Olefins and Functional Derivatives in the Presence of Alcohols

The reaction of olefins and their functional derivatives with carbon monoxide and alcohols to saturated carboxylic add esters generally proceeds at a lower velocity than the formation of the free acids as illustrated in the last chapter [504]. In the presence of nickel halogenide catalysts, reaction temperatures between 180-200 °C and pressures from 100 to 200 atm are required. Yields are in the range of 90 %. With cobalt catalysts reaction temperatures between 140 to 170 °C are recommended [505]. 

Reaction time has to be as short as possible in order to suppress side reactions. Especially the conversion of alcohols to carboxylic acids with one more C-atom, which will be discussed subsequently, or formation of ethers and free acids may be undesirable reactions [504]. The carbonylation rate of olefins with carbon monoxide/ROH in the presence of Co carbonyls can be accelerated remarkably by addition of small portions of hydrogen to carbon monoxide, which favors the formation of hydrocarbonyl. The same effect can be achieved by addition of pyridine. 

By addition of pyridine as well as hydrogen, carbonylation of olefins proceeds with nearly the same reaction velocity as observed in hydroformy-lation reactions [506, 507]. 

Besides nickel and cobalt, almost all of the catalysts discussed in the last chapter which were suited for the formation of free acids can be applied, e. g. rhodium, palladium and, with certain restrictions, iron. Cobalt hydrocarbonyl catalyzes the stoichiometric ester synthesis at mild reaction conditions [35, 121]. The initially formed acylcobalt carbonyls react rapidly with alcohols even at 50 °C and, in the presence of Na-alcoholate, even at 0 °C to give esters [121]. Dienes with isolated double bonds react with carbon monoxide and alcohols at mild reaction conditions in the presence of Pd/HCl to give unsaturated monocarboxylic acid esters and at more severe conditions to give saturated dicarboxylic acid esters [508]. 

Also trienes such as cyclododecatriene-1,5,9 yield mono- and dicarboxylic acid esters [488, 509]. Cyclododecane tricarboxylic acid esters are formed with bis-triphenyl phosphine palladium dichloride as catalyst [448]. The catalyst can be recycled [517]. Nearly quantitative syntheses of monocarboxylic acid esters of cyclododecadiene and of tricarboxylic acid esters of cyclododecane can be achieved with complex Pd-catalysts. 

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