Phenol

General Information

Phenol, also known as carbolic acid, is an aromatic organic compound. Pure phenol is a white crystalline solid that is volatile. It is mildly acidic and requires careful handling due to its propensity to cause chemical burns. 

Although similar to alcohols, phenols have unique distinguishing properties. Unlike in alcohols where the hydroxyl group is bound to a saturated carbon atom, in phenols the hydroxyl group is attached to an unsaturated aromatic (alternating double and single bond) hydrocarbon ring such as benzene. Consequently, phenols have greater acidity than alcohols due to stabilization of the conjugate base through resonance in the aromatic ring.

Industrial uses involve its conversion to plastics or related materials.  In research laboratories phenol, when suspended in chloroform, is commonly used in the extraction of DNA from biological samples. The liquid-liquid extraction of aqueous samples are mixed with equal volumes of a phenol:chloroform solution. After combining, the mixture is centrifuged and two immiscible phases form. The less dense aqueous phase is on top, and the organic phase (phenol:chloroform) is on the bottom. The proteins will partition into the lower organic phase while the nucleic acids (as well as other contaminants such as salts, sugars, etc.) remain in the upper aqueous phase. If the mixture is acidic, DNA will precipitate into the organic phase while RNA remains in the aqueous phase due to DNA being more readily neutralized than RNA.

Health and Safety

Phenol and its vapors are corrosive to the eyes, skin, and respiratory tract. The corrosive effect on skin and mucous membranes is due to a protein-degenerating effect. Repeated or prolonged skin contact with phenol may cause dermatitis, and potentially second and third-degree burns. Inhalation of phenol vapor may cause lung edema. Phenol may adversely effect the central nervous system and heart. Long-term, or repeated exposure, to phenol may have harmful effects on the liver and kidneys.

While there is no evidence that phenol causes cancer in humans it is readily absorbed through the skin; systemic poisoning can occur in addition to the local caustic burns. Resorptive poisoning by a large quantity of phenol can occur even with only a small area of skin, rapidly leading to paralysis of the central nervous system and a severe drop in body temperature. Phenol is also a reproductive toxin causing increased risk of abortion and low birth weight indicating retarded development in utero.

Chemical burns from skin exposures can be decontaminated by washing with polyethylene glycol or isopropyl alcohol; flushing with copious amounts of water will help to remediate the burn. Removal of contaminated clothing is required, as well as immediate hospital treatment for large splashes.

Safe Use

Standard Operating Procedure - Processes that include the use of phenol must be detailed by an EH&S approved Standard Operating Procedure (SOP). Please contact EH&S if your lab does not currently have an approved SOP for the use of phenol. Training must be provided to any researcher on the hazards, use, and proper cleanup procedures of phenol. The Safety Data Sheet (SDS) should also be reviewed before conducting work. 

Personal Protective Equipment - The minimum lab attire should always be worn when conducting work with phenol: long pants, closed-toe shoes and protective eyewear (safety glasses or splash goggles). A properly fitting lab coat and chemically resistant gloves should also be worn. When only working with phenol a chloroprene glove will be appropriate, use of a thicker glove is recommended if larger volumes are used. Unfortunately, chloroprene gloves do not provide sufficient protection against chloroform. The best glove to use when conducting work with phenol-chloroform mixtures is a butyl/viton multilayered glove. The Ansell ChemTek™ Butyl/Viton gloves provide excellent dexterity while maintaining chemical protection.