Dediazoniations of Arenediazonium Ions. Part XXI. Dediazoniation of Arenediazonium Ions Complexed with Crown Ethers

Abstract

The evaluation of the dediazoniation kinetics of various m-and p-substituted benzenediazonium tetrafluoroborates' in 1,2-dichloroethane at 50" in the presence of 18-crown-6, 2 1-crown-7 and dicyclohexano-24-crown-8 demonstrates that the rate constant for the dediazoniation within the complex (k2) is smallest, and the equilibrium constant for complex formation (K) is largest for the complexes with 21-crown-7 (cf Scheme 1). The logarithms of the equilibrium constants ( K ) for complex formation with each of the crown ethers studied correlate well with Hammetf's substituent constants, D , to give reaction constants p= 1.18-1.38.A linear correlation between the logarithms of the rate constants for the dediazoniation within the complex with those of the dediazoniation rate constants of uncomplexed diazonium ions (log k2 vs. log. k l ) , found for most substituted diazoniurn salts, indicates that the dediazoniation mechanism of the complexed diazonium ions is not significantly different from that of the free ions. For very electrophilic diazonium ions (p-Cl, rn-CN), k2 was much larger than expected on the basis of the linear log k2 vs. log k , relationship. Analysis of the dediazoniation products showed that this was due to a change in mechanism from heterolytic to homolytic dediazoniation.The complexation rate of diazonium salts by crown ethers (k,) is practically diffusion controlled and does not change much with the size of the crown ether. The decornplexation rate ( k d ) , however, is significantly lower for complexes with 2 1crown-7, than for those with 18-crown-6 and dicyclohexano-24-crown-8, and is therefore the reason for the variations in the equilibrium constant ( K ) and thus for the fact that complexes of arenediazonium salts with 21-crown-7 are the most stable.The amounts of the N,-NB rearrangement, as well as those of the exchange of the I5N-labelled diazonio group with external nitrogen during dediazoniation of p-toluenediazonium salt were independent of the addition of crown ethers. ') Part xx: see [I].

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

“…The corresponding effects in the presence of 15-crown-5, 18-crown-6 and 21-crown-7 have been reported. 6,17 Measurements were made of the uncomplexed benzenediazonium salt and of the salt in the presence of at least five host concentrations, where the total concentration of the salt was kept constant: [PhN Table 2. In the presence of benzo-substituted crown ethers the value of max for benzenediazonium ion cannot be determined exactly, owing to the absorption of the benzene ring (see Apparatus and measurements) and therefore any values of max are not included in Table 2.…”

“…With the benzenediazonium ion, whose diazonium group has a cylindrical diameter of about 0·24 nm, 18-crown-6 and 21-crown-7 can form insertion-type complexes 5,6 (1, Figure 1), but 15-crown-5, 17 with its cavity diameter 2 of only 0·17-0·22 nm, forms only much weaker chargetransfer complexes Zollinger et al 6 argued that in the charge-transfer complex the acceptor center of the arenediazonium ion is either the ␤-N-atom and/or the combined -electron system of the aryl part and the diazonio group, while the donor centers are one or several of the oxygen atoms in the crown ether.…”

“…A diversity of techniques, including absorption spectrometry, calorimetry, conductometry, kinetic methods, NMR spectrometry and potentiometry, have been used to determine the complexation behaviour in solution. [1][2][3][4][5][6] In addition, it is observed that fast atom bombardment mass spectrometry (FAB-MS) is a rapid and good method for the characterization of complexation in the gas phase. [7][8][9][10] Arenediazonium salts possess considerable importance in the chemical industry, which has initiated a great number of the studies.…”

“…Subsequently many investigations have been published on the host-guest complexation between crown ethers and arenediazonium ions but only a few considered both the thermodynamic and kinetic stability of the com-plexes. 5,6,[15][16][17][18] Zollinger et al 6 have studied the dediazoniation of arenediazonium ions complexed with crown ethers in 1,2-dichloroethane using as complexing agents 18-crown-6, 21-crown-7 and dicyclohexano-24-crown-8. We have studied by kinetic and spectroscopic methods, in solution, the complexation of crown ethers (15-crown-5, 18-crown-6 and 21-crown-7) with arenediazonium ions.…”

Synthesis of Some Biologically Active Halogenopurines

“…22,23 The diazotization is generally carried out using accessible sodium nitrite in strongly acidic medium at reduced temperature. [22][23][24][25][26][27] [34][35][36][37] However, many of these procedures require high reaction temperature, expensive and special apparatus, troublesome work-up procedures, harsh reaction conditions, etc. Phase transfer catalysis (PTC) is a versatile synthetic technique that has been widely applied to intensify otherwise slow heterogeneous reactions involving an organic substrate and an ionic reactant, either dissolved in water (liquid-liquid) or present in solid state (liquid-solid).…”