Heptanal or heptanaldehyde is an

alkyl In organic chemistry, an alkyl group is an alkane missing one hydrogen. The term ''alkyl'' is intentionally unspecific to include many possible substitutions. An acyclic alkyl has the general formula of . A cycloalkyl group is derived from a cy ...

aldehyde In organic chemistry, an aldehyde () (lat. ''al''cohol ''dehyd''rogenatum, dehydrogenated alcohol) is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred ...

. 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 Castor oil is a vegetable oil pressed from castor beans, the seeds of the plant ''Ricinus communis''. The seeds are 40 to 60 percent oil. It is a colourless or pale yellow liquid with a distinct taste and odor. Its boiling point is and its den ...

was already described in 1878. The large-scale production is based on the pyrolytic cleavage of

ricinoleic acid Ricinoleic acid, formally called 12-hydroxy-9-''cis''-octadecenoic acid, is a fatty acid. It is an Unsaturated fatty acid, unsaturated omega-9 fatty acid and a hydroxy acid. It is a major component of the seed oil obtained from the seeds of casto ...

(Arkema method) and on the

hydroformylation In organic chemistry, hydroformylation, also known as oxo synthesis or oxo process, is an industrial process for the production of aldehydes () from alkenes (). This chemical reaction entails the net addition of a formyl group () and a hydrogen ...

of 1-hexene with rhodium 2-ethylhexanoate as a catalyst upon addition of some

2-ethylhexanoic acid 2-Ethylhexanoic acid (2-EHA), commonly known as octoic acid, is the organic compound with the formula CH3(CH2)3CH(C2H5)CO2H. It is a carboxylic acid that is widely used to prepare lipophilic metal derivatives that are soluble in nonpolar organic s ...

(Oxea method): : Hydroformylierung von 1-Hexen IS

Heptanal naturally occurs in the

essential oil An essential oil is a concentrated hydrophobic liquid containing volatile (easily evaporated at normal temperatures) chemical compounds from plants. Essential oils are also known as volatile oils, ethereal oils, aetheroleum, or simply as the ...

s of ylang-ylang (''

Cananga odorata ''Cananga odorata'', known as ylang-ylang ( ) or cananga tree, is a tropical tree that is native to the Philippines, Malaysia, Indonesia, New Guinea, the Solomon Islands, and Queensland, Australia. It is also native to parts of Thailand and Vie ...

''), clary sage (''

Salvia sclarea ''Salvia sclarea'', the clary or clary sage (clary deriving from Middle English ''clarie'', from Anglo-Norman ''sclaree'', from Late or Medieval Latin '' sclarēia'' meaning ''clear''), is a biennial (short-lived) herbaceous perennial in the g ...

''), 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 Miscibility () is the property of two substances to mix in all proportions (that is, to fully dissolve in each other at any concentration), forming a homogeneous mixture (a solution). Such substances are said to be miscible (etymologically ...

with

alcohols In chemistry, an alcohol (), is a type of organic compound that carries at least one hydroxyl () functional group bound to a Saturated and unsaturated compounds, saturated carbon atom. Alcohols range from the simple, like methanol and ethanol ...

and practically insoluble in water. Because of its sensitivity to oxidation, heptanal is filled under

nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

and stabilized with 100 ppm

hydroquinone Hydroquinone, also known as benzene-1,4-diol or quinol, is an aromatic organic compound that is a type of phenol, a derivative of benzene, having the chemical formula C6H4(OH)2. It has two hydroxyl groups bonded to a benzene ring in a ''para' ...

. Heptanal forms flammable vapor-air mixtures. The compound has a

flash point The flash point of a material is the "lowest liquid temperature at which, under certain standardized conditions, a liquid gives off vapours in a quantity such as to be capable of forming an ignitable vapour/air mixture". The flash point is somet ...

of 39.5 °C. The explosion range is between 1.1% by volume as the

lower explosion limit Flammability limits or explosive limits are the ranges of fuel concentrations in relation to oxygen from the air. Combustion can range in violence from deflagration through detonation. Limits vary with temperature and pressure, but are normally ...

(LEL) and 5.2% by volume as the upper explosion limit. Its

ignition temperature The autoignition temperature or self-ignition temperature, often called spontaneous ignition temperature or minimum ignition temperature (or shortly ignition temperature) and formerly also known as kindling point, of a substance is the lowest temp ...

is 205 °C.

Uses

Heptanal can be used for the production of

1-heptanol 1-Heptanol is an alcohol with a seven carbon chain and the structural formula of CH3(CH2)6OH. It is a clear colorless liquid that is very slightly soluble in water, but miscible with ether and ethanol. Overview There are three other isomers of he ...

via

hydrogenation Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to redox, reduce or Saturated ...

: :

The oxidation of heptanal with

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

in the presence of a rhodium catalysts leads at 50 °C to

heptanoic acid Enanthic acid, also called heptanoic acid, is an organic compound composed of a seven-carbon chain terminating in a carboxylic acid functional group. It is a colorless oily liquid with an unpleasant, rancid odor. It contributes to the odor of som ...

in 95% yield. Heptanal reacts with benzaldehyde in a Knoevenagel reaction under basic catalysis with high yield and selectivity (> 90%) to

jasminaldehyde Jasminaldehyde (also known as jasmine aldehyde and α-pentylcinnamaldehyde) is a fine chemical used as an aroma compound in perfumes. It is responsible for jasmine's characteristic scent. Synthesis Jasminaldehyde used in industry is commonly der ...

, which is mostly used in fragrances for its

jasmine Jasmine (botanical name: ''Jasminum'', pronounced ) is a genus of shrubs and vines in the olive family of Oleaceae. It contains around 200 species native to tropical and warm temperate regions of Eurasia, Africa, and Oceania. Jasmines are wid ...

-like aroma as a ''cis''/''trans'' isomer mixture. : Jasminaldehyd 2 IS

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. : 2-Pentyl-2-nonenal IS

Full hydrogenation provides the branched

primary alcohol A primary alcohol is an alcohol in which the hydroxy group is bonded to a primary carbon atom. It can also be defined as a molecule containing a “–CH2OH” group. In contrast, a secondary alcohol has a formula “–CHROH” and a tertiary ...

2-pentylnonan-1-ol, also accessible from the

Guerbet reaction The Guerbet reaction, named after Marcel Guerbet (1861–1938), is an organic reaction that converts a primary Alcohol (chemistry), alcohol into its β-alkylated Dimer (chemistry), dimer Alcohol (chemistry), alcohol with loss of one equivalent of w ...

from heptanol.G.H. Knothe
''Lipid Chemistry, Guerbet Compounds''
{{Webarchive, url=https://web.archive.org/web/20160521114621/http://lipidlibrary.aocs.org/OilsFats/content.cfm?ItemNumber=39194 , date=2016-05-21, AOCS Lipid Library, 22 December 2011.

References

Alkanals