Rhodium monoxide

Analysis of the product obtained at high temperatures in air led both Berzelius and Wilm 4 to conclude that an oxide of composition represented by the formula RhO is produced but Claus 5 adduced evidence in favour of the,assumption that it is not a separate chemical entity, but a mixture of unoxidised metal and its sesquioxide. Leidie 6 in 1889 repeated the experiments of former investigators, obtaining somewhat similar results. He wisely pointed out that these cannot be regarded as conclusive evidence either way, and for the present the existence of rhodium monoxide must be regarded as uncertain. 

The unit has virtually the same flow sheet (see Fig. 2) as that of methanol carbonylation to acetic acid (qv). Any water present in the methyl acetate feed is destroyed by recycle anhydride. Water impairs the catalyst. Carbonylation occurs in a sparged reactor, fitted with baffles to diminish entrainment of the catalyst-rich Hquid. Carbon monoxide is introduced at about 15—18 MPa from centrifugal, multistage compressors. Gaseous dimethyl ether from the reactor is recycled with the CO and occasional injections of methyl iodide and methyl acetate may be introduced. Near the end of the life of a catalyst charge, additional rhodium chloride, with or without a ligand, can be put into the system to increase anhydride production based on net noble metal introduced. The reaction is exothermic, thus no heat need be added and surplus heat can be recovered as low pressure steam. 

Patents on the catbonylation of methyl chlotide [74-87-3] using carbon monoxide [630-08-0] in the presence of rhodium, palladium, and tidium complexes, iodo compounds, and phosphonium iodides or phosphine oxides have been obtained (26). In one example the reaction was conducted for 35... 

Process Technology. In a typical oxo process, primary alcohols are produced from monoolefins in two steps. In the first stage, the olefin, hydrogen, and carbon monoxide [630-08-0] react in the presence of a cobalt or rhodium catalyst to form aldehydes, which are hydrogenated in the second step to the alcohols. 

Often the aldehyde is hydrogenated to the corresponding alcohol. In general, addition of carbon monoxide to a substrate is referred to as carbonylation, but when the substrate is an olefin it is also known as hydroformylation. The eady work on the 0x0 synthesis was done with cobalt hydrocarbonyl complexes, but in 1976 a low pressure rhodium-cataly2ed process was commerciali2ed that gave greater selectivity to linear aldehydes and fewer coproducts. 

The acetic anhydride process employs a homogeneous rhodium catalyst system for reaction of carbon monoxide with methyl acetate (36). The plant has capacity to coproduce approximately 545,000 t/yr of acetic anhydride, and 150,000 t/yr of acetic acid. One of the many challenges faced in operation of this plant is recovery of the expensive rhodium metal catalyst. Without a high recovery of the catalyst metal, the process would be uneconomical to operate. 

Other Methods. A variety of other methods have been studied, including phenol hydroxylation by N2O with HZSM-5 as catalyst (69), selective access to resorcinol from 5-methyloxohexanoate in the presence of Pd/C (70), cyclotrimerization of carbon monoxide and ethylene to form hydroquinone in the presence of rhodium catalysts (71), the electrochemical oxidation of benzene to hydroquinone and -benzoquinone (72), the air oxidation of phenol to catechol in the presence of a stoichiometric CuCl and Cu(0) catalyst (73), and the isomerization of dihydroxybenzenes on HZSM-5 catalysts (74). 

Ruthenium. Ruthenium, as a hydroformylation catalyst (14), has an activity signiftcandy lower than that of rhodium and even cobalt (22). Monomeric mthenium carbonyl triphenylphosphine species (23) yield only modest normal to branched regioselectivities under relatively forcing conditions. For example, after 22 hours at 120°C, 10 MPa (1450 psi) of carbon monoxide and hydrogen, biscarbonyltristriphenylphosphine mthenium [61647-76-5] ... 

With Alcohols, Ethers, and Esters. Carbon monoxide reacts with alcohols, ethers, and esters to give carboxyHc acids. The reaction yielding carboxyHc acids is general for alkyl (53) and aryl alcohols (54). It is cataly2ed by rhodium or cobalt in the presence of iodide and provides the basis for a commercial process to acetic acid. 

With Unsaturated Compounds. The reaction of unsaturated organic compounds with carbon monoxide and molecules containing an active hydrogen atom leads to a variety of interesting organic products. The hydroformylation reaction is the most important member of this class of reactions. When the hydroformylation reaction of ethylene takes place in an aqueous medium, diethyl ketone [96-22-0] is obtained as the principal product instead of propionaldehyde [123-38-6] (59). Ethylene, carbon monoxide, and water also yield propionic acid [79-09-4] under mild conditions (448—468 K and 3—7 MPa or 30—70 atm) using cobalt or rhodium catalysts containing bromide or iodide (60,61). 

In one patent (31), a filtered, heated mixture of air, methane, and ammonia ia a volume ratio of 5 1 1 was passed over a 90% platinum—10% rhodium gauze catalyst at 200 kPa (2 atm). The unreacted ammonia was absorbed from the off-gas ia a phosphate solution that was subsequently stripped and refined to 90% ammonia—10% water and recycled to the converter. The yield of hydrogen cyanide from ammonia was about 80%. On the basis of these data, the converter off-gas mol % composition can be estimated nitrogen, 49.9% water, 21.7% hydrogen, 13.5% hydrogen cyanide, 8.1% carbon monoxide, 3.7% carbon dioxide, 0.2% methane, 0.6% and ammonia, 2.3%. 

Olefins can be aminomethylated with carbon monoxide [630-08-0] (CO) and amines in the presence of rhodium-based catalysts. Eor example, pipera2ine reacts with cyclohexene [110-83-8] to form W,Af-di-(l-cyclohexylmethyl)-pipera2ine [79952-94-6] (55). 

The use of a catalyst such as cadmium oxide increases the yield of dibasic acids to about 51% of theoretical. The composition of the mixed acids is about 75% C-11 and 25% C-12 dibasic acids (73). Reaction of undecylenic acid with carbon monoxide using a triphenylphosphine—rhodium complex as catalyst gives 11-formylundecanoic acid, which, upon reaction with oxygen in the presence of Co(II) salts, gives 1,12-dodecanedioic acid in 70% yield (74). 

G-19 Dicarboxylic Acids. The C-19 dicarboxyhc acids are generally mixtures of isomers formed by the reaction of carbon monoxide on oleic acid. Since the reaction produces a mixture of isomers, no single chemical name can be used to describe them. Names that have been used include 2-nonyldecanedioic acid, 2-octylundecanedioic acid, l,8-(9)-heptadecanedicarboxyhc acid, and 9-(10)-carboxystearic acid. The name 9-(10)-carboxystearic acid can be used correctiy if the product is made with no double bond isomerization (rhodium triphenylphosphine catalyst system). 

C-19 dicarboxyhc acid can be made from oleic acid or derivatives and carbon monoxide by hydroformylation, hydrocarboxylation, or carbonylation. In hydroformylation, ie, the Oxo reaction or Roelen reaction, the catalyst is usually cobalt carbonyl or a rhodium complex (see Oxo process). When using a cobalt catalyst a mixture of isomeric C-19 compounds results due to isomerization of the double bond prior to carbon monoxide addition (80). 

G. Fisher and co-workers, "Mechanism of the Nitric Oxide—Carbon Monoxide—Oxygen Reaction Over a Single Crystal Rhodium Catalyst," in M. 

The eliminaUon of carbon monoxide from nonfluonnated acyl fluorides, however, does not result in a fluonne compound Although it was claimed earlier that benzoyl fluoride can be converted into fluorobenzene by using tris(triphenyl-phosphme)rhodium chloride, recent studies proved that the product is benzene and not fluorobenzene [91]... 

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