Catalytic hydrogenations cyclohexane

Benzene can undergo addition reactions which successively saturate the three formal double bonds, e.g. up to 6 chlorine atoms can be added under radical reaction conditions whilst catalytic hydrogenation gives cyclohexane. 

The most common stereoselective syntheses involve the formation and cleavage of cyclopentane and cyclohexane derivatives or their unsaturated analogues. The target molecule (aff-cts)-2-methyl-l,4-cyclohexanediol has all of its substituents on the same side of the ring. Such a compound can be obtained by catalytic hydrogenation of a planar cyclic precursor. Methyl-l,4-benzoquinone is an ideal choice (p-toluquinone M. Nakazaki, 1966). 

A reaction that introduces a second chirality center into a starting material that already has one need not produce equal quantities of two possible diastereomers Con sider catalytic hydrogenation of 2 methyl(methylene)cyclohexane As you might expect both CIS and trans 1 2 dimethylcyclohexane are formed... 

Dutch State Mines (Stamicarbon). Vapor-phase, catalytic hydrogenation of phenol to cyclohexanone over palladium on alumina, Hcensed by Stamicarbon, the engineering subsidiary of DSM, gives a 95% yield at high conversion plus an additional 3% by dehydrogenation of coproduct cyclohexanol over a copper catalyst. Cyclohexane oxidation, an alternative route to cyclohexanone, is used in the United States and in Asia by DSM. A cyclohexane vapor-cloud explosion occurred in 1975 at a co-owned DSM plant in Flixborough, UK (12) the plant was rebuilt but later closed. In addition to the conventional Raschig process for hydroxylamine, DSM has developed a hydroxylamine phosphate—oxime (HPO) process for cyclohexanone oxime no by-product ammonium sulfate is produced. Catalytic ammonia oxidation is followed by absorption of NO in a buffered aqueous phosphoric acid... 

Cyclohexanol. This alcohol is produced commercially by the catalytic air oxidation of cyclohexane or the catalytic hydrogenation of phenol. 

A route to phenol has been developed starting from cyclohexane, which is first oxidised to a mixture of cyclohexanol and cyclohexanone. In one process the oxidation is carried out in the liquid phase using cobalt naphthenate as catalyst. The cyclohexanone present may be converted to cyclohexanol, in this case the desired intermediate, by catalytic hydrogenation. The cyclohexanol is converted to phenol by a catalytic process using selenium or with palladium on charcoal. The hydrogen produced in this process may be used in the conversion of cyclohexanone to cyclohexanol. It also may be used in the conversion of benzene to cyclohexane in processes where benzene is used as the precursor of the cyclohexane. 

Reactions such as catalytic hydrogenation that take place at the less hindered side of a reactant are common in organic chemistr-y and are examples of steric effects on reactivity. Previously we saw steric effects on structure and stability in the case of cis and trans stereoisomers and in the preference for equatorial substituents on cyclohexane rings. 

Assume that you are in a laboratory carrying out the catalytic hydrogenation of cyclohexene to cyclohexane. How could you use a mass spectrometer to determine when the reaction is finished ... 

The production of alcohols by the catalytic hydrogenation of carboxylic acids in gas-liquid-particle operation has been described. The process may be based on fixed-bed or on slurry-bed operation. It may be used, for example, for the production of hexane-1,6-diol by the reduction of an aqueous solution of adipic acid, and for the production of a mixture of hexane-1,6-diol, pentane-1,5-diol, and butane-1,4-diol by the reduction of a reaction mixture resulting from cyclohexane oxidation (CIO). 

The solid is used as a heterogeneous catalyst or as a water-soluble system in biphasic conditions in the hydrogenation of benzene and pheny-lacetylene [65]. The heterogeneous system Rh-PVP is investigated in the solid/liquid catalytic hydrogenation of benzene with a ratio of 1/34000 at 80 °C and 20 bar H2. The conversion into cyclohexane is about 60% after 200 h of reaction time. In a water/benzene biphasic condition at 30 °C and under 7 bar H2, complete hydrogenation (Scheme 2) for a molar ratio of 2000 is observed after 8 h giving a TOF = 675 h (related to H2 consumed), never-... 

Hexamethylenediamine (HMDA), a monomer for the synthesis of polyamide-6,6, is produced by catalytic hydrogenation of adiponitrile. Three processes, each based on a different reactant, produce the latter coimnercially. The original Du Pont process, still used in a few plants, starts with adipic acid made from cyclohexane adipic acid then reacts with ammonia to yield the dinitrile. This process has been replaced in many plants by the catalytic hydrocyanation of butadiene. A third route to adiponitrile is the electrolytic dimerization of acrylonitrile, the latter produced by the ammoxidation of propene. 

Exhaustive catalytic hydrogenation of triptycene affords an equilibrium mixture of perhydrotriptycene isomers. As expected, Boyd s force field (37) calculations, with a modified torsional constant, reproduced the observed composition fairly well (Table 6). All important conformations were taken into account for each isomer. The most stable conformations agree with the results of the X-ray analysis (131) and have the characteristic that the cyclohexane rings are invariably either boat or deformed chair. The most stable conformation of all is 20 (ttt). The predominant conformation of ccc, in which all cyclohexane rings are boat, has an enthalpy only 2.56 kcal/mol above that of 20. The difference is virtually all due to angle and torsional terms. 

A finishing reactor with a fixed bed of catalyst completes the catalytic hydrogenation of any residual, unreacted benzene. The effluent from this reactor is then cooled and flashed to remove most of the hydrogen and then fractionated to produce high purity cyclohexane. 

Apart from the reaction of cyclohexanecarboxylic acid with methyllithium, cyclohexyl methyl ketone has been prepared by the reaction of cyclohexylmagnesium halides with acetyl chloride or acetic anhydride and by the reaction of methylmagnesium iodide with cyclohexanecarboxylic acid chloride. Other preparative methods include the aluminum chloride-catalyzed acetylation of cyclohexene in the presence of cyclohexane, the oxidation of cyclohexylmethylcarbinol, " the decarboxylation and rearrangement of the glycidic ester derived from cyclohexanone and M)utyl a-chloroj)ropionate, and the catalytic hydrogenation of 1-acetylcycIohexene. "... 

Among the electron-rich alkenes, vinylsulfides are especially amenable to cation-radical reduction an important feature is the absence of hydrogenolysis of carbon-sulfur bonds. The reduction of [(phenylthio)methylene]cyclohexane is efficient (88%), and the retention of the phenylthio group clearly contrasts with catalytic hydrogenation (Mirafzal et al. 1993). This provides versatile functionality for further synthetic operations. 

Adipic acid (1,4-butanedicarboxylic acid) is used for the production of nylon-6,6 and may be produced from the oxidation of cyclohexane as shown in structure 17.1. Cyclohexane is obtained by the Raney nickel catalytic hydrogenation of benzene. Both the cyclohexanol and cyclohexanone are oxidized to adipic acid by heating with nitric acid. 

Pyrrolidone is a lactone used for the production of nylon-4. This reactant may be produced by the reduction ammoniation of maleic anhydride. s-Caprolactam, used in the production of nylon-6, may be produced by the Beckman rearrangement of cyclohexanone oxime (structure 17.11). The oxime may be produced by the catalytic hydrogenation of nitrobenzene, the photolytic nitrosylation of cyclohexane (structure 17.9), or the reaction of cyclohexanone and hydroxylamine (structure 17.10). Nearly one-half of the production of caprolactam is derived from phenol. 

Hydrogen undergoes catalytic hydrogenation adding to unsaturated hydrocarbons, such as alkenes and alkynes forming alkanes. The reaction is catalyzed by nickel, platinum or palladium catalysts at ambient temperature. Hydrogenation of benzene over platinum catalyst yields cyclohexane, C6H12. 

Our fluorous silica technology was also tested (1) on the catalytic hydrogenation of styrene. The fluorous silica phase contained a fluorinated version of Wilkinson s catalyst (Figure 3) deposited onto the surface of the fluorous silica. The organic phase consisted of styrene dissolved in cyclohexane. No fluorous solvent was used. 

Nakazaki s synthetic approach is conspicuous by its remarkable straightforwardness it has been proved to be so far the simplest synthetic route to the target compounds. In their first synthesis of 61a54a), Nakazaki and coworkers started from cyclododecyne (62a), whose oligomerization with two molecules of butadiene afforded the bicyclic 63a. The cis[10.8] precursor 64a, obtained by partial catalytic hydrogenation with Raney nickel catalyst, was dissolved in cyclohexane, which contained xylene as photosensitizer, and the solution was irradiated with a medium pressure Hg lamp for 12 h. Examination of the reaction mixture by means of GLC indicated that the product was a 2.4 1 mixture of (Z) 64a and (E) 61 a, and the further study54b) showed that this ratio could be raised to 1 2 by irradiation of a hexene solution with a low pressure Hg lamp. 

Benzene, naphthalene, toluene, and the xylenes are naturally occurring compounds obtained from coal tar. Industrial synthetic methods, called catalytic reforming, utilize alkanes and cycloalkanes isolated from petroleum. Thus, cyclohexane is dehydrogenated (aromatization), and n-hexane(cycli> zation) and methylcyclopentane(isomerization) are converted to benzene. Aromatization is the reverse of catalytic hydrogenation and, in the laboratory, the same catalysts—Pt, Pd, and Ni—can be used. The stability of the aromatic ring favors dehydrogenation. 

On catalytic hydrogenation over a rhodium catalyst, the compound shown gave a mixture containing d,s-1 -tm-buty I-4-methyl cyclohexane (88%) and rra/rs-1-rerr-buty 1-4-methyl cyclohexane (12%). With this stereochemical result in mind, consider the reactions in (a) and (b). 

Catalytic hydrogenation of benzene cannot be stopped at cyclohexene or cyclohexadiene it proceeds to cyclohexane. This is because the rate of the first addition step is much slower than of the subsequent steps ... 

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