2- Butene hydroformylation

Butene Hydroformylation, A mote recendy developed process for the synthesis of isoprene is butene hydroformylation followed by dehydration. This process has not been practiced commercially, but processing steps are similar to commercial processes (119). 2-Butene is hydroformylated to 2-methylbutanol which is then dehydrated to isoprene. 

E)-2-phenyl-2-butene. Hydroformylation of this alkenylbenzene leads to four aldehydes (two of them diastereoisomers) and to the following saturated hydrocarbons ... 

As shown by the data of Table I, adding increasing amounts of the three phosphines used in the present studies to tris(tri-phenylphosphine)rhodium(I) carbonyl hydride produces catalyst systems of reduced activity as indicated by the reduced reaction rate. As expected, an increasing excess of triphenylphosphine results in an increased 1-butene hydroformylation selectivity towards the n-... 

Figure 8. Arrhenius plots for 03P-Rh-catalyzed 1-butene hydroformylation...

As indicated in the introduction, bis-l,3-diphenylphosphino-propane (dppp) and bis-l,2-diphenylphosphinoethane (dppe) were reacted with tris(triphenylphosphine)rhodium(II) carbonyl hydride in toluene-deuterobenzene solution to derive cis-chelate complex hydroformylation catalysts. These complexes were expectedly non-selective terminal hydroformylation catalysts for 1-butene hydroformylation (see Table I) because of their cis-stereochemistry. They were also somewhat less active due to their specific structural features. The structure of these complexes in solution was studied in detail by P-31 NMR spectroscopy. 

The fact that 2-phenylbutane, which is the main product formed during 2-phenyl-1-butene hydroformylation, is optically inactive while the aldehydes arising from the same reaction are optically active, has been taken as an indication that the intermediate in hydrogenation is either a configurationally labile a,a-disubstituted benzyl cobalt complex 15) or the corresponding free radical20). 

Starting in 1999, the Ruhrchemie/Rhone-Poulenc process will be operated in plants having a capacity of about 600,000 metric tons per year, which corresponds to over 10% of the aimual world production of C4 products the first licensed plant is operating in Korea (Hanwha Chem. Corp.). On the Ruhrchemie site, a butene hydroformylation plant [to produce n-valeraldehyde (pentanal)j is also operating without problems. 

The examples described above of the successful use of SILP catalysis were aU gas-phase reactions under conditions where no condensation of substrates or products in the gas stream was possible. (Note that capillary condensation inside the porous network of a SILP catalyst might nonetheless occur under certain circumstances.) This is an important prerequisite for effective SILP catalysis as a continuous flow of liquid could remove the thin film of IL from the support (either by dissolution or mechanical displacement), rendering the catalyst inactive in most cases. In case of propene and 1-butene hydroformylation, the formation of the so-caUed heavies 18 and 19 via aldol condensation of the respective aldehyde products (see Scheme 15.3) was reported to reduce the catalyst activity over time, whereas the selectivity remained unchanged [15]. 

The first concept has been realized in the Ruhrchemie-Rh6ne Poulenc process for propene and butene hydroformylation. This process will be discussed in detail below. The catalyst is retained in the aqueous phase by applying a water-soluble phosphine ligand. The product constitites the organic solvent. 

Two process variants have been described. A type n process [91] resembles the Union Carbide process for butenes hydroformylation (see 8.6.1). Rapid oxidation of the diphosphite ligands by air ingress in vacuum distillation columns is mitigated by addition of an excess of sacrificial ligand (tri-orthotolylphosphine). In a type IVA process, very much like the Kuraray process (see 8.6.4.1), apolar and polar solvents are applied to effect the desired combinahon of one-phase reachon fohowed by phase separation, with most Rh/diphosphite catalyst in the apolar layer [92,93]. 

Gas recycle hydroformylation processes have been licensed worldwide and operate for ethylene and propylene hydroformylation. Butene hydroformylation has been demonstrated in a pilot plant but it was found that problems linked to the formation and removal of heavies make the process in fact technically unfeasible for all olefins heavier than propylene. 

---