Hydroformylation: Fundamentals, Processes and Applications in Organic Synthesis

Book Preface

In 2013 a number of large chemical companies and academic institutions across the world celebrated a significant anniversary: “75 Years of Hydroformylation.” Of particular importance was the event organized by Oxea GmbH, which took place in Oberhausen, Germany [1]. This was where in 1938, at the Ruhrchemie plant, Otto Roelen accidentally discovered that the reaction of ethylene with CO and H2 in the presence of a catalyst consisting of cobalt, thorium, and magnesium oxide yields not only alkanes but also diethyl ketone and propionaldehyde, the so-called oxo products. He therefore named this reaction the oxo process, a term which is still used today, especially by industrial chemists. It was also in Oberhausen that the first technical plant was constructed, although the outbreak of the Second WorldWar meant that the planned production of 10000metric tons could not initially be realized. After 1945, the huge potential of the new process was immediately recognized.These days,more than 10 million metric tons of aliphatic aldehydes of different chain lengths are produced annually in plants across the globe: up to 100 000 t/y by the giants of the chemical industry, and much smaller quantities by small companies producing fine chemicals. Moreover, a survey of patent activities and academic publications between 2010 and 2015 offers clear evidence that hydroformylation is still an important focus of industrial research (Table 1).

Hydroformylation can be directly related to the chemical equation consisting of a particular reactant, reagent, catalyst, and product (Figure 1).

The starting product is normally an olefin (with the exception of epoxides), which receives its reactivity from the π-electrons of the double bond. While in related reactions such as hydrogenation this bond is transformed to resemble a chemically (almost) inert alkane, the hydroformylation generates the divalent formyl group, which is due to the C==O double bond and the different electronegativities of C and O, which are even more reactive than the starting C==C structure. In addition, the free electron pairs at oxygen confer on the carbonyl group Lewis-base properties.

In nature, the carbonyl group is one of themost pivotal groups, able to reactwith numerous nucleophiles. It also represents simultaneously both the starting point and the precondition for numerous C–C bond formations and breakage reactions in the neighborhood. However, only a fewmicroorganisms are able to incorporate the toxic CO into organic compounds. Until now, this enzymatic approach has been used only to prepare products of low molecular weight, such as acetate, ethanol, butyrate, and butanol [3]. In higher living organisms, carbonyl groups can only be created from olefins by hydration and subsequent dehydrogenation. An alternative possibility of obtaining carbonyl groups would be the hydration of alkynes to yield aldehydes via enols. However, because of the high reactivity of the triple bond, alkynes are very rare in living organisms. In synthetic chemistry, this pathway has been rather problematic, since an anti-Markovnikov addition of water to terminal C==C bonds is not favored [4].

The hydroformylation reaction is catalyzed by transition metals, which, with the remarkable exception of cobalt, play no role in living organisms.These metals include ruthenium, palladium, iridium, and platinum.Most are both very rare and very expensive.