Hydrodimerization

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. 

Telomerizations provide an opportunity to make functionalized organic products from simple, abundant precursor molecules, e.g., butadiene and water see also Section 6.9. 

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Dir, whereas for small distances d < r), /r Did. The large effective obtainable enables fast heterogeneous reaction rates to be measured under steady-state conditions. Zhou and Bard measured a rate constant of 6 x 10 Ms for the electro-hydrodimerization of acrylonitrile (AN) and observed the short-lived intennediate AN for this process [65]. 

Until the 1960s, adipic acid [124-04-9] was virtually the sole intermediate for nylon-6,6. However, much hexamethylenediamine is now made by hydrodimerization of acrylonitrile (qv) or via hydrocyanation of butadiene (qv). Cyclohexane remains the basis for practically the entire world output of adipic acid. The U.S. capacity for adipic acid for 1993 was 0.97 X 10 t/yr (233). 

Scheme 5.2-5 Formation of the active Pd-catalyst from [BMIM]2 PCICI4 for the hydrodimerization of 1,3-butadiene.

Zimtaldehyd und 3-Oxo-1-phenyl-1-alkene liefern ebenfalls Hydrodimere z. B. ... 

Perhaps the best known example of adsorption effects in electrosynthetic reactions is the beneficial role of tetraalkylammonium ions in the hydrodimerization of acrylonitrile... 

Reactions of this type are called electrochemical hydrodimerization. They are of great value for the synthesis of various bifunctional compounds. A reaction that has found wide commercial nse is the hydrodimerization of acrylonitrile to adiponitrile (the dinitrile of adipic acid) ... 

The hydrodimerization of butadiene and water (Eqn. (16)), a variant of telomerization, is carried out industrially in Japan. 

A wide variety of activated olefins (126) undergo reductive electrochemical dimerization to compounds of structure 127 (electrolytic hydrodimerization) 129 i. While the product 127 is capable of existing in either dl or meso modifications, relatively little attention has been paid to the stereochemistry of hydrodimers... 

Before discussing what is known concerning the stereochemistry of hydrodimerization, it will be useful to discuss probable mechansims of hydrodimerization. It appears that a different mechanism is followed in acid than in neutral or alkaline media. In acid the first step is a one-electron reduction of the pro-tonated starting material to form a neutral radical, which then dimerizes. Thus for mesityl oxide (128) ... 

Steric factors are also important in hydrodimerizations carried out in acidic media. Excessive steric hindrance about the 0-carbon in an a, 0-unsaturated carbonyl compound can retard tail-to-tail coupling, e.g., 2 130 - 131, and lead to products of head-to-head (and occasionally head-to-tail) coupling. Thus in the reduction of mesityl oxide at pH lg.4 there is also formed a small amount of ketone 140, apparently formed via head-to-head coupling of 130 and subsequent pinacol rearrangement of 139 134) ... 

Useful information concerning the stereochemistry of hydrodimerization comes from a study of the electrochemical behavior of taws-2,2,6,6-tetra-... 

Hydroformylation comprises the state-of-the-art of bulk chemical production via aqueous-biphasic processes. At present five plants produce worldwide some 800,000 tpy of oxo products [1], Another bulk process - the hydrodimerization of butadiene and water, a variant of telomerization - is mn by Kururay with a capacity of 5000 tpy (Equation 5.2 [3 lb,36]). 

In this chapter are summarized the photochemical reactions wherein the primary chemical event is inter- or intramolecular hydrogen transfer to the excited chromophor. In intermolecular reactions hydrogen abstraction usually implies reduction or hydrodimerization of the excited molecule intramolecular hydrogen abstraction is frequently followed by either ring closure of the diradical or fragmentation to afford unsaturated molecules. 

Rate data have appeared (161) for the hydrodimerization of acrylonitrile to adiponitrile, which is catalyzed by various ruthenium-phosphine complexes (/, p. 101). 

Monsanto (1) A process for making adiponitrile, an intermediate in the manufacture of Nylon 66, by the electrolytic hydrodimerization (EHD) of acrylonitrile ... 

Scheme 4. Possible reaction pathways for the hydrodimerization of acrylonitrile to adiponitrile. The asterisk indicates that electron transfer can be from the cathode or from [CH2CHCN] in homogeneous solution...

At the cathode, olefins with electron deficient double bonds can be hydrodimer-ized (Eq. 1). This reaction has been developed for acrylonitrile [22] in a technical adipodinitrile synthesis [23] with a scale of more than 300.000 tons per year. The scope of this hydrodimerization has been substantiated with many examples [24-33]. 

Formally related reactions are observed when anthracene [210] or arylole-fines [211-213] are reduced in the presence of carboxylic acid derivatives such as anhydrides, esters, amides, or nitriles. Under these conditions, mono- or diacylated compounds are obtained. It is interesting to note that the yield of acylated products largely depends on the counterion of the reduced hydrocarbon species. It is especially high when lithium is used, which is supposed to prevent hydrodimerization of the carboxylic acid by ion-pair formation. In contrast to alkylation, acylation is assumed to prefer an Sn2 mechanism. However, it is not clear if the radical anion or the dianion are the reactive species. The addition of nitriles is usually followed by hydrolysis of the resulting ketimines [211-213]. 

CathodicaUy reduced hydrocarbons not only undergo homogeneous ET and nucleophilic attack but also coupling reactions resulting in hydrodimerization and polymerization. 

Reduction of stilbene [18] or dipheny-lacetylene [214] in DME yields 1,2,3,4-tetraphenylbutane, whereas phenanthrene [214] provides 9,9, 10,10 -tetra-hydro-9.9 -biphenanthrene. Hydrodimerization was also observed with benzalfluo-rene [225]. If DME is replaced by acetonitrile, protonation completely dominates hydrodimerization [18]. In carefully dried ethers, using alkali or alkaline earth metals salts as supporting electrolyte, 1,1-diphenylethylene can be reduced ca-thodicaUy to give stable solutions of 1,1,4,4-tetraphenylbutane dianions [226]. These dianions can be cleaved by flash... 

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