Product butadiene hydrodimerization

Figure 4. Extraction method for separating butadiene hydrodimerization products from catalyst-containing reaction mixture.

Hydroformylation comprises the state-of-the-art of bulk chemical production via aqueous-biphasic processes. At present five plants produce worldwide some 800,000 tpy of oxo products [1], Another bulk process - the hydrodimerization of butadiene and water, a variant of telomerization - is mn by Kururay with a capacity of 5000 tpy (Equation 5.2 [3 lb,36]). 

Interestingly, various phosphonium salts have been applied [13] as constituents of palladium catalysts for hydrodimerization of butadiene and isoprene about the same time when the results of Kuraray were disclosed. These were obtained by quatemization of aminoalkylphosphines with methyl iodide or HQ (Ph2P-R-NH2 type compounds are known to yield phosphonium salts with these reagents). Although the catalysts prepared in situ from [PdCU] were reasonably active (TOF-s of 10-20 h ) the reactions always yielded complex product mixtures with insufficient selectivity towards the desired 1,7-octadienyl derivatives. 

On the industrial level, aqueous two-phase systems are used more often than nonaqueous two-phase systems. The Kuraray Co. operates a pilot plant for the hydrodimerization of 1,3-butadiene in a two-phase system with a Pd/tppms catalyst (140). The reaction is carried out in sulfolane-water, from which the products, the octadienols, separate. The final products can be octanol or nonanediol made by subsequent isomerization and hydroformylation. The capacity of the Kuraray process is about 5000 tons/year. 

The key reaction of this 1-octanol process is telomerization of butadiene with a palladium complex catalyst. Known attempts to commercialize the palladium complex-catalyzed telomerization have failed, in spite of great efforts, for the following reasons (1) palladium complex catalysts are thermally unstable and tbe catalytic activity markedly decreases when, as a means of increasing the thermal stability, the ligand concentration is increased (2) a sufficiently high reaction rate to satisfy industrial needs cannot be obtained (3) low selectivity and (4) distillative separation of reaction products and unreacted butadiene from the reaction mixture causes polymeric products to form and the palladium complex to metallize. Kuraray succeeded in 1991 in commercializing the production of 1-octanol using hydrodimerization of butadiene. 

Apart from the oxo process, a series of other reactions are carried out industrially, even if on a smaller scale. Kuraray carries out the hydrodimerization of butadiene and water to produce n-octanol (or 1,9-nonanediol) on a scale of about 5000 metric tons per year [55]. Applications which are significantly smaller up to now are, for example, the production of vitamin precursors by Rh6ne-Poulenc (cf. Scheme 2, [56]) and the production of substituted phenylacetic acids by carbonylation (Scheme 3) [57]) or of biaryls by Suzuki cross coupling (Scheme 4), both by Hoechst AG (now Clariant AG, [57,58]). 

Hydrodimerization is a special case of telomerization, where a (solvent) molecule A-B (the telogen, e.g., HzO) reacts with n molecules of an unsaturated molecule M (the taxogen) to yield oligomers or polymers of relatively low molecular mass (Eqs. 15 and 16). An important special case is the Kuraray 1-octanol process resulting from the products of Eq. (17) by subsequent hydrogenation. This industrially relevant reaction includes hydrodimerization of 1,3-butadiene [17]. Efficient catalysts are palladium-phosphine complexes, e.g., Pd2+/TPPMS (TPPMS = p(Qh4 -m-SO Na+)(C6H5)2). Little is as yet known on mechanisms. 

If water serves as telogen together with 2 mol of taxogen, the telomerization becomes a special hydrodimerization (Eq. 2). The consequent product in the case of butadiene as taxogen can be hydrogenated to produce 1-octanol, which has a considerable market as a raw material for plastidzers for poly(vinyl chloride). 

Aqueous, two-phase catalysis is also utilized industrially in a number of other processes apart from hydroformylation. The hydrodimerization of butadiene and water, a telomerization variant yielding 1-octanol or 1,9-nonanediol (cf. Section 6.9), is carried out at a capacity of 5000 tonnes per annum by the Kuraray Corporation in Japan. Rhone-Poulenc is operating two-phase, aqueous, catalytic C—C coupling processes (using TPPTS obtained from Ruhrchemie) for small-scale production of various vitamin precursors such as geranylacetones. Moreover, TPPTS-modified Ru catalysts have been proposed for the homogeneously catalyzed hydrogenation to convert unsaturated ketones into saturated ones. 

The linear telomerization reaction of dienes (the taxogen) with nucleophiles such as alcohols, amines, carboxylic acids, water, etc. (the telogen), catalyzed by ligand-modified Pd or Ni complexes, provides an elegant method for the synthesis of useful compounds. With water as telogen, the telomerization becomes a hydrodimerization. In the case of butadiene as taxogen, the reaction product is the versatile 2,7-octadien-l-ol (1) which may the basis for a series of various derivatives (Scheme 1). 

Other commercially important reactions include the hydrodimerization of 1,3-butadiene to octa-2,7-dien-l-ol carried out using palladium catalysts in [C4-mim][BF4]. The catalyst precursor [Pd(mim)2Cl2] was prepared in situ from an imidazoUum tetrachloropalladate(II) salt, [C4-mim]2[PdCl4], dissolved in the ionie liquid solvent. The reaction proceeds in a liquid-liquid two-phase system, where the products separate from the catalytic reaction mixture as a separate layer on eooling. 

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