Rhodium-platinum oxide

The catalyst exerts some influence on the bonds broken in hydrogenolysis of saturated cyclopropanes (775), but in vinyl and alkylidene cyclopropanes the effect is pronounced. Platinum or palladium are used frequently. In one case, Nishimura s [124a) catalyst, rhodium-platinum oxide (7 3), worked well where platinum oxide failed (.75). An impressive example of the marked influence of catalyst is the hydrogenation of the spirooctane 42, which,... 

Reduction of aromatic nitro group takes preference to the reduction of the aromatic ring. Under certain conditions, however, even the benzene ring was reduced. Hydrogenation of nitrobenzene over platinum oxide or rhodium-platinum oxide in ethanol yielded aniline while in acetic acid cyclohexylamine was produced [55]. Heating of nitrobenzene with formic acid in the presence of copper at 200° gave a 100% yield of aniline, whereas similar treatment in the presence of nickel afforded 67% of cyclohexylamine [71]. 

Reduction of carbocyclic rings in aromatic ketones can be accomplished by catalytic hydrogenation over platinum oxide or rhodium-platinum oxide and takes place only after the reduction of the carbonyl group, either to the alcoholic group, or to a methylene group [5S]. 

The following commercial powder catalysts (all from Degussa) were used in the screening runs rhodium-platinum oxide (45,65% Rh, 19,8% Pt), rhodium oxide (58,2% Rh), platinum oxide (80,6% Pt), palladium-on-carbon (5% Pd) and platinum-on-carbon (5% Pt). 

Zymalkowski and Strippel hydrogenated dihydroxybenzenes with only slight hydrogenolysis over rhodium-platinum oxide in acetic acid at room temperature and 10 MPa H2 and obtained the corresponding cyclohexanediols in 92-96% yields (eq. 11.17).97 The hydrogenations at atmospheric pressure required much longer reaction times, and the yield of cyclohexanediol decreased to 86% with resorcinol. The proportions of cis isomer in the cyclohexanediols obtained at 10 MPa H2 were 81% from catechol, 68% from resorcinol, and 68% from hydroquinone and always greater than those obtained at atmospheric pressure (75,49, and 52%, respectively). 

Naphthol was similarly hydrogenated to 2-decalols in 90% yield over 7 3 rhodium-platinum oxide in acetic acid (eq. 11.77).166... 

However, the same author obtained tetrahydrofurfuryl alcohol in nearly quantitative yield, with a rhodium-platinum oxide catalyst in ethanol, and also in glacial acetic acid, i.e., without hydrogeno-lysis.207 Nickel skeleton catalysts also yield mainly alcohols as hydrogenolysis products at 175° in a continuous system ... 

Aromatic nitriles hydrogenate to primary amine over palladium-on-carbon in ethanol-HCl or acetic acid" finely divided Ni (Raney Ni) in ethanol/NH3 [equation (f)]. Rhodium hydroxide and (7 3) rhodium-platinum oxide inhibited by LiOH convert ben-zonitrile to benzylamine, and isophthalonitrile or terephthalonitrile to the corresponding diamines [equation (g)]. ... 

Acetophenone hydrogenated 3.5 hrs. with rhodium platinum oxide in acetic acid at room temp, and atmospheric pressure -> cyclohexylmethylcarbinol. Y 80%.—Rhodium platinum (3 1) oxide is more active than PtOg and PdO in the hydrogenation of various organic compounds under ordinary conditions, and is especially effective where it is desired to avoid hydrogenolysis. F. e. s. S. Nishimura, Bull. Ghem. Soc. Japan 54, 32 (1961). 

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