Hydrocyanation, catalysis

Carbonylation Processes by Homogeneous Catalysis Hydrocyanation by Homogeneous Catalysis Mechanisms of Reaction of OrganometaUic Complexes Ohgomeriza-tion Polymerization by Homogeneous Catalysis Osmium Inorganic Coordination Chemistry. 

By simply hydrolyzing the easily accessible 2-hydroxy-2-methylalkanenitriles with concentrated acid, 2-hydroxy-2-methylalkanoic acids are obtained without measurable racemization (Table 3). The reaction sequence from the starting ketone to the carboxylic acid can be carried out in one pot without isolation of the cyanohydrin. The enantiomeric excesses of the (/ )-cyanohydrins and the (ft)-2-hydroxyalkanoic acids are determined from the ( + )-(/T)-Mosher ester derivatives and as methyl alkanoates by capillary GC, respectively. The most efficient catalysis by (R)-oxynitrilase is observed for the reaction of hydrocyanic acid with 2-alkanoncs. 3-Alkanoncs are also substrates for (ft)-oxynitrilase, to give the corresponding (/ )-cyanohydrins32. 

Huthmacher, K. Krill, S. Reactions with Hydrogen Cyanide (Hydrocyanation). In Applied Homogeneous Catalysis with Organometallic Compounds Cornils, B., Herrmann, W. A., Eds. VCH Weinheim, Germany, 1996 pp 465-486. 

Tolman, C. A. McKinney, R. J. Seidel, W. C. Druliner, J. D. Stevens, W. R. Homogeneous Catalysed Olefin-hydrocyanation. In Homogeneous Catalyzed Olefin Hydrocyanation Advances in Catalysis Series 33 Academic Press New York, 1985, pp 1-46. 

RajanBabu, T. V. Casalnuovo, A. L. Hydrocyanation of Carbon-Carbon Double Bonds. In Comprehensive Asymmetric Catalysis Jacobsen, E. N., Pfaltz, A., Yamamoto, H., Eds. Springer-Verlag Berlin, 1999 pp 367-378. 

Nickel is frequently used in industrial homogeneous catalysis. Many carbon-carbon bond-formation reactions can be carried out with high selectivity when catalyzed by organonickel complexes. Such reactions include linear and cyclic oligomerization and polymerization reactions of monoenes and dienes, and hydrocyanation reactions [1], Many of the complexes that are active catalysts for oligomerization and isomerization reactions are supposed also to be active as hydrogenation catalysts. 

In an extension of an early work on the nickel-catalyzed addition of hydrogen cyanide to unsaturated compounds, a basic reaction in various large-scale processes in the polymer industry, the hydrocyanation of butadiene (equation 15) and the efficiency of catalysis of this reaction by low-cost copper salts has been studied extensively by Belgium researchers47,48. 

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]. 

Direct reaction of hydrocyanic acid with ethyleneimine does not yield the desired p-aminopropionitrile (68). However, ring opening of tosylated aziridines to give the corresponding tosylated p-aminopropionitriles is possible using trimethylsilyl cyanide [7677-24-9] with lanthanoid tricyanide catalysis (69,70). 

An enantioselective Strecker reaction involving Brpnsted acid catalysis uses a BINOL-phosphoric acid, which affords ees up to 93% in hydrocyanations of aromatic aldimines in toluene at -40 °C.67 The asymmetric induction processes in the stereoselective synthesis of both optically active cis- and trans-l-amino-2-hydroxycyclohexane-l -carboxylic acids via a Strecker reaction have been investigated.68 A 2-pyridylsulfonyl group has been used as a novel stereocontroller in a Strecker-type process ees up to 94% are suggested to arise from the ability of a chiral Lewis acid to coordinate to one of the sulfonyl (g)... 

Several studies have tackled the structure of the diketopiperazine 1 in the solid state by spectroscopic and computational methods [38, 41, 42]. De Vries et al. studied the conformation of the diketopiperazine 1 by NMR in a mixture of benzene and mandelonitrile, thus mimicking reaction conditions [43]. North et al. observed that the diketopiperazine 1 catalyzes the air oxidation of benzaldehyde to benzoic acid in the presence of light [44]. In the latter study oxidation catalysis was interpreted to arise via a His-aldehyde aminol intermediate, common to both hydrocyanation and oxidation catalysis. It seems that the preferred conformation of 1 in the solid state resembles that of 1 in homogeneous solution, i.e. the phenyl substituent of Phe is folded over the diketopiperazine ring (H, Scheme 6.4). Several transition state models have been proposed. To date, it seems that the proposal by Hua et al. [45], modified by North [2a] (J, Scheme 6.4) best combines all the experimentally determined features. In this model, catalysis is effected by a diketopiperazine dimer and depends on the proton-relay properties of histidine (imidazole). R -OH represents the alcohol functionality of either a product cyanohydrin molecule or other hydroxylic components/additives. The close proximity of both R1-OH and the substrate aldehyde R2-CHO accounts for the stereochemical induction exerted by RfOH, and thus effects the asymmetric autocatalysis mentioned earlier. 

Although several enzymes can enantioselectively catalyze the hydrocyanation of R2C=0 and R2C=NR bonds [7], (asymmetric) hydrocyanation of C=C double bonds has no precedents in biology. In homogeneous catalysis asymmetric hydrocyanation is still underdeveloped, as is apparent from the relatively few reports in the literature. In the following paragraphs a short overview will be given divided into the two major substrate classes investigated, cyclic (di)enes and vinylarenes. 

The hydrocyanation reactions of electrophilic aldehydes, ketones and their corresponding imines gives direct access to synthetic derivatives of several important structures, including a-hydroxy carboxylic acids, / -amino alcohols and a-tertiary and a-quaternary-a-amino acids. The asymmetric hydrocyanation reaction provides access to chiral synthons, which have proven useful for the construction of many structurally complex and biologically active compounds. Catalysis of these reactions is especially attractive with respect to avoiding the cost and relative chemical inefficiency associated with the use of chiral auxiliaries. 

The hydrocyanation reaction is important not only because it is practiced industrially on a large scale, but also because it clearly illustrates some of the fundamental postulates of homogeneous catalysis. The potential of the hydrocyanation reaction in asymmetric catalysis has also been explored and appears to be promising (see Chapter 9). 

From what has been discussed so far in this chapter, it is clear that homogeneous catalysis has had spectacular success in imparting high enantioselectiv-ities in the making of new C-H and C-O bonds. An enantioselective method for making new C-C bonds is also potentially very useful. Hydroformylation, hydrocyanation, and carbonylation are reactions that deal with the formation of new C-C bonds. All these have been turned into enantioselective catalytic systems with varying degrees of success. Considerable success has also been... 

The first mechanism is. in fact, reminiscent of the well-known copper-catalyzed dimerization of acetylene viny(acetylene being the main by-product of this process. This side reaction can, however, be inhibited to some extent by the use of cobalt salts as additives [IS]. The cyanation of acetylene and of alkenyl halides is also promoted by Co and Ni cyanides and Pd catalysis. A reducing reagent, such as Zn or NaBll4, has been used in conjunction with cobalt cyanide complexes, and the formation of. succinonitrile has been reported to result from the basebase-catalyzed hydrocyanation of acrylonitrile. 

Copper catalysis presents some definite advantages over nickcl(O) complexes, since it is not verysensitive to the presenceof small amounts of water or oxygen, but the second hydrocyanation step cannot be conveniently performed with these catalysts and, thus, remains an unsolved problem. 

Sponsored by the European Community, a Ct chemistry course was organized at Aachen by Prof. Keim. Dr Bchr and Dr Roper of the Technical University of Aachen, Prof, Teyssie and Prof. Hubert of the University of Liege and Prof. L go of the University of. Milan. The three-day course devoted to the application of predominantly liom( cneous transition metal based catalysis in C molecules formed the skeleton for this botrk. In nine chapters the following topics are covered the reduction of CO and reactions with CO. the chemistry of methanol, activation of carbon dioxide, hydrocyanation. methane chemistry and carbene chemistry. 

Carbonyl Complexes of the Transition Metals Coordination Organometallic Chemistry Principles Hydrocyanation by Homogeneous Catalysis. 

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