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Benzaldehyde



Benzaldehyde
IUPAC name Benzaldehyde
Systematic name Benzenecarbaldehyde
Other names Phenylmethanal
Benzenecarboxaldehyde
Benzoic aldehyde
Identifiers
CAS number 100-52-7
SMILES c1ccccc1C=O
Properties
Molecular formula C7H6O
Molar mass 106.13 g/mol
Appearance colorless liquid
Density 1.0415 g/ml, liquid
Melting point

−26 °C

Boiling point

178.1 °C

Solubility in water Slightly soluble
(0.6 wt at 20 °C)
Viscosity 1.4 cP at 25 °C
Thermochemistry
Std enthalpy of
formation
ΔfHo298
−86.8 kJ/mol
Std enthalpy of
combustion
ΔcHo298
−3525.1 kJ/mol
Hazards
MSDS J. T. Baker
EU classification Harmful (Xn)
NFPA 704
2
2
0
 
R-phrases R22
S-phrases (S2), S24
Flash point 63 C (Closed Cap)
Related Compounds
Related aldehydes anisaldehyde
vanillin
Related compounds Benzyl alcohol
Benzoic acid
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

Infobox disclaimer and references

Benzaldehyde (C6H5CHO) is a chemical compound consisting of a benzene ring with an aldehyde substituent. It is the simplest representative of the aromatic aldehydes and one of the most industrially used members of this family of compounds. At room temperature it is a colorless liquid with a characteristic and pleasant almond-like odor: benzaldehyde is an important component of the scent of almonds, hence its typical odor. It is the primary component of bitter almond oil extract, and can be extracted from a number of other natural sources in which it occurs, such as apricot, cherry, and laurel leaves, peach seeds and, in a glycoside combined form (amygdalin), in certain nuts and kernels. Currently benzaldehyde is primarily made from toluene by a number of different processes.

Additional recommended knowledge

Contents

Production

Benzaldehyde can be obtained by many processes. Currently liquid phase chlorination or oxidation of toluene are among the most used processes. There are also a number of discontinued applications such as partial oxidation of benzyl alcohol, alkali treating of benzal chloride and reaction between benzene and carbon monoxide.

Reactions

On oxidation, benzaldehyde is converted into unpleasant smelling benzoic acid. Benzyl alcohol can be formed from benzaldehyde by means of hydrogenation or by treating the compound with alcoholic potassium hydroxide thus undergoing a simultaneous oxidation and reduction which result in the production of potassium benzoate and benzyl alcohol. Reaction of benzaldehyde with anhydrous sodium acetate and acetic anhydride yields cinnamic acid, while alcoholic potassium cyanide can be used to catalyze the condensation of benzaldehyde to benzoin.


Benzaldehyde can also undergo disproportionation in concentrated alkali (Cannizzaro's reaction): one molecule of the aldehyde is reduced to the corresponding alcohol and another molecule is simultaneously oxidized to the salt of a carboxylic acid. The speed of this reaction depends on the substituents present in the aromatic ring.

Uses

While it is commonly employed as a commercial food flavourant (almond flavour) or industrial solvent, benzaldehyde is used chiefly in the synthesis of other organic compounds, ranging from pharmaceuticals to plastic additives. It is also an important intermediate for the processing of perfume and flavouring compounds and in the preparation of certain aniline dyes.

The synthesis of mandelic acid starts from benzaldehyde:


First hydrocyanic acid is added to benzaldehyde and the resulting mandelic acid nitrile is subsequently hydrolysed to a racemic mixture of mandelic acid. (The scheme above depicts only one of the two formed enantiomers).

Glaciologists LaChapelle and Stillman reported in 1966 that benzaldeyde and N-heptaldehyde inhibit the recrystallization of snow and therefore the formation of depth hoar. This treatment may prevent avalanches caused by unstable depth hoar layers. However, the chemicals are not in widespread use because they damage vegetation and contaminate water supplies.[citation needed]

Biology


Almonds, apricots, apples and cherry kernels, contain significant amounts of amygdalin. This glycoside breaks up under enzyme catalysis into benzaldehyde, hydrocyanic acid and two molecules of glucose.

References

     
    This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Benzaldehyde". A list of authors is available in Wikipedia.
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