Benzyl alcohol (also known as α-cresol) is an aromatic alcohol with the formula C<sub>6</sub>H<sub>5</sub>CH<sub>2</sub>OH. The benzyl group is often abbreviated "Bn" (not to be confused with "Bz" which is used for benzoyl), thus benzyl alcohol is denoted as BnOH. Benzyl alcohol is a colorless liquid with a mild pleasant aromatic odor. It is useful as a solvent for its polarity, low toxicity, and low vapor pressure. Benzyl alcohol has moderate solubility in water (4 g/100 mL) and is miscible in alcohols and diethyl ether. The anion produced by deprotonation of the alcohol group is known as benzylate or benzyloxide.
Natural occurrences
Benzyl alcohol is produced naturally by many plants and is commonly found in fruits and teas. It is also found in a variety of essential oils including jasmine, hyacinth and ylang-ylang. It is also found in castoreum from the castor sacs of beavers. Benzyl esters also occur naturally.
Preparation
Benzyl alcohol is produced industrially from toluene via benzyl chloride, which is hydrolyzed:
: C<sub>6</sub>H<sub>5</sub>CH<sub>2</sub>Cl + H<sub>2</sub>O → C<sub>6</sub>H<sub>5</sub>CH<sub>2</sub>OH + HCl
Another route entails hydrogenation of benzaldehyde, a by-product of the oxidation of toluene to benzoic acid.
For laboratory use, Grignard reaction of phenylmagnesium bromide (C<sub>6</sub>H<sub>5</sub>MgBr) with formaldehyde and the Cannizzaro reaction of benzaldehyde also give benzyl alcohol. The latter also gives benzoic acid, an example of an organic disproportionation reaction.
Reactions
Like most alcohols, it reacts with carboxylic acids to form esters. In organic synthesis, benzyl esters are popular protecting groups because they can be removed by mild hydrogenolysis.
Benzyl alcohol reacts with acrylonitrile to give N-benzylacrylamide. This is an example of a Ritter reaction:
:C<sub>6</sub>H<sub>5</sub>CH<sub>2</sub>OH + NCCHCH<sub>2</sub> → C<sub>6</sub>H<sub>5</sub>CH<sub>2</sub>N(H)C(O)CHCH<sub>2</sub>
Benzyl alcohol spontaneously polymerizes to give poly(p-phenylene methylene). This potentially dangerously exothermic dehydration is induced by acid catalysts:
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Applications
Benzyl alcohol is used as a general solvent for inks, waxes, shellacs, paints, lacquers, and epoxy resin coatings. Thus it can be used in paint strippers, especially when combined with compatible viscosity enhancers to encourage the mixture to cling to painted surfaces.
It is a precursor to a variety of esters and ethers, used in the soap, perfume, and flavor industries. E.g. benzyl benzoate, benzyl salicylate, benzyl cinnamate, dibenzyl ether, benzyl butyl phthalate.
Benzyl alcohol is used as an additive in flavorings used in aromatic alcoholic beverages, and chocolates and other confections. Its aroma is described as floral, rose, phenolic, balsamic, sweet, and fruity.
It can be used as a local anesthetic, especially with epinephrine.
As a dye solvent, it enhances the process of dyeing wool, nylon, and leather.
Use in health care
Benzyl alcohol is used as a bacteriostatic preservative at low concentration in intravenous medications, cosmetics, and topical drugs.
Benzyl alcohol, sold under the brand name Ulesfia, was approved by the U.S. Food and Drug Administration (FDA) in 2009, as a 5% solution for the treatment of head lice in people 6 months of age and older. It affects the louse's spiracles, preventing them from closing.
Benzyl alcohol is not considered to be a carcinogen, and no data are available regarding teratogenic or reproductive effects.