Reaction butadiene hydrodimerizations

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

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. 

From 1974 onwards the scope of different reactions using biphasic catalyst systems, preferably with precious metals, was tested in laboratory-scale experiments. Among these were butadiene hydrodimerization, hydrogenation of acrylonitrile or cyclohexene, hydroformylation of propene, and some other conversions to fine... 

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. 

In order to improve the activity in the absence of co-solvent, the use of a surfactant was studied in the presence of TPPTS-based catalyst [55]. Monflier et al. reported the hydrodimerization of 1 in the presence of surfactants in order to improve butadiene mass transfer in pure water solution [56-58]. Such an additive used in very low amount avoided the presence of an organic co-solvent. It was shown in the case of hydrodimerization that neutral or cationic surfactants played a significant role in the process. Similar behaviors were reported for the telomerization of 1 with 21. While 30% conversion of 1 was achieved in pure water after 24 h reaction time at 50°C using 0.4 mol% of catalyst, the conversion reached 87% when polyether surfactant (POEA) was added to the reaction medium under similar reaction conditions (Table 12). It was found that the conversion is strongly affected by the nature of the surfactant (Table 13). 

Finally, a third means of ligand formation from an imidazolium cation, described by Dupont and co-workers, should be mentioned here [34]. They investigated the hydrodimerization/telomerization of 1,3-butadiene with palladium(II) compounds in [BMIM][BF4] and described the activation of the catalyst precursor complex [BMIM]2[PdCl4] by a palladium(lV) compound formed by oxidative addition of the imidazolium nitrogen atom and the alkyl group with cleavage of the C-N bond of the [BMIM] ion, resulting in bis(methyHmidazole) dichloropalladate (Scheme 5.2-5). However, this reaction was only observed in the presence of water. 

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. 

For the hydrodimerization of butadiene with water, attempts have been made to increase the reactivity by adding acidic solids [4], salts such as sodium phosphate [5], emulsifiers [6], carbon dioxide [7], or the like, with no satisfactory results. In particular, the reaction rate increases under a carbon dioxide pressure, but carbonate ions, not carbon dioxide itself, are considered to play an important role in this effect. It is known that the carbonate ion concentration in water is very low even under a carbon dioxide pressure. If the carbonate ion is the true reactant, the reaction rate should increase with the carbonate ion concentration. Since inorganic carbonates show almost no effect, the addition of various tertiary amines having no active hydrogen, under a carbon dioxide pressure was tested [8]. Diamines and bifunctional amines inhibited the reaction. The reaction rate increased only in the presence of a monoamine having a p/f of at least 7, almost linearly with its concentration (Figure 3). 

Telomerizations have been among the first reactions tested under biphasic conditions [45, 190], starting with butadiene and methanol on Pd/TPPMS catalysts and yielding l-methoxy-2,7-octadiene. The telomerization in the presence of water as reactant (hydrodimerization cf Scheme 1) has been commercialized [15, 31, 42-44]. These biphasic developments of the Kuraray Corporation yield 1-octanol or 1,9-nonanediol, respectively (cf [15, 31, 42 4, 86, 133, 137, 244 e] and Section 2.3.5). Similar developments (but without technical realization) have been described by BASF [134], Mitsubishi [135], and Shell [136], and others [215 d, 242, 268]. The telomerization of butadiene and ammonia may also be biphasic [243]. 

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]). 

This process consists of four steps hydrodimerization, extraction, hydrogenation, and distillation [12-14], The telomerization step comprises feeding butadiene and water continuously to the reaction zone in the presence of a separately prepared... 

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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