A KINETIC-STUDY FOR THE REACTION OF 2,4-DINITROPHENYL BENZOATE WITH SECONDARY CYCLIC AMINES

Apparent second-order rate constants (k(app)) have been measured spect rophotometrically for the reaction of 2,4-dinitrophenyl benzoate (DNPB ) with 6 secondary cyclic amines in H2O containing 20 mole % DMSO at 2 5.0 +/- 0.1 degrees C. The Bronsted-type plot (log k(app) vs. pK(a)) s hows a break at pK(a) near 9.1, e.g. two straight lines with beta(app) values of 0.67 and 0.44 for the low basic (pK(a)<9.1) and the highly basic (pK(a)>9.1) amines, respectively. Using an estimated k(2) value of 3x10(9) sec(-1), all the other microconstants (k(1), k(-1), and K) involved in the present aminolysis have been calculated. The k(-1), va lue decreases with increasing the basicity of amines while k, and K va lues increase with increasing the amine basicity, as expected. Good li near Bronsted-type plots have been obtained for these microconstants o f the present aminolysis of DNPB. The magnitudes of the slope of the B ronsted-type plots, k(1) and k(-1), have been calculated to be 0.43 an d -0.24, respectively, indicating the k(-1), step is about two folds l ess sensitive than the k(1) step to the amine basicity. The K value ha s been calculated to be 0.66, which appears to be much smaller than th e one for other aminolyses showing general base catalysis. The small K value has been attributed to the absence of general base catalysis in the present aminolysis of DNPB.