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Stability of 2‐naphthalenediazonium ion and its complexation with crown ethers and acyclic polyethers in solution
Author(s) -
Kuokkanen Toivo,
Palokangas Jarmo,
Talvensaari Merja
Publication year - 2001
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.411
Subject(s) - chemistry , adduct , aqueous solution , 18 crown 6 , thermal decomposition , enthalpy , heterolysis , kinetics , reaction rate constant , inorganic chemistry , ion , organic chemistry , physics , quantum mechanics , catalysis
The effects of solvent, temperature and pH (in aqueous solution) on the rate of decomposition of 2‐naphthalenediazonium tetrafluoroborate were studied by UV spectrometry. The host–guest complexation and the kinetics of thermal dediazoniation of this model naphthalenediazonium ion, in the presence of four crown ethers and three acyclic polyethers, were studied in 1,2‐dichloroethane (DCE) at 40 °C by UV spectrometry. Fast atom bombardment mass spectrometry (FAB‐MS) was used for the gas phase complexation and characterization. The values of the activation enthalpy Δ H # for the thermal dediazoniation of the uncomplexed salt were observed to be high, and the corresponding values of activation entropy Δ S # were clearly positive. All hosts, except short 12‐crown‐4, formed 1:1 complexes under FAB conditions. The complexation 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 ions, the thermodynamic and kinetic stabilities were observed to be greater for the inclusion complex—the largest for 21‐crown‐7 and its derivatives, formed 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 thermodynamic and kinetic macrocyclic effect were discussed. The results are consistent with a heterolytic S N 1‐like mechanism involving the decomposition of the uncomplexed and complexed naphthalenediazonium ion into a highly reactive naphthyl cation, followed by fast product‐determining reactions with nucleophiles to give the products. Copyright © 2001 John Wiley & Sons, Ltd.