Nickel carbonyl as catalyst

Another method that appears to have commercial potential is the ozonolysis of cyclooctene. Ozonolysis is carried out using a short chain carboxyHc acid, preferably propanoic acid, as solvent. The resultant mixture is thermally decomposed in the presence of oxygen at about 100°C to give suberic acid in about 60—78% yield (38—40). Carboxylation of 1,6-hexanediol using nickel carbonyl as catalyst is reported to give suberic acid in 90% yield (41). 

Hydrocarboxylation can also be accomplished under mild conditions (160°C and 50 atm) by the use of nickel carbonyl as catalyst. This is more often applied to triple bonds to give a,P-unsaturated acids, in which cases the conditions are milder still. Acid catalysts are used along with the nickel carbonyl, but basic catalysts can also be employed.567 Other metallic... 

Acrylic acid (CH2=CHC02H, melting point 13.5°C, boiling point 141°C, density 1.045, flash point 68°C) and acrylates were once prepared by reaction of acetylene and carbon monoxide with water or an alcohol, with nickel carbonyl as catalyst. 

Acrylic Acid, Acrylates, and Acrylonitrile. Acrylic acid [79-10-7], C3H402, and acrylates were once prepared by reaction of acetylene and carbon monoxide with water or an alcohol, using nickel carbonyl as catalyst. I11 recent years tliis process has been completely superseded in the United States by newer processes involving oxidation of propylene (2). I11 western Europe, however, acetylene is still important in acrylate manufacture (see Acrylic acid and derivatives Acrylic ester polymers). 

The acid-catalyzed hydrocarboxylation of alkenes (the Koch reaction) can be performed in a number of ways. In one method, the alkene is treated with carbon monoxide and water at 100-350°C and 500-1000-atm pressure with a mineral acid catalyst. However, the reaction can also be performed under milder conditions. If the alkene is first treated with CO and catalyst and then water added, the reaction can be accomplished at 0-50°C and 1-100 atm. If formic acid is used as the source of both the CO and the water, the reaction can be carried out at room temperature and atmospheric pressure.The formic acid procedure is called the Koch-Haaf reaction (the Koch-Haaf reaction can also be applied to alcohols, see 10-77). Nearly all alkenes can be hydrocarboxylated by one or more of these procedures. However, conjugated dienes are polymerized instead. Hydrocarboxylation can also be accomplished under mild conditions (160°C and 50 atm) by the use of nickel carbonyl as catalyst. Acid catalysts are used along with the nickel carbonyl, but basic catalysts can also be employed. Other metallic salts and complexes can be used, sometimes with variations in the reaction procedure, including palladium, platinum, and rhodium catalysts. The Ni(CO)4-catalyzed oxidative carbonylation with CO and water as a nucleophile is often called Reppe carbonylationP The toxic nature of nickel... 

Like many carbonylation processes, the hydrocarboxylation and hydroesterification reactions were first reported by Reppe. These first reactions involved the hydrocarboxylation of alkynes. These reactions were conducted with nickel carbonyl as catalyst and occurred with very low turnover numbers. Hydrocarboxylation and hydroesterification have now been studied extensively in both academic and industrial laboratories. As a result of these investigations, commercialization of this chemistry as part of new industrial processes has occurred, and the mechanism of these processes is now generally accepted. This section of Chapter 17 presents the scope and industrial applications of hydrocarboxylation and hydroesterification, the types of catalysts that have been used for these processes, and the elementary steps that constitute the catalytic cycle for olefin and alkyne hydroesterification. 

Several other types of hydrocarboxylations and hydroesterifications have been conducted with rates and selectivity that are appropriate for the synthesis of fine chemicals and commodity chemicals. One target for hydroesterification has been methyl methacrylate, the monomer of polyfmethyl methacrylate), which is the polymer often called "acrylic". It is estimated that 2.1 million metric tons of methyl methacrylate was produced in 2005. Much of this material is produced from acetone cyanohydrin, but two alternative routes could involve catalytic carbonylation. The first route would involve the hydroesterification of methylacetylene, and this chemistry relates to the original route to methyl methacrylate by carbonylation of methylacetylene using nickel carbonyl as catalyst. The second route involves the sequence of ethylene hydoesterification, aldol addition of the resulting ester to formaldehyde, and dehydration. This sequence comprises Lucite s new "Alpha" process and is shown in Equation 17.33. The route to methyl methacrylate by hydrocarboxylation of ethylene produces water as the only byproduct. 

The reaction is carried out in the Hquid phase at 373—463 K and 3 MPa (30 atm) of carbon monoxide pressure using nickel salt catalyst, or at 313 K and 0.1 MPa (1 atm) using nickel carbonyl as both the catalyst and the source of carbon monoxide. Either acryHc acid or methyl acrylate may be produced directly, depending on whether water or methanol is used as solvent (41). New technology for acryHc acid production uses direct propjdene oxidation rather than acetylene carbonylation because of the high cost of acetjdene. This new process has completely replaced the old in the United States (see... 

Furthermore, 2,2-difluoro-3-hydroxyesters are readily obtained from ClCFjCOOMe and carbonyl compounds by electrolysis in a one-compartment cell using a sacrificial zinc anode and a nickel complex as catalyst. The catalytic cycle for this reaction is shown in Scheme 9 with nickel zinc exchange being a key step. In this process, the CHjCyDMF solvent (9 1) system leads to suppression of undesired Claisen condensation and an increase in the yield of 2,2-difluoro-3-hydroxyester formation. It is notable that high yields are obtained even with ketones and enolizable aldehydes, which are not good participants in the Reformatsky reaction alternative for producing these substances. 

The addition of HCN to olefins catalyzed by complexes of transition metals has been studied since about 1950. The first hydrocyanation by a homogeneous catalyst was reported by Arthur with cobalt carbonyl as catalyst. These reactions gave the branched nitrile as the predominant product. Nickel complexes of phosphites are more active catalysts for hydrocyanation, and these catalysts give the anti-Markovnikov product with terminal alkenes. The first nickel-catalyzed hydrocyanations were disclosed by Drinkard and by Brown and Rick. The development of this nickel-catalyzed chemistry into the commercially important addition to butadiene (Equation 16.3) was conducted at DuPont. Taylor and Swift referred to hydrocyanation of butadiene, and Drinkard exploited this chemistry for the synthesis of adiponitrile. The mechanism of ftiis process was pursued in depth by Tolman. As a result of this work, butadiene hydrocyanation was commercialized in 1971. The development of hydrocyanation is one of tfie early success stories in homogeneous catalysis. Significant improvements in catalysts have been made since that time, and many reviews have now been written on this subject. ... 

Regarding the use of well-defined nickel complexes as catalysts for reduction of carbonyl groups, only three examples are described in the literature. In 2009, Guan and coworkers [77] described the efficiency of a nickel PCP-pincer complex performing the hydrosilylation of aldehydes. In the same year, the catalytic hydrosilylation of ketones via a transient Ni-H complex supported by a monoanionic bidentate amidophosphine ligand was reported by Mindiola [78]. Later, Jones investigated well-defined PNP nickel pincer complexes, which catalyzed the hydrosilylation of aldehydes [79] (Fig. 10.16). 

In one process, the reaction is conducted in solution in tetrahydrofuran at about 200°C and 60—200 atmospheres. Nickel bromide is used as catalyst. The solution of acrylic acid in tetrahydrofuran, after separation of the unconverted acetylene and carbon monoxide in a degassing column, passes to a distillation tower where tetrahydrofuran is taken overhead and acrylic acid is the bottom product. The reaction between acetylene, carbon monoxide and water may also be carried out by using nickel carbonyl as the source of carbon monoxide. In this case, milder reaction conditions are possible (cf.. Section 6.2.3). 

Some catalysts are ha2ardous materials, or they react to form ha2ardous substances. For example, catalysts used for hydrogenation of carbon monoxide form volatile metal carbonyl compounds such as nickel carbonyl, which are highly toxic. Many catalysts contain heavy metals and other ha2ardous components, and environmentally safe disposal has become an increasing concern and expense. 

The use of CO is complicated by the fact that two forms of adsorption—linear and bridged—have been shown by infrared (IR) spectroscopy to occur on most metal surfaces. For both forms, the molecule usually remains intact (i.e., no dissociation occurs). In the linear form the carbon end is attached to one metal atom, while in the bridged form it is attached to two metal atoms. Hence, if independent IR studies on an identical catalyst, identically reduced, show that all of the CO is either in the linear or the bricked form, then the measurement of CO isotherms can be used to determine metal dispersions. A metal for which CO cannot be used is nickel, due to the rapid formation of nickel carbonyl on clean nickel surfaces. Although CO has a relatively low boiling point, at vet) low metal concentrations (e.g., 0.1% Rh) the amount of CO adsorbed on the support can be as much as 25% of that on the metal a procedure has been developed to accurately correct for this. Also, CO dissociates on some metal surfaces (e.g., W and Mo), on which the method cannot be used. 

The most conventional investigations on the adsorption of both modifier and substrate looked for the effect of pH on the amount of adsorbed tartrate and MAA [200], The combined use of different techniques such as IR, UV, x-ray photoelectron spectroscopy (XPS), electron microscopy (EM), and electron diffraction allowed an in-depth study of adsorbed tartrate in the case of Ni catalysts [101], Using these techniques, the general consensus was that under optimized conditions a corrosive modification of the nickel surface occurs and that the tartrate molecule is chemically bonded to Ni via the two carbonyl groups. There were two suggestions as to the exact nature of the modified catalyst Sachtler [195] proposed adsorbed nickel tartrate as chiral active site, whereas Japanese [101] and Russian [201] groups preferred a direct adsorption of the tartrate on modified sites of the Ni surface. 

The phase-transfer catalysed reaction of nickel tetracarbonyl with sodium hydroxide under carbon monoxide produces the nickel carbonyl dianions, Ni,(CO) 2- and Ni6(CO)162, which convert allyl chloride into a mixture of but-3-enoic and but-2-enoic acids [18]. However, in view of the high toxicity of the volatile nickel tetracarbonyl, the use of the nickel cyanide as a precursor for the carbonyl complexes is preferred. Pretreatment of the cyanide with carbon monoxide under basic conditions is thought to produce the tricarbonylnickel cyanide anion [19], as the active metal catalyst. Reaction with allyl halides, in a manner analogous to that outlined for the preparation of the arylacetic acids, produces the butenoic acids (Table 8.7). 

The Reppe process was commercialized in the 1950s. It involves the reaction pf acetylene, carbon monoxide, and an alcohol (methyl, ethyl, etc.) to give an acrylic ester (an acrylate). The process is carried out at 125°F and 15—30 psi in a nickel carbonyl/aqueous hydrochloric acid solution. The nickel carbonyl acts as both a catalyst and a secondary source of carbon monoxide. 

Ni(CO)4 is the sole binary carbonyl complex of the elements of group 10 that is stable (Table 8.1). However, very few studies in which Ni(CO)4 is used in the preparation of catalysts have been reported [43]. This is probably due to the difficulty of manipulation of Ni(CO)4 and its very high toxicity. However, surface Ni(CO)4 species have been identified after the interaction of CO with highly dispersed supported nickel catalysts prepared by other routes [44]. Recent interest in the use of Ni(CO)4 has focused on the controlled production of nickel nanoparticles for specific purposes, such as in automotive converters [45]. The use of nickel tetracarbonyl as an agent for the nucleation process in the growth of single-wall carbon nanotubes has also been reported [46]. 

The activity of the nickel catalyst is affected by major variations in carbon monoxide partial pressure. With very low carbon monoxide partial pressure, nickel precipitates as a metal powder and occasionally as nickel iodide. Stability of the catalyst is improved with higher CO partial pressure up to a point above which the catalyst activity drops linearly. The optimum level of carbon monoxide is different from one catalyst mixture to another. This behavior is characteristic of all the nickel catalyzed carbonylation reactions we studied. In the Li-P system, optimum carbon monoxide partial pressure is in the range of 700 to 800 psi (Table V). On the other hand, the optimum carbon monoxide partial pressure for the Li-Sn system is in the range of 220 to 250 psi, at 160 C, and 450 psi at 180 C (Table VI). It is presumed that the retarding effect of higher carbon monoxide partial pressure is associated with stabilizing an inactive carbonyl species. 

Carbonylation of methanol to form acetic acid has been performed industrially using carbonyl complexes of cobalt ( ) or rhodium (2 ) and iodide promoter in the liquid phase. Recently, it has been claimed that nickel carbonyl or other nickel compounds are effective catalysts for the reaction at pressure as low as 30 atm (2/4), For the rhodium catalyst, the conditions are fairly mild (175 C and 28 atm) and the product selectivity is excellent (99% based on methanol). However, the process has the disadvantages that the proven reserves of rhodium are quite limited in both location and quantity and that the reaction medium is highly corrosive. It is highly desirable, therefore, to develop a vapor phase process, which is free from the corrosion problem, utilizing a base metal catalyst. The authors have already reported that nickel on activated carbon exhibits excellent catalytic activity for the carbonylation of... 

A similar addition to alkynes results in the formation of the corresponding unsaturated acids and derivatives.14,23,121-124 Cobalt, nickel, and iron carbonyls, as well as palladium complexes, are the most often used catalysts.14... 

As mentioned earlier, nickel carbonyl is a volatile intermediate in the Mond process for nickel refining. This compound also is used for vapor plating of nickel in the semiconductor industry, and as a catalyst in the chemical and petrochemical industries. The toxicity of the compound has been known for many years Exposure of laboratory animals to the compound has induced a number of ocular anomalies, including aiioplidialiiiiaandinicrophtlialmia, and has been shown to be a carcinogenic for rats. 

A second example of metal transport by single-component gas involves the formation of metal carbonyls that are unstable in carbon monoxide. Shen et al. (72) discovered that supported nickel particles are not stable in carbon monoxide. Under certain conditions, CO combines with the metal in the particles to form volatile metal carbonyls, such as nickel carbonyl. These volatile species carry the metal out of the reactor, resulting in a rapid net loss of metal. In some cases, metal is not carried out of the reactor, but new metal particles form at pore mouths, blocking them and effectively deactivating the catalyst. 

Many of the carbonylation reactions of nickel involve [Ni(CO)4] as catalyst. These are outside the scope of the present work and the companion volumes Comprehensive Organometallic Chemistry should be consulted. 

If these catalysts are heated to 80° C. in a stream of CO, nickel is removed from the carrier as nickel carbonyl that volatilizes out of the heated sample (7). The amount of nickel eliminated can be determined by heating the gas stream after it has passed the catalyst sample. A nickel mirror is then deposited on the wall of the reaction vessel and can be weighed. After one day about 90-95 % of the nickel proves to be removed. The remaining residues have surface areas (Fr) that still are related to the original Ni content... 

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