POTASSIUM CRYPTATE CATALYSIS IN THE ELIMINATION-REACTION OF A SULFONATE ESTER

In the reaction of p-nitrophenyl methanesulfonate (1) with alkali-metal ethoxides, it is found that potassium ethoxide in the presence of excess 2.2.2 cryptand is more reactive than potassium ethoxide alone or in the presence of excess 18-crown-6. An upward curvature in the plot of k(obs) vs [KOEt]o in the presence of 2.2.2 cryptand is interpreted as arising from parallel reactions of free ethoxide ion and the ion pair of ethoxide ion with cryptated potassium ion ([K subset-of 2.2.2]+EtO-), the latter being more reactive than the former. It is shown that the ester reacts predominantly by an E1cb-type elimination mechanism, and the potassium cryptate appears to stabilize the transition state for leaving-group departure by electrostatic interactions through an 18-membered ring ''window'' in the cryptand.