Phenols benzene synthesis

Catalysis (27-30) which allows for the direct oxidation of benzene to produce phenol. Economic analyses have shown that these are attractive only in specific instances where, for example, a cheap source of N20 is available. Nevertheless, these developments have shown that direct oxidation is possible and further innovations in this area should probably be expected. The demands for acetone and phenol have generally tended to follow each other. However, as bisphenol A becomes an even more important end use for phenol and acetone, there will be a need for a separate source of phenol. The synthesis of bisphenol A requires two moles of phenol for every one mole of acetone, while the peroxidation of cumene produces one mole of each. Still, processes such as the direct oxidation of benzene are unlikely to have a major impact on cumene demand in the short term since there are competing processes such as Mitsui s for converting acetone back to propylene. 

Figure 2.11 shows schematically the individual processes for the synthesis of caprolactam. The solid lines indicate processes that have been practiced commercially. As can be seen, all processes start from materials that belong to the group consisting of phenol, benzene, toluene, and cyclohexane. The chemistry of different processes has been reviewed [27,90,91]. Commercially, processes 1, 2, and 3 as shown in Figure 2.11 are important. The principal intermediates are cyclohexanone and cyclohexanone oxime for process 1, cyclohexanone oxime for process 2 [92-95], and cyclohexane carboxylic add for process 3. 

This reaction sequence is much less prone to difficulties with isomerizations since the pyridine-like carbons of dipyrromethenes do not add protons. Yields are often low, however, since the intermediates do not survive the high temperatures. The more reactive, faster but less reliable system is certainly provided by the dipyrromethanes, in which the reactivity of the pyrrole units is comparable to activated benzene derivatives such as phenol or aniline. The situation is comparable with that found in peptide synthesis where the slow azide method gives cleaner products than the fast DCC-promoted condensations (see p. 234). 

A Methylamino)phenol. This derivative (15) is easily soluble ia ethyl acetate, ethanol, diethyl ether, and benzene. It is also soluble ia hot water, but only spatingly soluble ia cold water. Industrial synthesis is by heating 3-(A/-methylamino)benzenesulfonic acid with sodium hydroxide at 200—220°C (179) or by the reaction of resorciaol with methylamiae ia the presence of aqueous phosphoric acid at 200°C (180). 

A Methylamino)phenol. This derivative, also named 4-hydroxy-/V-methy1ani1ine (19), forms needles from benzene which are slightly soluble in ethanol andinsoluble in diethyl ether. Industrial synthesis involves decarboxylation of A/-(4-hydroxyphenyl)glycine [122-87-2] at elevated temperature in such solvents as chlorobenzene—cyclohexanone (184,185). It also can be prepared by the methylation of 4-aminophenol, or from methylamiae [74-89-5] by heating with 4-chlorophenol [106-48-9] and copper sulfate at 135°C in aqueous solution, or with hydroquinone [123-31 -9] 2l. 200—250°C in alcohoHc solution (186). 

By far the preponderance of the 3400 kt of current worldwide phenolic resin production is in the form of phenol-formaldehyde (PF) reaction products. Phenol and formaldehyde are currently two of the most available monomers on earth. About 6000 kt of phenol and 10,000 kt of formaldehyde (100% basis) were produced in 1998 [55,56]. The organic raw materials for synthesis of phenol and formaldehyde are cumene (derived from benzene and propylene) and methanol, respectively. These materials are, in turn, obtained from petroleum and natural gas at relatively low cost ([57], pp. 10-26 [58], pp. 1-30). Cost is one of the most important advantages of phenolics in most applications. It is critical to the acceptance of phenolics for wood panel manufacture. With the exception of urea-formaldehyde resins, PF resins are the lowest cost thermosetting resins available. In addition to its synthesis from low cost monomers, phenolic resin costs are often further reduced by extension with fillers such as clays, chalk, rags, wood flours, nutshell flours, grain flours, starches, lignins, tannins, and various other low eost materials. Often these fillers and extenders improve the performance of the phenolic for a particular use while reducing cost. 

It IS by a similar process that alizaiin has been synthesised w ith the oliject of ascertaining its constitution (see Notes on Prep. 110, p. 316), When two molecules of phenol and one molecule of phthalic anhydride are heated together with cone, sulphuric acid, then phenolphthalein is formed (Baeyei). Its constitution has been determined by its synthesis from phthalyl chloride and benzene by means of the Friedel-Crafts leaction (see Notes on Piep. 100, p. 309). Phthalyl chloride and benzene yield in presence of AlCl., phthalophenone. 

The 1,3,4-oxadiazole 113 is formed from the azo compound 112 by the action of triphenylphosphine <96SL652>. A general synthesis of 1,3.4-oxadiazolines consists in boiling an acylhydrazone with an acid anhydride (e.g., Scheme 18) <95JHC1647>. 2-Alkoxy-2-amino-l,3,4-oxadiazolines are sources of alkoxy(amino)carbenes the spiro compound 114, for instance, decomposes in boiling benzene to nitrogen, acetone and the carbene 115, which was trapped as the phenyl ether 116 in the presence of phenol <96JA4214>. 

Iron impregnated on activated carbon was used as catalyst for the direct synthesis of phenol from benzene. The effect of Sn addition to the catalyst was studied. The prepared catalysts were characterized by BET, SEM and XRD analysis. The catalyst 5.0Fe/AC showed good activity in the conversion of benzene and addition of Sn seemed to improve the selectivity of phenol in the reaction. 

Phenol is the starting material for numerous intermediates and finished products. About 90% of the worldwide production of phenol is by Hock process (cumene oxidation process) and the rest by toluene oxidation process. Both the commercial processes for phenol production are multi step processes and thereby inherently unclean [1]. Therefore, there is need for a cleaner production method for phenol, which is economically and environmentally viable. There is great interest amongst researchers to develop a new method for the synthesis of phenol in a one step process [2]. Activated carbon materials, which have large surface areas, have been used as adsorbents, catalysts and catalyst supports [3,4], Activated carbons also have favorable hydrophobicity/ hydrophilicity, which make them suitable for the benzene hydroxylation. Transition metals have been widely used as catalytically active materials for the oxidation/hydroxylation of various aromatic compounds. 

These compounds contain a furan ring fused to a benzene moiety in the 2,3-position. This synthesis was also described by Flynn et al. [73] and is shown in Scheme 25 involved the coupling of 2-iodo-5-methoxyphenol 104, 4-methoxyphenylethyne 105 to form the intermediate o-alkynylphenolate 106. Aryl iodide 107 was added to the phenolate in DMSO with heat. Oxidative addition, palladium(II)-induced cyclization and reductive elimination resulted in the product 108 with an 88% yield. 

Tsutsui T, Hayashi N, Maizumi H, et al. 1997. Benzene-, catechol-, hydroquinone- and phenol-induced cell transformation, gene mutations, chromosome aberrations, aneuploidy, sister chromatid exchanges and unscheduled DNA synthesis in Syrian hamster embryo cells. Mutat Res 373 113-123. 

A large number of studies have investigated the metabolism of benzene per se or in relation to toxification and, particularly, myelotoxicity. Most evidence shows that benzene oxide (10.1, Fig. 10.8) is not the ultimate toxic species, as was initially believed. Indeed, phenol and quinone metabolites of benzene are more active in forming adducts with macromolecular nucleophiles and eliciting cellular toxicity. For example, the efficacy of benzene metabolites (see Fig. 10.8) to inhibit DNA synthesis in a mouse lymphoma cell line decreased in the order benzoquinone (10.17) > hydroquinone (10.16)... 

Since zeolite catalysts are successfully introduced in the refining and petrochemical industries, it is not surprising that most of the recent advances concern incremental improvements of existing processes with the development of new generations of catalysts (e.g., dewaxing, ethylbenzene and cumene synthesis). The number of newer applications is much more limited, for example, direct synthesis of phenol from benzene and aromatization of short-chain alkanes, etc. However, both the improvement and development of processes contribute significantly to environmental advances. 

At the end of World War II, Fischer-Tropsch technology was under study in most industrial nations. Coal can be gasified to produce synthesis gas (syngas), which can be converted to paraffinic liquid fuels and chemicals by the Fischer-Tropsch synthesis. Liquid product mainly contains benzene, toluene, xylene (BTX), phenols, alkylphenols and cresol. The low cost and high availability of crude oil, however, led to a decline in interest in liquid fuels made from coal. 

In addition to the epoxidation of olefins, zeolitic materials have been studied for other fine chemical transformations. Table 12.21 indexes the zeolites used for oxidative dehydrogenation of propane, direct hydroxylation of benzene to phenol and e-caprolactam synthesis. A recent review summarizes other reactions for which there is not enough space in the table [138, 139]. 

This chapter focuses on several recent topics of novel catalyst design with metal complexes on oxide surfaces for selective catalysis, such as stQbene epoxidation, asymmetric BINOL synthesis, shape-selective aUcene hydrogenation and selective benzene-to-phenol synthesis, which have been achieved by novel strategies for the creation of active structures at oxide surfaces such as surface isolation and creation of unsaturated Ru complexes, chiral self-dimerization of supported V complexes, molecular imprinting of supported Rh complexes, and in situ synthesis of Re clusters in zeolite pores (Figure 10.1). 

The three-step cumene process, including the liquid-phase reactions and using sulfuric acid, is energy-consuming, environmentally unfavorable and disadvantageous for practical operation the process also produces as an unnecessary byproduct acetone, stoichiometrically. Furthermore, the intermediate, cumene hydroperoxide, is explosive and cannot be concentrated in the final step, resulting in a low one-path phenol yield, ( 5%, based on the amount of benzene initially used). Thus, direct phenol synthesis from benzene in one-step reaction with high... 

Previous studies have used many oxidants for direct phenol synthesis from benzene, such as O2 [74-80], H2O2 [81-89], N2O [90-99], Hj -1- Oj [100, 101], air/ CO [102] and O2/H2O [103], Among these oxidants, the selective oxidation of benzene with economically and environmentally favorable O2 has been nominated as one of the ten most difficult challenges for catalysis [104—106] and, indeed, there have been no reports on the direct phenol synthesis with greater than 5% conversion and 50% selectivity over the last 40 years. 

In this section, we discuss the high performance of the Rejo cluster/HZSM-5 catalyst, its active structure and dynamic structural transformation during the selechve catalysis, and the reaction mechanism for direct phenol synthesis from benzene and O2 on this novel catalyst [73, 107]. Detailed characterization and determination of active Re species have been conducted by XRD, Al solid-state MAS NMR, conventional XAFS and in situ time-resolved energy dispersive XAFS, which revealed the origin and prospects of high phenol selectivity on the novel Re/HZSM-5 catalyst [73]. 

Table 10.6 shows the catalytic performances of the selective benzene oxidation on the zeolite-supported Re catalysts under steady-state reaction conditions [107]. Catalyhc activity and selectivity largely depended on the types of zeolites and the preparation methods. The Re catalysts prepared by CVD of MTO exhibited higher catalyhc achvity and phenol selechvity than those prepared by the convenhonal impregnation method as supports (Table 10.6). Physical mixing of MTO with the supports provided poor phenol synthesis.

Notably, NH3 is indispensable for the catalytic phenol synthesis. In the absence of NH3, neither benzene combustion nor phenol formation occurred on the Re-CVD/HZSM-5 catalyst (Table 10.6). Other amine compounds such as pyridine and isopropylamine did not promote the catalytic reaction at aU, which indicates that the role of NH3 in the catalysis is not due to its basic function. Fe/ZSM-5 has been reported to be active and selective for phenol synthesis from benzene using N2O as an oxidant [90, 91], but N2O did not act as an active oxidant on the Re-CVD/ HZSM-5 catalyst Furthermore, no positive effects were observed by the addition of both N2O and H2O. Notably, the NH3-pretreated Re-CVD/HZSM-5 catalyst selectively converted benzene into phenol with O2 in the absence of NH3, as discussed below. 

The Re monomer was completely inactive for the mixture of benzene and O2. NH3 treatment of the Re monomers at 553 K generated the catalyhc achvity. After around 30 min of the NH3 treatment, phenol synthesis activity appeared and the phenol formahon rate dramatically increased between 40 and 60 min of the NH3 treatment, followed by a gentle rate rise upon further treatment The reaction rate saturated at 3.75 x 10 s after 120min. Further NH3 treatment longer than 120 min did not improve the catalyhc activity. Notably, the phenol selechvity kept almost constant (90.1-93.9%) during the NH3 treatment at 553 K. 

Scheme 10.4 (a) Structural changes in the Re-CVD/HZSM-5 (19) catalyst during direct phenol synthesis from benzene and O2 and treatment with NH3 (b) proposed model structure of the N-interstitial Reio-cluster catalyst supported in the pore of HZSM-5 (calculated by DFT). 

Re species are in a dimeric form with a direct Re-Re bond. Re Lj-edge XANES in part (ii) of Figure 10.9a did not show the pre-edge peak attributed to tetrahedral conformation of Re and the edge posihon shifted to lower energy. These results indicate that the NH3 treatment reduced the Re monomers accompanied with dimerization. Negligible catalytic achvity at this stage demonstrates that small Re clusters such as dimers do not act as achve species for direct phenol synthesis from benzene and O2. 

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