EFFECT OF RING SIZE ON THE COMPLEXATION AND DECOMPOSITION OF BENZENEDIAZONIUM ION IN THE PRESENCE OF CROWN ETHERS IN 1,2-DICHLOROETHANE AND THE GAS PHASE

Abstract

The host–guest complexation and the kinetics of the thermal dediazoniation of benzenediazonium tetrafluoroborate in the presence of unsubstituted and (di)benzene- and dicyclohexane-substituted crown ethers containing 4–10 oxygen atoms were studied by UV spectrophotometry in 1,2-dichloroethane at 40°C. The complexation equilibrium constants K and the stabilizing ability of the complexation (k2/k1) were calculated by a kinetic method. Complexation in the gas phase was observed and characterized by fast atom bombardment mass spectrometry (FAB-MS). All complexing agents except 12-crown-4 formed 1:1 complexes [crown ether–PhN2]+ under FAB conditions. The complexation caused a hypsochromic shift Δλmax in the UV spectrum of the benzenediazonium salt, which was largest for hosts containing six oxygen atoms. The thermodynamic and kinetic stability were much greater for insertion-type complexes containing six or more oxygen atoms in the host molecule than for the charge-transfer complexes formed with 15-crown-5. In contrast, 12-crown-4 destabilized benzenediazonium ion owing to the increase in homolytic dediazoniation. 21-Crown-7 was the strongest complexing and stabilizing agent for benzenediazonium ion; with a larger hole size in the host the effects weakened. The effects of benzene and cyclohexane substituents in crown ethers on the thermodynamic and kinetic stability were small compared with the effects of the number of oxygen atoms. © 1997 by John Wiley & Sons, Ltd.