Reactivity in nucleophilic substitution. Part IV. A carbonyl elimination reaction of 9-fluorenyl toluene-p-sulphonate

Abstract

In 90% methanolic acetone, 9-fluorenyl toluene-p-sulphonate undergoes first-order solvolysis leading to 9-fluorenyl methyl ether. For the same system, addition of small concentrations of potassium hydroxide completely changes the reaction mechanism and the products are 9-fluorenone and potassium toluene-p-sulphinate. A detailed kinetic investigation of the latter reaction has been made and an alpha deuterium kinetic isotope effect (k_H/k_D= 2·3) measured. It is suggested that the carbonyl elimination is of the E_CO2 type involving concerted proton removal and carbonyl group formation. Changing the methanol content of the solvent gives an insight into the competing solvolysis and elimination. For the solvent mixtures investigated, unimolecular solvolysis is the predominant reaction in the absence of base. In the presence of potassium hydroxide, carbonyl elimination accounts for 100% of the reaction in 90% methanolic acetone, 50% of the reaction in 80% methanolic acetone, and only 15% of the reaction in 65% methanolic acetone.