| Abstract |
A kinetic study of the silver(I) activated homogeneous and heterogeneous quaternization of coordinated triethylamine by butyl iodide in toluene was performed. Silver iodide was used as solid catalyst. The experimental data was analysed resorting to the multistep kinetic model previously proposed by Santos and Barbosa for the same reaction with ethyl iodide. The solution quaternization rate constant, k(Q) and the surface quaternization parameter k(Q) b(Et3NAgNO3) were obtained together with estimates of the adsorption coefficients, b(Bul), and b(Etl), for the alkyl iodides on the solid. The presence of a competitive solution reaction between silver nitrate and the alkyl halide was confirmed and its solution rate constant, k(c), calculated. The data shows silver(I) coordination lead to large increases in the surface and solution amine quaternization rates. A comparison with results previously obtained for the same reaction with ethyl iodide allowed further understanding about the effect of coordinated silver nitrate ion pairs on the quaternization processes. Silver dual role as an electrophilic activator and as a structural promoter was scrutinized through a comparison of rate constants ratios with increasing alkyl chain length. Clear evidence of an electrophilic activation progressively smeared by stereochemical packing constraints in the solution and superficial transition states was obtained. (C) 2009 Elsevier B.V. All rights reserved. |
