Benzaldehyde

nfpa_f2.png nfpa_r0.png Chemical infobox

Benzaldehyde
General
Other names	Phenylmethanal Benzenecarboxaldehyde Benzoic aldehyde Benzene carbaldehyde
Molecular formula	C₆H₅CHO
SMILES	c1ccccc1C=O
Molar mass	106.13 g/mol
Appearance	colorless liquid
CAS number	^*
Properties
Density and phase	1.0415 g/ml, liquid
Solubility in water	Slightly soluble (0.6 wt at 20 °C)
Solubility in ethanol	Miscible
Melting point	−26 °C
Boiling point	178.1 °C
Viscosity	1.4 cP at 25 °C
Thermodynamic data
Standard enthalpy of formation Δ_fH°_liquid	−86.8 kJ/mol
Standard enthalpy of combustion Δ_cH°_liquid	−3525.1 kJ/mol
Standard molar entropy S°_liquid	? J.K⁻¹.mol⁻¹
Hazards
EU classification	Harmful (Xn)
R-phrases
S-phrases	,
NFPA 704
Supplementary data page
Structure and properties	n, ε_r, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Regulatory data	Flash point, RTECS number, etc.
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)

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.

Production

Benzaldehyde can be obtained by many process. Currently liquid phase chlorination or oxidation of toluene are among the most used processes. There is 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).

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.

External links

Aldehydes | Aromatic compounds | Solvents

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Production

Reactions

Uses

Biology

External links