A series of aromatic primary amine dyes were designed and applied for the modification of silk fibroin with Mannich-type reaction in the previous studies. Most aromatic primary amine dyes achieved the expected results with the participation of formaldehyde. However, those azo dyes with ortho-amino aromatic structure lost their colour and did not have any modification on silk fibroin under the same conditions of treatment. Therefore, the decolorization phenomenon of ortho-aniline aromatic azo dyes was analyzed using infrared, mass spectrometry, NMR and Gaussian computation and the results indicated that an intramolecular Mannich reaction occurred between ortho-amino aromatic azo dyes and formaldehyde. In addition, a secondary effect of reduction of dyes by formaldehyde took place, in which the conjugated chromogenic system of the dye molecules was destroyed, producing benzimidazole, o-phenylenediamine and nitrogen-containing heterocyclic substances with polymethyl substitution. This decolorization of dye was studied as a detection or monitoring method for formaldehyde, and it showed advantages of sensitive response, clear visual indication, and no volatilization of organic solvent.

在先前的研究中，设计了一系列芳香族伯胺染料并将其用于通过曼尼希型反应对丝素蛋白进行改性。大多数芳族伯胺染料在甲醛的参与下均达到了预期的效果。然而，那些具有邻氨基芳族结构的偶氮染料在相同的处理条件下失去了它们的颜色并且对丝素蛋白没有任何修饰。因此，利用红外，质谱，NMR和高斯计算分析了邻苯胺芳族偶氮染料的脱色现象，结果表明邻氨基芳族偶氮染料与甲醛之间发生了分子内曼尼希反应。此外，还发生了甲醛还原染料的次要作用，其中染料分子的共轭显色系统被破坏，生成苯并咪唑，邻苯二胺和具有聚甲基取代基的含氮杂环物质。研究了这种染料的脱色作为甲醛的检测或监测方法，它显示出灵敏的响应，清晰的视觉指示以及有机溶剂不会挥发的优点。