Ethyl 1,3-dihydroxy-2-naphthoate

B. Ethyl l,3-dihydroxy-2-naphthoate. In a 1-1. flask 1 volume (87 ml.) of the crude ester is added in one lot to 3 volumes (261 ml.) of concentrated sulfuric acid without cooling, and the solution is allowed to stand for about 1 week (Note 4). The whole mixture, including any precipitate which may have formed, is poured slowly with stirring into a mixture of 1 kg. of icc and 500 ml. of water (Note 5) the solid yellow ester is filtered with suction, washed with a small amount of cold water, pressed in the filter for 30 minutes with a rubber dam, and finally dried in a vacuum desiccator. The yield of ester melting at 80° is 58-68 g. (50-59%, based on the malonic ester used). 

The yield of ethyl l,3-dihydroxy-2-naphthoate is decreased to 45% if the sulfuric acid solution is allowed to stand for only 2 days. 

The authors propose the following mechanism (Scheme 47) The benzoxepine is protonated, yielding the enol. Subsequent proton transfer gives the unstable oxonium ion. Rearrangement via C—O bond cleavage and formation of a new C—C bond generates an aromatic compound, ethyl 3,4-dihydroxy-2-naphthoate. This intermediate then reacts with o-phenylenediamine to yield the respective phenazine. 

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