Hydrogenation of Phenol

Allied-Signal Process. Cyclohexanone [108-94-1] is produced in 98% yield at 95% conversion by liquid-phase catal57tic hydrogenation of phenol. Hydroxylamine sulfate is produced in aqueous solution by the conventional Raschig process, wherein NO from the catalytic air oxidation of ammonia is absorbed in ammonium carbonate solution as ammonium nitrite (eq. 1). The latter is reduced with sulfur dioxide to hydroxylamine disulfonate (eq. 2), which is hydrolyzed to acidic hydroxylamine sulfate solution (eq. 3). 

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. 

The oxidation of cyclohexane to a mixture of cyclohexanol and cyclohexanone, known as KA-od (ketone—alcohol, cyclohexanone—cyclohexanol cmde mixture), is used for most production (1). The earlier technology that used an oxidation catalyst such as cobalt naphthenate at 180—250°C at low conversions (2) has been improved. Cyclohexanol can be obtained through a boric acid-catalyzed cyclohexane oxidation at 140—180°C with up to 10% conversion (3). Unreacted cyclohexane is recycled and the product mixture is separated by vacuum distillation. The hydrogenation of phenol to a mixture of cyclohexanol and cyclohexanone is usually carried out at elevated temperatures and pressure ia either the Hquid (4) or ia the vapor phase (5) catalyzed by nickel. 

Dihydrothebainone-A-5 6-methyl enolate, CjaHjjOjN, m.p. 164-165-5°, [a] ° — 115-7° (EtOH). Cold N/HCl converts it into dihydrothebainone hydrochloride. The isomeric dihydrothebainone-J-6 7-methyl enolate is formed on catalytic hydrogenation of phenolic dihydrothebaine. It has m.p. 127-8°, [a] ° — 8° (EtOH) and yields dihydrothebainone on acid hydrolysis. ... 

II. Low-Pressure Hydrogenation of Phenols over Rhodium Catalysts... 

Closely related to the use of rhodium catalysts for the hydrogenation of phenols is their use in the reduction of anilines. The procedure gives details for the preparation of the catalyst and its use to carry out the low-pressure reduction of /j-aminobenzoic acid. Then, as in the preceding experiment, advantage is taken of the formation of a cyclic product to carry out the separation of a mixture of cis and trans cyclohexyl isomers. 

An important industrial synthesis of cyclohexanone is by partial hydrogenation of phenol over palladium, carried out in either liquid or vapor phase. 

Hydrogenation of phenols to the corresponding saturated alcohols usually can be accomplished cleanly if appropriate conditions and catalysts are chosen. At one time, palladium was the preferred catalyst for achieving this reaction, both elevated pressures (1000-2000 psig) and temperatures (80-175°C) usually being used (9,35,49,67). 

A procedure similar to that used in the investigation of the hydro-demethylation of xylenes was also employed in a study of the consecutive hydrogenation of phenol via cyclohexanone to cyclohexanol in gaseous phase on a platinum on silica gel catalyst (p. 27) at 150°C [scheme (VI)] at this temperature both reactions were irreversible under the excess hydrogen used. 

The kinetics of hydrogenation of phenol has already been studied in the liquid phase on Raney nickel (18). Cyclohexanone was proved to be the reaction intermediate, and the kinetics of single reactions were determined, however, by a somewhat simplified method. The description of the kinetics of the hydrogenation of phenol in gaseous phase on a supported palladium catalyst (62) was obtained by simultaneously solving a set of rate equations for the complicated reaction schemes containing six to seven constants. The same catalyst was used for a kinetic study also in the liquid phase (62a). 

In our study we first investigated separately the kinetics of the hydrogenation of phenol and of the hydrogenation of cyclohexanone (7), and from twenty-six different equations, using statistical treatment of the data, we found the best equations for the initial reaction rates to be... 

Fig. 7. Dependence of relative molar concentrations n-Jn of reaction components on reciprocal space velocity W/F (hr kg mole-1) in the consecutive hydrogenation of phenol. Temperature 150°C, catalyst Pt-SiCh (1% wt. Pt), initial molar ratio of reactants G = 9. The curves were calculated (1—phenol, 2—cyclohexanone, 3—cyclohexanol) the points are experimental values. From Ref. (61). Reproduced by permission of the copyright owner.

A Comparison of the Degrees of Conversion to Cyclohexanol (xi) in the Hydrogenation of Phenol and of Cyclohexanone, respectively ... 

The corresponding values of the constants are listed in Table IX.Using these values and substituting the conversions for partial pressures as in the hydrogenation of phenol (see p. 32), by numerically solving the system of five differential equations we obtained the curves presented in Fig. 9, which agreed well with experimental points. 

From the results of this kinetic study and from the values of the adsorption coefficients listed in Table IX, it can be judged that both reactions of crotonaldehyde as well as the reaction of butyraldehyde proceed on identical sites of the catalytic surface. The hydrogenation of crotyl alcohol and its isomerization, which follow different kinetics, most likely proceed on other sites of the surface. From the form of the integral experimental dependences in Fig. 9 it may be assumed, for similar reasons as in the hy-drodemethylation of xylenes (p. 31) or in the hydrogenation of phenol, that the adsorption or desorption of the reaction components are most likely faster processes than surface reactions. 

Finally, Jessop and coworkers describe an organometalhc approach to prepare in situ rhodium nanoparticles [78]. The stabilizing agent is the surfactant tetrabutylammonium hydrogen sulfate. The hydrogenation of anisole, phenol, p-xylene and ethylbenzoate is performed under biphasic aqueous/supercritical ethane medium at 36 °C and 10 bar H2. The catalytic system is poorly characterized. The authors report the influence of the solubility of the substrates on the catalytic activity, p-xylene was selectively converted to czs-l,4-dimethylcyclohexane (53% versus 26% trans) and 100 TTO are obtained in 62 h for the complete hydrogenation of phenol, which is very soluble in water. 

A small amount of adipic acid, 2%, is made by hydrogenation of phenol with a palladium or nickel catalyst (150°C, 50 psi) to the mixed oil, then nitric acid oxidation to adipic acid. If palladium is used, more cyclohexanone is formed. Although the phenol route for making adipic acid is not economically advantageous because phenol is more expensive than benzene, the phenol conversion to greater cyclohexanone percentages can be used successfully for caprolactam manufacture (see next section), where cyclohexanone is necessary. 

Cyclohexanol and cyclohexanone are made by the air oxidation of cyclohexane (81%) with a cobalt(II) naphthenate or acetate or benzoyl peroxide catalyst at 125-160°C and 50-250 psi. Also used in the manufacture of this mixture is the hydrogenation of phenol at elevated temperatures and pressures, in either the liquid or vapor phase (19%). The ratio of alcohol to ketone varies with the conditions and catalysts. 

The increase of the quantity of catalyst enhances the rate, but it does not influence the stereochemistry in the hydrogenation of phenol derivatives (6). The cis product formation is favored in acidic medium, and the trans product formation in neutral or alkaline medium (7). On Ru and Rh, about twice as much cis isomer is formed as trans isomer, whereas on Pt and Pd, the isomers are obtained in approximately equivalent amounts. Isomerization during the hydrogenation can be excluded (8). 

Zeolite catalysts in many forms are used for important commercial processes. The studies were extended to L zeolites, mordenite, erionite, and dealuminated faujasites and mordenites. More attention is paid now to zeolites with univalent and multivalent cations and to multicomponent catalysts. Among these some important examples are the tellurium-containing catalyst for hydrocarbon dehydrocyclization (42), the difunctional Ni- and Pd-zeolite catalysts for benzene hydrodimerization to phenylcyclohexane (42), the catalyst for the hydrogenation of phenol cyclohexanol (44), the 4% Ni/NaY which forms butanol, 2-ethylhexanol, 2-ethylhexanal, and 2-ethylhexanol from a mixture of n-butyraldehyde and hydrogen. 

Adipic acid can also be made by hydrogenation of phenol with a palladium or nickel catalyst (150°C, 50 psi) to the mixed oil, then nitric acid oxidation to adipic acid. If palladium is used, more cyclohexanone is formed. 

The hydrogenation of phenol at elevated temperatures and pressures, in either the liquid or vapor phase and with a nickel catalyst, is also used in the manufacture of cyclohexanol. 

Sasaki K, Kunai A, Harada J, Nakabori S. Electrolytic hydrogenation of phenols in aqueous acid solutions. Electrochim Acta 1983 28 671-674. 

A manufacturing process that is specific for cyclohexylamines is the catalytic hydrogenation of anilines or phenols in the presence of ammonia. The catalytic hydrogenation of aniline is the classical method for the manufacture of cyclohexylamine. Hydrogenation of phenol in the presence of ammonia produces predominantly cyclohexyl or dicyclohexylamine depending upon catalysts, reaction conditions and reactant ratios116. 

About 90% of the caprolactam is produced by the conventional cyclohexanone process. Cyclohexanone is obtained by catalytic oxidation of cyclohexane with air, or by hydrogenation of phenol and dehydrogenation of the cyclohexanol byproduct. The conversion of cyclohexanone to cyclohexanone oxime followed by Beckmann rearrangement gives caprolactam. About 10% of caprolactam is produced by photonitrosation of cyclohexane or by nitrosation of cyclohexanecarboxylic acid in the presence of sulfuric acid264. 

The hydrogenation of phenol can take place either in vapor or in liquid phase. Both processes today employ palladium-based catalyst, but with different supports and activators. 

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