phenol overview

• application
• specification
• MSDS

Phenol, also known under an older name of carbolic acid, is a toxic, colourless crystalline solid with a sweet tarry odor. Its chemical formula is C₆H₅OH and its structure is that of a hydroxyl group (-OH) bonded to a phenyl ring; it is thus an aromatic compound.

The word phenol is also used to refer to any compound which contains a six-membered aromatic ring, bonded directly to a hydroxyl group (-OH). In effect, phenols are a class of organic compounds of which the phenol discussed in this article is the simplest member.

Properties

Phenol has a limited solubility in water (8.3 g/100 ml). It is slightly acidic: the phenol molecule has weak tendencies to lose the H⁺ ion from the hydroxyl group, resulting in the highly water-soluble phenoxide anion C₆H₅O⁻. Compared to aliphatic alcohols, phenol shows much higher acidity; it even reacts with aqueous NaOH to lose H⁺, whereas aliphatic alcohols do not. One explanation for the increased acidity is resonance stabilization of the phenoxide anion by the aromatic ring.


In this way, the negative charge on oxygen is shared by the ortho and para carbon atoms.In another explanation, increased acidity is the result of orbital overlap between the oxygen's lone pairs and the aromatic system. In a third, the dominant effect is the induction from the sp² hybridized carbons; the comparatively more powerful inductive withdrawal of electron density that is provided by the sp² system compared to an sp³ system allows for great stabilization of the oxyanion. In making this conclusion, one can examine the pK_a of the enol of acetone, which is 10.9 in comparison to phenol with a pK_a of 10.0.

Production

Phenol can be made from the partial oxidation of benzene or benzoic acid, by the cumene process, or by the Raschig process. It can also be found as a product of coal oxidation.

Hydrothermal chemistry

Under laboratory conditions mimicking hydrothermal circulation (water, 200°C, 1.9 GPa), phenol is found to form from sodium hydrogen carbonate and iron powder (1.8% chemical yield). This discovery made in 2007 may be relevant to the origin of life question as phenol is a fragment of the biomolecule tyrosine.