the name of lacmoid. It condenses readily with aldehydes, yielding with formaldehyde, on the addition of catalytic hydrochloric acid, methylene diresorcin [(HO)C6H3(O)]2CH2. 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. In addition to electrophilic aromatic addition, resorcinol (and other polyols) undergo nucleophilic substitution via the enone tautomer. Nitration with concentrated nitric acid in the presence of cold concentrated sulfuric acid yields trinitroresorcin (styphnic acid), an explosive. Occurrence and use Derivatives of resorcinol are found in different natural sources. Alkylresorcinols are found in rye. Polyresorcinols are found as pseudotannins in plants. Adhesives Resorcinol is mainly used in the production of resins. As a mixture with phenol, it condenses with formaldehyde to afford adhesives. Such resins are used as adhesives in the rubber industry and others are used for wood glue. Related to its conversion resins with formaldehyde, resorcinol is the starting material for resorcinarene rings. Medical uses It is present in over-the-counter topical acne treatments at 2% or less concentration, and in prescription treatments at higher concentrations. Monoacetylresorcinol, C6H4(OH)(O–COCH3), is used under the name of Euresol. It is used in hidradenitis suppurativa with limited evidence showing it can help with resolution of the lesions. Resorcinol is one of the active ingredients in products such as Resinol, Vagisil, and Clearasil. In the 1950s and early 1960s the British Army used it, in the form of a paste applied directly to the skin. One such place where this treatment was given to soldiers with chronic acne was the Cambridge Military Hospital, Aldershot, England. It was not always successful. 4-Hexylresorcinol is an anesthetic found in throat lozenges. Chemical uses Resorcinol is 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. It is an analytical reagent for the qualitative determination of ketoses (Seliwanoff's test). It is the starting material for the initiating explosive lead styphnate. Related compounds Resazurin, C12H7NO4, obtained by the action of nitrous acid on resorcinol, forms small dark red crystals possessing a greenish metallic glance. When dissolved in concentrated sulfuric acid and warmed to 210 °C, the solution on pouring into water yields a precipitate of resorufin, C12H7NO3, an oxyphenoxazone, which is insoluble in water but is readily