Hydrogenation rhodium/alumina

Hydrogenation, of gallic add with rhodium-alumina catalyst, 43, 62 of resorcinol to dihydroresorcinol, 41,56 Hydrogen peroxide, and formic acid, with indene, 41, 53 in oxidation of benzoic add to peroxy-benzoic add, 43, 93 in oxidation of ieri-butyl alcohol to a,a/r, a -tetramcthyltetra-methylene glycol, 40, 90 in oxidation of teri-butylamine to a,<, a, a -tetramethyltetra-methylenediamine, 40, 92 in oxidation of Crystal Violet, 41, 2, 3—4... 

Figure 8. Differential tunneling spectrum of CO on rhodium/alumina heated to k20° K in hydrogen. Modes due to hydrocarbon are number 1 to 7 The hydrocarbon species is identified as an ethylidene moiety.

Although hydrogenation of pyrrole over a rhodium/alumina catalyst gives some 1-pyrroline (Scheme 6.18a), a better method is to dehydro-halogenate A-chloropyrrolidine by heating it with alcoholic potassium hydroxide (Scheme 6.18b). 2,5-Dihydro-1//-pyrrole, containing 15% pyrrolidine, is obtained by the zinc/hydrochloric acid reduction of pyrrole. 

Hydrogenation of C=C, C=NOH, C=N. Ham and Coker found rhodium-alumina the catalyst of choice for hydrogenation of vinylic and allylic halides with minimal hydrogenolysis, for example ... 

Cycloheptanone oxime can be converted into the amine in good yield by high-pressure hydrogenation of the oxime with Raney nickel and ammonia, but Freifelder " found that the reaction is so strongly exothermal that on a large scale it may get out of hand. He then found that the hydrogenation can be accomplished smoothly by low-pressure hydrogenation in the presence of rhodium-alumina. The temperature was allowed to rise spontaneously to 60° and kept there until reduction... 

Hydrogenation of aryl amines. Rhodium-alumina appears to be the catalyst of choice for the low-temperature hydrogenation of anilines, particularly alkoxy derivatives, to cyclohexylamines. " Hydrogenolysis is not extensive, and usually secondary amines are formed in only small amounts. 

Low-temperature hydrogenation of resorcinol over rhodium-alumina in alkaline solution affords a convenient procedure for the preparation of 1,3-cyclohexanedione. ... 

Dehydrogenation. Newman and Lednicer found rhodium-alumina to be an effective catalyst for the transfer of hydrogen from hexahydrohexahelicene (1) to benzene to produce hexahelicene (2). Similar exchange over palladium catalyst... 

Table XIX presents a selection of the results obtained in a study of the reaction of ethylene with deuterium over rhodium-alumina (31), together with some calculated distributions obtained by the method previously employed. The proportion of deuterated ethylenes in the initial products rises from 30% at —18° to 75% at 110°. In contrast to the behavior of palladium, ethane-dj is the major ethane throughout and hydrogen exchange is significant at all but the lowest temperature studied. The parameters used in the calculations attribute the greatest effect of temperature to the variation of the chance of ethylene desorption, which rises from 25% at —18° to 62% at 110°. The effect of temperature on the chance of alkyl reversal is relatively small. Another resjject in which the reaction over rhodium differs from that over palladium is that the chance of acquisition of deuterium in the hydrogenation steps is higher, and indeed it appears that, as with iridium, molecular deuterium may be substantially responsible for the conversion of ethyl radicals to ethane. E — E, is 3 kcal mole and E, — E, is 4.5 kcal mole. The reaction is first-order in hydrogen and zero in ethylene.

These reactions have been studied 31) over rhodium-alumina between — 20 and 175°, and very marked changes of behavior have been observed in this temperature range. At low temperatures, relative rates of isomerization are small (see Fig. 18) and the behavior of rhodium is entirely reminiscent of that of platinum. However, with increasing temperature the relative rates of isomerization increase very quickly (see also Fig. 18), and above about 80° the behavior of rhodium is reminiscent of that of palladium. The course of the reaction of 1-butene with hydrogen at 166° is shown in Fig. 19 the initial transjcis ratio is about 1.6. 

Fig. 19. The isomerization of 1-butene during its hydrogenation over rhodium-alumina at 166 (31). The dotted lines show the equilibrium concentrations expected at this temperature.

Catalytic hydrogenation of oximes to amines requires conditions resembling those for catalytic hydrogenation of nitro compounds and nitriles.20d The catalyst should be as active as possible, e.g., Raney nickel101 (if necessary, platinized), platinum oxide,102 palladium-charcoal,103 palladium-barium sulfate,104 or rhodium-alumina.105 This rhodium catalyst also serves for reduction of an amidoxime to the amidine.106 Hydrogenation may be effected under pressure, but the temperature should be kept as low as possible to avoid formation of secondary amines. 

Catalytic hydrogenation (rhodium on alumina) converts (f )-phenylalaninol methyl ether to (/ )-2-amino-3-cyclohe. yl-l-methoxypropane [1 / )- 1]2. 

Rhodium and ruthenium catalysts may alternatively be used and sometimes show useful selective properties. Rhodium allows hydrogenation of alkenes without concomitant hydrogenolysis of an oxygen function. For example, hydrogenation of the plant toxin, toxol 5 over rhodium-alumina gave the dihydro compound 6 (7.6) with platinum or palladium catalysts, however, extensive hydrogenolysis took place and a mixture of products was formed. 

Rhodium-alumina Benzene ring hydrogenation with formation of sec. alcohols from ketones... 

Rhodium-alumina/ammonia Ring hydrogenation of N-heterocyclic carboyxlic acids... 

Rhodium-alumina/acetic acid Hydrogenation of N-heterocycles... 

Rhodium-alumina hydrogen chloride Ethers from ketals s. 17, 104... 

Rhodium-alumina acetic acid Hydrogenation of N-heterocycles with reduction of ketones to sec. alcohols... 

Conditions cited for Rh on alumina hydrogenation of MDA are much less severe, 117 °C and 760 kPA (110 psi) (26). With 550 kPa (80 psi) ammonia partial pressure present ia the hydrogenation of twice-distilled MDA employing 2-propanol solvent at 121°C and 1.3 MPa (190 psi) total pressure, the supported Rh catalyst could be extensively reused (27). Medium pressure (3.9 MPa = 566 psi) and temperature (80°C) hydrogenation usiag iridium yields low trans trans isomer MDCHA (28). Improved selectivity to aUcychc diamine from MDA has been claimed (29) for alumina-supported iridium and rhodium by iatroduciag the tertiary amines l,4-diazabicyclo[2.2.2]octane [280-57-9] and quiaucHdine [100-76-5]. 

Cost. The catalytically active component(s) in many supported catalysts are expensive metals. By using a catalyst in which the active component is but a very small fraction of the weight of the total catalyst, lower costs can be achieved. As an example, hydrogenation of an aromatic nucleus requires the use of rhenium, rhodium, or mthenium. This can be accomplished with as fittie as 0.5 wt % of the metal finely dispersed on alumina or activated carbon. Furthermore, it is almost always easier to recover the metal from a spent supported catalyst bed than to attempt to separate a finely divided metal from a liquid product stream. If recovery is efficient, the actual cost of the catalyst is the time value of the cost of the metal less processing expenses, assuming a nondeclining market value for the metal. Precious metals used in catalytic processes are often leased. 

Hydrogenation. Hydrogenation is one of the oldest and most widely used appHcations for supported catalysts, and much has been written in this field (55—57). Metals useflil in hydrogenation include cobalt, copper, nickel, palladium, platinum, rhenium, rhodium, mthenium, and silver, and there are numerous catalysts available for various specific appHcations. Most hydrogenation catalysts rely on extremely fine dispersions of the active metal on activated carbon, alumina, siHca-alumina, 2eoHtes, kieselguhr, or inert salts, such as barium sulfate. 

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