Benzaldehyde

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Benzaldehyde
Benzaldehyde from bitter almond oil by NileRed.jpg
Benzaldehyde distilled from bitter almond oil, with traces of water.
Names
IUPAC name
Benzaldehyde
Systematic IUPAC name
Benzenecarbaldehyde
Other names
Benzenecarbonal
Benzenecarboxaldehyde
Benzoic aldehyde
Phenylmethanal
Properties
C7H6O
C6H5CHO
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)
Thermochemistry
−36.8 kJ/mol
Hazards
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.

Properties

Chemical

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

Physical

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

Availability

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.

Preparation

The most 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.

Projects

  • Flavoring agent
  • Make mandelic acid
  • Make bee repellent

Handling

Safety

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.

Storage

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.

Disposal

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.

References

  1. https://www.youtube.com/watch?v=a95a0iMOICU
  2. https://www.youtube.com/watch?v=rYKoj247rhg

Relevant Sciencemadness threads