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. 

The dehydrocyclization activity of rhodium-alumina is lower than that of platinum-alumina. Hydrogenolysis predominates over all the other reactions with this catalyst (57). The effect of temperature on the anthracene/phenanthrene ratio in the product from 2- -butylnaphthalene is the same over iridium-alumina catalyst as that observed over platinum-alumina more phenanthrene and less anthracene are formed at high temperatures (58). 

Rhodium-alumina catalysts with only 0.002 wt % Rh had a good activity for converting NO to nitrogen using simulated exhaust but inadequate oxidation activity. The latter situation can be improved by the addition of Pt or Pd, which have a well known ability for CO and hydrocarbon oxidation. However, more ammonia was formed under reducing conditions using R-Rh or Pd-Rh and also the delicate balance of reactions (CO + NO, CO + H2, etc.), which determines NO removal on the lean-side of the stoicheiometric point (i.e., excess of oxygen), was upset. Deposition of Pt... 

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... 

Hydrogenolysis of ketah In the presence of rhodium-alumina and a trace of hydrochloric acid, a ketal can be reductively cleaved to an ether and an alcohol. Platinum and ruthenium were almost inactive, and palladium was about half as active as rhodium. 

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. 

Dehydrohalogenation Benzyltrimethylammonium mcsitoate. r-Butylamine. Calcium carbonate. j Uidine. Diazabicyclo[3.4.0]nonene-5. N.N-Dimethylaniline (see also Ethoxy-acetylene, preparation). N,N-Dimelhylformamide. Dimethyl sulfoxide-Potassium r-but-oxide. Dimethyl sulfoxide-Sodium bicarbonate. 2,4-Dinitrophenylhydrazine. Ethoxy-carbonylhydrazine. Ethyldicyclohexylamine. Ethyidiisopropylamine. Ion-exchange resins. Lithium. Lithium carbonate. Lithium carbonate-Lithium bromide. Lithium chloride. Methanolic KOH (see DimethylTormamide). N-PhenylmorphoKne. Potassium amide. Potassium r-butoxide. Pyridine. Quinoline. Rhodium-Alumina. Silver oxide. Sodium acetate-Acetonitrile (see Tetrachlorocyclopentadienone, preparation). Sodium amide. Sodium 2-butylcyclohexoxide. Sodium ethoxide (see l-Ethoxybutene-l-yne-3, preparation). Sodium hydride. Sodium iodide in 1,2-dimethoxyethane (see Tetrachlorocyclopentadienone, alternative preparation) Tetraethylammonium chloride. Tri-n-butylamine. Triethylamine. Tri-methyiamine (see Boron trichloride). Trimethyl phosphite. 

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 3 Metal dispersion and activity of rhodium alumina...

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.

Product Distributions from the Reaction of Ethylene with Deuterium over Rhodium-Alumina" (5% Conversion) 31)... 

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. 18. Dependence of initial yield of isomerized olefin on temperature over rhodium-alumina (31). O—fro 1-butene 3 —fr° ci -2-butene —from

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.

The rhodium dispersion becomes progressively worse on the higher temperature and, therefore, lower surface area alumina phases, NO uptake also falls sharply as the ageing temperature of each Rh/A1 0 phase is increased. The lower NO uptake can be explained partially by rhodium sintering (as the oxide) and also by a metal support interaction (Ref. 36). The interaction is less for the high temperature, less reactive alumina phases but even here NO absorption is not measurable after ageing at 850 C. The rhodium/alumina interaction is also observed when temperature programmed reduction (TPR) is performed (Fig. 14(A) and (B). 

This trend is consistent with the work of Oh, Fisher, et.al. [12], who showed that as they went from a low dispersion, single crystal catalyst to a highly dispersed rhodium/alumina catalyst, the activation energy increased from 30 to 45 kcal/mole. 

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. 

---