Resorcinol (ACS Reagent)

Resorcinol (or resorcin) is a benzenediol (m-dihydroxybenzene). 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 does the isomeric pyrocatechol. 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 chromatographyexperiments. 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 condenseswith 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.^[10] With the anhydrides of dibasic acids, it yields fluoresceins. When heated with calcium chloride—ammonia to 200 °C it yields meta-dioxydiphenylamine.^[11] 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.^[12] 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.^[13] In alcoholic solution it condenses with sodium acetoacetate to form 4-methylumbelliferone.^[14]

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