A Kinetic and X-Ray Diffraction Study of the Solid State Rearrangement of Methyl P-Dimethylaminobenzenesulfonate. Reaction Rate Enhancement Due to Proper Orientation in a Crystal1a

Methyl p-dimethylaminobenzenesulfonate rearranges in the solid state, as a melt, and in solution to a zwitterionic product, p-trimethylammoniumbenzenesulfonate. By a combination of kinetic and field desorption mass spectrometric techniques, we have found that the reaction is intermolecular and that it proceeds at a considerably faster rate in the crystal than it does either in the melt or in solution. The structure of the starting sulfonate has been solved by single crystal x-ray diffraction, and this study revealed that the molecules in the crystal are nearly ideally oriented for reaction in the solid state. Powder diffraction studies have shown that due to the constraints of the starting crystal lattice, the product is initially formed in a metastable crystalline form which slowly reverts to its thermodynamically most stable crystalline modification.