Acrylic acid, synthesis from acetylene

If the same reaction is carried out at temperatures between 250-270 °C and slightly increased CO-partial pressure, succinic acid is obtained as the main product [384]. High acetylene partial pressure in the acrylic ester synthesis from acetylene, carbon monoxide and alcohol in the presence of... 

Acrolein and condensable by-products, mainly acrylic acid plus some acetic acid and acetaldehyde, are separated from nitrogen and carbon oxides in a water absorber. However in most industrial plants the product is not isolated for sale, but instead the acrolein-rich effluent is transferred to a second-stage reactor for oxidation to acrylic acid. In fact the volume of acrylic acid production ca. 4.2 Mt/a worldwide) is an order of magnitude larger than that of commercial acrolein. The propylene oxidation has supplanted earlier acrylic acid processes based on other feedstocks, such as the Reppe synthesis from acetylene, the ketene process from acetic acid and formaldehyde, or the hydrolysis of acrylonitrile or of ethylene cyanohydrin (from ethylene oxide). In addition to the (preferred) stepwise process, via acrolein (Equation 30), a... 

A further development of the Reppe acrylic acid synthesis is the reaction, described in recent literature, of the noble metal-catalyzed carbonylation of higher acetylenes to give the corresponding acrylic acid derivatives. Thus, for example, the Pd-catalyzed carbonylation of propyne (eq. (10)) in the presence of methanol leads directly to methyl methacrylate [23]. Based on this work. Shell has developed a new production process for methyl methacrylate [24]. The propyne required can be isolated from the product streams from crackers, (cf. Section 2.3.2.3). 

The selection of the catalyst system will often be determined by the process technique used. In the catalytic processing of acrylic acid-n-butyl ester synthesis from acetylene, carbon monoxide and n-butanol with nickel halogenide, troublefree continuous operation could not be achieved. 

Actual operating capacities of Reppe carbonylation processes are difficult to estimate since only a few data are available in the literature. However, it is known that some of the syntheses are carried out on an industrial scale, e. g. the synthesis of acrylates from acetylene, carbon monoxide and alcohols (BASF) [1004, 1005], the acetic acid synthesis from methanol and carbon monoxide and the synthesis of higher molecular weight saturated carboxylic acids from olefins, carbon monoxide and water. Propionic acid (30,000 tons/year) and to a smaller extent heptadecanoic dicarboxylic acid are manufactured via the carbonylation route at BASF. Butanol is made from propylene in Japan [1003, 1004]. 

These processes have supplanted the condensation reaction of ethanol, carbon monoxide, and acetylene as the principal method of generating ethyl acrylate [140-88-5] (333). Acidic catalysts, particularly sulfuric acid (334—338), are generally effective in increasing the rates of the esterification reactions. Care is taken to avoid excessive polymerization losses of both acrylic acid and the esters, which are accentuated by the presence of strong acid catalysts. A synthesis for acrylic esters from vinyl chloride (339) has also been examined. 

Coal was also the feedstock for synthesis gas vide infra). Many contributions to acetylene chemistry are due to Reppe. His work on new homogeneous metal (mainly nickel) catalysts for acetylene conversion, carried out in the period from 1928 to 1945, was not published until 1948. Under the influence of nickel iodide catalysts, acetylene, water and CO were found to give acrylic acid. A process based on this chemistry was commercialized in 1955. 

Acetylene-Based Routes. Walter Reppe, die father of modem acetylene chemistry, discovered the reaction of nickel carbonyl with acetylene and water or alcohols to give acrylic acid or esters (75,76). This discovery7 led to several processes which have been in commercial use. The original Reppe reaction requires a stoichiometric ratio of nickel carbonyl to acetylene. The Rohm and Haas modified or semicatalytic process provides 60 —80% of the carbon monoxide from a separate carbon monoxide feed and the remainder from nickel carbonyl (77—78). The reactions for the synthesis of ethyl acrylate are... 

Control of reactivity by catalysis provides the capability to shift to lower cost feedstocks. In the twentieth century, advances in catalysis have allowed the substitution of acetylene with olefins and subsequently with synthesis gas as primary feedstocks. For example, production of acrylic acid, traditionally produced by the Reppe process from acetylene and CO, has now been replaced by catalytic oxidation of propylene. The emergence of paraffins, the hydrocarbon feedstock of the future, will depend on development of catalysts for selective alkane C-H activation (2). 

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. 

The synthesis of acrylic esters from acetylene, CO, and alcohols probably involves a similar three-step mechanism with CH2=CH—M as the initial addition product. Nickel carbonyl in aqueous acid is the preferred catalyst (176). 

Probably the nickel carbonyl-catalyzed synthesis of acrylates from CO, acetylene, and hydroxylic solvent (78) involves an acetylene-hydride insertion reaction, followed by a CO insertion, and hydrolysis or acyl halide elimination. The actual catalyst in the acrylate synthesis is probably a hydride formed by the reversible addition of an acid to nickel carbonyl. 

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