benzaldehyde

Benzaldehyde
IUPAC name	Benzaldehyde
Systematic name	Benzenecarbaldehyde
Other names	Phenylmethanal Benzenecarboxaldehyde Benzoic aldehyde
Identifiers
CAS number	[100-52-7]
SMILES	O=Cc1ccccc1
InChI	1/C7H6O/c8-6-7-4-2-1-3-5-7/h1-6H
ChemSpider ID	235
Properties
Molecular formula	C7H6O
Molar mass	106.12 g mol−1
Appearance	colorless liquid
Density	1.0415 g/ml, liquid
Melting point	−26 °C
Boiling point	178.1 °C
Solubility in water	0.6 g/100 ml (20 °C)
Solubility in methanol	methanol 9.85 M [1]
Viscosity	1.4 cP (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)
R-phrases	R22
S-phrases	(S2), S24
NFPA 704	2 2 0
Flash point	63 °C
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 references

Benzaldehyde (C₆H₅COH) 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.

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 the odorless 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 flavorant (almond flavor) 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 flavoring 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 benzaldehyde 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

1. ^ Solubility of benzaldehyde in methanol

External links

• International Chemical Safety Card 0102
• European Chemicals Bureau
• Benzaldehyde description at ChemicalLand21.com