Benzenes oxidation to phenol

Hyman MR, AW Sansome-Smith, JH Shears, PM Wood (1985) A kinetic study of benzene oxidation to phenol by whole cells of Nitrosomonas europaea and evidence for the further oxidation of phenol to hydroqui-none. Arch Microbiol 143 302-306. 

Let us consider the reaction of benzene oxidation with hydrogen peroxide in the Fenton system as the classical situation [30], In the absence of iron ions benzene does not in practice interact with H202. The addition of bivalent iron salt to the system C6H6-H202-H20 induces benzene oxidation to phenol and diphenyl according to the following mechanism ... 

Benzene Oxidation to Phenol Making Phenolic Resins for Building... 

One step benzene oxidation to phenol using N O over acid zeolites... 

Benzene oxides also undergo circumambulatory 1,5-oxygen shifts. Finally, the conversion of benzene oxide to phenol was proposed and subsequently found to proceed via an acid-catalyzed reaction part of which involves an intermediate diol. " ... 

Hyman, MR. Page, C.L. Arp, D.J. (1994). Oxidation of methyl fluoride and dimethyl ether by ammonia monooxygenase in Nitrosomonas europaea. Applied and Environmental Microbiology, Vol.60, pp. 3033-3035 Hyman, M.R. Samsone-Smith, A.W. Shears, J.H. Wood, P.M (1985). A kinetic study of benzene oxidation to phenol by whole cells of Nitrosomonas europaea and evidence for the further oxidation of phenol to hydroquinone. Archives of Microbiology, Vol.143, No.3, pp. 302-306... 

Figure 26.1. Rates of N2O decomposition and benzene oxidation to phenol at 648 K vs a-site concentration. Adapted from Ref. 7.

Benzoquinone [106-31-4J, (quinone) has been reported as a by-product of benzene oxidation at 410—430°C. Benzene can be oxidized to phenols... 

Oxepin has also been converted photochemically to phenol in 74% yield. This reaction occurs under irradiation conditions by which benzene oxide is excited to a triplet state, e.g. by irradiation in acetone as solvent.207 A rare example for a nucleophilic catalysis of the aromatization of an oxepin/benzene oxide to a phenol has been reported for /err-butyl oxepin-4-carboxylate which undergoes a rearrangement reaction in the presence of trimethylamine to give a mixture of /m-butyl 3-hydroxybenzoate (94%) and 4-hydroxybenzoate (6%).243... 

Fig. 10.1. Simplified mechanisms of the spontaneous and acid-catalyzed isomerization of arene oxides to phenols via a carbonium ion intermediate (benzene oxide (10.1) as the... 

It is well known that U.S. space vehicles obtain their auxiliaiy power in space by the use of fuel cells (Chapter 13), electrochemical devices in which the spontaneous tendency of hydrogen to combine with oxygen drives the cell and produces electricity, with water as a by-product (pure enough to drink). It stands to reason then, that one might think of producing substances more economically valuable than water in this electrogenerative way. Such work is into its first decade and Fig. 7.190 shows an example benzene is oxidized to phenol with electricity as a by-product Clearly, the economics of such a process depend on the cost of the H2 and whether one can sell the electricity. This gives rise to a speculation. 

Oxidation to Phenols. Direct hydroxylation of benzene to phenol can be achieved in a free-radical process with H202 or 02 as oxidants.739-744 Metal ions [Fe(II), Cu(II), Ti(HI)] may be used to catalyze oxidation with H202. Of these reactions, the so-called Fenton-type oxidation is the most widely studied process.742 Oxidation in the presence of iron(II) sulfate was reported in early studies to yield phenol. Since phenol exhibits higher reactivity than benzene, varying amounts of isomeric dihydroxybenzenes were also formed. 

Benzoquinone [106-51-4], C6H402 (quinone) has been reported as a by-product of benzene oxidation at 410—430°C. Benzene can be oxidized to phenols with hydrogen peroxide and reducing agents such as Fe(II) and Ti(II). Frequendy ferrous sulfate and hydrogen peroxide are used (Fenton s reagent), but yields are generally low (12) and the procedure is of limited utility. Benzene has also been oxidized in the vapor phase to phenol in low yield at 450—800°C in air without a catalyst (13). 

It was reported independently by three research groups that MFI-type zeolites selectively catalyze the reaction of N20 with benzene to give phenol C6H6 + N20 —> C6H5OH + N2 [93-96]. Fe/ZSM-5 shows remarkable performance in benzene hydroxylation to phenol with N20 as oxidant, which is the first example of a successful gas phase direct phenol synthesis from benzene [97]. No other catalysts show similar high performances to the Fe/ZSM-5 catalyst. At present, iron is the sole element capable of catalyzing the benzene-to-phenol reaction [98]. Direct oxidation of benzene to phenol by N20 has been commercialized in the so-called AlphOx process in Solutia Inc., US A, where N20 is obtained as a by-product in adipic acid production with nitric acid [97, 99, 100] a selectivity >95% to phenol is achieved at >40% conversion at around 4000 C. But the process is cost-effective only if N20 can be obtained cheaply as a by-product in adipic acid production. 

The H-ZSM-5 coatings were tested for the one-step oxidation of benzene by nitrous oxide to phenol. The grids had a total area of 9 cm2, a wire diameter of 250 pm and a mesh size of 800 pm. Fifteen grids formed a stack separated by steel rings. By acid pretreatment of the grids, defects were generated which are known to become crystallization centers during the synthesis of the zeolite. 

In 1983, Mimoun and co-workers reported that benzene can be oxidized to phenol stoichiometrically with hydrogen peroxide in 56% yield, using peroxo-vana-dium complex 1 (Eq. 2) [20]. Oxidation of toluene gave a mixture of ortho-, meta-and para-cresols with only traces of benzaldehyde. The catalytic version of the reaction was described by Shul pin[21] and Conte [22]. In both cases, conversion of benzene was low (0.3-2%) and catalyst turned over 200 and 25 times, respectively. The reaction is thought to proceed through a radical chain mechanism with an electrophilic oxygen-centered and vanadium-bound radical species [23]. 

Discussion Point DPS The conversion of benzene into phenol should simply involve the insertion of one oxygen into a C-H bond, but this seems difficult to achieve, particularly on an industrial scale. Suggest reasons for this and propose a possible new strategy to oxidize benzene directly to phenol. 

The term dihydrodiol is widely used in reference to vicinal dihydroxydihydro-derivatives of aromatic hydrocarbons. Although most known and potential benzene oxide or substituted benzene oxide metabolites tend to be quite unstable, a recent study has described the isolation of a relatively stable arene oxide metabolite of 2,2, 5,5 -tetrachlorobiphenyl. Perhaps because of the generally high susceptibility of benzene oxide 1 and many substituted benzene oxides to isomerize to phenols, relatively little has been reported on the kinetics and regiospecificity of their microsomal epoxide hydrolase (EC 3.3.2.3) catalyzed trans hydration to dihydro-... 

From Hydrocarbons.—In the presence of aluminium chloride (Friedel-Craft reagent) benzene may be oxidized to phenol. 

The observations that the pH-independent reactions of deuterium-labeled 5-met-hoxyindene oxide and 6-methoxy-1,2,3,4-tetrahydronaphthalene-1,2-oxide show significant primary kinetic deuterium isotope effects for the ketone-forming reactions, whereas the pH-independent reactions of deuterium-labeled naphthalene oxide and benzene oxide do not, are quite puzzling. Clearly, more work needs to be done to fully understand why transition-state structures for rearrangement of arene oxides to phenols differ from those for rearrangement of benzylic epoxides to ketones. 

Among the transformations of heterocycles, the rearrangement oxepines (381)—benzene oxides (382) phenols (383) is best known (equation 181). This rearrangement was described in detail in several surveys 334-336 -pijg most studied aspect of the arene oxide chemistry is the ring expansion to oxepines, on the one hand, and aromatization reaction to phenols, on the other. 

Table 2.15 summarizes the main reactions of industrial interest in the liquid and vapor phases, the type of catalysts used, conversions and selectivities in the industrial processes. While O2 is the only oxidizing agent in the second sub-class (apart from the recent case of benzene hydroxylation to phenol using N2O as the oxidant), O2 and oxygen transfer agents (alkyl hydroperoxide or H2O2) are used in the liquid phase. 

In the BIC/Solutia process, using a zeolite that contains only small amounts of iron, benzene can be oxidized to phenol with a selectivity of over 95% at around 300 °C, but N2O selectivity is lower than 95% [He]. 

With worldwide phenol consumption exceeding 5 million tons in 1995, optimizing production routes of this essential chemical becomes very important. As an alternative to the traditional cumene process, a one-step-synthesis of phenol from benzene is highly desirable. With a ZSM5 type zeolite in its acid form as catalyst and nitrous oxide as oxidant, benzene may be directly oxidized to phenol [1-4] ... 

These effects were reflected by the change of selectivity to phenol upon a variation of the feed concentrations in Figure 5 Benzene selectivity to phenol shows the strong influence of benzene feed concentration on the product distribution. Upon increasing the benzene feed concentration from 2.1% to 12.5%, the selectivity to phenol increased from about 45% to nearly 95%. The influence of nitrous oxide feed concentration on selectivity to phenol is less pronounced. An increase of the nitrous oxide partial pressure led to a decreased selectivity to phenol. In the same way selectivity to benzoquinone increased. But due to a stoichiometric consumption of three molecules nitrous oxide per molecule of benzoquinone it is obvious that its selectivity is even more strongly dependent on the nitrous oxide partial pressure [6]. 

The successful commercialization of the overall process concept depended on the viability of the first step which is a breakthrou technology. The data reported in the literature showed high selectivity of benzene conversion to phenol and good productivity. However, the catalyst coked quickly - in most reported cases the catalyst lost its activity in a matter of a few hours. Another problem of the reported chemistry is the low N20-to-phenol selectivity. In fact, the stoichiometry of benzene oxidation to CO2 by N2O implies that 1% of benzene selectivity loss to deep oxidation is accompanied by 15% selectivity loss in N2O conversion. Considering that the supply of nitrous oxide is limited, the efiBciency of its utilization is very important for the commercial operation. 

The desire to convert benzene directly to phenol with 30% hydrogen peroxide was mentioned in Chap. 4. A polymer-supported salicylimine vanadyl complex (1 mol%) was used to catalyze this reaction. Phenol was obtained in 100% yield at 30% conversion.217 There was no leaching of the metal. The catalyst was recycled ten times after which it started to break up. Oxidation of ligands is often a problem with oxidation catalysts. Inorganic supports not subject to such oxidation need to be tried to extend the life of such catalytic agents. 

---