Difference between revisions of "Phenol"
Latest revision as of 19:59, 25 October 2020
Fresh phenol in crushed form.
| IUPAC name
| Preferred IUPAC name
| Other names
|Molar mass||94.11 g/mol|
|Appearance|| Transparent crystalline solid|
Brown-pinkish solid (old)
|Melting point||40.5 °C (104.9 °F; 313.6 K)|
|Boiling point||181.7 °C (359.1 °F; 454.8 K)|
| 8.3 g/100 ml (20 °C)|
Miscible (>40 °C)
|Solubility|| Soluble in acetone, aqueous alkali hydroxides, carbon disulfide, chloroform, diethyl ether, ethanol, glycerol, isopropanol, methanol|
Moderate soluble in benzene
|Solubility in benzene||8.33 g/100 ml|
|Vapor pressure||0.4 mmHg (20 °C)|
|Acidity (pKa)|| 9.95 (water)|
|Safety data sheet||Sigma-Aldrich|
|Flash point||79 °C|
|Lethal dose or concentration (LD, LC):|
LD50 (Median dose)
| 317 mg/kg (rat, oral)|
270 mg/kg (mouse, oral)
LC50 (Median concentration)
| 19 ppm (mammal)|
81 ppm (rat)
69 ppm (mouse)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Phenol, also known as carbolic acid, is an aromatic organic compound with the molecular formula C6H5OH.
Phenol is weakly acidic, though still more acidic than aliphatic alcohols (about one million times more acidic), and at high pH gives the phenoxide (or phenolite) anion, C6H5O−.
- PhOH ⇌ PhO− + H+; (K = 10−10)
Phenol will slowly oxidize in air, resulting in various quinones, which are pink or dark colored.
Highly colored transition metal complexes form from aqueous phenol solutions and certain metal ions. Most notably, the iron(III) ion forms a deep purple complex with phenol, similar to its salicylic acid complex.
- C6H5OH + Zn → C6H6 + ZnO
Phenol is a volatile white crystalline solid, with a distinct sweet and tarry odor. It is sparingly soluble in water (8.3 g/100 mL at 20 °C), but soluble in most organic solvents, such as ethanol, methanol, diethyl ether, acetone, chloroform. Phenol has a melting point of 40.5 °C and a boiling point of 181.7 °C. Its density is 1.07 g/cm3.
Phenol is sold by chemical suppliers.
There are several ways to prepare phenol.
Historically, phenol was obtained from the pyrolysis of coal tar.
The industrial method relies on the oxidation of cumene with air at 90-130°C in the presence of alkali additives (Udris-Sergeev process), resulting in cumene hydroperoxide, followed by cleavage with sulfuric acid into phenol and acetone:
- C6H5CH(CH3)2 + O2 → C6H5C(CH3)2OOH → C6H5OH + CH3COCH3
Other methods involve the hydrolysis of chlorobenzene, using a base (Dow's Process) or steam (Raschig–Hooker process), direct oxidation of benzene with nitrous oxide, oxidation of toluene with air or the reaction of a strong base with benzenesulfonate.
The most cheap and accessible method involves the thermal decomposition of salicylic acid, that can either be purchased from the pharmacy or obtained from sodium salicylate by adding a strong acid. Gently heating salicylic acid in a tube yields molten phenol, giving off carbon dioxide and phenol vapors. A condenser can be used to recover the resulting phenol vapor, to increase the yield. Distillation under vacuum will also improve the yield.
- Nucleic acid extraction
- Carbolic soap
- Mono-, di- and trinitrophenol (picric acid) sinthesis
- Cyclohexanone synthesis
- Phenolphthalein synthesis
- Make benzene
Phenol and its vapors are corrosive to the eyes, the skin, and the respiratory tract. Its corrosive effect on skin and mucous membranes is due to a protein-degenerating effect. Repeated or prolonged skin contact with phenol may cause dermatitis, or even second and third-degree burns. Inhalation of phenol vapor may cause lung edema. It may cause harmful effects on the central nervous system, heart, resulting in dysrhythmia, seizures, and coma. Long-term or repeated exposure of the substance may have harmful effects on the liver and kidneys.
Phenol should be stored in closed bottles, to reduce the smell. As it oxidizes in air, turning pinkish, it's best to store it in air-tight containers, or in a Schlenk tube filled with inert gas, especially if stored for long periods of time.
Phenol can be destroyed via incineration, however, due to it's high flash point (79 °C), this is difficult to do without releasing lots of irritating phenol fumes, unless you use an incinerator equipped with an afterburner. Burning phenol will release carbon monoxide, soot, VOCs, PAHs and unburnt phenol vapors. Phenol can also be mixed with a more flammable solvent and burned as a diluted solution, best in an oxygen-rich atmosphere.
Zinc dust will reduce phenol to benzene at high temperatures. However, since benzene is more volatile and toxic then phenol, this isn't a good disposal method.
Phenol, especially phenol water has been successfully neutralized with Fenton's reagent. If concentrated phenol is used, the resulting gasses which will aerosolize some phenol and byproducts. This is dangerous in an enclosed area, as phenol is irritant and toxic if inhaled. Since phenol is water soluble, it's best to use diluted aqueous solutions. The neutralization should be performed in a fumehood, or outside. UV light will accelerate the decomposition, and it's a good idea to use an UV lamp.
In one experiment involving the Fenton solution, a mixture of H2O2/Fe+2 in a ratio of 10/1 destroyed the phenol from an aqueous solution in 3 hours. The reaction takes place at pH = 5.6 and at 25°C, with stirring.
- A Treatise on Chemistry, Volume 3, Part 3, Henry Enfield Roscoe, Macmillan & Company, 1891, p. 21