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 oilF. Krafft, Distillation of castor oil, under reduced pressure, Analyst, 3, 329a (1878). was already described in 1878. The large-scale production is based on the pyrolytic cleavage of ricinoleic acidA. Chauvel, G. Lefebvre, Petrochemical Processes: Technical and Economic Characteristics, vol. 2, p. 277, Editions Technip, Paris, 1989, . (Arkema method) and on the hydroformylation of 1-hexene:
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).G. A. Burdock, Fenaroli's Handbook of Flavor Ingredients, Fifth Edition, 2005, CRC Press, Boca Raton, Fl., .
Properties Heptanal is a slightly volatile colorless liquid. It has a pervasive fruity to oily-greasy odor, It is miscible with alcohols but practically insoluble in water. Because of its sensitivity to oxidation, heptanal is stored under nitrogen and stabilized with 100 ppm hydroquinone.Acros Organics (rev. 19 Nov 2012). Heptaldehyde, stabilized (safety data sheet).
Heptanal is flammable. 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.H. Springer and P. Lappe, on behalf of Celanese Chem Europe GmbH (3 May 2001). Verfahren zur Herstellung aliphatischer Carbonsäuren aus Aldehyden , German patent DE 10010771. Heptanal reacts with benzaldehyde in a Knoevenagel reaction under basic catalysis with high yield and selectivity (> 90%) to jasminaldehyde, which is mostly used in fragrances for its jasmine-like aroma as a cis/trans isomer mixture.alpha-Amylzimtaldehyd (rev. 4 Aug 2000) at the Riechstofflexikon [Odorant Dictionary], vol. A.
A by-product of the given reaction is the unpleasant rancid smelling (Z)-2-pentyl-2-nonenal.J. M. Hornback, Organic Chemistry, 2nd edition, p. 886, Thomson Brooks/Cole, 2006, . Nevertheless, heptanal can be converted into (Z)-2-pentyl-2-nonenal virtually quantitatively in the presence of aqueous boric acid upon azeotropic removal of water.
Full hydrogenation provides the branched primary alcohol 2-pentylnonan-1-ol, also accessible from the Guerbet reaction from heptanol.G.H. Knothe: Lipid Chemistry, Guerbet Compounds , AOCS Lipid Library, 22 December 2011.
References