Benzaldehyde

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Benzaldehyde
Skeletal (structural) formula Ball-and-stick model
Identifiers
CAS number 100-52-7 YesY
PubChem 240
ChemSpider 235 YesY
UNII TA269SD04T YesY
EC-number 202-860-4
KEGG D02314 YesY
ChEBI CHEBI:17169 YesY
ChEMBL CHEMBL15972 YesY
RTECS number CU437500
Jmol-3D images Image 1
Image 2
Properties
Molecular formula C7H6O
Molar mass 106.12 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)
Solubility in water .695 g/100 mL
Solubility soluble in liquid ammonia
log P 1.48
Acidity (pKa) 14.90
Refractive index (nD) 1.5456
Viscosity 1.321 cP (25 °C)
Thermochemistry
Std enthalpy of
formation
ΔfHo298
−36.8 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
Flammability code 2: Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. Flash point between 38 and 93 °C (100 and 200 °F). E.g., diesel fuel Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g., calcium Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point 64 °C (147 °F; 337 K)
Explosive limits 1.4-8.5%
LD50 1300 mg/kg (rat, oral)
Related compounds
Related compounds Benzyl alcohol
Benzoic acid
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

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.[1] Benzaldehyde was first extracted from bitter almonds in 1803 by the French pharmacist Martrès.[2] In 1832 German chemists Friedrich Wöhler and Justus von Liebig first synthesized benzaldehyde.[3]

Production[edit]

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.[4]

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,[5] followed by distillation of the formed benzaldehyde. This reaction also yields acetaldehyde.

Occurrence[edit]

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.

amygdalin

Reactions[edit]

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.

Cannizzaro reaction

Uses[edit]

It 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:

mandelic acid synthesis

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.[6] 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[edit]

Benzaldehyde has been classified as a hazardous substance by the United States Environmental Protection Agency.[7]

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.[8]

References[edit]

  1. ^ http://www.freepatentsonline.com/1416128.pdf, United States Patent 1416128 - Process of treating nut kernels to produce food ingredients.
  2. ^ 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.
  3. ^ 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.
  4. ^ Friedrich Brühne and Elaine Wright “Benzaldehyde” in Ullmann's Encyclopedia of Industrial Chemistry, 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a03_463
  5. ^ 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.
  6. ^ 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.
  7. ^ http://www.epa.gov/iris/subst/0332.htm
  8. ^ Friedrich Brühne; Elaine Wright (2007), "Benzaldehyde", Ullmann's Encyclopedia of Industrial Chemistry (7th ed.), Wiley, p. 11 

External links[edit]