Heptanal

Production

The formation of heptanal in the fractional distillation of castor oil was already described in 1878. The large-scale production is based on the pyrolytic cleavage of ricinoleic acid (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):

:[[File:Hydroformylierung von 1-Hexen IS.svg|400px|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 flammable, slightly volatile colorless liquid of pervasive fruity to oily-greasy odor, 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.

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:

:[[File:Heptanol-Synthese.svg|upright|Synthese von 1-Heptanol]]

The oxidation of heptanal with oxygen in the presence of a rhodium catalysts leads at 50 °C to heptanoic acid in 95% yield. Heptanal reacts with benzaldehyde in a Knoevenagel reaction under basic catalysis with high yield and selectivity ( 90%) to jasminaldehyde,

:[[File:Jasminaldehyd 2 IS.svg|500px|α-pentylcinnamal (jasminal) by aldol condensation of benzaldehyde with heptanal]]

A by-product of the given reaction is the unpleasant rancid smelling (Z)-2-pentyl-2-nonenal. 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.

:[[File:2-Pentyl-2-nonenal IS.svg|500px|2-Pentyl-2-nonenal by self-condensation of heptanal]]

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

References

References

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7. {{GESTIS
8. Acros Organics (rev. 19 Nov 2012). ''Heptaldehyde, stabilized'' (safety data sheet).
9. H. Springer and P. Lappe, on behalf of Celanese Chem Europe GmbH (3 May 2001). [http://www.patent-de.com/20010503/DE10010771C1.html ''Verfahren zur Herstellung aliphatischer Carbonsäuren aus Aldehyden''] {{Webarchive. link. (2016-03-04 , German patent DE 10010771.)
10. (2013). "Synthesis of natural fragrance jasminaldehyde using silica-immobilized piperazine as organocatalyst". Catalysis Science & Technology.
11. J. M. Hornback, ''Organic Chemistry, 2nd edition'', p. 886, Thomson Brooks/Cole, 2006, {{ISBN. 0-534-49317-3.
12. (February 1968). "Aldehyde and ketone condensation reactions catalyzed by boric acid". The Journal of Organic Chemistry.
13. link. (2016-05-21, AOCS Lipid Library, 22 December 2011.)