Alkali fusion of 1,6-Naphthalenedisulfonic acid yields 1,6-dihydroxynaphthalene, and sulfonation with oleum produces naphthalene-1,3,6-trisulfonic acid. However, the main outlet for naphthalene-1,6-disulfonic acid is via nitration to 1- nitronaphthalene-3,8-disulfonic acid, which is the intermediate for 1-aminonaphthalene-3,8- disulfonic acid.
Separation from the 1,5-disulfonic acid process (see above) usually meets requirements for the preparation of Naphthalene-1,6-disulfonic acid. It can also be prepared by sulfonation of naphthalene-2- sulfonic acid with oleum, which gives naphthalene-1,7-disulfonic acid as a byproduct.
