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Sulfo J acid (2-amino-5-naphthol-1,7-disulfonic acid) is a key intermediate for the manufacture of high-performance dyes and pigments. Conventional sulfonation routes based on oleum or sulfur trioxide, although effective, suffer from severe corrosivity, environmental burden, and safety concerns. In this study, an efficient and greener aqueous sulfonation protocol is developed using sodium bisulfite as the sulfonating agent and sodium hypochlorite as a catalytic oxidant. The process enables selective conversion of J acid to sulfo J acid within 4 h under near-neutral pH and moderate temperature (55–60 °C). Reaction parameters including temperature, pH, reagent molar ratio, and catalyst addition mode were systematically optimized. Under optimal conditions, the method achieves up to 80% yield with 98.98% purity as determined by HPLC. Mechanistic analysis suggests a redox-assisted activation of bisulfite leading to regioselective sulfonation at the 7-position of the naphthalene ring. The elimination of oleum, use of a fully aqueous medium, and high product purity render this methodology highly attractive for sustainable industrial production of dye intermediates. • A green, oleum-free sulfonation route for sulfo J acid using NaHSO 3 and catalytic NaOCl is developed. • Redox-assisted activation of bisulfite enables regioselective sulfonation at the 7-position in aqueous medium. • The optimized process achieves up to 80% yield and 98.98% purity within a short reaction time of 4 h. • Mild reaction conditions (pH 7.5–8, 55–60 °C) minimize by-product formation and improve process safety. • The methodology offers a scalable and industrially viable alternative for dye and pigment intermediate manufacture.