Benzyl alcohol

Preparation

Benzyl alcohol is produced industrially from toluene via benzyl chloride, which is hydrolyzed:

C₆H₅CH₂Cl + H₂O → C₆H₅CH₂OH + 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 (C₆H₅MgBr) 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:

C₆H₅CH₂OH + NCCHCH₂ → C₆H₅CH₂N(H)C(O)CHCH₂

Benzyl alcohol spontaneously polymerizes to give poly(p-phenylene methylene). This potentially dangerously exothermic dehydration is induced by acid catalysts:

n C₆H₅CH₂OH → (C₆H₄CH₂)_n + n H₂O

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 injectable 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. These then become clogged with water or mineral oil or other matter and cause the insect to die from asphyxiation.

Benzyl alcohol is used effectively for treating lice infestations as the active ingredient in lotion shampoo with 5% benzyl alcohol.

Benzyl alcohol is an ingredient used in the manufacture of soaps, topical creams, skin lotions, shampoos, and facial cleansers and is popular due to its anti-bacterial and anti-fungal properties. It is a common ingredient in a variety of household products.

Safety

Sensitization to benzyl alcohol occurs very rarely, mainly in patients with stasis dermatitis.

Benzyl alcohol is not considered to be a carcinogen, and no data are available regarding teratogenic or reproductive effects.

Benzyl alcohol has low acute toxicity with an LD₅₀ of 1.2 g/kg in rats. It oxidizes rapidly in healthy individuals to benzoic acid, conjugated with glycine in the liver, and excreted as hippuric acid. Very high concentrations can result in toxic effects including respiratory failure, vasodilation, hypotension, convulsions, and paralysis.

Benzyl alcohol is toxic to neonates and is associated with the gasping syndrome.