A Versatile Direct Approach to ortho‐Substituted Azobenzenes from Benzotriazoles

Abstract

. ‥ und Trumpf: Das verborgene Potenzial von Benzotriazolen als Diazonium‐Synthons zeigt sich in den Reaktionen von 1‐[(Nonafluorbutyl)sulfonyl]‐1H‐1,2,3‐benzotriazol mit Natriumphenoxid zu ortho‐substituierten Azobenzolen. Die Reaktion kann durch unterschiedliche Lösungsmittel in Richtung ortho‐ oder para‐Substitution gelenkt werden (siehe das Gemälde von Mathias Hansen, das die Zweigeteiltheit symbolisiert).

New Unsymmetrical Zinc‐Phthalocyanine Conjugated with One Azo‐Dye Moiety: Synthesis via Opening the Fused Triazole Ring and Spectral Properties

“…Compound 3 , as expected from its structure, gives 1 H and 13 C NMR spectra which depend on the basicity of the solvent. Previous studies on the analogous azo‐dyes derived from benzotriazole show relatively strong acidity of the hydroxy group in the naphthalene moiety 5,6. The OH proton in these compounds appears in the range of 15–16 ppm as a broadened signal, and can be easily removed by mild bases.…”

“…Section). One must take into account the relative instability of this compound due to the reactivity of the triflated triazole moiety, reactivity observed also for simple benzotriazoles,5,6 especially under daylight exposure. Therefore, 2 was protected from light during the workup and its purification by column chromatography.…”

“…The triflyl group on the triazole ring activates its opening in presence of strong nucleophiles, such as phenolate or naphtholate anions, in such a way that formation of the azo‐dye takes place, similar to azo‐coupling 5,6. In the case of triflated, triazole‐fused phthalocyanine 2 , this process is complete in a few minutes after addition of 2 to sodium naphtholate in toluene, resulting in an “ink‐blue” solution.…”

“…This can be due to the reason explained below. According to the mechanism of coupling between activated benzotriazole and phenolate or naphtholate,5 only the trans isomer of 3 can be formed. The latter one can form several conformers stabilized via hydrogen bonding.…”

“…Peripheral functionalization of the phthalocyanine with one conjugated azo‐dye moiety imparts peculiar optical properties to the Pc molecule, which will be discussed below. This synthesis is based on the recent findings that 1 H ‐benzotriazole can be activated towards coupling with nucleophiles such as phenolates, naphtholates and some others, leading to the opening of the triazole ring and formation of an azo moiety in high yields 5,6. The activation of benzotriazole is achieved by introduction of strong electron‐withdrawing groups such as nonaflyl5 or triflyl6 onto the triazole ring at the 1N‐position.…”