Phase hydrocyanation

The remarkably versatile Ci building block HCN may be used in the aqueous two-phased hydrocyanation, too (Equation 5.3 [37]). Also, some fine chemicals such as intermediates for vitamins, phenyl acetic acid, etc. are manufactured on an industrial scale using this technology (Equations 5.4 and 5.5 [12e,31b,38]). 

Irradiation of ethyleneimine (341,342) with light of short wavelength ia the gas phase has been carried out direcdy and with sensitization (343—349). Photolysis products found were hydrogen, nitrogen, ethylene, ammonium, saturated hydrocarbons (methane, ethane, propane, / -butane), and the dimer of the ethyleneimino radical. The nature and the amount of the reaction products is highly dependent on the conditions used. For example, the photoproducts identified ia a fast flow photoreactor iacluded hydrocyanic acid and acetonitrile (345), ia addition to those found ia a steady state system. The reaction of hydrogen radicals with ethyleneimine results ia the formation of hydrocyanic acid ia addition to methane (350). Important processes ia the photolysis of ethyleneimine are nitrene extmsion and homolysis of the N—H bond, as suggested and simulated by ab initio SCF calculations (351). The occurrence of ethyleneimine as an iatermediate ia the photolytic formation of hydrocyanic acid from acetylene and ammonia ia the atmosphere of the planet Jupiter has been postulated (352), but is disputed (353). 

Some companies are successfully integrating chemo- and biocatalytic transformations in multi-step syntheses. An elegant example is the Lonza nicotinamide process mentioned earlier (.see Fig. 2.34). The raw material, 2-methylpentane-1,5-diamine, is produced by hydrogenation of 2-methylglutaronitrile, a byproduct of the manufacture of nylon-6,6 intermediates by hydrocyanation of butadiene. The process involves a zeolite-catalysed cyciization in the vapour phase, followed by palladium-catalysed dehydrogenation, vapour-pha.se ammoxidation with NH3/O2 over an oxide catalyst, and, finally, enzymatic hydrolysis of a nitrile to an amide. 

HCN (hydrocyanic acid) is named using these rules. However, in this case, it does not matter if the phase or water is indicated. 

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. 

For preparative purposes, the use of biphasic solvent systems consisting of an aqueous phase and a water-immiscible organic phase for PaHNL and llhl INI. catalysis has proven to have a broad applicability, also including, for example, pyrrole derivatives [30] (see Table 9.3, Section 9.2.2.3) and to be suitable for industrial scale. DSM established enzymatic hydrocyanation processes, e.g., for the production of (S)-m-phenoxymandelonitrile [31, 32] and large-scale production of (R) -2 - (2 -furyl) - 2 -hydroxyace tonitrile [33]. 

Acrylonitrile was first produced in Germany and the United States on an industrial scale in the early 1940s. These processes were based on the catalytic dehydration of ethylene cyanohydrin. Ethylene cyanohydrin was produced from ethylene oxide and aqueous hydrocyanic acid at 60°C in the presence of a basic catalyst. The intermediate was then dehydrated in the liquid phase at 200°C in the presence of magnesium carbonate and alkaline or alkaline earth salts of fonnic acid. A second commercial route to acrylonitrile was the catalytic addition of hydrogen cyanide to acetylene. The last commercial plants using these process technologies were shut down in 1970 (Langvardt, 1985 Brazdil, 1991). 

The addition of hydrogen cyanide (HCN) to carbon-carbon double bonds activated by electron-withdrawing groups in the presence of a base as a catalyst (a variation of the Michael Reaction) has been known for a long time. Nitriles were also obtained by hydrocyanation of branched olefins, such as isobutylene and trimethylethylene, in vapor phase reactions in particular the reactions over alumina (3) and cobalt-on-alumina (4) were reported in the late 1940s and early 1950s. Addition of HCN to conjugated dienes in the presence of cuprous salts (vapor and liquid phase) was reported as early as 1947 (5). 

As noted above, enzymatic hydrocyanations are preferably performed at pH < 5, to suppress the non-enzymatic bacl ound reaction whereas the pH optimum of the common nitrilases is 7. A compromise pH is obviously required and we accordingly assessed the effects of the pH on the MeHnL-mediated hydrocyanation of benzaldehyde (2a, see Figure 16.3) in a biphasic aqueous-diisopropyl ether (DIPE) medium. We found that enantioselectivity was maintained at pH 5.5, which we adopted as a compromise pH for the bienzymatic reactions, provided that the aqueous buffer phase accounted for <10% of the reaction volume. PfNLase was the obvious choice for the second step as it stayed active at pH 5.5 and converted (S)- and (R)-la at comparable rates. 

In homogeneous catalysis often a reaction takes place between a gaseous reactant and a liquid reactant in the presence of a catalyst that is dissolved in the liquid phase. Examples are carbonylations, hydroformylations, hydrogenations, hydrocyanation, oxidations, and polymerizations. Typically, reactants such as oxygen, hydrogen, and/or carbon monoxide have to be transferred from the gas phase to the liquid phase, where reaction occurs. The choice of reactor mainly depends on the relative flow rates of gas and liquid, and on the rate of the reaction in comparison to the mass and heat transfer characteristics (see Fig. 8.2). 

Naked cyanide ion. Alkyl halides are converted into nitriles by potassium cyanide in the presence of a catalytic amount of 18-crown-6. Acetonitrile (or benzene) is used as solvent, and the two-phase system is stirred vigorously at 25-83°. Little or no reaction occurs in the absence of the crown ether, an indication that the ether is functioning also as a phase-transfer catalyst. Primary halides are also converted quantitatively into nitriles chlorides react much faster than bromides. A few percent of elimination products are formed in the reaction of secondary halides. Cyclohexyl halides give only cyclohexene by elimination. o-Dichlorobenzene fails to react. Methacrylonitrile undergoes hydrocyanation to 1,2-dicyanopropane (92% yield). 

Hydrocyanation. Hydrocyanalion of a, 3-unsaturated ketones can be effected by addition of the substrate in CeHe or CH3CN containing 18-crown-6 to dry KCN. Acetone cyanohydrin is then added and the two-phase system is stirred for 3-20 hours. No reaction is observed in the absence of the crown ether, acetone cyanohydrin, or potassium cyanide. Although the last reagent is only required in catalytic amounts, an equivalent is usually employed. The thermodynamic product predominates, particularly with CeHe as solvent and at ambient temperatures. ... 

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