Benzaldehyde
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| Names | |||
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| IUPAC name
Benzaldehyde
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| Systematic IUPAC name
Benzenecarbaldehyde Phenylmethanal | |||
| Other names
Benzoic aldehyde
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| Identifiers | |||
3D model (JSmol)
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| ChEBI | |||
| ChEMBL | |||
| ChemSpider | |||
| ECHA InfoCard | 100.002.601 | ||
| KEGG | |||
PubChem CID
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| RTECS number |
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| UNII | |||
CompTox Dashboard (EPA)
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| Properties | |||
| C7H6O | |||
| Molar mass | 106.124 g·mol−1 | ||
| Appearance | colorless or yellowish liquid strongly refractive | ||
| Odor | almond-like | ||
| Density | 1.0415 g/ml, liquid | ||
| Melting point | −26 °C (−15 °F; 247 K) | ||
| Boiling point | 178.1 °C (352.6 °F; 451.2 K) | ||
| 0.3 g/100 mL (20 °C)[1] | |||
| Solubility | soluble in liquid ammonia | ||
| Solubility | .695 g/100 mL | ||
| log P | 1.48 | ||
| Acidity (pKa) | 14.90 | ||
Refractive index (nD)
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1.5456 | ||
| Viscosity | 1.321 cP (25 °C) | ||
| Thermochemistry | |||
Std enthalpy of
formation (ΔfH⦵298) |
−36.8 kJ/mol | ||
Std enthalpy of
combustion (ΔcH⦵298) |
−3525.1 kJ/mol | ||
| Hazards | |||
| NFPA 704 (fire diamond) | |||
| Flash point | 64 °C (147 °F; 337 K) | ||
| 192 °C (378 °F; 465 K) | |||
| Explosive limits | 1.4-8.5% | ||
| Lethal dose or concentration (LD, LC): | |||
LD50 (median dose)
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1300 mg/kg (rat, oral) | ||
| Related compounds | |||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Benzaldehyde (C6H5CHO) is an organic compound consisting of a benzene ring with a formyl substituent. It is the simplest aromatic aldehyde and one of the most industrially useful. This colorless liquid has a characteristic pleasant almond-like odor. In fact, benzaldehyde is the primary component of bitter almond oil and can be extracted from a number of other natural sources.[2] Benzaldehyde was first extracted from bitter almonds in 1803 by the French pharmacist Martrès.[3] In 1832 German chemists Friedrich Wöhler and Justus von Liebig first synthesized benzaldehyde.[4]
Production
Benzaldehyde can be obtained by many processes. In the 1980s, an estimated 18 million kilograms were produced annually in Japan, Europe, and North America, a level that can be assumed to continue. Currently liquid phase chlorination and oxidation of toluene are the main routes. Numerous other methods have been developed, such as the partial oxidation of benzyl alcohol, alkali hydrolysis of benzal chloride, and the carbonylation of benzene.[5]
Benzaldehyde can be synthesized from cinnamaldehyde obtained from the oil of cinnamon by refluxing in aqueous/alcoholic solution between 90 °C and 150 °C with a base (most commonly sodium carbonate or bicarbonate) for 5 to 80 hours,[6] followed by distillation of the formed benzaldehyde. This reaction also yields acetaldehyde.
Occurrence
Almonds, apricots, apples and cherry kernels, contain significant amounts of amygdalin. This glycoside breaks up under enzyme catalysis into benzaldehyde, hydrogen cyanide and two molecules of glucose.
Benzaldehyde contributes to the scent of oyster mushrooms (Pleurotus ostreatus).[7]
Reactions
On oxidation, benzaldehyde is converted into the odorless benzoic acid, which is a common impurity in laboratory samples. Benzyl alcohol can be formed from benzaldehyde by means of hydrogenation. 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 undergoes disproportionation upon treatment with concentrated alkali (Cannizzaro reaction): one molecule of the aldehyde is reduced to the corresponding alcohol and another molecule is simultaneously oxidized to sodium benzoate.
Uses
It has a cherry scent in concentrated form and in a diluted form is commonly employed to confer almond flavor. Benzaldehyde is used chiefly as a precursor to other organic compounds, ranging from pharmaceuticals to plastic additives. The aniline dye malachite green is prepared from benzaldehyde and dimethylaniline. It is a precursor to certain acridine dyes as well. Via aldol condensations, benzaldehyde is converted into derivatives of cinnamaldehyde and styrene. The synthesis of mandelic acid starts from benzaldehyde:
First hydrocyanic acid is added to benzaldehyde, and the resulting nitrile is subsequently hydrolysed to 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.[8] 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]
Safety
Benzaldehyde has been classified as a hazardous substance by the United States Environmental Protection Agency.[9]
Benzaldehyde is used as a flavoring and fragrance in food, cosmetics, pharmaceuticals, and soap and is "generally regarded as safe" (GRAS) by the US FDA.[10]
References
- ^ "GESTIS Substance database". Institute for Occupational Safety and Health of the German Social Accident Insurance. Retrieved 21 August 2012.
- ^ http://www.freepatentsonline.com/1416128.pdf, United States Patent 1416128 - Process of treating nut kernels to produce food ingredients.
- ^ In 1803 C. Martrès published a manuscript on the oil of bitter almonds: "Recherches sur la nature et le siège de l'amertume et de l'odeur des amandes amères" (Research on the nature and location of the bitterness and the smell of bitter almonds). However, the memoir was largely ignored until an extract was published in 1819: Martrès fils (1819) "Sur les amandes amères," Journal de Pharmacie, vol. 5, pages 289-296.
- ^ Wöhler and Liebig (1832) "Untersuchungen über das Radikal der Benzoesäure" (Investigations of the radical of benzoic acid), Annalen der Pharmacie, vol. 3, pages 249-282.
- ^ Friedrich Brühne and Elaine Wright “Benzaldehyde” in Ullmann's Encyclopedia of Industrial Chemistry, 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a03_463
- ^ http://www.patentstorm.us/patents/pdfs/patent_id/4617419.html, Process for preparing natural benzaldehyde and acetaldehyde, natural benzaldehyde and acetaldehyde compositions, products produced thereby and organoleptic utilities therefor, Charles Wienes, Middletown; Alan O. Pittet, Atlantic Highlands, both of N.J.
- ^ Beltran-Garcia, Miguel J.; Estarron-Espinosa, Mirna; Ogura, Tetsuya (1997). "Volatile Compounds Secreted by the Oyster Mushroom (Pleurotus ostreatus)and Their Antibacterial Activities". Journal of Agricultural and Food Chemistry. 45 (10): 4049. doi:10.1021/jf960876i.
- ^ E. LaChapelle and R. M. Stillman (1966) "The control of snow metamorphism by chemical agents," Symposium international sur les aspects scientifiques des avalanches de neige, 5-10 avril 1965, Davos, Suisse (Belgium: Association Internationale d'Hydrologie Scientifique, 1966), pages 261-266. See also: E. LaChapelle and R.M. Stillman (1962) "Project C : Progress Report No. 4 : The chemical modification of depth hoar -- part II," Alta Avalanche Study Center, Wasatch National Forest, U.S. Department of Agriculture Forest Service.
- ^ http://www.epa.gov/iris/subst/0332.htm
- ^ Friedrich Brühne; Elaine Wright (2007), "Benzaldehyde", Ullmann's Encyclopedia of Industrial Chemistry (7th ed.), Wiley, p. 11