Nucleophilic Displacement at Sulfur Center (). Solvolysis of para-Substituted Benzenesulfonyl Chlorides in MeOH-MeCN Mixtures

[摘要] Solvolysis of p-CH3, p-H, p-Cl and p-NO2-benzenesulfonyl chlorides have heen studied in MeOH-MeCN mixtures. A nonlinear Hammett plot with a ratio order of p-NO2 > p-CH3 > p-H > p-Cl was obtained; the reaction was thought to proceed by an SN1-SN2 borderline mechanism. In all cases the reactivity was a maximum at 90¡­95%(v) methanol, whereas methanol monomer selectivity defined as fi = k1/ki (k1; observed pseudo-first order rate constant: ki; hypothetical rate constant for MeOH solution having the same polymer structure as in the pure MeOH) was a maximum at 80% methanol with a decreasing order of fi as p-NO2 > p-Cl > p-H > p-CH3. This was interpreted as the decrease in tightness of transition state; the larger the fi, the tighter is the MeOH attached to the substrate, and hence the more susceptible the substrate becomes to the approaching monomer methanol.

[学科分类] 化学（综合）