1.3- Butadiene reactions with carbon dioxide

Besides of butadiene also other 1,3-dienes may be possible starting chemicals for the reaction with carbon dioxide however, all our attempts to react isoprene with carbon dioxide failed. Investigations concerning the co-reaction of butadiene, isoprene and carbon dioxide led to two novel 6-lactones (Equation 8). 

In general reactivity, organocalcium compounds behave more like organolith-ium derivatives than like Grignard reagents. Thus Bu"CaI resembles Bu"Li in forming Bu"CO as well as Bu CO H (after hydrolysis) on reaction with carbon dioxide. Alkylcalcium halides also bring about the polymerization of butadiene or of styrene by an anionic mechanism. 

The following mechanism was proposed for the reaction of carbon dioxide with butadiene ... 

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

Sasaki Y, Inoue Y, Hashimoto H (1976) Reaction of carbon dioxide with butadiene catalysed by palladium complexes. Synthesis of 2-ethylidenehept-5-en-4-olide. J Chem Soc, Chem Commun 605-606... 

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%. 

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. 

Butadiene, which is bound in a n -manner to iron, reacts stoichio-metrically with carbon dioxide to form an allyl carboxylato complex in yields up to 75 % [38]. This allyl complex shows a dynamic behaviour Presumably three isomeric structures exist in solution, two of them with a n"-allyl bonding (Figure 16). Subsequent reactions of the allyl carboxylato complexes yield carboxylic acids. Acidic hydrolysis in methanol at -30°C gives methyl-3-pentenoate and methyl-4-pentenoate in a ratio of 10 1. If the iron allyl complex reacts with further carbon dioxide at 90 C, a second insertion of CO2 into the Fe-C-bond occurs after hydrolysis with hydrochloric acid in methanol the Z- and E-dimethyl esters of 3-hexenedioic acid are formed. 

Similar to the iron chemistry (compare Chapter 2.3), also nickel complexes allow the reaction of one molecule of butadiene with two molecules of CO2 yielding a,u-dicarboxylic acids [48]. In the reaction of butadiene and CO2 in the presence of nickelbis(cyclooctadiene) and tetramethylethylenediamine first a nickelamonocarboxylate is formed (Figure 19). By further treatment with carbon dioxide and by addition of pyridine a nickeladicarboxylate complex is obtained in yields up to 72 %. Decomposition of the complex with methanol/hydrochloric acid gives cis-dimethyl-3-hexenedioate. 

It is remarkable, that the reaction of butadiene and CO2 proceeds only in solvents containing a nitrile group such as acetonitrile, pfopionitrile or benzonitrile. In other solvents such as toluene, acetone or tetrahydrofurane only oligomers of butadiene are formed. This effect is so evidently that it can be presumed that the solvent is involved in the catalytic cycle of the reaction. The conversion of butadiene with carbon dioxide to the 6-lactone is very sensitive against the reaction conditions applied. In order to optimize the reaction various parameters have been investigated. 

It can be assumed that the reaction of butadiene with carbon dioxide yields first the kinetically preferred 6-lactone and that - at higher temperatures and catalyst concentrations - the thermodynamically more stable Y-lactones are formed. 

It is well known that oxiranes react with carbon dioxides yielding organic carbonates. Several transition metal catalysts permit very mild conditions and give high yields and selectivities in this reaction [63-65], but palladium catalysts proved to be particularly effective [66]. The question arose which reaction occurs when both butadiene and an oxirane are possible reaction partners of CO2. 

The role of R3AI is reduced to the alkylation of lanthanoids. Some support for this supposition is provided by the formation of carboxylates when the reaction mixture after butadiene polymerization on the NdCl3(THF)2 t3Al system is treated with carbon dioxide [9]. The protolysis of the product gives polybutadiene with COOH terminal groups. Quantum-chemical studies to model the active centres of butadiene polymerization on the Nd-Al catalytic system are also in agreement with this supposition on the mechanism of polymerization. 

The palladium catalyzed reaction of butadiene with carbon dioxide affords mixtures of the cyclic adducts 32 and 33 and linear adducts. The yield of the six-membered ring lactone increases when using a catalyst containing more basic phosphine ligands (PCys, P-i-Prs). ... 

The reaction of butadiene with carbon dioxide to give a 5-lactone is not known. However, this reaction can be accomplished starting with the mono-epoxide 90 and reacting it with carbon monoxide. When the reaction is catalyzed by iron or cobalt, the shown 5-lactone 91 is formed. However, if a rhodium catalyst is used a y3,y-unsaturated lactone 92 is... 

In the reaction of isoprene with carbon dioxide in the presence of Pd(o) complexes mixtures of lactones are obtained. Also, teleromization of butadiene with carbon dioxide is accomplished with the same catalyst... 

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. 

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. 

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 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. 

Phosphites and 2,2-bis(trifluoromethyl)-5(2//)-oxazolone 71 react with elimination of carbon dioxide to give 2-aza-4-phospha-l,l-bis(trifluoromethyl)-l,3-butadiene 72 that can be used as a synthon for the previously unknown hydrogen-substituted nitrile ylide 72a in [3 + 2]-cycloaddition reactions. Examples of cycloadditions of 72a with dipolarophiles to give heterocyclic compounds 12t-ll are shown in Scheme 7.18. 

The linear dimerisation of butadiene with palladium(II) catalyst precursors has been investigated in [C4Ciim]+ with a variety of different anions.[24] Observed turnover frequencies, which range from 37-49 mol mol h, are affected only slightly by the nature of the ionic liquid or catalyst precursor. Best activities were obtained with four equivalents of triphenylphosphine per palladium at a reaction temperature of 70°C. Contrary to the reaction in THF, no formation of metallic palladium was observed and reuse of the catalyst solution was possible. Pressurising the reaction mixture with 5-10 bar of carbon dioxide led to a decrease in reaction rates, which was explained by decreased substrate solubility in the C02-expanded ionic liquid. 

According to a patent [Y. Tokitoh, T. Higashi, K. Hino, M. Murosawa and N. Yoshimura, US Patent 5 057 631 (1991), to Kuraray Industries] the reaction is conducted with butadiene in sulfolane / water in the presence of Pd(OAc)2 as catalyst precursor and a soluble triarylphosphine (or its phosphonium bicarbonate, which is formed from octadienol itself and carbon dioxide) as ligand. The selectivity to 2,7-octadien-l-ol is 92-94% (TOF > 1000), while the isomeric l,7-octadien-3-ol accounts for another 3 5%. The product is extracted with hexane, while the aqueous sulfolane solution, containing the catalyst ca. 1 mmol/1) and triethylamine, is recycled. In the absence of carbon dioxide, the main product is 1,3,7-octatriene, an open-chain butadiene dimer. 

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