Hexanal Pentanal (also called valeraldehyde) is the organic compound with molecular formula C4H9CHO.

Also C4 mixtures can be used as starting material like the so-called raffinate II, which is produced by steam cracking and contains (Z)- and (E)-2-butene, 1-butene, butane and isobutane.

The conversion to the product is accomplished with synthesis gas in the presence of a catalyst consisting of a rhodium-bisphosphite complex and a sterically hindered secondary amine with a selectivity toward pentanal of at least 90%.

[5] Pentanal undergoes the reactions characteristic of any alkyl aldehyde, i.e., oxidations, condensations, and reductions.

2-Octanone, produced for use in the fragrance industry, is obtained by the condensation of acetone and pentanal, followed by hydrogenation of the alkene.