Aerial Oxidation of Protonated Aromatic Amines. Isolation, X‑ray Structure, and Redox and Spectral Characteristics of N- Containing Dyes

This work reports the results of our investigation on the aerial oxidation of aromatic amines that are promoted by protic acid. While primary aromatic amines produce substituted phenazines as major products, N-phenyl-o-phenylenediamine produces polycyclic aromatic heterocycles like azaacene and secondary and tertiary amines give exclusively the dyes containing a triphenylmethane moiety. Isolation of the compounds and the effects of substitutions on the aromatic rings have been investigated. In this context, plausible reaction steps that are involved have been discussed. Single-crystal X-ray structure analyses of the representative compounds are solved to authenticate their formation. In almost every case, a high degree of delocalization of electron was noted. The compounds have been characterized thoroughly and show rich spectral properties. For example, the phenazine molecules exhibited absorption peaks between 475 and 605 nm because of the charge-transfer transition from the amine and tricyclopyrazine moiety. Their acidochromic and solvatochromic behaviors, which are supported by theoretical calculations, are investigated. The polycyclic azacene molecule exhibits strong absorption in the visible region and fluoresces with high quantum yield. The phenazine dyes undergo a quasi-reversible reduction at a low cathodic potential that varies linearly as a function of Hammett’s constant.本工作报道了质子酸(protic acid)催化芳胺(aromatic amine)需氧氧化反应的研究结果。其中，伯芳胺主要生成取代吩嗪(phenazine)类产物；N-苯基邻苯二胺(N-phenyl-o-phenylenediamine)则生成氮杂并苯(azaacene)类多环芳香杂环化合物；而仲胺与叔胺仅生成含三苯甲烷(triphenylmethane)结构单元的染料。本研究对目标化合物的分离方法，以及芳环取代基的影响展开了系统探究。在此研究背景下，本文还对该反应可能涉及的合理反应路径进行了讨论。通过对代表性化合物进行单晶X射线衍射(single-crystal X-ray diffraction)结构解析，验证了其产物结构的正确性。绝大多数目标产物均表现出高度的电子离域特性。所有化合物均经过全面的结构表征，展现出丰富的光谱特性。例如，吩嗪类分子因存在胺基与三环吡嗪(tricyclopyrazine)结构单元间的电荷转移跃迁，其紫外-可见吸收峰位于475~605 nm波长区间。本研究结合理论计算，深入探究了此类化合物的酸致变色(acidochromic)与溶剂致变色(solvatochromic)行为。该多环氮杂并苯分子在可见光区具有强吸收特性，且荧光量子产率较高。吩嗪类染料可在较低阴极电势下发生准可逆还原反应，其还原电势与哈米特常数(Hammett’s constant)呈线性相关关系。