esorcinol (or resorcin) is a phenolic compound. It is an organic compound with the formula C6H4(OH)2. It is one of three isomeric benzenediols, the 1, 3-isomer (or meta-isomer). Resorcinol crystallizes from benzene as colorless needles that are readily soluble in water, alcohol, and ether, but insoluble in chloroform and carbon disulfide.[6]Resorcinol is produced in several steps from benzene, starting with dialkylation with propylene to give 1, 3-diisopropylbenzene. Oxidation and Hock rearrangement of this disubstituted arene gives acetone and resorcinol.[6]Resorcinol is an expensive chemical, produced in only a very few locations around the world (as of 2010 only four commercial plants were known to be operative: in the United States, Germany, China, and Japan), and as such it is the determining factor in the cost of PRF adhesives.[7] Production in the United States ended in 2017 with the closure of Indspec Chemical's plant in Petrolia, Pennsylvania.[8] Many additional routes exist for resorcinol. It was formerly produced by disulfonation of benzene followed by hydrolysis of the 1, 3-disulfonate. This method has been discarded because it cogenerates so much sulfur-containing waste. Resorcinol can also be produced when any of a large number of resins (such as galbanum and asafoetida) are melted with potassium hydroxide, or by the distillation of Brazilwood extract. It may be synthesized by melting 3-iodophenol, phenol-3-sulfonic acid with potassium carbonate. Diazotization of 3-aminophenol or on 1, 3-diaminobenzene followed by hydrolysis provides yet another route.[9] Many ortho- and para-compounds of the aromatic series (for example, the bromophenols, benzene-para-disulfonic acid) also yield resorcinol on fusion with potassium hydroxide.Partial hydrogenation of resorcinol gives dihydroresorcinol, also known as 1, 3-cyclohexanedione.[10][11] 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 tribromoresorcinol. These properties are what give it its use as a colouring agent for certain chromatography experiments.