Kinetics of thermal decomposition of 4-carboxyl-2,6-dinitrobenzenediazonium ion (CDNBD).

The kinetics of thermal decomposition of 4-carboxyl-2,6-dinitrobenzenediazonium ion (CDNBD), an arenediazonium ion newly developed as a derivatizing reagent for drug analysis, are described. The arenediazonium ion, in an optimized concentrated sulfuric acid/orthophosphoric acid medium, was incubated for various time intervals at 30 degrees, 45 degrees, 55 degrees , 65 degrees , 75 degrees, and 85 degrees C. The amount of ion left after each time interval was quantified selectively by colorimetric assay at 490 nm, using mefenamic acid as a model diazo-coupling component. The rate constants for the decomposition were determined graphically. An Arrhenius plot was used to delineate the dependence of the rate constant on temperature and to predict the half-life at 25 degrees C and lower temperatures. The diazonium ion decomposed by first-order kinetics. The rate constants of decomposition, which increased progressively with temperature, were 3.18 +/- 0.41 x 10(-5), 1.19 +/- 0.07 x 10(-4), 4.87 +/- 0.15 x 10(-4), 12.88 +/- 0.73 x 10(-4), and 21.32 +/- 2.74 x 10(-4) (s(-1)) with corresponding half-lives of 363, 97.06, 23.72, 8.97, and 5.42 min at 30 degrees, 45 degrees, 55 degrees, 65 degrees, and 75 degrees C, respectively. CDNBD is highly stable in concentrated acid medium, with half-life values of about 10 h, 10 days, and 7.3 months at 25 degrees, 0 degrees, and -20 degrees C, respectively. The reagent stability profile shows that it could be readily adapted for routine applications in instrumental chemical analysis.