Stability of 2-naphthalenediazonium ion and its complexation with crown ethers and acyclic polyethers in solution

The effects of solvent, temperature and pH (in aqueous solution) on the rat e of decomposition of 2-naphthalenediazonium, tetrafluoroborate were studie d by UV spectrometry. The host-guest complexation and the kinetics of therm al dediazoniation of this model naphthalenediazonium ion, in the presence o f four crown ethers and three acyclic polyethers, were studied in 1,2-dichl oroethane (DCE) at 40 degreesC by UV spectrometry. Fast atom bombardment ma ss spectrometry (FAB-MS) was used for the gas phase complexation and charac terization. The values of the activation enthalpy DeltaH(#) for the thermal dediazoniat ion of the uncomplexed salt were observed to be high, and the corresponding values of activation entropy AS' were clearly positive. All hosts, except short 12-crown-4, formed 1: 1 complexes under FAB conditions. The complexat ion equilibrium constant K and the values of the stabilizing ability of the complexation (k(2)/k(1)) in DCE were calculated using a kinetic method. In accordance with earlier studies of arene- and 1-naphthalene diazonium, ion s, the thermodynamic and kinetic stabilities were observed to be greater fo r the inclusion complex-the largest for 21-crown-7 and its derivatives, for med with crown ethers containing at least six oxygen atoms-than for the non -specific adduct formation formed with 15-crown-5. The values of the thermo dynamic and kinetic macrocyclic effect were discussed. The results are cons istent with a heterolytic S(N)1-like mechanism involving the decomposition of the uncomplexed and complexed. naphthalonediazonium ion into a highly re active naphthyl cation, followed by fast product-determining reactions with nucleophiles to give the products. Copyright (C) 2001 John Wiley & Sons, L td.