Sulfuric Acid → 2-Naphthol-6-sulfonic acid

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Schaeffer's Salt is the common name for the sodium salt of 2-naphthol-6-sulfonic acid. As indicated, this product is obtained by sulfonation of 2-naphthol and forming the sodium salt of the intermediate 2-naphthol-6-sulfonic acid. In preparing Schaeffer's Salt, 2-naphthol is sulfonated directly with concentrated sulfuric acid at a temperature of about 100° C. under conditions such as to provide the maximum amount of 2-naphthol-6-sulfonic acid and follows conventional procedures. After the sulfonation is substantially complete, the resulting mixture is conventionally referred to as a sulfonation mixture. The sulfonation mixture will contain unreacted 2-naphthol, 2-naphthol-6-sulfonic acid, by-product 6,6'-oxybis(2-naphthalene sulfonic acid) and by-product 2-naphthol-3,6-disulfonic acid, with the major product being 2-naphthol-6-sulfonic acid. Preparation of the sulfonation mixture follows conventional procedure and forms no part of the present invention per se.

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