Reppe’s synthesis

One of the first and perhaps most interesting examples of a metal-assisted, symmetry-forbidden reaction was Reppe s synthesis of cyclo-octatetraene from acetylene 34). in a careful study of this system, Schrauzer proposed a concerted mechanism in which the four a bonds of the cyclo-octatetraene are essentially formed simultaneously 35). He proposed an octahedral complex (54) with four acetylene hgands fitted to adjacent ligand coordination positions, spatially defining the incipient cyclooctatetraene. 

The reaction between formaldehyde and acetylene is exothermic M = -100 kJ/mol) and the control of temperature is critical. To solve this problem it has been chosen to limit the temperature increase by injecting cold acetylen at different levels in the bed (T) This arrangement with the flowsheet of the Reppe s synthesis of butynediol is shown on Figure Propargyl alcohol is formed according to the following equation ... 

Of course, butadiene is no more obtained commercially by this route. Nevertheless the production of butanediol by the Reppe s synthesis remains important. It is used by BASF, GAF and Dupont. 

The widely known Repp s synthesis of cyclo-octatetraene by tetra-merization of acetylene undoubtedly involves a metal jt-complex intermediate. However, a clear-cut mechanism for this reaction has not yet been advanced. The formation of a cyclobutadiene ring by cyclodimerization of... 

The first two reactions (Table VII) date as far back as 1953, to Reppe s chemistry, and refer to processes occurring via metallacycles. An interesting application to natural products is the synthesis of muscone, which, however, has been obtained in a better way using alkylisonitriles (151) in place of carbon monoxide (example 3, Table VII). 

The synthesis of carboxylic acids by carbonylation of unsaturated hydrocarbons or alcohols was developed mainly by Reppe and his co-workers in the laboratories of BASF at Ludwigshafen. Many industrially important processes such as the synthesis of acrylic acid, propionic acid, and acetic acid were elaborated there in the period from the late 1930s to the mid-1950s [1, 2]. Reppe s introduction of metal carbonyls as catalysts for carbonylation reactions was of paramount importance and many processes, which are still industrially relevant today, were developed rapidly (eq. (1), [3]). 

Thermal cyclooligomerizations of olefins and alkynes require severe and often dangerous reaction conditions and the yields of cyclic products are usually very low. Acetylene ean be trimerized to benzene at 500 °C [1] and butadiene (BD) dimerizes at 270 °C and under high pressure to give small amounts of 1,5-cyclo-octadiene [2]. Reppe s discovery in 1940 that acetylene can be cyclotetramerized to cyclooctatetraene (COT) using a nickel catalyst [3] shows that transition metals can act as templates for the synthesis of cyclic hydrocarbons from acetylenic or olefinic building blocks (Scheme 1). 

Norbomadiene may be carbonylated essentially under the conditions of Reppe s acrylic ester synthesis. Cycloheptenecarboboxylates (XVIII)... 

Reppe s cyclooctatetraene synthesis also appears to be ir complex concerted (41). The formation of Binor-S of (XI), and of CaHg thus may be formally related, tt complex, multicenter processes. Accordingly, the reaction of acetylene with Zn[Co(CO)4]2 produced small amounts of cyclooctatetraene (52). This is the first reported case in which cyclooctatetraene was formed using a catalyst containing metals other than nickel, and on a binuclear catalyst center. 

Recent research on acetylene as the basic hydrocarbon in the synthesis of a number of important oxygen-containing compounds has centered on the work of Walter Reppe and his associates of Germany. Prior to Reppe s work, the most important oxygen-containing derivatives of acetylene were acetaldehyde and acetone. 

Walter Reppe s breakthrough in the butadiene synthesis was central to the new... 

Walter Reppe also used his new base to expand the chemistry of acetylene. His first major breakthrough, in the summer of 1939, was the addition of carbon monoxide to acetylene in the presence of alcohols (or water) and a nickel catalyst to form acrylates. Carbon monoxide had attracted attention for many years as a readily available, cheap and reactive carbon compound. I.G. Farben employed it in the Pier methanol synthesis, Ruhrchemie used it in the Fischer-Tropsch synthetic petrol process, and Du Pont had carried out research on the addition of carbon monoxide to olefins at very high pressure and temperatures. Additional impetus for the use of carbon monoxide in acetylene chemistry was provided by the introduction of covered carbide furnaces at I.G. Farben s Knapsack plant in 1938, which permitted the collection of by-product carbon monoxide. The polymers of acrylic esters were already used for treating leather and for paint, but acrylic acid was made from ethylene oxide, and consequently was rather expensive. Reppe s process reached the pilot plant stage by 1945, and was subsequently used on a large scale by BASF and its American partners. 

Furthermore, Reppe s research is a good illustration of the founder effect (or bandwagon effect ), whereby positive feedback tends to segregate competing technologies. Acetylene was adopted as the feedstock for BASF s butanol synthesis. 

The overwhelming majority of template reactions carried out to date have been stoichiometric. However, many catalytic processes are known which have been realised by the template approach. The classic example of a template catalytic process is Reppe s cyclooctatetraene and benzene synthesis, in which a nickel atom brings together four and three acetylene molecules, respectively, prior to cyclo-tetra(tri)merisation (Eq. 1.23) [34]. 

Triphenylphosphine stabilizes the nickel atom by forming a complex. As it blocks at least one of the coordination positions on the nickel atom, only three acetylene molecules may add to it, thus making the formation of cyclooctatetraene impossible (79). Complexes of nickel with 1,1-dicyano-and 1,1,2-tricyanoethylene behave similarly, yielding approximately stoichiometric quantities of benzene and cyclooctatetraene CgHg, but affording exclusively benzene in the presence of triphenylphosphine 51, 82). The original catalysts for Reppe s (2, 83) cyclooctatetraene synthesis were all... 

Since Reppe s discovery of the cyclotrimerization of acetylene to benzene in the presence of nickel carbonyl-phosphine complexes, the use of nickel catalysts in many organic transformations has become popular. Transition metal complex catalysis provides many elegant entries to carbon-carbon bond-forming reactions in organic synthesis. One notable example is carbocyclic ring expansion mediated by nickel(O) complexes. ... 

Industrially, large quantities of vinyl ethers can be prepared following Reppe s ethynylation reaction that involved reacting acetylene gas with alcohols [101]. Due to the challenges and hazards associated with the experiment as well as the required handling of acetylene gas (under pressure) alternative approaches to the synthesis of vinyl ethers are typically used in small laboratory settings. One such approach used common iridium complexes to catalyze... 

The reactions of the palladium-cyclobutadiene complexes with excess alkyne produced persubstituted cyclooctatetraenes in analogy to Reppe s catalytic cyclooctatetraene synthesis (Pollock and Maitlis, 1966 Reppe and Schweckendiek, 1948). Although the cyclobutadiene ligand can be transferred between metals [Eq. (76)] (Maitlis, 1971b), liberation of the ligand... 

J. W. Copenhaver, M. H. Bigelow, Acetylene and Carbon Monoxide Chemistry (New York, 1949) p 246 W. Reppe, Acetylene Chemistry, U.S. Dept. Commerce PB 18852-S (1949) Neue Entwicklungen auf dem Gebiet des Acetylens und Kohlenoxyds (Berlin 1949) H. Kroper, Houben-Weyl 4/II, 413-422 (1955) D. W. F. Hardie, Acetylene, Manufacture and Uses (New York, 1965) p 67 L. F. Fieser, M. Fieser, Reagents for Organic Synthesis (New York, 1967) pp 61, 183, 185, 190, 519, 720, 722, 723. Review of carbonylations A. Mullen, Carbonylations Catalyzed by Metal Carbonyls-Reppe Reactions in New Syntheses with Carbon Monoxide, J. Falbe, Ed. (Springer-Verlag, Berlin, 1980) pp 243-308. Mechanistic study of cyclooctatetraene synthesis R. E. 

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