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 krel(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 krel values with the calculated energies for the conversion XC6H5→ XC6H4– and with the log krel 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.