Rhodium butane

Since 1960, the Hquid-phase oxidation of ethylene has been the process of choice for the manufacture of acetaldehyde. There is, however, stiU some commercial production by the partial oxidation of ethyl alcohol and hydration of acetylene. The economics of the various processes are strongly dependent on the prices of the feedstocks. Acetaldehyde is also formed as a coproduct in the high temperature oxidation of butane. A more recently developed rhodium catalyzed process produces acetaldehyde from synthesis gas as a coproduct with ethyl alcohol and acetic acid (83—94). 

Liquid-phase oxidation of lower hydrocarbons has for many years been an important route to acetic acid [64-19-7]. In the United States, butane has been the preferred feedstock, whereas ia Europe naphtha has been used. Formic acid is a coproduct of such processes. Between 0.05 and 0.25 tons of formic acid are produced for every ton of acetic acid. The reaction product is a highly complex mixture, and a number of distillation steps are required to isolate the products and to recycle the iatermediates. The purification of the formic acid requires the use of a2eotropiag agents (24). Siace the early 1980s hydrocarbon oxidation routes to acetic acid have decliaed somewhat ia importance owiag to the development of the rhodium-cataly2ed route from CO and methanol (see Acetic acid). 

About 86% of Hoechst s butanal is produced with the Rhc )ne-Poulenc water-soluble rhodium catalyst the remainder is stiU based on cobalt. 

The 0X0 process for higher alcohols CO -1- H9 -1- C3H6 /1-butanal further processing. Catalyst is rhodium triphenylphos-phine coordination compound, 100°C (212°F), 30 atm (441 psi). 

An example of a large scale application of the aqueous biphasic concept is the Ruhrchemie/Rhone-Poulenc process for the hydroformylation of propylene to n-butanal (Eqn. (15)), which employs a water-soluble rhodium(I) complex of trisulphonated triphenylphosphine (tppts) as the catalyst (Cornils and Wiebus, 1996). 

Arylation of alkynes via addition of arylboronic acids to alkynes represents an attractive strategy in organic synthesis. The first addition of arylboronic acids to alkynes in aqueous media catalyzed by rhodium was reported by Hayashi et al.89 They found that rhodium catalysts associated with chelating bisphosphine ligands, such as 1,4-Ws(diphenyl-phosphino)butane (dppb) and 1,1 -/ E(diphenylphospliino)fcrroccnc... 

Chiral diphosphites based on (2R,3R)-butane-2,3-diol, (2R,4R)-pentane-2,4-diol, (25, 5S)-hexane-2,5-diol, (lS -diphenylpropane-hS-diol, and tV-benzyltartarimide as chiral bridges have been used in the Rh-catalyzed asymmetric hydroformylation of styrene. Enantioselectivities up to 76%, at 50% conversion, have been obtained with stable hydridorhodium diphosphite catalysts. The solution structures of [RhH(L)(CO)2] complexes have been studied NMR and IR spectroscopic data revealed fluxional behavior. Depending on the structure of the bridge, the diphosphite adopts equatorial-equatorial or equatorial-axial coordination to the rhodium. The structure and the stability of the catalysts play a role in the asymmetric induction.218... 

A breakthrough in hydro formylation was achieved with the introduction of a tri-arylphosphine-modified, in particular triphenylphosphine-modified, rhodium catalyst. [5] This innovation provided simultaneous improvements in catalyst stability, reaction rate and process selectivity. Additionally, products could be separated from catalyst under hydro formylation conditions. One variant is described as Gas Recycle (Figure 2.1) since the products are isolated from the catalyst by vaporization with a large recycle of the reactant gases. [6] The recycle gas is chilled to condense butanals. 

Aldehyde dimer may undergo dehydration to give an a, -unsaturated carbonyl. From butanal, the conjugated carbonyl is ethylpropylacrolein (Equation 2.10). The conjugated system of this material competes for coordination sites on the rhodium catalyst so that hydroformylation inhibition is observed.[8] The formation of 2-ethylhex-2-enal can be limited by minimizing the concentration of dimers. Dimers are removed along with the product in a liquid recycle separation system. 

After years of use catalyst solutions typically contain 20 mg-L"1 iron and 0.7 mg-L"1 of nickel, thus showing no corrosivity. The Rh content of crude aldehyde is in the ppb range this corresponds to losses of less than 10 9 g kg"1 n-butanal, totalling some kg rhodium over a twenty-year period and a production of approximately 5 million metric tons of n-butanal. 

Butyne-l,4-diol has been hydrogenated to the 2-butene-diol (97), mesityl oxide to methylisobutylketone (98), and epoxides to alcohols (98a). The rhodium complex and a related solvated complex, RhCl(solvent)(dppb), where dppb = l,4-bis(diphenylphosphino)butane, have been used to hydrogenate the ketone group in pyruvates to give lactates (99) [Eq. (15)], and in situ catalysts formed from rhodium(I) precursors with phosphines can also catalyze the hydrogenation of the imine bond in Schiff bases (100) (see also Section III,A,3). 

H. B. Kagan, T.-P. Dang, Asymmetric Catalytic Reduction with Transition Metal Complexes. I. A Catalytic System of Rhodium(I) with (-)-2,3-0-Isopropylidene-2,3-dihydroxy-l,4-bis(diphenylphosphino)butane, a New Chiral Diphosphine, J. Am. Client Soc. 1972, 94, 6429-6433. 

Butanal by hydroformylation of propene is the most important oxo product in terms of volume. Six million metric tons per year of butanals were consumed in 2003, vis-a-vis a capacity of 7.6 million metric tons. Highly chemo- and regioselective processes based on ligand-modified rhodium catalysts have been developed and replaced the original cobalt high pressure technology. 

Other methods for the preparation of acetic acid are partial oxidation of butane, oxidation of ethanal -obtained from Wacker oxidation of ethene-, biooxidation of ethanol for food applications, and we may add the same carbonylation reaction carried out with a cobalt catalyst or an iridium catalyst. The rhodium and iridium catalysts have several distinct advantages over the cobalt catalyst they are much fester and fer more selective. In process terms the higher rate is translated into much lower pressures (the cobalt catalyst is operated by BASF at pressures of 700 bar). For years now the Monsanto process (now owned by BP) has been the most attractive route for the preparation of acetic acid, but in recent years the iridium-based CATTVA process, developed by BP, has come on stream. 

The third generation process concerns the Ruhrchemie/Rhone-Poulenc process utilizing a two-phase system containing water-soluble rhodium-tppts in one phase and the product butanal in the organic phase. The process has been in operation since 1984 by Ruhrchemie (or Celanese, nowadays). The system will be discussed in section 8.2.5. Since 1995 this process is also used for the hydroformylation of 1-butene. 

In the presence of carbon monoxide this rhodium catalyst has no activity for hydrogenation and the selectivity based on starting material is virtually 100%. The butanal produced contains no alcohol and can be converted both to butanol and to other products as desired. 

Figure 1.3 Stable intermediates in the enamide hydrogenation by (S,S)-trans-bis(2,3-diphenylphosphino-butane)rhodium, detected by P NMR. The various multiplicities arise from j Rh, P) and J( P, P).

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