# 1911 Encyclopædia Britannica/Resorcin

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​RESORCIN (meta-dioxybenzene), C$_6$H$_4$(OH)$_2$, one of the dihydric phenols. It is obtained on fusing many resins (galbanum, as afoetida, &c.) with caustic potash, or by the distillation of Brazil-wood extract. It may be prepared synthetically by fusing meta-iodophenol, phenol meta-sulphonic acid, and benzene meta-disulphonic acid with potash; by the action of nitrous acid on meta-amino phenol; or by the action of 10% hydrochloric acid on meta-phenylene diamine (J. Meyer, Ber., 1897, 30, p. 2569). Many ortho and para-compounds of the aromatic series (for example, the brom-phenols, benzene para-disulphonic acid) also yield resorcin on fusion with caustic potash. It crystallizes from benzene in colourless needles which melt at 119° C. and boil at 276.5° C. (L. Calderon), or 280° C. (C. Graebe), and is readily soluble in water, alcohol and ether, but insoluble in chloroform and carbon bisulphide. It reduces Fehling’s solution, and ammoniacal silver solutions. It does not form a precipitate with lead acetate solution, as the isomeric pyrocatechin does. Ferric chloride colours its aqueous solution a dark violet, and bromine water precipitates tribromresorcin. Sodium amalgam reduces it to dihydroresorcin, which when heated to 150–160° C. with concentrated baryta solution gives γ-acetylbutyric acid (D. Vorländer); when fused with caustic potash, resorcin yields phloroglucin, pyrocatechin 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)$_2$C$_6$H$_3$·CO·CH$_3$ (M. Nencki and N. Sieber, Jour. prak. Chem., 1881 [2], 23, p. 147). With the anhydrides of dibasic acids it yields fluoresceins (q.v.). When heated with calcium chloride ammonia to 200° C. it yields meta-dioxydiphenylamine (A. Seyewitz, Bull. Soc. Chim., 1890 [3], 3, p. 811). 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 ​(M. C. Traub and C. Hock, Ber., 1884, 17, p. 2615). It condenses readily with aldehydes, yielding with formaldehyde, on the addition of, a little hydrochloric acid, methylene diresorcin [(HO)$_2$·C$_6$H$_3$]$_2$·CH$_2$, whilst with chloral hydrate, in the presence of potassium bisulphate, it yields the lactone of tetra-oxydiphenyl methane carboxylic acid (J. T. Hewitt and F. G. Pope, Jour. Chem. Soc., 1897, 71, p. 1084). In alcoholic solution it condenses with sodium acetoacetate to form β-methylumbelliferone, C$_{10}$H$_8$O$_3$ (A. Michael, Jour. prak. Chem., 1888 [2], 37, 470). With concentrated nitric acid, in the presence of cold concentrated sulphuric acid, it yields trinitro-resorcin (styphnic acid), which forms yellow crystals, exploding violently on rapid heating.
In medicine, resorcin, which is official in the United States under the name of resorcinol, was formerly used as an anti pyre tic, but it has been given up. The dose is 2 to 8 grs. 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 and eczema of a' sub-acute character. Weak, watery solutions of resorcin (10 or 15 grs. to the ounce) 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 10 minims of the 2% solution has been given internally. It has also been employed in the treatment of gastric ulcer in doses of 2 to 4 grs. in pill, 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. Mono-acetyl resorcin, C$_6$H$_4$(OH)·O·COCH$_3$, is used under the name of “euresol.”
Resazurin, C$_{12}$H$_7$NO$_4$, obtained by the action of nitrous acid on resorcin (P. Weselsky and R. Benedikt, Monats., 1880, 1, p. 889), forms small dark red crystals 'possessing a greenish metallic glance. When dissolved in concentrated sulphuric acid and warmed to 210° C., the solution on pouring' into water yields a precipitate of resorufin, C$_{12}$H$_7$NO$_3$, an oxyphenoxazone, which is insoluble in water, but is readily soluble in hot concentrated hydrochloric acid, and in solutions of caustic alkalis. The alkaline solutions are of a rose-red colour and show a cinnabar-red fluorescence. A tetrabromresorufin is used as a dye-stuff under the name of Fluorescent Resorcin Blue.
Thioresorcin is obtained by the action of zinc and hydrochloric acid on the chloride of benzene meta-disulphonic acid. It melts at 27° C. and boils at 243° C. Resorcin disrilphonic Acid (HO)$_2$C$_6$H$_2$(HSO$_3$)$_2$, is a deliquescent mass obtained by the action of sulphuric acid on resorcin (H. Fischer, Monats., 1881, 2, p. 321). It is easily soluble in water and decomposes when heated to 100° C.