Benzaldehyde

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Benzaldehyde
Identifiers
CAS number100-52-7 YesY
PubChem240
ChemSpider235 YesY
UNIITA269SD04T YesY
EC-number202-860-4
KEGGD02314 YesY
ChEBICHEBI:17169 YesY
ChEMBLCHEMBL15972 YesY
RTECS numberCU437500
Jmol-3D imagesImage 1
Image 2
Properties
Molecular formulaC7H6O
Molar mass106.12 g mol−1
Appearancecolorless or yellowish liquid
strongly refractive
Odoralmond-like
Density1.0415 g/ml, liquid
Melting point

-26 °C, 247 K, -15 °F

Boiling point

178.1 °C, 451 K, 353 °F

Solubility in water.695 g/100 mL
Solubilitysoluble in liquid ammonia
log P1.48
Acidity (pKa)14.90
Refractive index (nD)1.5456
Viscosity1.321 cP (25 °C)
Thermochemistry
Std enthalpy of
formation
ΔfHo298
−36.8 kJ/mol
Std enthalpy of
combustion
ΔcHo298
−3525.1 kJ/mol
Hazards
MSDSJ. T. Baker
EU classificationHarmful (Xn)
R-phrasesR22
S-phrases(S2), S24
NFPA 704
NFPA 704.svg
2
3
1
Flash point64 °C (147 °F)
Autoignition
temperature
192 °C (378 °F)
Explosive limits1.4-8.5%
LD501300 mk/kg (rat, oral)
Related compounds
Related compoundsBenzyl alcohol
Benzoic acid
 YesY (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references
 
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Benzaldehyde
Identifiers
CAS number100-52-7 YesY
PubChem240
ChemSpider235 YesY
UNIITA269SD04T YesY
EC-number202-860-4
KEGGD02314 YesY
ChEBICHEBI:17169 YesY
ChEMBLCHEMBL15972 YesY
RTECS numberCU437500
Jmol-3D imagesImage 1
Image 2
Properties
Molecular formulaC7H6O
Molar mass106.12 g mol−1
Appearancecolorless or yellowish liquid
strongly refractive
Odoralmond-like
Density1.0415 g/ml, liquid
Melting point

-26 °C, 247 K, -15 °F

Boiling point

178.1 °C, 451 K, 353 °F

Solubility in water.695 g/100 mL
Solubilitysoluble in liquid ammonia
log P1.48
Acidity (pKa)14.90
Refractive index (nD)1.5456
Viscosity1.321 cP (25 °C)
Thermochemistry
Std enthalpy of
formation
ΔfHo298
−36.8 kJ/mol
Std enthalpy of
combustion
ΔcHo298
−3525.1 kJ/mol
Hazards
MSDSJ. T. Baker
EU classificationHarmful (Xn)
R-phrasesR22
S-phrases(S2), S24
NFPA 704
NFPA 704.svg
2
3
1
Flash point64 °C (147 °F)
Autoignition
temperature
192 °C (378 °F)
Explosive limits1.4-8.5%
LD501300 mk/kg (rat, oral)
Related compounds
Related compoundsBenzyl alcohol
Benzoic acid
 YesY (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
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 source | 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 source | 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 source | 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 source | 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 source | edit]

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

References[edit source | 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

External links[edit source | edit]