Substituent effects in formation of aryl carbanions. Base cleavage of aryltrimethylstannanes in dimethyl sulphoxide–water

Abstract

The rates of cleavage of some XC₆H₄SnMe₃ compounds by 9 : 1 or 100 : 3 v/v Me₂SO–aqueous KOH at 40 °C have been measured; the values of k_rel(the rate for X = X relative to that for X = H) in 9 : 1 v/v Me₂SO–H₂O, with those for 100 : 3 v/v Me₂SO–H₂O in parentheses, are (X )p-NMe₂, 0.22 (0.089); p-OMe, 0.78 (0.65); p-Me, 0.66 (0.44); m-Me, 0.59 (0.58); p SMe, 3.2 (3.4); p Cl, 15.8 (25); m-Cl, 70 (144); m-CF₃, 115 (240), p-NMe₃I, 192 (530); p-NO₂, 950 (3 370). Correlations of the log k_rel values with the calculated energies for the conversion XC₆H₅→ XC₆H₄^– and with the log k_rel values for cleavage of the corresponding XC₆H₄SiMe₃ compounds in 9 : 1 v/v Me₂SO–aqueous KOH indicate that the electrophilic assistance to cleavage of the tin compounds falls with the proton availability in the medium, and is absent or slight in 100 : 3 v/v Me₂SO–H₂O.