1,3-Dihydroxynaphthalene

1,3-Dihydroxynaphthalene is an organic compound with the formula. It is one of several isomers of dihydroxynaphthalene.
It can be prepared by hydrolysis of 1,3-diaminonaphthalene. An alternative laboratory route is decarboxylation of 1,3-dihydroxynaphthalene-2-carboxylic acid, which in turn is obtained by cyclization of esters of phenylacetylmalonate.
The compound attracted some interest because its conjugate base exists as the dionate tautomer:
The pKa of 1,3-dihydroxynaphthalene is 7.35, which is anomalous compared to the pKa's of phenol and 1-naphthol, which are respectively 9.95 and 9.85. This anomaly is explained by the tautomerism.