Applications of Resorcinol

Resorcinol (or resorcin) is a dihydroxy benzene. It is the 1,3-isomer of benzenediol with the formula C6H4(OH)2.
Properties
Resorcinol crystallizes from benzene as colorless needles that are readily soluble in water, alcohol, and ether, but insoluble in chloroform and carbon disulfide. It reduces Fehling’s solution and ammoniacal silver solutions. It does not form a precipitate with lead acetate solution, as the isomeric pyrocatechol does. Iron(III) chloride colors its aqueous solution a dark-violet, and bromine water precipitates tribromoresorcin. These properties are what give it its use as a colouring agent for certain chromatography experiments. Sodium amalgam reduces it to dihydroresorcin, which when heated to 150 to 160 °C with concentrated barium hydroxide solution gives γ-acetylbutyric acid (D. Vorlgnder); when fused with potassium hydroxide, resorcinol yields phloroglucin, pyrocatechol, and diresorcin. It condenses with acids or acid chlorides, in the presence of dehydrating agents, to oxyketones, e.g. with zinc chloride and glacial acetic acid at 145 °C it yields resacetophenone (HO)2C6H3~CO.CH3. With the anhydrides of dibasic acids, it yields fluoresceins. When heated with calcium chloride—ammonia to 200 °C it yields meta-dioxydiphenylamine. With sodium nitrite it forms a water-soluble blue dye, which is turned red by acids, and is used as an indicator, under the name of lacmoid. It condenses readily with aldehydes, yielding with formaldehyde, on the addition of catalytic hydrochloric acid, methylene diresorcin [(HO)C6H3(O)]2•CH2. Reaction with chloral hydrate in the presence of potassium bisulfate yields the lactone of tetra-oxydiphenyl methane carboxylic acid. In alcoholic solution it condenses with sodium acetoacetate to form 4-methylumbelliferone.
Applications
Medical
Used externally, it is an antiseptic and disinfectant, and is used 5 to 10% in ointments in the treatment of chronic skin diseases such as psoriasis, hidradenitis suppurativa, and eczema of a sub-acute character. It is present in over-the-counter topical acne treatments at 2% or less concentration, and in prescription treatments at higher concentrations. Weak, watery solutions of resorcinol (25 to 35 g/kg) are useful in allaying the itching in erythematous eczema. A 2% solution used as a spray has been used with marked effect in hay fever and in whooping cough. In the latter disease 0.6 mL of the 2% solution has been given internally. It can be included as an anti-dandruff agent in shampoo or in sunscreen cosmetics. It has also been employed in the treatment of gastric ulcers in doses of 125 to 250 mg in pills, and is said to be analgesic and haemostatic in its action. In large doses, it is a poison, causing giddiness, deafness, salivation, sweating, and convulsions. It is also worked up in certain medicated soaps. Monoacetylresorcinol, C6H4(OH)(O-COCH3), is used under the name of euresol. Resorcinol is one of the main active ingredients in products like Resinol and Vagisil. Resorcinol is also an active ingredient in certain Clearasil products.
Chemical
Resorcinol is also used as a chemical intermediate for the synthesis of pharmaceuticals and other organic compounds. It is used in the production of diazo dyes and plasticizers and as a UV absorber in resins.
An emerging use of resorcinol is as a template molecule in supramolecular chemistry. The -OH groups on resorcinol form hydrogen bonds to target molecules, holding them in the proper orientation for a reaction. Many such reactions are able to be carried out in the solid state, thereby reducing or eliminating the use of solvents that may be harmful to the environment. (see Green chemistry)
Resorcinol is an analytical reagent for the qualitative determinaion of ketoses (Seliwanoff’s test).
Resorcinol is the starting material for resorcinarene molecules and the initiating explosive lead styphnate (Reference: Army TM 9-1300-214, p. 7–12).
Resorcinol reacts with formaldehyde to form a thermoset resin, which can form the basis of an aerogel.
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