Anhydrous and hydrated 4-aminotoluene-3-sulfonic acid

Melvin A. Leonard, Philip J. Squattrito

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


The crystal structures of 4-aminotoluene-3-sulfonic acid, C7H9NO3S, (I), and its hemihydrate, C7H9NO3S.-0.5H2O, (II), are reported. The acid molecules in both crystals exist as zwitterions (ammoniotoluenesulfonate) and pack in layers in which the phenyl rings are nearly parallel. In (I), the ammonium and sulfonate groups are arranged so that a two-dimensional network of intra- and intermolecular N-H⋯O hydrogen bonds exists on the faces of each layer. Each ammonium H atom is involved in a single hydrogen bond and there are no strong interactions between the layers. In the hydrate (II), the two crystallographically independent molecules adopt a more complicated double-layer structure in which the polar groups and water molecules are located between every other layer. An extensive two-dimensional network of N-H⋯O and O-H⋯O hydrogen bonds holds these double layers together, while only weak interactions involving the methyl and phenyl H atoms occur between these slabs. This two-dimensional nature of the intermolecular hydrogen bonding contrasts with that observed in similar sulfonic acids.

Original languageEnglish
Pages (from-to)648-651
Number of pages4
JournalActa Crystallographica Section C: Crystal Structure Communications
Issue number5
StatePublished - May 15 1997


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