The Synthesis of Organic Chemicals by Catalytic Reactions of Carbon Dioxide

Abstract

AbstractDifferent reactions are discussed in which carbon dioxide adds to unsaturated hydrocarbons after activation by transition metal catalysts. Alkynes react in the presence of nickel or rhodium complexes to yield substituted pyrones. Alkenes are also described to react with CO2 yielding acids and esters; however, the proof, that carbon dioxide is really involved in this reaction, is still lacking. The best studied reaction is the chemistry of carbon dioxide and butadiene. Using palladium, nickel and ruthenium catalysts γ‐ and Δ‐lactones are formed by the reaction of two molecules of butadiene and one molecule of CO2. The catalyst and the reaction parameters could be optimized thus enabling the synthesis of the Δ‐lactone in an industrial scale. A mechanism is proposed in which a carboxylate complex is discussed to be the key intermediate, and a similar palladium complex could be. isolated in a related stoichiometric experiment. Using rhodium catalysts, a γ‐lactons is formed in which three molecules of butadiene are connected to one molecule of carbon dioxide. Also the co‐reaction of butadiene, isoprene and CO2 yields novel lactones. All these products may become of interest as fine chemicals, for instance fragrances. Another possible use of the lactones is their conversion into open‐chained products. The splitting of the Δ‐lactone yields new carboxylic acids and esters with hydroxy or methoxy substituents, which may become useful starting molecules for chemical syntheses.