Cinnamic aldehyde or cinnamaldehyde (more precisely trans-cinnamaldehyde, the only naturally-occurring form) is the chemical compound that gives cinnamon its spice.

Cinnamaldehyde occurs naturally in a the bark of cinnamon trees and other species of the genus Cinnamomum like camphor and cassia. These trees are the natural source of cinnamon, and the essential oil of cinnamon bark is about 90% cinnamaldehyde.

Structure and physical properties

A yellow oily liquid more viscous than water, cinemaldehyde smells strongly of cinnamon.

Concentrated cinnamaldehyde is a skin irritant, and the chemical is toxic in large doses, but no agencies suspect the compound is a carcinogen or poses a long-term health hazard. Most cinnemaldehyde is excreted in urine as cinnamic acid, an oxidized form of cinnamaldehyde.

An aromatic hydrocarbon and aldehyde, cinnamaldehyde has a mono-substituted benzene ring. A conjugated double bond (alkene) makes geometry of the compound planar. Cinnamaldehyde is technically trans-cinnamaldehyde because the terminal carbonyl is on the opposite side of the arromatic ring over the rigid double bond.

A technique to synthesize cinnamaldehyde was published in 1884. Several methods of synthesis are now known, but cinnamaldehyde is most economically obtained from the steam distillation of the oil of cinnamon bark. The compound can be prepared from related compounds like cinnamyl alcohol, (the alcohol form of cinnamaldehyde), but the first synthesis from unrelated compounds was the condensation of benzaldehyde and acetaldehyde.

Applications

The most obvious application for cinnamaldehyde is as a flavouring. 50 grams can be purchased for around $20.00, and concentrations required for flavoring food items like chewing gum, ice cream, candy, and beverages range from 9 to 4900 ppm (that is, less than 0.5%).

Cinnamaldehyde is used in some perfumes of natural, sweet, or fruity scents. Almond, apricot, butterscotch, and other aromas may partially employ the compound for their pleasant smells.

Cinnamaldehyde is also used as a fungicide. Proven effective on over 40 different crops, cinnamaldehyde is typically applied to the root systems of plants. Its low toxicity and well-known properties make it ideal for agriculture. To a lesser extent, cinnemaldehyde is an effective insecticide, and its scent is also known to repel animals like cats and dogs.

Cinnamaldehyde is also known as a corrosion inhibitor for steel and other ferrous alloys in corrosive fluids. It can be used in combination with additional components such as dispersing agents, solvents and other surfactants.