Ethylene glycol, telomerization

The new recycling concept was apphed to several C - C bond-forming reactions, for example, to the telomerization of butadiene with ethylene glycol or carbon dioxide, to the isomerizing hydroformylation of frans-4-octene and to the hydroamino-methylation of 1-octene with morpholine. 

The telomerization of butadiene with ethylene glycol was chosen as an example for a reaction of a polar and a non-polar substrate to a semipolar product (Scheme 1). 

Scheme 1 Telomerization of butadiene with ethylene glycol...

One difficulty in the determination of an appropriate solvent system for the telomerization of butadiene with ethylene glycol is the change of polarity in the reaction mixture during the reaction. 

The catalyst system Pd(acac)2/TPPTS (TPPTS = trisulfonated triphenylphos-phine) was used in the experiments in which the telomerization of butadiene with ethylene glycol in TMS systems was investigated. However, the catalyst precipitates from many solvent mixtures as a yellow oil or solid, as soon as a homogenous phase is obtained. For this reason the solubihty of the catalyst was determined in various solvent systems. A solution of the catalyst in the mixture of ethylene glycol and water (si) and toluene (s2) was used in a weight ratio of 1 3. The various mediators s3 were added until a clear solution was formed or the catalyst precipitated. Only with DMF or DMSO can a clear solution be obtained. The addition of the catalyst to the polar phase causes an increase in the amount of s3 required to achieve a homogeneous system in the solvent system si toluene DMF the ratio increases from 1 5 4 to 1 5 4.4. 

Telomerization of Butadiene with Ethylene Glycol in TMS Systems... 

Catalysis experiments were performed to investigate the telomerization of butadiene with ethylene glycol in selected TMS systems (e.g. si toluene DMF 1 5 4 or sl 2-octanol DMSO 1.35 3 5.2). With Pd/TPPTS as the catalyst a maximum yield of only 10% of the desired products could be achieved. With Pd/TPPMS the yield increased up to 43% in the TMS system si toluene isopropyl alcohol, but additional water had to be added to obtain a phase split after the reaction. The catalyst leaching is very high and 29% of the palladium used is lost to the product phase. 

Table 1 Telomerization of butadiene with ethylene glycol in TMS systems. Reaction conditions 0.06 mol % Pd(acac)2 based on ethylene glycol, Pd/P =1 3 butadiene/ethylene glycol = 2.5 1, si = ethylene glycol water 2 1, 80 °C 4 h 1200 rpm...

Selective modification of polyols such as ethylene glycol, 1,3-propylene glycol, or glycerol with butadiene (1) has been studied [7-10]. The monosubstituted compounds are preferred due to their potential applications as surfactants, PVC plasticizers, or even in cosmetics. The telomerization of 1 with ethylene glycol yields a complex mixture including linear and branched mono- and ditelomers, as well as 1,3,7-octatriene and vinyl cyclohexene (Fig. 2) [11]. 

Recently, the Pd/TOMPP catalytic system was used in the telomerization of butadiene with a series of polyols and TON up to 10,000 was achieved with ethylene glycol or 1,3-propanediol [14],... 

To circumvent the formation of ditelomers and to attempt recycling of the catalysts, the telomerization of polyols was studied in the presence of water using water soluble catalysts such as Pd/TPPTS (TPPTS = tris(m-sulfonato-phenyl) phosphine trisodium salt) [9, 12, 16, 17]. Behr et al. studied the telomerization of ethylene glycol under biphasic conditions. Under such reaction conditions, 80% of mono-telomer are formed and only traces of ditelomer and butadiene dimers are detected (Fig. 4). This is attributed to the solubility of the monomer in the catalyst phase. However, the catalyst is unstable and decomposes rapidly, leading to almost inactive catalyst after three runs. This is due to TPPTS oxidation during the work-up of the reaction and can be avoided by addition of 2.5 equiv. ligand in the solution prior to each run. 

Fig. 4 Telomerization of butadiene with ethylene glycol under biphasic conditions reuse of the catalyst...

Ethylene glycol (EG) may be obtained from cellulose by many ways, for instance, by the catalytic conversion over carbide catalysts [71], It is the simplest linear polyol available and often serves as a model for more complex substrates. Many reports are therefore available on the telomerization of EG. The possible telomer products are shown in Scheme 14, the linear mono-telomer typically being the desired compound. The mono-telomer can be used, after saturation of the double bonds, as a plasticizer alcohol in polyvinylchloride production, whereas application in cosmetics and surfactants has also been indicated [72]. Early examples include the work of Dzhemilev et al., who first reported on the telomerization of butadiene with EG in 1980, yielding a mixture of the mono- and di-telomers and butadiene dimers using a palladium catalyst activated by AlEt3 [73]. Kaneda also reported the use of EG in... 

Table 1 Selected results of the telomerization of 1,3-butadiene with ethylene glycol for optimized...

Parvulescu et al. noted an interesting change in EG telomer product selectivity upon immobilization of an Pd/TPPTS catalyst on a basic support [58]. In an attempt to address the issues associated with recovery and reuse of the telomerization catalyst, the anionic TPPTS ligand was immobilized on various layered double hydroxides by ion exchange methods (Scheme 11). The use of these catalysts in the telomerization of methanol and ethylene glycol resulted in a remarkable shift in... 

Behr A, Urschey M (2003) Palladium-catalyzed telomerization of butadiene with ethylene glycol in liquid single phase and biphasic systems control of selectivity and catalyst... 

Recently, a nice example has been studied in which biphasic catalysis was not only used for catalyst recycling but also to increase the selectivity of the catalytic reaction. In the telomerization of butadiene with the bifunctional nucleophile ethylene glycol both monotelomers and ditelomers can be formed [113, 114]. When the reaction is carried out in a single liquid phase, for instance in tetrahydrofurane with a catalyst formed from palladiumbis-acetylacetonate and triphenylphosphine, the monotelomers are formed in a maximum yield of 60% with more than 20% of ditelomers as byproducts. When palladiumcarbene-complexes were used, the mono/ di-ratio switched to 1 3, thus increasing the formation of the ditelomer. However, if the monotelomers are the favored products, for instance for the production of detergents, no sufficient reaction control by choice of the ligand was possible so far. 

An application of this principle is in the telomerization of butadiene with ethylene glycol. One-phase reactions yield both mono- and ditelomers, while the two-phase system using a water/glycol phase containing a polar palladium catalyst avoids the... 

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