The ephemeral dihydrate of sulfanilic acid

Abstract

Evaporation of an aqueous solution of sulfanilic acid (systematic name: 4-aminobenzene-1-sulfonic acid) at 273 K affords a crystalline dihydrate, CHNOS·2HO. The organic molecule exists as a zwitterion; two zwitterions are aligned in an antiparallel fashion about a crystallographic centre of inversion. They interact directly via two N-H...O hydrogen bonds between the ammonium group of one zwitterion and the sulfonate group of its symmetry-related counterpart, and their aromatic rings are π-stacked, with an interplanar distance of 3.533 (3) Å. One of the cocrystallized water molecules connects the resulting pairs into layers and the second crosslinks the layers into a three-dimensional network. All H atoms connected to N or O atoms find acceptors in suitable geometries. In the resulting crystal, polar and hydrogen-bond-dominated slabs alternate with stacks of organic arene rings. Although the new dihydrate shows efficient space filling, with a packing coefficient of 75.7%, it is unstable and undergoes fast desolvation at room temperature. In this process, the orthorhombic ansolvate forms as a pure phase.

Polymorphism and Peroxomorphism in Peroxosolvates of Zwitterionic Sulfonic Acids: Features of H-Bonding and Crystal Packing

“…They exhibit regular values of bond lengths and angles in comparison with ordinary organic molecules . These geometric parameters also well correspond to those found in the structures of starting compounds and/or their hydrates (taurine, , sulfanilic acid, − orthanilic acid, metanilic acid, − 3-pyridinesulfonic acid, and hydroxy­(quinolinium-2-yl)­methanesulfonate). The O–O bond distances lie within the normal range for solvent H 2 O 2 molecules (1.442(7)–1.470(2) Å) .…”