KINETICS OF THE DIAZO COUPLING BETWEEN 1-NAPHTHOL AND DIAZOTIZED SULFANILIC ACID

In previous publications, the diazo coupling of 1-naphthol with diazotized sulfanilic acid was described by a two-reaction scheme. Primary coupling in the ortho position was neglected. The ratio of reactivities in the para and ortho positions is, however, only about 12. A four-reaction scheme gives a more accurate description of these couplings. The four rate constants have been determined by the stopped-flow method under standard conditions (25 °C, pH = 9.9, I = 444.4 mol-m-3). Spectrophotometric and HPLC methods have been used to analyze product mixtures. Extinction coefficients for the two monoazo dyes and the bisazo dye are tabulated under the above conditions. Differences of up to 8.5% for the bisazo dye exist relative to our earlier (1985) publication. In the range of product distributions up to Xs= 0.15, the new spectrophotometric analytical method leads to somewhat higher Xsvalues. © 1990, American Chemical Society. All rights reserved.