Benzaldehyde
From Wikipedia, the free encyclopedia
| Benzaldehyde | |
|---|---|
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| General | |
| Other names | Phenylmethanal Benzenecarboxaldehyde Benzoic aldehyde Benzene carbaldehyde (IUPAC Formal) |
| Molecular formula | C7H6O |
| SMILES | c1ccccc1C=O |
| Molar mass | 106.13 g/mol |
| Appearance | colorless liquid |
| CAS number | [100-52-7] |
| 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 ΔfH°liquid |
−86.8 kJ/mol |
| Standard enthalpy of combustion ΔcH°liquid |
−3525.1 kJ/mol |
| Standard molar entropy S°liquid |
? J.K−1.mol−1 |
| Hazards | |
| EU classification | Harmful (Xn) |
| R-phrases | R22 |
| S-phrases | S2, S24 |
| Flash Point | 63 C (Closed Cap) |
| NFPA 704 |
2
2
0
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| Supplementary data page | |
| Structure and properties |
n, εr, 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) |
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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.
Contents |
[edit] 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
[edit] 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.
[edit] 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).
[edit] 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.
