Submitted to: Society of Environmental Toxicology and Chemistry (SETAC)
Publication Type: Abstract Only
Publication Acceptance Date: 11/11/2001
Publication Date: N/A
Technical Abstract: Formulated endosulfan exists as a 7:3 alpha to beta isomeric mixture but the observed ratio in the environment varies. The alpha form is the overwhelmingly-predominant isomer in air samples, beta is favored in rain and alpha is generally greater in snow. The asymmetry of alpha-endosulfan and the corresponding symmetry of beta-endosulfan were recently established. Data have also been presented demonstrating that the beta isomer converts to the alpha isomer, but that the reverse process does not occur under the same conditions. This study explains the observed phenomenon using physical properties, spectral evidence and computational chemistry. Differential scanning calorimetry data indicated several phase changes in isomerically pure and mixtures of endosulfan. A eutectic concentration of approximately 63:37 alpha to beta was observed. NMR data of mixtures confirmed that both isomers influence the conformer populations in solution. Computational chemistry demonstrated that the S=O configuration is responsible for initiating the conversion of beta-endosulfan to alpha. Further calculations indicated that in mixtures, the asymmetrical conformation of the sulfite in alpha can induce asymmetry in beta-endosulfan and allow the conversion to occur. These same data preclude the probability of the reverse process and offer an explanation for isomeric compartmentalization.