1.2. Hydroformylation

Hydroformylation is the simultaneous addition of one mole each of hydrogen and carbon monoxide across a carbon–carbon double bond of alkene to produce linear and branched aldehydes having one more carbon atom than the original compound (Scheme 1). The reaction was discovered accidentally in 1938 by Otto Roelen. Although much progress has been made since then through the development of more efficient metal catalysts, hydroformylation continues to be the subject of innumerable studies, motivated by the need to increase the selectivity to linear or branched aldehydes, to reduce by-product formation, and to achieve milder and more environmentally friendly reaction conditions [40]. Today’s hydroformylation plants operate with catalysts based on rhodium or cobalt, while platinum, palladium, and ruthenium catalysts are of research intrest [40], [50].

The homogeneous hydroformylation reaction is one of the oldest processes making use of soluble transition metal catalysts and it is one of the largest volume of industrial applications of these catalysts. In the catalysts, the most extensively utilized ligands are phosphanes and carbon monoxide. Phosphane ligands offer several benefits over unmodified systems, including increased catalyst stability, improved reaction rates and selectivities, and enhanced partitioning into two-phase systems. [51], [52], [53]

Most of the seven million tons of aldehydes produced annually by this process are hydrogenated to alcohols or oxidized to carboxylic acids. Esterification of the alcohols produces plasticizers — the largest end-use. Detergents and surfactants make up the next largest category, followed by solvents, lubricants, and chemical intermediates. Asymmetric hydroformylation of several functionalised alkenes opens the way to production of chiral aldehydes, which can be used as a starting material for the synthesis of agro- and pharmaceutical chemicals. [40], [41], [45], [51]

The most important hydroformylation process on industrial scale, propene hydroformylation, provides about 75% of all oxo chemicals consumed in the world [III]. Traditionally, the aim of this process has been to produce regioselectively the linear aldehyde, n-butanal. Via reactions to 2-ethylhexanol the n-butanal is converted to dioctyl phthalate, a plasticizer utilized in a wide range of PVC applications [40]. Recently, intrest has focused on selective formation of the branched form, isobutanal, which now represents 9% of total production capacity and finds use in the production of polyols, such as neopentyl glycols [III].