Acrylic acid Catalytic converter

In the early versions, ethylene cyanohydrin was obtained from ethylene chlorohydrin and sodium cyaioide. In later versions, ethylene oxide (from the direct catalytic oxidation of ethylene) reacted with hydrogen cyanide in the presence of a base catalyst to give ethylene cyanohydrin. Tlois was hydrolyzed and converted to acrylic acid and by-product ammonium acid sulfate by treatment with about 85% sulfuric acid. 

The reaction is carried out in aqueous tetrahydrofuran, if acrylic acid is the desired product, or in aqueous alcohol if the ester is required. Nickel is introduced as bromide or iodide and is converted into carbonyl complexes under the reaction conditions, typically 200°C/100atm. One catalytic cycle which has been postulated for this process is shown in Fig. 12.18. Selectivity in the formation of acrylic acid from acetylene is better than 90%. Even from propyne, where anti-Markovnikov addition of [Ni]—H competes with the desired pathway, selectiv-ities of over 80% to methyl methacrylate H2C=C(Me)C02Me are achieved. The major by-product is methyl crotonate, MeCH=CHC02Me. 

Additives such as ascorbic acid (21, Scheme 10.10) or squaric add result in a further improvement of the epoxidation with H2O2, catalyzed by the Mn-tmtacn complex. A limited number of substrates have been studied so far but nearly quantitative yields of epoxides with retention of the olefin configuration were found employing catalyst loadings of only 0.03 mol%. Electron-defident methyl acrylate and the terminal olefin 1-octene were also converted into the corresponding epoxides with yields of 97 % and 83 %, respectively. A typical oxidation is shown in Scheme 10.10. The exact role of ascorbic acid as co-catalyst remains undear, but the H2O2 efficiency with this Mn catalytic system is one of the highest reported so far. 

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