Benzoic acid

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Benzoic acid
Names
IUPAC name
Benzoic acid
Preferred IUPAC name
Benzoic acid
Systematic IUPAC name
Benzenecarboxylic acid
Other names
Carboxybenzene
Dracylic acid
E210
Phenylmethanoic acid
Properties
C7H6O2
Molar mass 122.12 g/mol
Appearance White solid
Odor Very faint benzaldehyde-like
Density 1.2659 g/cm3 (15 °C)
1.0749 g/cm3 (130 °C)
Melting point 122.41 °C (252.34 °F; 395.56 K)
Boiling point 249.2 °C (480.6 °F; 522.3 K) (decomposes at 370 °C)
1.7 g/L (0 °C)
2.7 g/L (18 °C)
3.44 g/L (25 °C)
5.51 g/L (40 °C)
21.45 g/L (75 °C)
56.31 g/L (100 °C)
Solubility Soluble in acetone, liq. ammonia, benzene, CCl4, chloroform, diethyl ether, ethanol, ethyl acetate, hexane, methanol, THF, toluene, xylene
Slightly soluble in hexane, petroleum ether
Solubility in 1,4-Dioxane 56 g/100 ml (25 °C)
Solubility in acetone 69.1 g/100 g (20 °C)
Solubility in benzene 10 g/100 ml
Solubility in carbon disulfide 3.3 g/100 ml
Solubility in carbon tetrachloride 4.0 g/100 ml
Vapor pressure 0.16 Pa (25 °C)
0.19 kPa (100 °C)
22.6 kPa (200 °C)
Acidity (pKa) 4.202
Thermochemistry
167.6 J·mol-1·K-1
-385.2 kJ/mol
Hazards
Safety data sheet Sigma-Aldrich
Flash point 121.5 °C
Lethal dose or concentration (LD, LC):
1700 mg/kg (rat, oral)
Related compounds
Related compounds
Sodium benzoate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Benzoic acid, is a colorless crystalline solid and the simplest aromatic carboxylic acid.

It has the formula C7H6O2, though it's more conveniently written as C6H5COOH.

Properties

Chemical

Oxidative decarboxylation of benzoic acid between 300−400 °C gives phenol. If Cu(II) salts are used, the reaction can proceed at lower temperatures, around 200 °C:

C6H5COOH +  ½ O2 → C6H5OH + CO2

Physical

Benzoic acid is a colorless solid, poorly soluble in water, but more soluble in organic solvents.

Availability

Benzoic acid can sometimes be found in food stores as food preservative, though most of the time it's just plain old sodium benzoate, as the latter is more soluble in water.

Higher purity benzoic acid can be purchased from chemical suppliers or more convenient from eBay or Amazon.

Preparation

Benzoic acid can be prepared by oxidizing toluene with potassium permanganate.

C6H5CH3 + KMnO4 → C6H5COOH + MnO2 + H2O

A more convenient and less smelly route involves the addition of an acid, such as diluted hydrochloric acid to sodium benzoate.

C6H5COONa + HCl → C6H5COOH + NaCl

Benzoic acid, being less soluble than sodium benzoate, will precipitate out of the solution. The crude benzoic acid is then filtered and washed with cold water then dried.

Oxidation of benzaldehyde in air will give benzoic acid.

Projects

Handling

Safety

Benzoic acid is practically non-toxic, though powdered form is irritant if inhaled.

Storage

Benzoic acid should be stored in closed bottles, away from alkali bases and ammonia.

Disposal

Benzoic acid doesn't require special disposal as it's harmless. Discard it as you wish.

References

Relevant Sciencemadness threads