The Ei reaction of substituted threo- and erythro-1-phenylethyl phenyl sulfoxides

Substituted (RS,SR)-1-phenylethyl phenyl sulfoxides (threo) (XC6H4S(O)CH(CH3)C6H4Y) and some substituted (RR,SS)-sulfoxides (erythro) were prepared and kinetic investigation for the thermal decomposition was carried out at 80.0, 90.0, and 100.0 °C in dioxane. Hammett plots for threo-XC6H4S(O)CH(CH3)C6H5 gave positive ρ-values (ρX=0.60–0.64 at three temperatures), while those for threo- and erythro-C6H5S(O)CH(CH3)C6H4Y snowed V-shape lines with bottoms at the m-OCH3 substituent though the effects of the substituents are small. Meanwhile, large kinetic isotope effects for threo- and erythro-C6H5S(O)CH(CD3)C6H4Y (Y=H, p-OMe, m-Cl) (kH⁄kD=4–6) were observed at all temperatures. The activation energies were in the range of 104–121 kJ mol−1 for all sulfoxides, while the activation entropies were relatively large (7–37 J K−1 mol−1) and were correlated with Hammett σ-values to give small negative trend. Reactions of all erythro-isomers examined were 2–3 times faster than those of the corresponding threo-isomers. ...

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