Browsing by Author "Mollett, Christopher C."

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    Kinetics and Mechanism of the Quatemization of Poly(4-vinyl pyridine) with Ethyl, n-Propyl, n-Butyl, n-Hexyl and Benzyl Bromide in Sulpholane
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (10), 1977) Boucher, Ernest A.; Groves, John A.; Mollett, Christopher C.; Fletcher, Peter W.
    Kinetic results for quaternization reactions of four n-alkyl bromides (C2, C3, C4, C6) and benzyl bromide, with poly(4-vinyl pyridine) in sulpholane, at a variety of concentrations and temperatures, have been analysed according to a neighbouring-group model. A particular system is characterized by the rate constants ki for reaction of a pyridyl group having i= 0, 1 or 2 already reacted neighbours. Values of k0 under comparable conditions are given. The ratios K=k1/k0 and L=k2/k0 for the series of reagents: C2(0.95, 0.54), C3(0.80, 0.37), C4(0.70, 0.31), C6(0.55, 0.27) and Bz(0.75, 0.34), indicate that retardation as reaction proceeds, in excess of that expected from second-order kinetics, is due predominantly to steric (rather than electrostatic) effects. All of the results for the time dependence of extent, ξ, of reaction are corrected on the supposition that 5 % of the polymer consists of unreactive impurity; previous studies have shown evidence of impurities, but these have not been allowed for in the few attempts at kinetic analysis. Activation energies E0 are fairly constant for C2 to C6: 68.8 ± 3.3, 66.2 ± 4.3, 65.8 ± 4.0 and 66.0 ± 3.5 kJ mol–1; cf. 52.6 ± 4.9 kJ mol–1 for benzyl bromide. The k1 and the k2 show the same temperature dependence, within experimental error, as the k0, i.e.E0=E1=E2.
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    Kinetics of Quaternization of 4-Methyl and 4-Ethyl Pyridine with n-Propyl and n-Butyl Bromide in Sulpholane
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (02), 1978) Boucher, Ernest A.; Khosravi-Babadi, Ezatollah; Mollett, Christopher C.
    Kinetic measurements have been carried out in sulpholane to provide a basis for comparison with quaternization reactions of poly(4-vinyl pyridine), and to clarify the roles of steric and inductive effects. Activation energies, and rate constants at 319.2 K, taken from Arrhenius plots of about ten points for each reaction are: (A) 4-mcthyl pyridine+n-propyl bromide E/kJ mol-1 = 66.0 + 1.1, 105A/(dm3 mol-1 s~‘) = 8.21 ; (B) 4-ethyl pyridine+n-propyl bromide 63.3 + 2.2, 8.70; (D) 4- methyl pyridine+n-butyl bromide 65.0 + 0.7, 7.10; (E) 4-ethyl pyridine+n-butyl bromide 63.0± 1.5, 7.71. Concentrations of base and reagent were nominally 0.2 and 0.6 mol dm-3. The ethyl pyridine has a A'-valuc slightly greater than that for the methyl pyridine, and k for propyl bromide is 10-15 % greater than that for butyl bromide. The ratios A(A)/A(B) = 0.94 and A(D)/A(E) = 0.92 are remarkably constant. Reactions (C) and (F) for n-propyl bromide and n-butyl bromide and poly(4- vinyl pyridine), reported previously, give the ratios A(C)/A(A) = 0.80, A(C)/A(B) = 0.75, A.(F)/A(D) = 0.81, A(F)/A(E) = 0.74. A linear dependence of In A on (e—l)/(2e+l) was found for system (B) where e is the dielectric constant, which depends on the concentrations of reactants.