P-置換ベンゼンジアゾニウム塩の1-ナフトールへのカップリング反応の速度論的研究

The coupling reaction of p-substituted benzenediazonium salts with 1-naphthol has been studied kinetically.The products were 2-(I), and 4-azo dyes (II) and a small amount of 2, 4-diazo dye (Table 4). The I / II ratio depended on pH, buffer composition of the reaction medium, and the electronegativity of the p-substituent.The formation of II was found to subject to a general base catalysis, while the formation of I was little affected by base (Fig.3). The catalytic effect decreased as the p-substituent becomes more electronegative in the order of OCH31-naphthol, the formation of the a-complex may be the rate determining step. On the other hand, deprotonation from the a-complex by bases is the rate determining step to form II. As the p-substituent in the diazo-component becomes more electronegative, the rate of deprotonation becomes relatively greater than that of the formation of the a-complex, thus in the case of p-nitrobenzenediazonium salt, the formation of the a-complex is the rate determining step.The kinetic data agree well the Yukawa-Tsuno relationship (Fig.4): r =0.58, p=3.7 (for the reaction at 2-position), p=3.2 (for the reaction at 4-position).