WCZR 2LSSolvolysis of w-halogenoalkyl sulphides has been investigated. Under appropriate conditions, the rate-limiting step is formation of a cyclic sulphonium salt. Three-membered cyclic sulphonium salts are formed more rapidly than their five-membered analogues and the enthalpy of activation for three-membered ring formation i s lower than that for five-membered ring formation. Attachment of a phenyl group adjacent to the leaving group accelerates formation of rings of both sizes but the three-membered ring is favoured to a considerably greater extent by an entropic and not an enthalpic change. The results are discussed in terms of special conjugative effects of threemembered rings. Bromide : chloride ratios have been measured for reactions giving three-and five-membered ring sulphonium salts. The relevance of bromide : chloride ratios in assessment of bond extension in transition states is considered.
Aryl 3-chloropropyl sulphones react with potassium t-butoxide in t-butyl alcohol to give aryl cyclopropyl sulphones in high yields. The effects of substituents in the aromatic nucleus upon the rate of the reaction have been determined, and a rectilinear Hammett plot with p = +2.32 is obtained. Hydrogen atoms of the methylene group adjacent to the sulphonyl group are rapidly exchanged under basic conditions in deuteriated solvents, and the rate of cyclisation of 3-chloro-1 ,I -dideuteriopropyl p-tolyl sulphone in t-butyl [2H]alcohol is twice that of the isotopically normal sulphone in t-butyl [lH]alcohol. These results suggest that a n intermediate carbanion is formed and that the p-value obtained for the reaction is a composite one which incorporates opposing effects upon the equilibrium concentration of the carbanion and its nucleophilicity in the subsequent ring-closure step. This finding is briefly discussed in relation to current views on cyclisation.
Bei 55°C entstehen unter N2‐Atmosphäre aus den Titelverbindungen (I) unter primärer Bildung der entsprechenden Carbanionen in einer Reaktion 1. Ordnung die Ethylene (II) mit sehr guten Rohausbeuten.
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