2-Hydroxynaphthalene-6-carboxylic acid

Benzoxepins require drastic conditions for the thermal rearrangement to naphthols. When 3-benzoxepin-2,4-dicarboxylic acid is heated to 300 C, a decarboxylation reaction takes place and 3-hydroxynaphthalene-2-carboxylic acid (10) is formed in 44% yield.91... 

Coupling components in this series that are of particular industrial importance are 2-hydroxynaphthalene-3-carboxylic acid arylamides in particular anilides, which also couple at the 1-position. 

The reduction by Na(Hg) of several o-hydroxynaphthalenecarboxylic acids in slightly acid solution containing boric acid has been investigated. 1-Hydroxynaphthalene-2-carboxylic acid [109] is, like salicyclic acid, reduced to the aldehyde (62% yield), isolated as the Schiff base, whereas 2-hydroxynaphthalene-3-carboxylic acid [110] under similar conditions yields mainly 2-hydroxy-1,2,3,4-tetrahydronaphtha-lene-3-carboxylic acid (75-80%) and 5% of the aldehyde. When hydrochloric acid rather than CO2 was used to neutralize the base formed during the reduction, the 2-oxo-l,2,3,4-tetrahydronaphthalene-3-carboxylic acid [111] was isolated (60%). On heating, the compound, a y6-keto acid, decarboxylated. 

Raeck, M. Derivatives of 2-hydroxynaphthalene-3-carboxylic acid amide. US Patent 1733468, 1929 Chem. Abstr. 1930, 24, 3005. 

Alkaline glucose converts the diazonium salts of l-amino-2-hydroxy-naphthalene-4-sulfonic acid and its halogen, nitro, carboxyl, or sulfonic acid derivatives into the corresponding 2-hydroxynaphthalene-4-sul-fonic acids.126 According to this patent, the yields are nearly quantitative. 

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