Do Phenyl Substituents Affect the Properties of Azobenzocrown Derivatives?

Abstract

New products of photo‐ and thermal rearrangements of 19‐membered azoxybenzocrown with phenyl substituents in benzene rings in the para positions to oligooxyethylene fragments are characterized in this work. The yields of photochemical transformations depend on the solvent. Para‐hydroxyazocrown is formed with yields over 50 % in propan‐2‐ol. Ortho‐hydroxyazobenzocrown is obtained with yields up to 70 % in toluene/acetic acid mixture. Macrocyclic Ph‐20‐ester is obtained in yield 90 % under thermochemical rearrangement conditions. Structure of new hydroxyazobenzocrowns and also atypical product of rearrangements, 20‐membered ester, was confirmed by X‐ray diffraction analysis. Azophenol ←0false→ ${ \mathbin{{\stackrel{\textstyle\rightarrow} { {\smash{\leftarrow}\vphantom{_{\vbox to.5ex{\vss}}}} } }} }$ quinone‐hydrazone tautomeric equilibrium of new hydroxyazobenzocrowns and the influence of metal cations on tautomeric equilibrium was investigated using 1H NMR and UV‐Vis spectroscopy in acetonitrile. The highest value of stability constant (logK 7.25) was obtained for strontium complex of p‐hydroxyazobenzocrown. For the first time p‐hydroxyazobenzocrown was used as a chromoionophore in the receptor layer of an optical sensor. Comparative analysis with data obtained previously for series 19‐membered analogs have shown the influence of the presence of substituents in benzene rings for the course and products distribution of photo and thermal rearrangement. The effect of substituents was also discussed against the tautomeric equilibrium and metal cation complexation properties.