Hydrocyanation of olefins

The hydrocyanation of olefins corresponds to the addition of HCN across a double bond. 

This type of reaction is now of major industrial importance because it constitutes a straiglitforward synthesis of nitriles. Wlien it is applied to a diolefm, such as butadiene, it leads to the formation of dinitriles, which are precursors of valuable monomers for the preparation of polymers (butadiene leads to adipo-nilrile. a nylon-b, fvprecursor). Du Font developed the first commercial process using butadiene and HCN for adiponitrile synthesis from butadiene, but this process does nut proceed through a hydrocyanation reaction it is. in fact, a copper-catalyzed halogenation reaction followed by a cyanaikm reaction (tquaiion (16)) of the chlorinated intermediate (Fquation (17)). 

The mixture of dichlorobutcncs is heated with HCN or NaCN in the presence of copper cyano complexes (Equation (17)). As 3,4-di-cyanobutene rearranges to the required 1,4-isomcr under the hydrocyanation conditions, the overall yield remains economically acceptable the last step being tlie hydrogenation of dicyanobutene to adiponitrile. 

The copper atalyzed isomerization (13) of dichlorobutenes has been explained by the formation of a copper(tll) n-allyl type intermediate (two isomers existing in equilibrium). 

The cyanaiion step would proceed throu the cyanide ion transfer within the coordination sphere of a n-allyl type copper intermediate  

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Hydrocyanation of olefins and dienes is an extremely important reaction [32] (about 75 % of the world s adiponitrile production is based on the hydrocyanation of 1,3-butediene). Not surprisingly, already one of the first Rhone Poluenc patents on the use of water soluble complexes of TPPTS described the Ni-catalyzed hydration of butadiene and 3-pentenenitrile (Scheme 9.10). The aqueous phase with the catalyst could be recycled, however the reaction was found not sufficiently selective. 

In this article, we will discuss the chemistry behind the du Pont adiponitrile process from a mechanistic viewpoint (10). It is not intended to be a comprehensive review of the hydrocyanation literature. We will restrict ourselves rather to homogeneous nickel-catalyzed hydrocyanation of olefins and will depend primarily on du Pont studies. Reviews which explore hydrocyanation in a more general way include those of Brown (77), Hubert and Puentes (72), and James (73). A general review of low-valent organo-nickel chemistry has been published by Jolly and Wilke (14). 

Drinkard, W. C. Hydrocyanation of olefins using selected nickel phosphite catalysts. US 3,496,215,1970. 

In its literal form, this reaction is only of academic interest because a molecule is unlikely to break up or isomerize irreversibly in two or more different ways. However, situations frequently encountered in practice are those of multistep parallel first-order decomposition reactions and of parallel reactions that involve coreactants but are pseudo-first order in the reactant A. An example of the first kind is dehydrogenation of paraffins, examples of the second kind include hydration, hydrochlorination, hydroformylation, and hydrocyanation of olefins and some hydrocarbon oxidation reactions. All these reactions are multistep, but the great majority are first order in the respective hydrocarbon, and pseudo-first order if any co-reactant concentration is kept constant. 

An example already encountered in this section is the use of DCN in hydrocyanation of olefinic compounds, confirming expectations as to the addition of D and CN to the double-bond carbon atoms (see previous section). 

Palladium-catalyzed hydrocyanation of olefins has been reported [31]. However, the corresponding reactions with conjugated dienes have not been reported explicitly. The analogous nickel-catalyzed hydrocyanation of conjugated dienes has been described [32] and is the basis for the commercial adiponitrile process. In this case, it has been shown [33] that the overall addition of HCN to the 1,3-diene occurs with cis stereochemistry consistent with path B in Scheme 8-1. 

Many other addition reactions of olefins, dienes, and acetylenes are known, which are catalyzed by metal carbonyls including Ni(CO)4, Fe(CO)5, and Co2(CO)8 and by carbonyl derivatives such as hydrocarbonyls or phosphine-substituted carbonyls. Among these are the hydro-carboxylation, hydroesterification, and hydrocyanation of olefins the synthesis of hydroquiniones from acetylenes, carbon monoxide, and water ... 

A number of olefins are converted in the presence of tetrakis(tri-o-tolyl phos-phite)nickel(O) into the corresponding nitriles. These additions yield the terminal nitriles predominantly [15]. Systematic investigations were performed on the hydrocyanation of olefins containing the norbomene skeleton 9 as a basic structure. Table 1 demonstrates the development of catalysts to gain stereocontrol of product formation. 

Steric effects, induced by the substituents of the alkyne derivative, dominate in general the regioselectivity of HCN addition when bulky alkynes are employed [63], The observed selectivity finds its analogy in the hydrocyanation of olefins already discussed. The decisive step involves formation of an -alkenyl-nickel complex. 

Familiar combinations include Y = H, X = olefin, acetylene, or diene Y = alkyl, X = CO Y = OH or OR, X = CO or olefin. Such reactions constitute important routes for addition to unsaturated molecules, and thus play a widespread role in catalytic reaction processes such as hydrogenation, hydrosilylation, and hydrocyanation of olefins, car-bonylation, etc. ... 

Two Pd(0)-DIOP complexes (Scheme 2), Pd(diop)2 (1)PLW] and Pd(i7 -CH2=CH2) (diop) (2),t which were catalysts of asymmetric hydrocyanation of olefins, were reported... 

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