Cyclohexanols catalytic hydrogenation

Aromatic rings in lignin may be converted to cyclohexanol derivatives by catalytic hydrogenation at high temperatures (250°C) and pressures (20—35 MPa (200—350 atm)) using copper—chromium oxide as the catalyst (11). Similar reduction of aromatic to saturated rings has been achieved using sodium in hquid ammonia as reductants (12). 

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 [108-93-0] is a colorless, viscous liquid with a camphoraceous odor. It is used chiefly as a chemical iatermediate, a stabilizer, and a homogenizer for various soap detergent emulsions, and as a solvent for lacquers and varnishes. Cyclohexanol was first prepared by the treatment of 4-iodocyclohexanol with ziac dust ia glacial acetic acid, and later by the catalytic hydrogenation of phenol at elevated temperatures and pressures. 

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. 

Phenols can be reduced by distillation over zinc dust or with HI and red phosphorus, but these methods are quite poor and are seldom feasible. Catalytic hydrogenation has also been used, but the corresponding cyclohexanol (see 15-14) is a side product. ... 

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... 

Catalytic hydrogenation transforms keto esters to hydroxy esters under very gentle conditions. In cyclic ketones products of different configuration may result. Ethyl 3,3-dimethylcyclohexanone-2-carboxylatC on hydrogenation over platinum oxide in acetic acid gave 96.3% yield of cis, and over Raney nickel in methanol gave 97% yield of trans ethyl 3,3-dimethyl-cyclohexanol-2-carboxylate, both at room temperature and atmospheric pressure [847]. 

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. 

Other cyclohexyl compounds are obtained by catalytic hydrogenation of the corresponding benzene derivatives. Thus cyclohexanol is obtained from benzenol, and cyclohexanamine is obtained from benzenamine (aniline) ... 

Several factors such as the structure of the substrate, the catalyst, the solvent, the reaction temperature, the pressure of hydrogen and other reaction conditions determine the stereochemistry of the catalytic hydrogenation of cyclic ketones, and it is sometimes difficult to predict the major pn uct of catalytic hydrogenation. One reason for the complexity of the stereochemistry of the hydrogenation of cyclic ketones, at least in part, is related to the isomerization of the products under the reaction conditions. Some cyclohexanols were isomerized in the presence of platinum or nickel catalysts at room temperature or at higher temperature under a hydrogen atmosphere, and the isomerization reached a cis-trans equili-brium. For example, rranj-3,3,5-trimethylcyclohexanol isomerized in the presence of a nickel catalyst. 

On completion, water is added to the mixture after which it is fractionated. Cyclohexane (b.p. 81°C) containing some benzene is collected from the top of the column, and after hydrogenation of the benzene, is recycled. The cyclo-hexanol-cyclohexanone mixture consists of approximately equal volumes of cyclohexanol (b.p. 161°C), cyclohexanone (b.p. 156°C), plus a mixture of several esters and ethers. It is collected from the bottom with 80+% yields on cyclohexane. An alternative route to cyclohexanol used by some plants is to catalytically hydrogenate phenol. 

Over 1.2 billion lbs of cyclohexane are produced annually, mostly from the catalytic hydrogenation of benzene. 60% of this cyclohexane is used to make adipic acid and 30% to make caprolactam, both of which are used to make nylon apparel and carpets. Cyclohexane also is used as a solvent and in making derivatives of cyclohexanol and cyclohexanone, which are used in making dyes, pesticides, and other specialties. 

H, A. Smith University of Tennessee)-. Dr. Siegel (Lecture 4) suggests that his experiments indicate that a cyclohexene-type intermediate is formed in the catalytic hydrogenation of benzene. Further evidence for this is found in the hydrogenation of phenols, for when these are reduced under a variety of conditions and over a number of catalysts, cyclohexanone is formed as an intermediate and is readily isolated. The best explanation for this appears to be the addition of two moles of hydrogen per mole of phenol to form a cyclohexenol which isomerizes to cyclohexanone before further hydrogenation takes place. The cyclohexanone is desorbed from the catalyst, and may be subsequently reduced to cyclohexanol. 

The catalytic hydrogenation of thymol is of importance for the preparation of ( ) menthol (1J, out it may also be used as a model reaction for the reduction of substituted aromatics. The factors controlling the cis/trans ratios in the alcohols obtained on hydrogenating substimted phenols have been studied in detail in the case of cresols [2], but data are lacking for other alkylphenols. Thymol is reduced to the corresponding cyclohexanols (menthol, neomenthol, isomenthol and neoisomenthol), directly or via the cyclohexanones (menthone, isomenthone). Some hydrogenolysis (p-menthanes) may also occur. 

Cyclohexane is a petroleum product obtained by distilling C4- 400°F boiling range naphthas, followed by fractionation and superfractionation also formed by catalytic hydrogenation of benzene. It is used extensively as a solvent for lacquers and resins, as a paint and varnish remover, and in the manufacture of adipic acid, benzene, cyclohexanol, and cyclohexanone. 

Catalytic hydrogenation of phenol and subsequent dehydrogenation of the resulting cyclohexanol... 

However, the production of caprolactam and adipic acid is predominantly based on cyclohexane (see Chapter 5.4). Cyclohexanol can be produced by catalytic hydrogenation of phenol. T e hydrogenation of phenol was first described by Paul Sabatier and Jean Baptiste Senderens in 1904. Figure 5.21 shows a flow diagram for the hydrogenation of phenol. 

The spectral details of dihydrojoubertiamine (35) and dehydrojouberti-amine (34) showed strong similarities to those of joubertiamine. Correlation of the structures of dihydrojoubertiamine and dehydrojoubertiamine was obtained via catalytic hydrogenation of each of these compounds to the cyclohexanol 37, as summarized in Scheme 8. 

Similarly, catalytic hydrogenation of phenol, produces cyclohexanol... 

The parent 7-oxanorbomane, 1, is commercially available. Its preparation starts with the catalytic hydrogenation of hydroquinone to generate a mixture of trans-and cfs-cyclohexane-l,4-diol [15-18]. cfs-Cyclohexane-l,4-diol can be isomerized into the more stable trans isomer with metallic sodium [17]. Dehydratation of the latter on A4 zeolites, on alumina [19], or over nickel-kieselguhr catalyst [20] provides 1. This reaction is exergonic (ArG° = ArH° — TArS° = -3.1 2.5 kcal/mol) at room temperature as its standard gas phase heat of reaction amounts to ArH° = -1-7.3 2.5 kcal/mol. A variation of entropy of reaction of ca. -1-35 eu is assumed for this fragmentation, what leads to —TArS° = 298(0.035) = — 10.4 kcal/mol. The standard gas phase heat of formation of frans-cyclohexane-1,4-diol (Scheme 1) is estimated from that of cyclohexanol (—69.0 2.0 kcal/mol) and the standard heat of oxidation of cyclohexane into cyclohexanol (—39.5 kcal/ mol) [21]. Chickos and Acree [22] give AfH°(l) = -43.4 0.5 kcal/mol (see also [23-25]). 

Linn and Halpern later found that the active catalyst in the ketone and anthracene hydrogenation reactions of Pez was likely to be Ru( 2-H2)(H)2(PPh3)3 (Fig. 3.6) [67]. For example, cyclohexanone is converted to cyclohexanol under mild conditions in toluene (see Table 3.3). The TOF depends on the substrate concentration, and the rate law for the catalytic reaction was determined to be given by Eq. (2), with k= 1.3x 10 M-1 s-1 at 20°C. 

---