Carbon monoxide, reaction with rhodium

The mechanism is well understood, involving complexation of the rhodium with iodine and carbon monoxide, reaction with methyl iodide (formed from the methanol with hydrogen iodide), insertion of CO in the rhodium-carbon bond, and hydrolysis to give product with regeneration of the complex and more hydrogen iodide. 

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. 

Dichlorotetracarbonyldirhodium has been obtained by the action of carbon monoxide at high temperature and pressure on a mixture of anhydrous rhodium(III) chloride and finely divided copper powder and by reaction of rhodium(III) chloride 3-hydrate with carbon monoxide saturated with methanol at moderate temperatures and atmospheric pressure. The preparation described here is a modification of the latter method, without use of methanol. This procedure is considerably simpler than the recently described preparation which involves adsorption of rhodium chloride on silica gel, chlorination, and subsequent carbonylation. ... 

The hydroformylation of alkenes is commonly run using soluble metal carbonyl complexes as catalysts but there are some reports of heterogeneously catalyzed reactions of olefins with hydrogen and carbon monoxide. Almost all of these are vapor phase reactions of ethylene or propylene with hydrogen and carbon monoxide catalyzed by rhodium, " 20 ruthenium,nickel, 22,123 cobalt, 23,124 and cobalt-molybdenum 23 catalysts as well as various sulfided metal catalysts. 23,125,126... 

Addition of trimethyl phosphite to benzene solutions of the chloro-bridged dimer [Rh(cod)Cl]a in the stoicheiometric amount 3 1 causes simultaneous bridge-splitting and olefin displacement, the final product being the monomeric species [Rh P(OMe)3 3Cl]. In the reaction with [Rh(CO)2Cl]2, trimethyl phosphite preferentially displaces one carbon monoxide at each rhodium atom and then proceeds to cleave the dimer. Further addition of phosphite causes displacement of chloride rather than carbon monoxide from /ra 5-[Rh(CO)- P(OMe)3 3Cl]. Both reactions can be followed using P H n.m.r. and i.r. spectroscopy, which enables a characterization of most of the species formed in solution. It is noteworthy that for the ratio P(OMe)3 Rh = 4 1 the spectra suggest the presence of five-co-ordinate [Rh(CO) P(OMe)3 4] which probably has a trigonal-bipyramidal structure with axial CO, ... 

There has been a review of palladium-catalysed carbonylative coupling reactions of aryl halides with carbon nucleophiles in the presence of carbon monoxide. It has been shown that rhodium is an efficient catalyst for the homocoupling reaction of arylzinc compounds in the presence of 1 atm of carbon monoxide to give diaryl ketones. Under similar conditions, palladium and nickel catalysts yield biaryls. The beneficial catalysis by rhodium is likely to derive from the ease of migration of the aryl ligand to carbon monoxide in the rhodium(III) intermediate. A rhodium catalyst has also been used in the formation of indole-3-carboxylates by reaction of indoles with alcohols in the presence of carbon monoxide. The catalytic cycle. Scheme 5, is likely to involve metallation of the indole at the 3-position, followed... 

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. 

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. 

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). 

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). 

Approximately 2.5 million tons of acetic acid is produced each year in the United States for a variety of purposes, including preparation of the vinyl acetate polymer used in paints and adhesives. About 20% of the acetic acid synthesized industrially is obtained by oxidation of acetaldehyde. Much of the remaining 80% is prepared by the rhodium-catalyzed reaction of methanol with carbon monoxide. 

Perhaps the most familiar example of heterogeneous catalysis is the series of reactions that occur in the catalytic converter of an automobile (Figure 11.12). Typically this device contains 1 to 3 g of platinum metal mixed with rhodium. The platinum catalyzes the oxidation of carbon monoxide and unburned hydrocarbons such as benzene, C6H6 ... 

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