CATION-ANION COMBINATION REACTIONS. 22. RATE AND EQUILIBRIUM CONSTANTS FOR REACTIONS OF PYRONIN AND THIOPYRONIN WITH NUCLEOPHILES.

Article abstract of DOI:10.1021/ja00340a022

Rate and equilibrium constants for the reactions of Pyronin, 3,6-bis(dimethylamino)xanthylium cation, and of Thiopyronin, 3,6-bis(dimethylamino)thioxanthylium cation, with several anionic and amine nucleophiles in water and methanol solutions have been determined. Rate and equilibrium constants for corresponding reactions of the two cations are quite similar, but small effects that may be attributed to polarizability interactions can be distinguished. Comparisons with earlier data for reactions of triarylmethyl cations clearly show the existence of large steric effects in the triarylmethyl systems. Simple relationships between rate and equilibrium constants do not exist for any of the systems, and it is shown that Marcus theory cannot be applied to electrophile-nucleophile combination reactions. Conclusions drawn from such attempted applications are without foundation.