Participation by Ether Oxygen (RO-3) in the Hydrolysis of Sulfonate Esters of 2-Methoxyethanol and 2-Methoxy-2-Methyl-1-Propanol. Implication Regarding the Nonlinear Ethanol-Trifluoroethanol Plot for Mustard Chlorohydrin

摘要

The lack of scrambling with deuterium-labeled reactants, a nonlinear ethanol-trifluoroethanol plot, and rate acceleration by added thiourea are used to show that sulfonate esters of methoxyethanol (MeOCH2CH2OH) undergo solvent-assisted displacement in a variety of solvents; neighboring group participation by ether oxygen (RO-3 participation) does not occur. This conclusion is in accord with predictions of rate based on the Taft treatment of substituent effects. On the other hand the branched derivative MeOCMe2CH2)Bs reacts with concerted RO-3 participation to give completely rearranged product. Its solvolysis rate is insensitive to added thiourea, the Taft treatment predicts modest anchimeric assistance, and a linear ethanol-trifluoroethanol plot is observed. We discuss the implications of these results relative to the previously observed nonlinear plot for mustard chlorohydrin.