Ab initio GB study of chemical intermediates in solution; Ethylenesulfonium ion in hydrolysis of 2-chloroethyl methyl sulfide

✍ Scribed by Osamu Kikuchi; Naoyuki Tomisawa; Ohgi Takahashi; Kenji Morihashi

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 249 KB
• Volume: 9
• Category: Article
• ISSN: 1042-7163
• DOI: 10.1002/(sici)1098-1071(1998)9:5<503::aid-hc7>3.0.co;2-6

✦ Synopsis

Ab initio MO theory including solvent effects has been applied to the structure and reactivity of methyl ethylenesulfonium ion, 1, in aqueous solution as a model of the three-membered cyclic sulfonium intermediate expected in the toxic action of sulfur mustard. The 6-31 ‫ם‬ G* geometry optimization of the cyclic sulfonium ion 1 suggested that the ring size of 1 is expanded slightly by solvation. The contour lines map of the interaction energy between 1 and Cl ‫מ‬ has a very shallow and wide well at 5-6 A ˚distance from 1. This is the solvent-separated ion pair, and the contact ion pair was not found between 1 and Cl ‫מ‬ . The calculated energy diagrams for the S N 2-type reactions of 1 with Cl ‫מ‬ , H 2 O, and OH ‫מ‬ that give ring-opened compounds indicated the following: (1) The energy of the 1 ‫ם‬ Cl ‫מ‬ system is similar to that of chloroethyl methyl sulfide (CEMS, 2), and the interconversion between 1 ‫ם‬ Cl ‫מ‬ and 2 occurs easily in aqueous solution. The 3-21 ‫ם‬ G(*) and 6-31 ‫ם‬ G* activation energies for the 2 r 1 ‫ם‬ Cl ‫מ‬ reaction, 20-22 kcal/mol, agree well with the experimental enthalpy of activation for the hydrolysis of 2. (2) The reaction of 1 with OH ‫מ‬ gives a very stable hydroxyl compound, 4, and no transition state was found. (3) The reaction of 1 with H 2 O gives an unstable addition product that is expected to be converted to 4 with the assistance of another H 2 O molecule. This mechanism is consistent with that proposed by Bartlett and Swain in their pioneering work