naphthionic acid[¦naf·thē¦än·ik ′as·əd]
l-naphthylamine-4-sulfonic acid; colorless crystals. Poorly soluble in water and alcohol. Naphthionic acid loses its water of crystallization upon heating to 130°C and, at higher temperatures, decomposes without melting to yield SO 2.
Naphthionic acid is prepared from α-naphthylamine sulfate, C10H7NH 2• H2SO4, by rearrangement into an at 180°-200°C. Naphthionic acid is an intermediate in the synthesis of azo dyes (for example, Congo red).