Phenol

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Phenol
Phenol clean NileRed.jpg
Fresh phenol in crushed form.
Names
IUPAC name
Phenol
Preferred IUPAC name
Phenol
Other names
Benzenol
Carbolic acid
Hydroxybenzene
Oxybenzene
Phenic acid
Phenylic acid
Properties
C6H6O
C6H5OH
Molar mass 94.11 g/mol
Appearance Transparent crystalline solid
Brown-pinkish solid (old)
Odor Sweet-tarry
Density 1.07 g/cm3
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)
29.1 (acetonitrile)
Thermochemistry
Hazards
Safety data sheet Sigma-Aldrich
Flash point 79 °C
Lethal dose or concentration (LD, LC):
317 mg/kg (rat, oral)
270 mg/kg (mouse, oral)
19 ppm (mammal)
81 ppm (rat)
69 ppm (mouse)
Related compounds
Related compounds
Anisole
Benzene
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Phenol, also known as carbolic acid, is an aromatic organic compound with the molecular formula C6H5OH.

Properties

Chemical

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)

It will react with sodium metal or sodium hydroxide to yield sodium phenoxide. However, as it is weaker than carbonic acid, phenol does not react with carbonates or bicarbonates.

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.

Phenol is reduced to benzene when it is distilled with zinc dust or its vapor is passed over granules of zinc at 400°C:[1]

C6H5OH + Zn → C6H6 + ZnO

Physical

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.

Availability

Phenol is sold by chemical suppliers.

Preparation

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.[2]

Projects

  • Nucleic acid extraction
  • Carbolic soap
  • Mono-, di- and trinitrophenol (picric acid) sinthesis
  • Cyclohexanone synthesis
  • Phenolphthalein synthesis
  • Make benzene

Handling

Safety

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.

Storage

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.

Disposal

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.[3]

References

  1. A Treatise on Chemistry, Volume 3, Part 3, Henry Enfield Roscoe, Macmillan & Company, 1891, p. 21
  2. https://www.youtube.com/watch?v=A0e0BDEE4Ic
  3. http://www.iasj.net/iasj?func=fulltext&aId=4631

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