SOLVOLYSIS OF 1-ALKYL-1-CHLORO-1-(4-METHYL)PHENYLMETHANES - NUCLEOPHILIC SOLVENT INTERVENTION AND EXTENDED Y-BNCL SCALE

The solvolysis of 1-alkyl-1-chloro-1-(4-methyl)phenylmethanes (4a-d) i n aqueous acetone, aqueous ethanol, aqueous methanol and ethanol-trifl uoroethanol was studied. Grunwald-Winstein-type correlation analysis u sing the Y-BnCl scale suggests significant nucleophilic solvent interv ention in the ease of 1-chloro-1-(4-methyl)phenylethane (4a). Increasi ng bulkiness of the 1-alkyl substituent from methyl (4a) to ethyl (4b) , to isopropyl (4c) and to tert-butyl (4d) resulted in a gradual chang e to limiting S(N)1 mechanisms. The observed excellent linear correlat ions with Y-BnCl and the good solubility in high-water-containing bina ry solvents made 4d a suitable reference standard For deriving more Y- BnCl values. A positive azide salt effect was realized in the solvolys is of 4a but not 4d. A small decrease in the beta-deuterium kinetic Is otope effect from 4a to 1-chloro-1-(4-methoxyphenyl)propane (5) sugges ted the presence of additional stabilization of the benzylic cationic transition state. However, no relationship between k(CH3)/k(CD3) and t he solvent effect was found. The superiority of employing the Y-BnCl s cale over the combination of Y-Cl and I scales in the mehanistic study was observed. (C) 1997 John Wiley & Sons, Ltd.