycloaddition chemistry as a key step in the assembly of this material [63,67]. It is noteworthy that the conversion of 269 to 270 is not thwarted by the fact that cycloaddition must occur with a sterically demanding trisubstituted double bond. 

Synthesis of Poly(phenylene Oxides) by Electrooxidative Polymerization of Phenols... 

Do JS, Yeh WC. Paired electrooxidative degradation of phenol with in situ electrogenerated hydrogen peroxide and hypochlorite. J Appl Electrochem 1996 26 673-678. 

Poly(oxy-1,4-phenylene) is obtained by electrooxidative polymerization of / -bromo-phenol in aqueous NaOH solution. The yield increases when aqueous NaOH is replaced by aqueous KOH or when the reaction is conducted at higher temperature. In contrast, p-chlorophenol electrooxidatively dimerizes to give the biologically and pharmacologically important dioxin, 2,7-dichlorodibenzo[, ][l,4]dioxine254. In an effort to find protective chemical coatings, electrooxidative polymerization of ra-chlorophenol and ra-bromophenol was observed255. 

Fig. 15.6 Influence of temperature on phenol electrooxidation. Condition 150 mL of 19 mM phenol with 2 wt% NaCl, 2 Ah and 3 MPa air initially charged...

The course of the electrooxidation of phenols and derivatives is remarkably complex, as indicated in Eq. (1). The many species involved are related to one another by a series of proton and electron transfers that may occur as the result of bimolecular interactions as well as by primary electrode processes [1-6]. 

Finally in this section it is worth noting that the oxidative coupling of phenols may be extended to form interesting polymers. Thus electrooxidative polymerization of phenol using basal-plane pyrolytic graphite electrodes gives thin black polymer films which are electrically conducting. ... 

Electrooxidation is also viable for phenol ether-phenol ether coupling and has been thoroughly investigated. For example a range of compounds (65) with R = H or Me, Z = CH2 or O, = 1 or 2, reacted at the anode to give fair yields of the corresponding biaryls (66), together with spirodienone products (see Section 2.9.3.2). 

The electrooxidations of allyl- and propenyl-phenols may follow even more different pathways leading to a rich diversity of products. At a carbon anode in methanol-lithium perchlorate, ferulic acid formed the tricyclic diacid (306 c/. Section 2.9.5), in a concentration-dependent process probably involving [4 + 2] dimerization of the primary oxidation product, the dienone acetal (307). 

Cp—Cp coupling occurs, probably via the first-formed palladium phenolate (315) to give the bisquinone methide (316), and the latter spontaneously undergoes intramolecular Diels-Alder reaction to the natural lignan carpanone (317) in 46% yield, with stereocontrol at five chiral centers. High yields, up to 94%, have been recorded using oxygen as oxidant with a metal(II)-salen complex as catalyst, e.g. cobalt(II) salen. A low yield of carpanone was also obtained in electrooxidation. 8... 

The formation of carbon surface oxides, phenols, quinones, lactones, and car-boxyhc acids upon the electrooxidation of carbon has been detected by physical methods such as infrared spectroscopy [262], ellipsometry [263], x-ray photoelectron spectroscopy [262,264,265], thermal desorption, and electrochemistry (see refs. [8, 96, 248, and 261] and references therein). Cyclic voltammograms of oxidized carbons exhibit increased charge in the potential interval from 0.4 to... 

Other examples of sonoelectrochemical breakdown of pollutants include enhanced removal of phenol from industrial effluents by electrooxidation.49 Thus, >80% oxidation of PhOH to maleic acid was achieved when ultrasound (25 kHz, 104 W m 2) was applied to a solution containing phenol (100 g L i) and NaCl (2 g L i) in an electrolyzer, instead of only 50% without ultrasound. Recent German and French patents describe respectively the oxidative decontamination of pollutants in watei o and an electrochemical cell for the treatment of swimming-pool waters. i... 

The electrooxidation of vanillin, 7, to dehydrovanillin, 8, in 65% yield was reported in 196 by VermiIlian and Pearl (15). They combined a thorough voltammetric study with preparative experiments and were able to clarify the mechanisms of phenol and phenoxide oxidation. Specifically, they pointed out that the oxidation of phenols in neutral solution was a two-electron oxidation and that oxidation of the phenoxide ion (in base) produced a one-electron oxidation and coupling reactions. This work prompted us to apply the method to the synthesis of some isoquinoline alkaloids. 

Electrooxidation of aromatic compounds has been intensively investigated, and many useful fine chemicals have been prepared by both side-chain and aromatic nucleus oxidation. Side-chain oxidation of alkylbenzenes may furnish benzyl alcohols, benzyl acetates, benzyl methyl ethers, Af-benzyl acetamides, benzaldehydes, benzoic acids, and so on. For instance, electrooxidation of p-methoxytoluene affords p-methoxybenzyl methyl ether, p-methoxybenzaldehyde, and/or its dimethylacetal depending on the choice of electrolysis media [3]. Many examples of electrooxidation of aromatic nucleus have been also reported. p-Quinones and their methyl acetals and semiquinones are prepared by electrooxidation of phenol derivatives and hydroquinones [3]. Nucleus-nucleus coupling of methoxybenzene derivatives... 

One of the first studies on organic electrooxidation in the presence of NaCl was reported by Mieluch et al. [47] using phenol as model organic compound. According to their results, the oxidation rate was enhanced in NaCl solution through the mediation of Cl or C10 ions, which were formed at the anode. Since then, many studies have been reported emphasizing the... 

The main difference between the two types of sensors is that the first type (based on phenol oxidases or peroxidase) uses a low applied potential (-100 - 0 mV vs. Ag/AgCl) (3), whereas the second type (based on CDH or GDH) needs a higher potential (300 - 400 mV V5. Ag/AgCl) (9,11,13) to be able to oxidize the phenols and therefore the risk of electrooxidizing interfering compounds in the sample is higher. Tyrosinase, laccase and peroxidase can all be used for both phenolic and diphenolic compounds, however, for laccase and tyrosinase the sensitivity is much higher for catecholic compounds (3). CDH and GDH require a quinone, therefore a diphenol or aminophenol is needed. 

Electrooxidation of Chlorinated Phenols on Electrodes Modified with Ni(II)-N4 Complexes... 

Ureta-Zanartu MS, Bustos P, Berrios C, Diez MC, Mora ML, Gutienez C (2002) Electrooxidation of 2,4-dichlorophenol and other polychlorinated phenols at a glassy carbon electrode. Electrochim Acta 47 2399-2406... 

Electroanalysis of phenol derivatives including CPs is commonly problematic at most solid electrodes mainly due to the electrode passivation resulting from oxidation products. The studies on reaction mechanism of electrooxidation of phe-noi5,43,44 j pg45,46 cidic media at BDD electrodes revealed that in the... 

---