benzaldehyde
Meaning of benzaldehyde: The smell of marzipan in a bottle, and the compound released when bitter almond or apricot kernels are crushed.
Definition of benzaldehyde
Benzaldehyde is a colorless, oily liquid with a strong almond odor, and it is the simplest of the aromatic aldehydes. It occurs naturally in bitter almonds, apricot and peach kernels and cherry pits, and it is also manufactured on a large scale. It is used as almond flavoring and as a starting material for dyes, fragrances and medicines.
Where does it come from naturally?
Certain seeds store a compound called amygdalin, in which a sugar is joined to a benzaldehyde unit and a cyanide group. Crushing or chewing the seed brings amygdalin into contact with an enzyme that splits it apart, releasing benzaldehyde, sugar and hydrogen cyanide together. The almond smell and the poison therefore come from the same reaction, which is why a marzipan odor has traditionally been treated as a warning sign where cyanide exposure is suspected. Bitter almond oil sold for flavoring has the cyanide removed.
How is it related to benzene?
It is built on the same six-carbon ring. Benzene is that ring alone; benzaldehyde is the ring with a small group of one carbon, one hydrogen and one oxygen attached to it. The ring itself is remarkably stable, so reactions take place at the attached group rather than in the ring, which is what makes the compound so useful as a building block. Left in contact with air it slowly oxidizes to benzoic acid, and the white crystals that form inside an old bottle are that acid.
What is it used for?
| Use | Where it appears |
|---|---|
| Flavoring | Almond and cherry flavors in food and confectionery |
| Fragrance | Soaps, perfumes and cosmetics |
| Chemical building block | Dyes, plastics and agricultural chemicals |
| Pharmaceutical synthesis | An intermediate on the route to several drugs |
Does it treat anything?
It has been investigated as an anticancer agent, and interest in it is tangled up with amygdalin and its semi-synthetic relative laetrile, both promoted for decades as cancer cures. Controlled testing did not show benefit, and cases of cyanide poisoning were reported in people taking them. Benzaldehyde itself is regarded as safe in the small quantities used to flavor food, while the concentrated liquid irritates skin, eyes and airways.
How is it recognized?
Chemists identify it by its odor, its boiling point and its spectrum, and by simple reactions that pick out an aldehyde group. It is also used in teaching laboratories for exactly that reason, since it is a stable liquid that demonstrates aldehyde chemistry cleanly.
Also known as
Used in a sentence
The sample was identified as benzaldehyde by its characteristic almond odor and its spectrum.
Good to know
The marzipan smell of crushed bitter almond or apricot kernels comes from benzaldehyde released alongside hydrogen cyanide, which is why eating quantities of such kernels has caused poisoning.
Word origin
Where “benzaldehyde” comes from
The name combines benzoin, the aromatic resin from which the related acid was first obtained, with aldehyde, a contraction of the Latin alcohol dehydrogenatus, meaning alcohol stripped of hydrogen.