Partial phenol conversion

In fact, the preparative bulk electrolysis of phenol on BDD anodes under galvanostatic conditions has shown that, depending on the experimental conditions, it is possible to obtain partial oxidation of phenol to aromatic compounds or its complete oxidation to CO2 [6]. In particular, at low-current density and low phenol conversion, only aromatic compounds (benzoquinone, hydroquinone and catechol) are formed during phenol oxidation [6],... 

The corresponding values of the constants are listed in Table IX.Using these values and substituting the conversions for partial pressures as in the hydrogenation of phenol (see p. 32), by numerically solving the system of five differential equations we obtained the curves presented in Fig. 9, which agreed well with experimental points. 

Fig. 8. Catalyst stability testing at partial conversion using phenol- and fluorobenzene-contaminated HBr feeds.

This discovery was quite unexpected, since iron oxide has been never reported as an active catalyst in either partial or full oxidation. The studies of two simplest reactions, i.e. O2 isotopic exchange and N2O decomposition, revealed a dramatic change of Fe properties in the ZSM-5 matrix compared to Fe203 [4]. Fe atoms lose their ability to activate O2 but gain remarkably in their ability to activate N2O. It gives rise to a great effect of the oxidant nature in the reaction of benzene oxidation over the FeZSM-5 zeolite (Table 1). Thus, in the presence of N2O benzene conversion is 27% at 623 K, while in the presence of O2 it is only 0.3% at 773 K. And what is more, there is a perfect change of the reaction route. Instead of selective phenol formation with... 

The gas phase oxidation of benzene with air is an important process for the production of maleic anhydride, which is the major partial oxidation product, besides products of complete oxidation. By-products are benzo-quinone, in particular at low conversion, and fumaric acid which is formed at the high conversion levels used in industrial installations [28]. Only traces of phenol and other by-products are formed. The important catalysts are based on V2Os and a maximum yield of 60—80% maleic anhydride is obtained at 350—500° C. 

The coexistence of NH3 is indispensable for selective benzene oxidation. Neither benzene oxidation nor combustion proceeded in the absence of NH3 (Table 2.5). Fe/ZSM-5 has been reported to be active and selective for phenol synthesis from benzene using N20 as an oxidant [97], but selective benzene oxidation did not proceed with N20 instead of 02. The addition of H20 to the system gave no positive effects on the catalytic performance, either. In addition, other amine compounds such as pyridine and isopropyl amine did not produce phenol. The phenol formation rate and selectivity increased with increasing NH3 pressure because the coexisting NH3 produces active Re clusters, as described below, and reached maximum conversion and selectivity at a partial pressure of NH3 of around 35—42kPa. 

The available rate data for the substitution reactions of phenol, diphenyl ether, and anisole are summarized in Table 5. The elucidation of the reactivity of phenol is hindered by its partial conversion in basic media into the more reactive phenoxide anion. Because of the high reaction velocity of phenol and the even greater reactivity of phenoxide ion the relative rates are difficult to evaluate. Study of the bromination of substituted phenols (Bell and Spencer, 1959 Bell and Rawlinson, 1961) by electrochemical techniques suitable for fast reactions indicates the significance of both reaction paths even under acidic conditions. 

Partial N-methylation can also be accomplished with Mel. For example, tetrandrine (48) gave on treatment with 1 equiv Mel a 4 1 mixture of the monoquatemary salts 365 and 33. The pure minor isomer could be obtained by sequential quatemization of tetrandrine with 1 equiv benzyl bromide, then 1 equiv Mel, conversion of the bisquatemary salt to the dichloride form with anion-exchange resin, and cleavage of the benzyl group by catalytic reduction (H2/Pd-EtOH) (20). Partial O-methylation of alkaloids containing more than one OH can be accomplished with CH2N2 either by prior partial protection of the phenols as 0-acetates (148) or by use of less than a stoichiometric amount of CH2N2 (132) (see, e.g., Section II,C, 122). 

By using this mild and versatile methodology, symmetrical diaryl ethers have been synthesized in a one-pot, two-step procedure starting from arylboronic acids and their partial conversion to the corresponding phenols by oxidation with hydrogen peroxide and a subsequent coupling of the formed phenols with the remaining arylboronic acids upon addition of copper(II) acetate, molecular sieves and triethyl amine (Scheme 7) [22],... 

Thus, as the first design decision we assume partial conversion of phenol to both cyclohexanone and cyclohexanol. As a result, the unreacted phenol must be recycled. Then cyclohexanol is converted to cyclohexanone in a separate reactor,... 

Design Alternative with Partial Conversion of Phenol In this section we demonstrate the advantage of performing reactor analysis and design in a recycle structure. As explained in Chapter 2, in contrast with a standalone viewpoint this approach allows the designer to examine systemic issues, the most important being the flexibility with respect to production rate and target selectivity, before... 

The oxidation of phenols and other organic substrates by MnP Is dependent on Mnll (23,30). Apparently the enzyme first oxidizes Mnll to Mnlll, and Mnlll subsequently oxidizes the organic substrates (30,31,47). As shown In Figure 3, addition of one equivalent of Mnll rapidly reduces MnP compound I to compound II (41). A second equivalent of Mnll reduces MnP compound II to the native ferric enzyme. Similarly, MnP compound I Is reducible by phenolic substrates, albeit at a slower rate. However, phenolic substrates are not able to reduce MnP compound II efficiently (41). Thus the enzyme Is unable to complete Its catalytic cycle efficiently In the absence of Mnll. This would seem to explain the absolute Mnll requirement for catalytic activity. In the conversion of MnP compound I to compound II, the porphyrin tt-cation Is reduced back to a normal porphyrin. This suggests that the porphyrin radical Is exposed In a peripheral site as recently suggested for HRP (48) and that this site may be available to organic substrates and to Mnll. In contrast, the FeIV 0 center of MnP compound II may be partially burled and only available to Mnll Ions. 

Three processes based on H2O2 are commercial they use different catalysts and show different performances (Table 2). The conversion of phenol is only partial to minimize further oxidations in which the expensive oxidant is also consumed (Equation 37). A compromise, different for each process, is normally made between the need to minimize the energy spent on the separation and recycle of phenol and that of maximizing the select vities. 

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