From Sciencemadness Wiki
Jump to: navigation, search
Benzaldehyde from bitter almond oil by NileRed.jpg
Benzaldehyde distilled from bitter almond oil, with traces of water.
IUPAC name
Systematic IUPAC name
Other names
Benzoic aldehyde
Molar mass 106.12 g/mol
Appearance Colorless liquid
Odor Almond-like
Density 1.050 g/cm3 (15 °C)
1.044 g/cm3 (20 °C)
Melting point −57.12 °C (−70.82 °F; 216.03 K)
Boiling point 178.1 °C (352.6 °F; 451.2 K)
0.3 g/100 ml (20 °C)
0.695 g/100 ml (25 °C)
Solubility Miscible with diethyl ether, ethanol, methanol
Soluble in anh. ammonia
Vapor pressure 1.27 mmHg (25 °C)
−36.8 kJ/mol
Safety data sheet Sigma-Aldrich
Flash point 64 °C
Lethal dose or concentration (LD, LC):
1,300 mg/kg (rat, oral)
Related compounds
Related compounds
Benzoic acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Benzaldehyde is an organic chemical compound, the simplest aromatic aldehyde. It has the formula C6H5CHO.



Benzaldehyde will slowly oxidize in air, forming mainly benzoic acid.

C6H5CHO + ½ O2 → C6H5COOH


Benzaldehyde is a colorless liquid, which has a characteristic almond-like odor. It is immiscible with water, but miscible with organic solvents, such as alcohols and ethers.


Benzaldehyde is difficult to acquire in many countries, due to its use in the manufacturing of illegal drugs. In US it is considered a List I chemical, meaning it cannot be legally purchased without a permit.

A good source of benzaldehyde is bitter almond oil, which is mostly crude benzaldehyde. It can be purified via vacuum distillation or steam distillation in an inert atmosphere.[1] However, keep in mind that since the bitter almond oil is basically crude benzaldehyde, legally there's no distinction between the oil and impure benzaldehyde. In US it's illegal to import bitter almond oil without proper paperwork.


Perhaps the most straightforward preparation of benzaldehyde is through the oxidation of benzyl alcohol in an aqueous solution containing an oxidizer. Benzyl alcohol is slightly soluble in water, although benzaldehyde's solubility in water is much lower. So with good stirring, proper stoichiometry, and plenty of time, it should be easy to produce using anything from household bleach to potassium permanganate. As a bonus, potassium permanganate is reduced to MnO2, which can also oxidize benzyl alcohol, so it's important to take this into account when calculating stoichiometry.

Another common route to benzaldehyde is the oxidation of toluene with chromyl chloride, process known as Étard reaction.[2]

Another more accessible route involves the retro-aldol reaction of cinnaldehyde with sodium carbonate. The yield of this reaction is pretty low, but cinnamon oil is more readily available than bitter almond oil. The reaction takes place in distilled water.

Oxidation of benzyl alcohol with sodium persulfate will give benzaldehyde.

Carbonylation of benzene is another route, but may not give a good yield and uses toxic carbon monoxide.


  • Flavoring agent
  • Make mandelic acid
  • Make bee repellent



Benzaldehyde has low toxicity, though it may be irritant. The lethal dose for a 70 kg adult is considered to be 50 ml. Benzaldehyde does not accumulate in any tissues, and is metabolized and then excreted in urine.

Some studies indicate that benzaldehyde might have anti-cancer properties.


Since benzaldehyde is sensitive to air and light, it should be stored in amber bottles, which are then made air-tight by sealing them with sealing tape, like parafilm. Schlenk flasks can also be used to store this compound.


Benzaldehyde should be mixed with a more volatile solvent and safely burned outside. Another more lengthy route involves oxidation to benzoic acid, which is less volatile and can be safely dumped in trash.



Relevant Sciencemadness threads