Pentanal is an organic compound with the molecular formula C4H9CHO. Classified as an alkyl aldehyde, it is a colorless, volatile liquid. Its smell has been described as fermented, bready, fruity, nutty, and berry.
Pentanal is obtained by hydroformylation of butenes. C4 mixtures can also be used as starting materials, such as 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 of at least 90% to pentanal.
Pentanal undergoes the reactions characteristic of any alkyl aldehyde, namely oxidation, condensation and reduction. 2-Octanone, used in the fragrance industry, is obtained by condensation of acetone and pentanal followed by hydrogenation of the olefin. [6]

2-Propyl-2-heptanal is obtained from the aldol condensation of pentanal, which is hydrogenated to saturated branched 2-propylheptanol. This alcohol is used as a raw material for the PVC plasticizer dipropylheptyl phthalate (DPHP).

Pentanal (valeraldehyde) is oxidized to produce valeric acid.
Slow hydroformylation of conjugated dienes over unmodified cobalt and rhodium catalysts. Only saturated monoaldehydes or monoalcohols are obtained. Hydroformylation of butadiene in the presence of (25) produces equimolar amounts of n-pentanal and is pentanal. The reaction proceeds first by addition of (25) to butadiene to form a stable η-allyl complex (54), which is then reacted with synthesis gas to form the monoaldehyde. 64 Ligand-modified rhodium carbonyls prevent the formation of η-allyl structures, and double hydroformylation was indeed observed in this way (Scheme 9). The best yield of the C6 product was obtained with triisopropylphosphine using a very high excess of tertiary phosphine.