Heptanal Explained

Heptanal or heptanaldehyde is an alkyl aldehyde. It is a colourless liquid with a strong fruity odor, which is used as precursor to components in perfumes and lubricants.

Production

The formation of heptanal in the fractional distillation of castor oil^[1] was already described in 1878. The large-scale production is based on the pyrolytic cleavage of ricinoleic acid^[2] (Arkema method) and on the hydroformylation of 1-hexene with rhodium 2-ethylhexanoate as a catalyst upon addition of some 2-ethylhexanoic acid (Oxea method):^[3]

Heptanal naturally occurs in the essential oils of ylang-ylang (Cananga odorata), clary sage (Salvia sclarea), lemon (Citrus x limon), bitter orange (Citrus x aurantium), rose (Rosa) and hyacinth (Hyacinthus).^[4]

Properties

Heptanal is a flammable, slightly volatile colorless liquid of pervasive fruity to oily-greasy odor,^[5] which is miscible with alcohols and practically insoluble in water. Because of its sensitivity to oxidation, heptanal is filled under nitrogen and stabilized with 100 ppm hydroquinone.^[6]

Heptanal forms flammable vapor-air mixtures. The compound has a flash point of 39.5 °C. The explosion range is between 1.1% by volume as the lower explosion limit (LEL) and 5.2% by volume as the upper explosion limit. Its ignition temperature is 205 °C.

Uses

Heptanal can be used for the production of 1-heptanol via hydrogenation:

The oxidation of heptanal with oxygen in the presence of a rhodium catalysts leads at 50 °C to heptanoic acid in 95% yield.^[7] Heptanal reacts with benzaldehyde in a Knoevenagel reaction under basic catalysis with high yield and selectivity (> 90%) to jasminaldehyde,^[8] which is mostly used in fragrances for its jasmine-like aroma as a cis/trans isomer mixture.^[9]

A by-product of the given reaction is the unpleasant rancid smelling (Z)-2-pentyl-2-nonenal.^[10] When good reasons are given, heptanal can be converted into (Z)-2-pentyl-2-nonenal virtually quantitatively in the presence of aqueous boric acid upon azeotropic removal of water.^[11]

Full hydrogenation provides the branched primary alcohol 2-pentylnonan-1-ol, also accessible from the Guerbet reaction from heptanol.^[12]

References

1. F. Krafft, Distillation of castor oil, under educed pressure, Analyst, 3, 329a (1878).
2. A. Chauvel, G. Lefebvre, Petrochemical Processes: Technical and Economic Characteristics, Band 2, S. 277, Editions Technip, Paris, 1989, .
3. Deutsche Patentschrift DE 102007053385, Verfahren zur Herstellung von Aldehyden, Erfinder: A. Fischbach et al., Anmelder: Oxea Deutschland GmbH, veröffentlicht am 20. Mai 2009.
4. G. A. Burdock, Fenaroli’s Handbook of Flavor Ingredients, Fifth Edition, 2005, CRC Press, Boca Raton, Fl., .
5. Richtwerte für gesättigte azyklische aliphatische C4- bis C11-Aldehyde in der Innenraumluft . Bundesgesundheitsblatt - Gesundheitsforschung - Gesundheitsschutz . 27 June 2009 . 52 . 6 . 650–659 . 10.1007/s00103-009-0860-2. 19557457 .
6. Acros Organics, Sicherheitsdatenblatt, Heptaldehyde, stabilized, überarb. am 19. November 2012.
7. Deutsche Patentschrift DE 10010771, Verfahren zur Herstellung aliphatischer Carbonsäuren aus Aldehyden, Erfinder: H. Springer, P. Lappe, Anmelder: Celanese Chem Europe GmbH, veröffentlicht am 3. Mai 2001.
8. Pérez-Sánchez . María . de María . Pablo Domínguez . Synthesis of natural fragrance jasminaldehyde using silica-immobilized piperazine as organocatalyst . Catalysis Science & Technology . 2013 . 3 . 10 . 2732 . 10.1039/C3CY00313B.
9. Riechstofflexikon A, alpha-Amylzimtaldehyd, Letzte Änderung am 4. August 2000.
10. J. M. Hornback, Organic Chemistry, 2nd edition, S. 886, Thomson Brooks/Cole, 2006, .
11. Offenhauer . Robert D. . Nelsen . Stephen F. . Aldehyde and ketone condensation reactions catalyzed by boric acid . The Journal of Organic Chemistry . February 1968 . 33 . 2 . 775–777 . 10.1021/jo01266a059.
12. G.H. Knothe: Lipid Chemistry, Guerbet Compounds, AOCS Lipid Library, 22 December 2011.