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1-(5-溴-2-吡啶偶氮)-2,7-萘二酚(5-Br-PADN)属于吡啶偶氮类显色剂。它与PAN相比较,在吡啶环上引入了一个吸电子基—溴原子,萘环上增加了一个给电子基团—酚羟基。由于两者的电子效应,使该显色剂分子共轭体系内电子的活化能降低,加之,它们的助色效应和加重效应的影响,希望其灵敏度和选择性较PAN有所改善。 作者自合成5-Br-PADN以来,已应用于钴、镍、铜的测定。最近,又研究了在阳离子表面活性剂溴化十六烷基三甲基铵(CTMAB)的存在下,5-Br-PADN与锌的显色反应。试验结果表明。在pH10.5的硼砂介质中,它与锌形成紫红色的络合物,其组成为:Zn:R=1:2。络合物的且_(max)为550nm,表观摩尔吸光系数为5.25×10~4。
1- (5-Bromo-2-pyridylazo) -2,7-naphthalenediol (5-Br-PADN) is a pyridine azo-based developer. Compared with PAN, it introduced an electron-withdrawing group - bromine atom on the pyridine ring and added an electron-donating group - phenolic hydroxyl group on the naphthalene ring. Due to the electronic effect of the two, the activation energy of the electron in the conjugated system of the color former is reduced. In addition, due to the influence of the auxiliary effect and the exacerbating effect, the sensitivity and selectivity of the color developer are expected to be improved compared with that of PAN. Since the synthesis of 5-Br-PADN has been applied to the determination of cobalt, nickel and copper. Recently, the color reaction of 5-Br-PADN with zinc in the presence of the cationic surfactant cetyltrimethylammonium bromide (CTMAB) was also studied. The results showed that. In a borax medium at pH 10.5, it forms a purple complex with zinc and has the composition Zn: R = 1: 2. The complex has a max (max) of 550 nm and an apparent molar absorptivity of 5.25 × 10 -4.