Conjugated dienes hydrocarboxylation

The acid-catalyzed hydrocarboxylation of olefins (the Koch reaction) can be performed in a number of ways.565 In one method, the olefin is treated with carbon monoxide and water at 100 to 350°C and 500 to 1000 atm pressure with a mineral-acid catalyst. However, the reaction can also be performed under milder conditions. If the olefin is first treated with CO and catalyst and then water added, the reaction can be accomplished at 0 to 50°C and 1 to 100 atm. If formic acid is used as the source of both the CO and the water, the reaction can be carried out at room temperature and atmospheric pressure.566 The formic acid procedure is called the Koch-Haaf reaction (the Koch-Haaf reaction can also be applied to alcohols, see 0-103). Nearly all olefins can be hydrocarboxylated by one or more of these procedures. However, conjugated dienes are polymerized instead. 

The course of hydrocarboxylation was studied further by sequential analyses of reaction mixtures and by detailed characterization of the purified carboxy acid products. Figure 1 plots kinetic runs with linoleic acid and methyl linoleate at 120°C. Analysis by GLC shows the rapid disappearance of diene followed successively by initial conjugation of the diene system, monocarboxylation, and then dicarboxylation. Cyclic ketones and other unidentified materials (not shown) are formed in minor amounts. Conjugated dienes (mixture of cis,trans and trans,trans) peak at 1 hr and then rapidly disappear. Monocarboxy acids peak around 6-8 hrs and disappear at later stages of the reaction. At 140°C, the carboxylation follows the same course (Figure 2A). Formation of conjugated dienes reach a maximum around 0.5 hr. Monocarboxy acids peak around 1 hr, decrease, and then level at 3-4 hrs. 

The hydrocarboxylation of conjugated dienes such as butadiene can yield monocarboxylate, dicarbox-ylate or diene dimerized carboxylated products. The carboxylation reaction is important because it is a potential route to adipic acid. 

Direct hydrocarboxylation of conjugated dienes with carbon monoxide and formic acid, using Pd—C catalysis and in the presence of triphenylphosphine and 1,4-bis(diphenylphosphino)butane (dppb), gives good yields of what is essentially addition of formic acid to the terminal alkene (equation 98)393. This is an extremely useful synthetic route to y,<5-unsaUirated acids. 

Nevertheless, it must be pointed out that the formation of such transient species has never been spectroscopically observed. Native CDs are effective inverse phase-transfer catalysts for the deoxygenation of allylic alcohols, epoxydation,or oxidation " of olefins, reduction of a,/ -unsaturated acids,a-keto ester,conjugated dienes,or aryl alkyl ketones.Interestingly, chemically modified CDs like the partially 0-methylated CDs show a better catalytic activity than native CDs in numerous reactions such as the Wacker oxidation,hydrogenation of aldehydes,Suzuki cross-coupling reaction, hydroformylation, " or hydrocarboxylation of olefins. Methylated /3-CDs were also used successfully to perform substrate-selective reactions in a two-phase system. 

For a long time experiments failed to produce normal carbonylation products starting from dienes. Under the usual conditions the conjugated dienes underwent a Diels-Alder reaction with subsequent hydrocarboxylation of the prior formed isolated alicyclic dienes. Thus, e. g. butadiene first reacted to give vinylcyclohexene which then yielded a mixture of dicarboxylic adds [493]. In other cases cyclic ketones were obtained from dienes and carbon monoxide (see section on ring closure reaction with carbon monoxide). 

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