Reaction catalytic hydrodimerization

Typical acceptors in Michael additions are reducible and their radical anions often undergo dimerization (hydrodimerizations). Either the radical anions or more likely the dimer dianions can act as EGBs toward the donor in the Michael addition. Since the reaction is catalytic in base when the product anion is more basic than the donor anion, the Michael addition can take place by reduction of a small fraction (2-10%) of the acceptor [129]. The reaction takes place in 20 to 77% yield... 

Lithium naphthalene and sodium naphthalene (11) in solvents such as THF, diglyme, or aliphatic amines were found to be effective agents for the hydrodimerization of isoprene. Although this reaction is not strictly catalytic, it contributes to a better understanding of the base-catalyzed oligomerization of unsaturated conjugated hydrocarbons. 

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. 

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. 

These reactions are catalytic with respect to hydroxide (the OH is always regenerated). They probably represent the major diflkulty with the process since the hydrodimerization reaction (6.1) itself dqwnds on protonation steps and leads to the foimation of hydroxide ion if a neutral solution is employed. In addition, any water reduction at the rather negative pwtential necessary for the reduction of acrylonitrile (about —1.8 V) will also lead to hydroxide ion. 

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