Pyridylazulenes:  Synthesis, Color Changes, and Structure of the Colored Product

Abstract

A facile method for the synthesis of 1- and 2-pyridylazulenes, and of 1,3-dipyridylazulenes, is described. Color and spectral changes of these pyridylazulenes upon the addition of either acid or metal ions were investigated in detail. The color changed from blue to red upon the addition of trifluoroacetic acid or soft metal ions, depending on the substitution patterns of the pyridyl group on the azulene skeleton. The structures of the protonated or coordinated products were examined on the basis of the spectral data. It was found that the protonation or coordination of metal ions occurred on the nitrogen atom of the pyridine ring, but not on the carbon atom of azulene ring. The transition intervals of several pyridylazulenes for use as pH indicators were also determined.

Synthesis of Azulene Derivatives That Have an Azathiacrown Ether Moiety and Their Selective Color Reaction Towards Silver Ions

“…The crude product was purified by chromatography on a silica gel column (6.5 g) with CH 2 Cl 2 as eluent to afford 8 (289 mg, 94 %) as a red oil, which was used without further purification. 6-(1-Aza-7,10-dioxa-4,13-dithiacyclopentadecanyl)azulene (6- [15]aneNS 2 O 2 -azulene) (4) A suspension of sodium cyclopentadienide prepared from cyclopentadiene (945 mg, 14.3 mmol) and NaOMe (808 mg, 15.0 mmol) in THF (4 mL) was added to 8 (289 mg, 0.591 mmol) in THF (2 mL). The reaction mixture was stirred at 80 8C for 11 h. The reaction mixture was poured into water (30 mL) and extracted with AcOEt (3 40 mL).…”

“…Recently, we reported the synthesis of pyridylazulenes, for example, 1, and investigated the color and spectral changes caused by the addition of an acid or metal ions. [4] The color changes from blue to red upon the addition of trifluoroacetic acid or soft heavy metal ions, such as Hg 2 + , Pb 2 + , and Cu 2 + , which indicates that pyridylazulenes are not selective for heavy metal ions.…”

“…A selective response towards a particular metal ion, or the colorimetric sensing of a specific metal ion, is currently a topical research area in molecular recognition chemistry, as exemplified by compounds such as azacrown ethers and calix [4]arene. [5] During our research on the specific and sensitive sensing of particular metal ions, in particular Hg 2 + ions, by using the chemistry of azulene, we synthesized compounds 2 and 3 (Scheme 1) and investigated their chromogenic properties, as Hg 2 + ions have high affinity for soft donors, such as sulfur.…”

Synthesis of 1‐Heteroaryl‐ and 1,3‐Bis(heteroaryl)azulenes: Electrophilic Heteroarylation of Azulenes with the Triflates of N‐Containing Heteroarenes

“…Recently, Wakabayashi et al reported the synthesis of 4a and 5a by Suzuki-Miyaura and Stille cross-coupling reactions, respectively. [20] However, their procedures required either the use of unstable 1-azulenylboronate reagents or 1,3-diiodoazulene under palladium-catalyzed conditions. Moreover, the yield of 5a was quite low (38 %).…”

Azulene–boronate esters: colorimetric indicators for fluoride in drinking water

“…Many prior reports of azulene-based colorimetric indicators for various analytes exist, including phosphate, [27][28][29][30] acetate, 30 cyanide, 30 hydrogen peroxide, 31 silver, 32 mercury and other heavy metals. [33][34][35] (Some of these indicators are not wholly selective and also exhibit a colorimetric response to fluoride [27][28][29][30] ). Of closest relevance to our present work is a report from Eichen et al 36 which describes a fluorescent azulene-based fluoride sensor that also exhibits a colorimetric response (green to violet) in DMSO.…”