Benzenes to cyclohexenes

Cyclohexane, produced from the partial hydrogenation of benzene [71-43-2] also can be used as the feedstock for A manufacture. Such a process involves selective hydrogenation of benzene to cyclohexene, separation of the cyclohexene from unreacted benzene and cyclohexane (produced from over-hydrogenation of the benzene), and hydration of the cyclohexane to A. Asahi has obtained numerous patents on such a process and is in the process of commercialization (85,86). Indicated reaction conditions for the partial hydrogenation are 100—200°C and 1—10 kPa (0.1—1.5 psi) with a Ru or zinc-promoted Ru catalyst (87—90). The hydration reaction uses zeotites as catalyst in a two-phase system. Cyclohexene diffuses into an aqueous phase containing the zeotites and there is hydrated to A. The A then is extracted back into the organic phase. Reaction temperature is 90—150°C and reactor residence time is 30 min (91—94). 

Many expensive reductions such as the Birch reduction of naphthalene to isotetralin, benzene to cyclohexene, with metallic sodium and liquid ammonia, or reduction with LiAlHa, can generally be carried out electrochemically at much lower cost and under safe conditions. Electrochemical processes allow fluorinations to be carried out without using fluorine gas. Conducting polymers have been made by electrochemical processes which operate under ambient conditions, and the polymer can be synthesized, doped and shaped in film form in a single step. 

Conversion of benzene to cyclohexene by partial catalytic hydrogenation is a very important industrial process, since it provides a new route to cyclohexanol, a precursor of nylon, when combined with hydration of cyclohexene. For example, Asahi Chemical Company of Japan developed a selective bilayer catalytic system including a Ru catalyst, Zr02 and ZnS04 under 50 atm of H2 pressure, a process affording the olefin with up to 60% selectivity after 90% conversion of benzene.72... 

Progress is being made in the search for catalysts to hydrogenate aromatic systems (see Section VII). This area is likely to become increasingly important if coal, which contains polyaromatic compounds, is utilized more for production of petrochemicals. Stereospecific production of fully m-C6D6H6 from perdeuterobenzene has been reported catalysts for selective hydrogenation of benzene to cyclohexene would be valuable. 

The partial hydrogenation of benzene to cyclohexene is difficult to carry out with heterogeneous metal catalysts, but it has been achieved by using pentammineos-mium(II).171 The reaction requires the presence of Pd(0), which itself is ineffective as a catalyst for the hydrogenation of benzene ... 

The partial hydrogenation of benzene to cyclohexene is of great industrial importance. A possible application of the product cyclohexene is its transformation to cyclohexanone. It was shown that ruthenium may give rise to increased selectivity toward cyclohexene.426 In addition, studies with various Ru-B catalysts demonstrated that boron effectively promotes the activity and selectivity of ruthenium for cyclohexene.427 428... 

Cobalt catalysts have been shown to hydrogenate arenes to saturated hydrocarbons. The Co(acac)2-AlHBu 2-PBun3 system hydrogenates benzene to cyclohexene, but the presence of styrene was necessary, otherwise the reaction ceased. The styrene was also hydrogenated.72... 

QiCqm] [various] Ru Olefins Arenes 4 bar, 75 °C mean particle size 2.6 nm precursor Ru(cod)(cot) low selectivity for the partial reduction of benzene to cyclohexene. [68]... 

Selective Hydrogenation of Benzene to Cyclohexene Obtaining trans substituted cyclohexanes suggested that desorbed cyclohexenes were intermediates in the hydrogenation of benzenes. The isolation of cyclohexene and substituted cyclohexenes from the hydrogenation of benzene and substituted benzenes was first reported for hydrogenations run over a Ru/C catalyst, but the maximum olefin concentrations observed in this early work were only 0.2-3.4%.7... 

Caprolactam (world production of which is about 5 million tons) is mostly produced from benzene through three intermediates cyclohexane, cyclohexanone and cyclohexanone oxime. Cyclohexanone is mainly produced by oxidation of cyclohexane with air, but a small part of it is obtained by hydrogenation of phenol. It can be also produced through selective hydrogenation of benzene to cyclohexene, subsequent hydration of cyclohexene and dehydrogenation of cyclohexanol. The route via cyclohexene has been commercialized by the Asahi Chemical Company in Japan for adipic acid manufacturing, but the process has not yet been applied for caprolactam production. 

The hydrogenation of benzene to cyclohexene, follovv ed by the hydration of cycloolefin, vas developed by Asahi, and is currently employed by this company and some Chinese producers as the first step in the manufacture of AA in 1990 Asahi built a plant vdth a capacity of 60 000 tons yr. The partial hydrogenation reaction product is a mixture of unreacted benzene, cyclohexene and by-product cyclohexane. Figure 7.2 sho vs a simplified fio v sheet of the Asahi process. 

Cyclohexylbenzene has been prepared by the hydrogenation of biphenyl and of cyclohexenylbenzene over nickel, by the reaction of cyclohexyl chloride or bromide with benzene in the presence of aluminum chloride, and by the addition of benzene to cyclohexene in the presence of aluminum chloride, sulfuric acid, or boron halides. ... 

Partial hydrogenation of benzene to cyclohexene is possible on supported Ru catalyst, or on an unsupported Ru catalyst poisonned by FeCl3, FeS04, TiC, or O-i-Ruthenium catalysts allow selective reduction of anthracene derivatives bridged by a... 

In recent years the Asahi Corporation has developed a benzene-to-cyclohexene process involving a liquid-liquid two-phase system (benzene-water) with a solid ruthenium catalyst dispersed in the aqueous phase. The low solubility of cyclohexene in water promotes rapid transfer towards the organic phase. An 80000 t annum plant using this process is in operation. Another way to scavenge the intermediate cyclohexene is to support the metal hydrogenation catalyst on an acidic carrier (e. g. silica-alumina). On such a bifunctional catalyst the cyclohexene enters catalytic alkylation of the benzene (present in excess) to yield cyclohexylbenzene [19], which can be converted, by oxidation and rearrangement reactions, into phenol and cyclohexanone. 

Properties of Sol-Gel Derived Ru/Cu/Si02 Catalysts and Role of Water in the Selective Hydrogenation of Benzene to Cyclohexene with the Catalysts... 

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