Carbon dioxide, telomerization

Pitter et al. built on the observation that nitrile solvents are beneficial for the carbon dioxide telomerization reaction and used hemilabile nitrile-tethered phosphine ligands. Butadiene conversions were in the range of 70-90%, and... 

Telomerization Reactions. Butadiene can react readily with a number of chain-transfer agents to undergo telomerization reactions. The more often studied reagents are carbon dioxide (167—178), water (179—181), ammonia (182), alcohols (183—185), amines (186), acetic acid (187), water and CO2 (188), ammonia and CO2 (189), epoxide and CO2 (190), mercaptans (191), and other systems (171). These reactions have been widely studied and used in making unsaturated lactones, alcohols, amines, ethers, esters, and many other compounds. 

From the beginning of the 1970s unhl the mid 1980s, several examples of the telomerization of dienes with water [76, 77] or methanol [78, 79] to isomeric mixtures of dienols or dienol ethers catalyzed by palladium-phosphine complexes in the presence of carbon dioxide have been reported. Neither the yield nor the selectivity were very high. However, when allene was employed as a diene , 3-methyl-2-meth-ylene-3-buten-l-ol was obtained with fairly good selectivity (up to 98%) (Eq. 6.43) [78]. 

Formation of 2,7-octadienyl alcohol (32) by the reaction of water has attracted much attention as a novel practical synthetic method for n-octanol, which is of considerable industrial importance. However, the reaction of water under usual conditions of the butadiene telomerization is very sluggish. Atkins, Walker, and Manyik found that the presence of a considerable amount of carbon dioxide showed a very favorable effect on the telomerization of water (40). Reaction of water (2.0 moles) with butadiene (1.0 moles) using Pd(acac)2 and PPh3 as the catalyst was carried out in the presence of carbon dioxide (0.5 mole) at 80-90°C. tert-Butyl alcohol, acetone, and acetonitrile were used as solvents. The products that were obtained are shown in Eq. (21) and Table I. 

There appeared several reports treating the activating effect of carbon dioxide on the dimerization or telomerization of butadiene, as described before. But in none of these reactions did carbon dioxide behave as a reactant. Sasaki, Inoue, and Hashimoto found that carbon dioxide was incorporated to a small extent into the dimer of butadiene (103). 

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 carbon dioxide to form a 5-lactone is an interesting example for a C - C bond-forming reaction with CO2 (Scheme 2). The product can be hydrogenated to 2-ethylheptanoic acid, which can be used in lubricants, as a stabilizer for PVC or as an intermediate for the production of solvents and softeners [7,15-19]. 

Scheme 2 Telomerization of butadiene with carbon dioxide...

The results of this analysis of the product and catalyst distribution show that only a limited range of systems may be apphcable for the telomeriza-tion of butadiene and carbon dioxide. The reaction was performed in the biphasic systems EC/2-octanol, EC/cyclohexane and EC/p-xylene. The yield of 5-lactone reached only 3% after a reaction time of 4 hours at 80 °C. hi the solvent system EC/2-octanol triphenylphosphine was used as the hgand. With the ligand bisadamantyl-n-butyl-phosphine even lower yields were achieved in a single-phase reaction in EC or in the biphasic system EC/cyclohexane. The use of tricyclohexylphosphine led to a similar result, only 1% of the desired product was obtained in the solvent system EC/p-xylene, which forms one homogeneous phase at the reaction temperature of 80 °C. Even at a higher temperature of 100 °C and a longer reaction time of 20 hours no improvement could be observed. Therefore, we turned our interest to another telomerization-type process. 

Many new sugar based products present the advantage of being non-toxic and biodegradable. The products resulting from the telomerization of 1 with appropriate nucleophiles such as alcohols, amines, water, or carbon dioxide serve generally as useful intermediates in the synthesis of various natural products and fine chemicals [60-63], as precursors for plasticizer alcohols [56, 64], components of diesel fuels [65], surfactants [11, 66], corrosions inhibitors, and non-volatile herbicides [67]. 

Combes, J. R. Guan, Z. DeSimone, J. M. Homogeneous Free-Radical Polymerizations in Carbon Dioxide. 3. Telomerization of 1,1-Difluoroethylene in Supercritical Carbon Dioxide. Macromolecules 1994, 27, 865-867. 

Scheme 20 Reaction mechanism for the telomerization of butadiene with carbon dioxide proposed by Behr et al., adapted from [24]...

Braunstein P, Matt D, Nobel D (1988) Carbon-dioxide activation and catalytic lactone synthesis by telomerization of butadiene and C02. J Am Chem Soc 110 3207-3212... 

Behr A, Heite M (2000) Telomerization of carbon dioxide and 1,3-butadiene process development in a miniplant. Chem Eng Technol 23 952-955... 

The increased reactivity of isocyanates, relative to carbon dioxide, was reflected in the wider range of cycloaddition partners. For example, terminal diynes as well as nontethered alkynes (e.g., 3-hexyne) were also successfully converted to 2-pyridones rather than undergoing rapid telomerization to aromatic by-products. Importantly, the cycloaddition of an asymmetrical... 

The first reported polymerization of fluoroolefins in carbon dioxide was by Fukui and coworkers [39,40]. Tetrafluoroethylene, chlorotrifluoroethylene,and other fluoroolefins were polymerized in the presence of CO2 using ionizing radiation [39, 40] and free-radical initiators [40]. DeSimone and coworkers reported the homogeneous telomerization of tetrafluoroethylene [41] and vinylidene fluoride [42] in CO2 using AIBN as an initiator. The kinetics of AIBN decomposition in CO2 is well understood [4]. However, peroxide initiators are preferred over azo initiators for producing stable endgroups in fluoroolefins... 

Dienes, especially butadiene, also react with carbon dioxide. Inotie and his co-workeis found that Pd(dppe)j catalyzes the telomerization of butadiene and CO to give the y-lactone 2 Cthylidcnc-5 hcpien-4-oUde in about a S% yield [182, 183]. The distribution of the products evidently depends on the solvent used and polar aproiic solvents such as DMF, DMSOand 1 mielhyl-2-pyrrolidone are most suitable for lactone formation. A temperature of 120 C is required. When the reaction is carried out at temperatures below lOO C and terminated before the complete conwrsion of butadiene, the free organic acids (the precursors of the >4actone) are isolated up to 10%. 

A significant inlluence of COj was observed in some telomerization reactions, that is, in dimerization with the additional incorporation of a nucleophilic mole cule. The interaction of butadiene and water in the presence of the Pd(acac) -iri phenyl phosphine system under argon leads to the formation of ociatricne as the main product. In the presence of carbon dioxide, however, the octadienols are the main reaction products, whereas the yield of octatriene is insignitlcant. It is worth noting that catalytically-smaU amounts of carbon dioxide are sufficient for tlus reaction [301,302]. 

Butadiene as raw material is available in high amounts from the C4 fraction of raffmation processes. The telomerization of butadiene itself catalyzed by different metal catalysts is a well documented reaction. Depending on the catalyst and on the conditions different telomeres may be synthesized. Carrying out the reaction under carbon dioxide instead of argon atmosphere, 1,3,7-octatriene becomes the main product Pioneering work of Inoue and co-workers in 1976 showed that the same reaction under carbon dioxide atmosphere lead to co-oligomeres 2, 5 and 6 when palladium complexes are used as catalysts (Scheme 1). 

From a mechanistic point of view the first steps of the catalytic cycle should be similar to the telomerization of butadiene itself (Scheme 2). The catalytic precursor generates the Pd(0) species A that reacts to the bis-(ri -allyl) complex C. The C,C bond formation between two C4 units is followed by insertion of carbon dioxide into a Pd,C bond affording the carboxylate intermediate D. Different pathways have been discussed to describe the multiple product formation (refer to ). Interestingly, a bis-(carboxylato) complex may be prepared directly from the reaction of lactone 1, palladium acetate and P(i-Pr)3. This complex was structurally characterized by Behr and co-workers and shows good activity as catalyst. Reviewing the literature, there are some remarkable facts and open questions of theoretical and technical interest ... 

Telomerization of butadiene into 2,7-octadien-l-ol was also performed in neat water in the presence of carbon dioxide and certain trialkylamines in the presence of Pd(OAc)2/tppts or Pd(OAc)2/tppms, the structure of these amines having an important influence on the rate and the selectivity of the reaction... 

Carbon dioxide has been object of detailed studies either as anion radical scavenger or as direct electrochemical substrate in organic syntheses. Among the dozens of examples of electroorganic syntheses of mono- and dicarboxylic acids even a telomerization of ethylene with C02 has been reported56,57. The reaction has the following stoichiometry ... 

In Figure 6 this principle is demonstrated for the telomerization of butadiene with carbon dioxide yielding a d-lactone (Eq. 4). The reaction is carried out in a homogeneous acetonitrile solution using a palladium catalyst. After distillation of the acetonitrile in the second unit, the product/catalyst mixture is treated with the extractant, 1,2,4-butanetriol, which dissolves the product but not the catalyst [55]. The catalyst is then recycled to the reactor in a small amount of the liquid product. The main quantity of the lactone is separated from the extractant by a second distillation step. 

Further work was done in the telomerization of butadiene with carbon dioxide yielding a a-lactone in good yields [116-118]. For the catalyst recycle the successive extraction of the product with 1,2,4-butanetriol was proposed and investigated in detail. Mortreux et al. studied the telomerization of butadiene with sucrose which could also be carried out efficiently in water-organic medium in the presence of Pd salt and TPPTS [119]. Mono- and dioctadienylether were selectively obtained using aqueous sodium hydroxide/isopropanol mixtures. 

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