Two monosodium salt hydrates of Colour Index Pigment Red 48

We report herein the crystal structures of a monohydrate of Colour Index Pigment Red 48 (P.R.48) (systematic name: monosodium 2‐{2‐3‐carboxy‐2‐oxo‐1,2‐dihydronaphthalen‐1‐ylidene]hydrazin‐1‐yl}‐4‐chloro‐5‐methylbenzenesulfonate monohydrate), Na⁺·C₁₈H₁₂ClO₆S^?·H₂O, and a dihydrate, Na⁺·C₁₈H₁₂ClO₆S^?·2H₂O. The two monosodium salt hydrates of P.R.48 were obtained from in‐house synthesized P.R.48. Both have monoclinic (P2₁/c) symmetry at 173 K. The crystal packing of both crystal structures shows a layer arrangement whereby N—H…O and O—H…O hydrogen bonds are formed.